A Real Life Introduction to the
JMI NGC-MAX Telescope Computer
Every
users manual these days seems to start with the
same "Introduction" section, and that section
always starts with the vendor congratulating you on your
wonderful purchase and telling you just how much fun
youre going to have with it.
You wont find that type of garbage here for two
reasons. First (and foremost) Im not associated
with JMI, the company that makes the NGC-MAX; Im a
customer who bought one of the boxes and made these notes
based on my own experience with it. The second reason is
that you already know how good you are so theres no
need for me to waste time telling you about it.
OK; now that weve got the opening pleasantries out
of the way, lets start with some background.
So what is this document?
This document does not replace the JMI instruction
booklet. It was written because some of the procedures
described in the JMI documentation werent as clear
as they could be and useful information was scattered all
over the place. Additionally, since Im learning how
to use the NGC-MAX with a German mount writing these
notes helps me by forcing me to explore some of the
procedures that I would probably have glossed over if I
didnt have to learn the details in order to write
about them.
For that reason the comments, observations, procedures,
and such are specific to the use of the NGC-MAX with a
German equatorial mount. There are only a few references
to other configurations here, and they should be viewed
as untested speculation.
These instructions are somewhat longer than what
youll find in the JMI manual. If youre
familiar with digital setting circles and the use of
devices such as the NGC-MAX, the procedures here may be a
bit too verbose unless you want to know a little more
about why you are told to perform some of the
steps than JMI tells you. If the NGC-MAX is the first
computer aid youve bought to help you use your
telescope and you dont have someone nearby to help
you learn how to use it, these pages are written for you.
And yes, theres a lot of text in the sections on
introducing the equipment, configuring it and setting it
up, and there isnt much text in the section on using
the NGC-MAX. This is deliberate; like most computers, the
key to being able to use the NGC-MAX is knowing why and
how it works the way it does: once that is taken care of
there isnt much additional instruction required
when you finally are ready to use it.
By the way, its always useful to have someone you
can ask questions of while youre learning how to
use a new tool. Find a nearby astronomy club and see if
someone there has experience with the NGC-MAX or a
similar product. The instructions here worked for me, but
nothing beats having someone at your elbow to answer
questions as they come up, especially in the field on a
dark night.
Assumptions made
here
To avoid having to use complex if-then-else constructs
Ill make the following assumptions about you:
You have some experience working with an amateur
telescope.
- You are familiar
with the concepts and use of both celestial
(RA/Declination) and terrestrial
(altitude/azimuth) coordinate systems.
- You understand the
concepts behind the use of a polar-aligned
equatorial mount.
- Youve become
somewhat familiar with the mount and telescope
that youll be using with the NGC-MAX
computer.
If its a complex mount such as a Losmandy
G-11 mount and all youve worked with is the
fork mount on a Meade ETX, read the instructions
for the mount and telescope first. When
youve got some experience using it
(including nighttime observing of stars without
the NGC-MAX) come back to this document. Yes,
its tempting to jump into the NGC-MAX as
soon as you get it, but youll have fewer
problems if you arent learning about the
mount and the NGC-MAX at the same time.
- Encoders compatible
with the NGC-MAX have been installed on the mount
youll be using.
- Youre in the
Northern hemisphere.
What you bought
The NGC-MAX and its junior siblings NGC-MiniMAX and
NGC-MicroMAX are display units that tell you where your
telescope is pointed and how to move it to point to some
particular object. Using devices called encoders
that are attached to your telescopes mount and
which tell the NGC-MAX how youve turned the
telescope on its axes, it calculates the coordinates that
describe where your telescope is currently pointed, or
alternatively it gives you the instructions needed to
guide you in moving the telescope to a predetermined
place in the sky. It can also be used to display the
coordinates of a specific object in the sky (for example,
M31), and can be asked to identify the object to which
the telescope is pointed.
The three products have different capabilities. NGC-MAX
has all the bells and whistles; the MiniMAX and the
MicroMAX do not have the ability to tell you what the
telescope is pointed to, and the MicroMAX is missing
information about the planets, does not have the built-in
timer, does not support the polar alignment function and
does not support the "perfect polar alignment"
mode. The data bases in the three products are also
different; the NGC-MAX having 12,047 unique objects, the
MiniMAX having 3,912, and the MicroMAX having only 245.
What it works with
The NGC-MAX can be used with fork and German equatorial
mounts, as well as classic and Dobsonian terrestrial
(altazimuth) mounts. Although it is recommended that
equatorial mounts be polar-aligned, this isnt
necessary to use an NGC-MAX.
The NGC-MAX accepts
inputs from standard relative-motion encoders. Any
reasonable encoder resolution is acceptable; the value is
entered (and calculated if necessary) while setting up
the NGC-MAX.
What the NGC-MAX
does
As noted earlier, the NGC-MAX can display the coordinates
of the point in the sky to which the telescope is aimed
(thus the occasional references to "digital setting
circles"). It can also tell you how to move the
telescope to have it point to a particular object in the
sky, or alternatively it can search its data base to
identify the object to which you have pointed the
telescope.
Additionally, the NGC-MAX
has a connector that can be cabled to a personal computer
to allow the computer to receive the current aiming
coordinates. Any personal computer (PC, Macintosh, or
whatever) that has a serial port that can handle 9600 bps
data can be used.
What the NGC-MAX
doesnt do
The NGC-MAX was not designed to control a telescope. It
has no connectors that can be attached to motor drives;
it merely displays where the telescope is pointed, or how
to move it so that it points to some particular object.
You can use a personal computer which reads information
from the NGC-MAX to determine where its pointing,
and uses that information to calculate what motor actions
are required, but that isnt part of the NGC-MAX
product.
A note about the
data bases
The data bases in the NGC-MAX includes the Messier
objects (which are called out by the M-number), the Sun
and major planets (called out by name), two standard
catalogs (Index Catalog and New General Catalog), and two
lists (created by JMI) of extrasolar objects, one for
stellar items and one for non-stellar ones.
Unfortunately, items in the JMI lists are numbered in
order of right ascension, requiring you to look up an
entry on a printed list before you can locate it in the
data base. For example, to look at the information for
Pollux you must find it in a printed copy of the list to
determine that its data base entry is called ST352. If
there is a way to search for an entry by its name (for
example, "Pollux") I havent found it.
If youre planning an observing session, either for
yourself or as a public demonstration, its a good
idea to look up beforehand the item numbers any objects
you expect to want to find using the NGC-MAX. Being able
to glance at your clipboard to see that you want ST352 is
much more impressive to your audience (and time-saving to
you) than having to search through many sheets to find
the entry for Pollux. Just as in final exams, a cheat
sheet is always useful.
The NGC-MAX allows you to
create your own entries in a special section of the data
base, but these user-created entries dont have the
amount of detail (such as text narratives) or angular
precision that are in the JMI-provided tables.
NGC-MAX edición
Español
The picture on the front of the JMI-provided
documentation for the NGC-MAX shows the NGC-MiniMAX
displaying the word "SPANISH" which suggests
that it can be configured to display text in Spanish.
This isnt documented anywhere in the NGC
advertisements or catalogs; if you need the messages to
be in Spanish please contact the place where you bought
the NGC-MAX, or contact JMI directly.
- Getting Started:
Introducing the NGC-MAX
OK; youve survived
the introduction and its summary of what youve
bought. Now lets see if we can find out more about
it.
Especially if youve never before worked with
digital setting circles you should if at all possible set
up your telescope mount inside your home or office and
try using the NGC-MAX to get used to it. You dont
need to mount the telescope tube itself; all thats
normally needed is enough of the mount to allow you to
connect the NGC-MAX cables, in a location where you can
get full motion in the two axes of rotation.
With the Losmandy mount, use the tripod section of the
base without the legs, and place the German mount in the
tripod without installing the attachment screws. This
lets you turn the mount in the tripod to look at parts of
the mount without having to move yourself. (Just
dont do this if it would be at risk of being
knocked over by energetic kids or large dogs!)
Whats in the
box
Now that youve got
the box open, lets see if everything is present and
accounted for. Roll call:
- The official
"MAX Computer Operators Guide"
from JMI,
- Three single sheets
that expand on the issues of encoder resolution,
describe the "SET DEC=0" display, and
discuss using the NGC-MAX with an altazimuth
mount,
- A listing of the
data base,
- The warranty card,
and
- A catalog of JMI
products
Below this mass of
papers, youll find:
- The NGC-MAX itself
- A holding tray that
can be attached to the telescope (maybe), and
- A videotape that
describes the use of the NGC-MAX.
The NGC-MAX comes with a
standard alkaline 9-volt battery installed.
Whats not in
the box
The NGC-MAX doesnt
include the encoders or the cables that link them to the
NGC-MAX. You can buy encoders and cables from JMI or any
of several other vendors, and you can either buy or build
the cable that links them to the NGC-MAX.
If you want to connect the NGC-MAX to a personal computer
you need to obtain or construct a cable to attach the
two. See the discussion in section 3 below and/or the JMI
documentation for details.
What you need
In addition to the
NGC-MAX you need a few other things:
- A telescope and its
mount (duh!),
- Encoders, installed
on the two axes of the mount,
- Cables to connect
the encoders to the NGC-MAX, and
- Information about
the encoders: in particular, you need to know its
resolution for each encoder (that is, how many
signals ("tics") it sends for one
complete revolution of the shaft to which it is
attached), and whether it reports a positive or
negative count as the shaft is turned clockwise
as viewed from above.
The encoder information
can be calculated if it isnt available. See the
single-page summary titled "How to determine the
correct encoder resolution" that is packed with the
NGC-MAX. If necessary assume that the resolution is
positive; this will be verified and if necessary
corrected later.
If the encoders were
installed by a technician at the store where you
purchased them, the resolution numbers are probably
provided to you with the paperwork in the NGC-MAX box.
They may be on a separate piece of paper, or they may be
written somewhere in the JMI-provided documentation for
the NGC-MAX. Some shops like to write them on page 11 of
the JMI manual, in the section on "Encoder
Resolution."
Initial Setup
(First Things First)
Many of the instructions
here begin with a heading to describe the step, a short
summary of what we accomplish by performing it, and the
details.
Does the display work?
We verify that the computer is able to perform its basic
power-on functions.
Youve probably
already done this as you unpacked the box, but take a
minute and turn the NGC-MAX on. Youll see an
initial herald message scroll across the display; it
should read something like "JMI NGC MAX 12K DATABASE
V3.52", after which the display will change to
something else. If it doesnt do this, check the
battery in the back of the display to make sure that
its correctly connected; if it is, try replacing
the battery with another alkaline cell. (Use alkaline
cells only. Do not use NiCd or other rechargeable
batteries.)
If the display still
doesnt show anything when you turn it on, contact
the store from which you bought it for additional help.
Introducing the
NGC-MAX controls
This section
introduces the display and buttons, and steps you through
a brief exercise that shows you some of the features. We
demonstrate how to use the four buttons to enter data and
select a specific object from the built-in data base.
You need to become
familiar with the way the NGC-MAX allows you to enter
data into it. Its not difficult, but neither is it
as simple as typing on a keyboard or using a mouse. The
demonstrations in this step dont require that the
NGC-MAX be connected to the encoders.
Turn the NGC-MAX off, wait five seconds, and then turn it
on. After the herald line has stopped scrolling, press
the UP button. The display should now read either:
SET DEC=0
or
MODE ALIGN STAR
Press the DIM button
several times. The display will cycle through five
brightness levels. Choose the lowest bright level that
lets you read the display without difficulty since the
brighter the display the faster the battery will be
exhausted. JMI claims that the NGC-MAX will run for 25
hours on a fresh battery, but that figure assumes that
the display is set to its lowest level. (You do
plan to keep a spare battery in the toolkit that you take
to telescope parties, dont you?)
To look up an entry in
one of the data bases, press the UP button repeatedly
until the display reads:
MODE CATALOG
and press the ENTER key.
The display will change to read:
M001
with the "M"
blinking. This tells you that the NGC-MAX is asking you
to select the data base from which you want to retrieve
an item. Press the UP and DOWN keys to change to other
data bases, including stars, planets, and so on.
The default catalog of objects in the NGC-MAX catalog
(set when you turn the NGC-MAX on) is the list of Messier
objects, which are available when the CATALOG display
shows the letter M. Whenever you select some object (in
the catalog listing, or during the alignment procedures,
or with the IDENTIFY function) that object becomes the
default which will be shown when you next enter the
CATALOG mode.
When youve selected the list you want, press ENTER.
For all the choices other than PLANETS you will now see
two, three, or four decimal digits with the leftmost one
blinking. Use the UP and DOWN keys to change the blinking
digit to the one you want, then press ENTER to move to
the next digit. When you press ENTER the last time the
display shows the coordinates of the selected object; for
items other than user-defined entries or planets, you can
press the ENTER key again for a scrolled description of
the object. For example, to display information about
M13:
Press MODE; press UP or
DOWN until MODE CATALOG is displayed. Press ENTER.
M001 is displayed. Press
ENTER twice; the second 0 is now blinking. Press UP,
ENTER, UP, UP to make the display show M013. Press ENTER
again and see the coordinates of the Hercules Globular
Cluster; press ENTER again and see the summary
information.
In this demonstration you will see the catalog offer you
M001 because youve not selected any other object
since you turned the NGC-MAX on. If some other object is
displayed you can get back to M001 by pressing UP or DOWN
to cycle through the types of objects (NGC, IC, NS, NEW,
PLANETS, and ST) until you get to the Messier list (M).
Whenever you change the type of object the object number
is reset to 1, so if ST746 is displayed when you enter
the CATALOG mode, just press the UP key once; the
blinking ST will change to a blinking M, and the digits
(746) will change to 001.
See the JMI manual for
more detailed procedures, especially if you want to use
the catalog of planetary positions.
Turn the NGC-MAX off.
Set up the mount
Youll need to have your mount set up in an area
with decent lighting in order to practice using the
NGC-MAX.
(Dark skies in an outside location is of course desirable
when you want to look at the stars, but its a lousy
place to teach yourself how to use a new toy
excuse me, "tool.")
Mount the display box
Start by finding a place
to hold the NGC-MAX box on the assembled telescope. I
find the tray that is shipped with it to be a nice idea,
but theres no place to mount it easily on my
Losmandy mount. To me the best solution to this is to use
a strip of Velcro tape to attach it to the side of the
tripod head. Use your imagination to find a place that
works for you.
Connecting the cables
We attach the cables
between the NGC-MAX and the encoders, and learn to tell
which cable goes to which encoder.
The NGC-MAX needs to be
connected to the two encoders on your mount. Your
encoders should have come with a Y-cable on which the
common connector plugs into the NGC-MAX and the branched
wires plug into the two encoders. An RJ-45 connector (the
same type used for twisted-pair Ethernet cables) is
installed at the NGC-MAX end of the cable; the connectors
on the other ends of the cable will depend on the type of
encoders used but will usually be RJ-12 connectors,
identical in shape and size to the RJ-11 connector used
on a standard telephone.
OK, which cable goes to
which encoder? The JMI manual says that the longer cable
will go to the declination encoder, but what if the two
cables are the same length? One way to find out is to
plug them in without regard to which is which; a test
later during the setup procedure will tell you if they
need to be reversed. No damage is done if the cables are
switched.
Another way to tell which
is which is to look at how they enter the RJ-45 connector
that plugs into the NGC-MAX. If you insert the plug into
its socket in the NGC-MAX and hold the box with the
display facing you and the cables at the top, you will
see that one cable is connected to the pins on your left,
and the other to the pins on your right. The cable on the
left should be connected to the RA encoder and the one on
the right to the DEC encoder.
How to remember which is
which? Its easy: normal star coordinate listings
show the RA before the DEC value and its the same
with the cables to the encoders (unless youre used
to reading from right to left).
Turn the NGC-MAX on
The box will display its herald line to tell you about
the circuitry inside. When its finished with this,
youll see a message that might read something like:
SET DEC=0
or
MODE ALIGN STAR
If the SET DEC=0 message
appears, press the ENTER key once.
Customize the NGC-MAX
settings
In this section we tell the NGC-MAX the type of mount you
have and the precision of the encoders.
Press the UP or DOWN key several times; youll see
that the word "MODE" remains on the display,
but several different modes are offered. Press the UP
and/or DOWN keys until the display shows:
MODE SETUP
Press the ENTER key; the display will change to:
SCOPE xx
where xx might be any of
the several two-letter abbreviations listed on page 11 of
the JMI manual. The ones were interested in are GQ
(German eQuatorial), GP (German Polar), EQ (EQuatorial),
and EP (Equatorial Polar). Press the UP and/or DOWN keys
until the GQ abbreviation appears, then press the ENTER
key. This tells the NGC-MAX that you have a German mount
that is not perfectly aligned to the North
Celestial Pole (NCP).
Press the ENTER key. The display will change to read:
SCROLL 5
unless youve changed it previously. This is the
rate at which information scrolls from right to left on
the display. For now leave it at 5; you can change it
later if you prefer. Press the ENTER key again.
The display now reads:
CHART SA
or
CHART UA
If you use either Sky Atlas 2000 or Uranometria,
choose one of the two options with the UP or DOWN key.
The NGC-MAX will display the chart number in these
publications with each object it reports. If you
dont use either chart, just leave the setting
unchanged.
Press ENTER again; the display will now show the letters
AZ and a signed, 5-digit number. This is the RA (or
azimuth) encoder resolution; enter the number supplied
with the encoder, including the + or sign using
the same procedure described earlier for selecting
entries from the catalog data base. When youve
entered the last digit of the resolution and press ENTER
the display will show the letters AL and a signed 5-digit
number. This is the declination (or altitude) encoder
resolution; again enter the data here. When you have
entered the last digit, the display returns to MODE
SETUP; youve finished the calibration step.
With this step and the
next one the most important items are setting the correct
resolution (the five digits) for both encoders, as well
as the sign of the precision for the RA encoder. The sign
of the declination encoder has a "correct"
value, but you may need to change it in the field,
depending on how you set up the telescope. See the
section "Setting up the NGC-MAX in the field"
below.
Testing the encoders
Heres where we
check the encoders to make sure that theyre working
correctly and that youve got the cables plugged
into the correct encoders. We also demonstrate why you
dont want to make an abrupt, fast movement of the
axes of your mount.
Turn the NGC-MAX off.
Position the RA axis so that the mounting bracket for the
telescope tube is at the highest point on its swing
(corresponding to the counterweights being at the
bottom), and position the DEC axis so that the telescope
tube would be pointing to the north had you set up the
mount and aligned it. Tighten the clutches on each axis.
Set the RA setting circle to 0h 00, and
on the declination setting circle note where the index
line is pointing.
(If your mount allows you to attach the telescope tube in
either of two directions, just choose one. It
doesnt affect this procedure.)
Wait until the NGC-MAX has been off for at least five
seconds, then turn it on. When the herald line stops
scrolling, press the MODE button if required to cause the
display to read MODE ALIGN STAR, then press UP or DOWN
until the display reads:
MODE ENCODER
Press ENTER; the display
will change to:
ER=000 ED=+000
Loosen the clutch for the RA axis and slowly turn the
mount clockwise about that axis (as seen from above) to a
RA position of 18h 00. The first number
in the display (ER) should have climbed to read 090. Now
turn the RA axis counterclockwise until the setting
circle shows 6h 00; the display should
now read ER=270. Return the RA axis to its original
position (0h 00) and the display should
read ER=000 again. Tighten the clutch. (An error of not
more than one degree on the display is acceptable.)
If the second number on the display (ED=) changes while
you move the RA axis, the cables are attached to the
wrong encoders. Swap them and mark one of them so that
next time you will know which one goes where. (I tie a
loose knot in the DEC cable and hold it with a small
Tie-Wrap; this has the effect of shortening it to make it
easy to figure out which encoder it goes to.)
Now loosen the DEC clutch and turn the mount clockwise as
seen from above the mount. As you make a complete turn
the display will count up from 0 to 179, then change to
179 and count up from there to 0. If you
nudge the DEC axis slightly the reading will change to +0
again; at this point you should have turned the DEC axis
exactly once, and the DEC reading should be the same as
when you started.
If either display counts in the wrong direction, go back
to the MODE SETUP display and change the sign of the
corresponding encoder resolution.
If the RA or DEC displays did not show the expected
results, see the troubleshooting guide on page 5 of the
JMI manual.
Now loosen the clutch on the DEC axis until it swings
without drag. While watching the display, turn the DEC
axis abruptly; if your turn was abrupt enough the display
will change to read ENCODER ERROR to tell you that the
change in the encoder output was arriving too fast for
computer in the NGC-MAX to process it. You have to be
turning an axis rather fast for this to occur, but
its possible.
Once the ENCODER ERROR message has appeared, your NGC-MAX
no longer knows where the telescope is pointed. You must
turn it off for at least five seconds, then turn it on
and re-align it.
Its worth noting that a low battery can cause the
NGC-MAX to give ENCODER ERROR messages.
Aiming at a specific
object
Here we demonstrate how the NGC-MAX tells you how to move
the telescope to aim it at a specific object. We perform
a bogus "alignment" of the telescope, tell it
to help us find M1, and watch the display change as we
move the mount.
One of the purposes for which many people buy devices
such as the NGC-MAX is to help them quickly aim the
telescope at a specific object in the sky. Hopefully few
telescope owners need such help when they want to find
Sirius on a clear night, but if youre looking for a
dim object under less than ideal conditions, it may take
even experienced observers a lot of time to find the
right point in the sky. NGC-MAX contains a data base of
12,019 objects (plus the ability to store 28 user-defined
additional objects); you can select any of these objects
and the display will tell you how to move the telescope
in both RA and declination to have it point at the
object.
To demonstrate this feature, we need to first make the
NGC-MAX think that weve correctly aligned it and
the telescope to the stars. We dont have to
actually align it for this demonstration (especially if
its in your basement!) so we go through the motions
here. Well do the alignment for real later in the
section on field setup.
Turn the NGC-MAX off for at least five seconds, then turn
it back on. After the herald line scroll ends, press the
UP or DOWN button repeatedly until the display reads MODE
SETUP. Press ENTER; the display will read SCOPE xx where
xx is a two-letter abbreviation for the telescope mount
type.
Press the UP or DOWN button until the display reads SCOPE
GP or SCOPE EP. Press the ENTER key, then the MODE key;
the display will again read MODE SETUP. (This tells the
NGC-MAX that we have an equatorial or German mount that
is supposedly aligned with the NCP.)
Press the UP or DOWN button repeatedly until the display
reads MODE ALIGN STAR, then press ENTER. The display
reads ALIGN ACHERNAR. Press ENTER. This procedure tells
the NGC-MAX that the telescope is pointed directly at the
star Achernar (a Eridani); with the assumption that the
mount is in fact aligned with the NCP this is all the
NGC-MAX needs to know in order to figure out where the
telescope is later pointed.
(There are several stars available if you dont want
to use Achernar. Press the UP and DOWN keys when ALIGN
ACHERNAR appears to see the others.)
The display briefly shows the message WARP=0, then
returns to ALIGN ACHERNAR. This completes our bogus
alignment.
To demonstrate the built-in catalog to help us find an
object, press MODE, then press UP until the display reads
MODE CATALOG. Press ENTER again; the identity of some
object in the data base will be displayed.
Earlier when we opened
the MODE CATALOG display the NGC-MAX showed M001 but this
time we see something else. Recall from a few paragraphs
back that whenever an object is selected in any menu it
becomes the default catalog object until power is turned
off or some other object is selected. We did our bogus
alignment with Achernar, so the catalog display opens
with ST063 displayed.
Use the procedures
described earlier in this section to select M001. When
M001 has been selected press ENTER repeatedly until none
of the display is blinking; you should now see:
M001 0534+220
which tells you that M1 can be found at RA 5h34
and declination +22° 0. (The display shows only
the tens digit of the minutes part of the declination, so
+220 can represent anywhere from +22° 00 to +22°
0959".)
Press MODE and UP to
display MODE GUIDE. Press ENTER; the display will now
read:
M001 59¬ 79
This display tells you
how to move the telescope; here it says that you need to
move it 59° to the left and 79° up. Move the telescope
in both RA and declination and youll see the
numbers change. When you are pointed where the NGC-MAX
expects M1 to be located both numbers will have reached
zero.
Of course, "up" and "left" are
relative terms when youre talking about circular
measurements. Dont worry about which way is which;
just move the telescope axes in whatever direction causes
the numbers to get closer to zero.
When you are within ten degrees of the desired
orientation, the display changes to show degrees and
tenths of a degrees (for example, the display 6¯ 5 is an
instruction to move the telescope down 6.5°).
Turn the NGC-MAX off.
This completes the initial setup and demonstration of
your NGC-MAX. This is generally a one-time procedure with
the exception of switching between polar and non-polar
modes, and telling the NGC-MAX which way is up (which
well get to in a few pages).
- Connecting the
NGC-MAX to a computer
Here we build the cable
required to connect the NGC-MAX to an
IBM-compatible computer.
One feature of the NGC-MAX is that it can be
connected to a personal computer to let it obtain
from the NGC-MAX information about where the
telescope is pointed. Skip this section if you
arent planning to use this feature.
The information provided to the personal computer
by the NGC-MAX tells it about the angular
position of the axes on your mount.
Unfortunately, the designers at JMI chose to
deliver encoder information over the computer
link rather than RA and declination coordinates.
If the telescope is perfectly polar-aligned then
its a trivial task to translate the encoder
data into RA and DEC values, but if the mount is
not polar-aligned the data is requires more
processing by the program running in the attached
computer.
Many programs that are compatible with the output
of the NGC-MAX handle this problem by never
assuming polar alignment. These programs (for
example, Software Bisques The Sky)
require that you go through a two-star
calibration to let the program determine where
the telescope is pointing. See the manual for the
program youre using to find out how it
expects you to align the program to the output of
the NGC-MAX.
Since there are many computer programs that can
be used with the NGC-MAX this document cant
offer help in using them; you need to read the
instructions for the one youre using. All
of them, of course, require that the NGC-MAX be
connected to the computer, and JMI does not
include with the NGC-MAX the cable that you need.
JMI will sell you the cable for $24 but its
easy to make it for much less, at least if
youre using an IBM-compatible computer.
You need only two items: a telephone extension
cord with the usual "modular jacks" on
each end, and an adapter to connect one end of
the cable to the serial port on your computer;
the two together should not cost more than about
$5. The telephone extension cord can be bought at
almost any retail store these days; the adapter
should be available from any good computer store
or can be ordered from computer parts mail-order
vendors.
Note: do not connect the cable from the NGC-MAX
to a modem or to a telephone line, even though it
uses the same connector as a normal telephone
cord.
The telephone
extension cord must have four wires in it, and
the connectors on each end must have four brass
pins. (Dont worry about which colors are
used for which connections in the cord; the
manufacturers of telephone extension cords seem
to ignore normal color-code standards.)
For an IBM-compatible computer, the serial port
on the computer is almost always either a 9-pin
or 25-pin male connector surrounded by a barrier
in the shape of the letter "D". The
female connector that plugs into this connector
is called a "DB9F" or "DB25F"
respectively.
Buy an adapter that has a DB9F (or DB25F)
connector on one end, and an RJ12 socket on the
other. (Telephone connectors are actually
"RJ11" style but the RJ12 has the same
mechanical dimensions.) One such product
Ive used is manufactured by a company
called AESP as model number G243, which sells for
less than $2.
Youll need to wire the inside of the
adapter to connect the RJ12 pins to the DB9 or
DB25 connector; it probably comes to you with the
wires from the RJ12 connector attached to pins
but not inserted into the 9-pin or 25-pin
connector block. Almost all adapters follow the
industry standard wire color codes, so locate the
back of the 9- or 25-pin block, and following the
instructions below push the pins firmly into the
block until you feel them lock. Gentle tugging on
the wire should not dislodge the pins.
On the DB9 connector, push the yellow wire into
the hole for pin 2, push the green wire into the
hole for pin 3, and push the red wire into the
hole for pin 5.
On a DB25 connector, the green wire goes to pin
2, the yellow wire to pin 3, and the red wire to
pin 7.
The remaining wires (white, black, and blue) are
not used; put tape over the exposed metal pins
and push them out of the way inside the adapter
shell. Now attach the DB9 or DB25 connector to
the adapter shell.
Use a permanent marker pen or some other device
to mark the adapter "NGC-MAX" so that
you dont accidentally use it for some other
purpose that requires a different wiring
configuration.
To test the new cable, plug one end of the
telephone extension cord into the RJ12 connector
on the NGC-MAX and the other into the adapter;
plug the adapter into the serial port of your
computer. Start an asynchronous terminal
communication program in the computer (for
example, HyperTerminal or KERMIT). Configure the
program to use the appropriate communications
port (usually COM1 or COM2), then set it to use a
speed of 9600 bits/second, 8 data bits, no
parity, one stop bit, and no flow control.
Now turn the NGC-MAX on. The terminal program
should display the version number of the firmware
in the NGC-MAX (on my system this displays
"V3.52") followed by a carriage return.
Send the character "Q" (uppercase, and
without the quotes). The NGC-MAX should respond
by sending two, 5-digit signed numbers followed
by a carriage return, with both numbers near zero
as shown below:
+00000
00002
If this result is
seen the cable and the NGC-MAX computer interface
are working correctly.
Note that the
output from the NGC-MAX ends in a carriage
return, but does not include a linefeed
character. The display in our test here will show
only a single line on the screen, with the output
from the NGC-MAX writing its data over and over
in the same positions.
JMI does not document its interface; some
experiments have shown that if you type the
uppercase letter P then the NGC-MAX responds with
three zeros (without any indication of what this
represents). Sending any other characters to the
NGC-MAX (including lowercase "p" or
"q") causes a single question mark to
be returned.
- Setting up the
NGC-MAX in the field
The encoders that are
connected to the NGC-MAX dont tell it where the
telescope is pointed; all that they to is to tell it how
far its orientation has changed when you move the
telescope from one part of the sky to another. Its
like the odometer in your auto: it tells you how far
youve traveled since you last reset it, but unless
you know where you were when you pressed the reset button
it cant help you figure out where you are now.
For this reason, each time you turn on the NGC-MAX (and
whenever you see the ENCODER ERROR message) you need to
tell it where some known points are as reported by the
encoders.
Choosing an
alignment option
When you set up your
telescope for a viewing session you can choose between
several different alignment options.
The NGC-MAX does not require that your telescope be
correctly aligned with the North Celestial Pole; this
would an unfortunate requirement for a product that
advertises itself as being compatible with both
equatorial and altazimuth mounts. However, experience has
shown that both the telescope and the NGC-MAX will be
much easier to use if you take the time to correctly
align your telescope when setting it up.
There are several advantages to polar alignment of a
telescope mounting; among them are:
- The clock drive of
the mount will (if correctly adjusted) track a
point in the sky. Without a computer that
controls the motors in your mount this is
possible only with polar alignment because a
clock drive is normally attached only to the RA
axis.
- The mechanical
setting circles on the mount are usable if they
were properly calibrated. They read the angular
position of the two shafts in your mount, and
only with polar alignment do they correspond with
RA and declination. The NGC-MAX provides computed
RA and declination values but having the
mechanical setting circles is still a good
backup. (Batteries do die, and usually do
so only after you get to your observing site!)
- Information provided
to an attached personal computer can be directly
translated into RA and declination values.
On the other side of the
equation, it takes time to properly align a telescope
mount, and it can take a lot of time to align it
perfectly (or as close to "perfectly" as is
appropriate for the quality of the telescope and mount).
Some users are blessed with the option to install a fixed
mounting that is permanently aligned, but most of us have
to put up with the hassles of alignment whenever we set
up our telescope.
Theres no One Right Answer to the question of which
method is best: setting up a telescope for an
astrophotography session almost always requires a
well-aligned telescope, but if the reason for setting up
the telescope is to let the neighbors see the glory of
M42 you dont really need to worry about more than
casual alignment. (Engineers sometimes call this last
alignment procedure the "TLAR" method:
"That Looks About Right.")
Here is a brief summary
of your options:
- If you know that the
telescope is already polar-aligned, use MODE
ALIGN STAR. You can also use this option if
youve previously polar-aligned the
telescope but need to realign the NGC-MAX because
it was turned off, or because it reported an
encoder error. This procedure uses a single star
to calibrate both axes.
- If Polaris and at
least one other bright star is visible you can
use the NGC-MAX to assist you in polar-aligning
the telescope.
- If you dont
need to ensure that the telescope is aligned to
the NCP, use MODE ALIGN. You can use any objects
in the data base of the NGC-MAX to perform the
alignment. This procedure uses two (or more)
stars to determine how to translate motion of the
two axes of the mount into RA and DEC values. If
you correctly align the NGC-MAX you can make use
of all its features, but your telescopes
clock drive will not keep the telescope pointed
to the same place in the sky, and the setting
circles on the mount cannot be used to determine
the telescopes orientation.
- If you need to align
the telescope to the NCP and Polaris isnt
visible, the NGC-MAX will not help because its
polar-alignment procedure relies on your ability
to sight Polaris. You will need to perform the
alignment by some other means and then align the
NGC-MAX itself using MODE ALIGN STAR, or you can
decide to forego polar alignment and set up using
MODE ALIGN, or you can accept errors in the
readout and set up the telescope as closely as
you can to alignment with the NCP and pretend
that its exactly correct.
If you will be setting up
your mount in alignment with the NCP, go to the MODE
SETUP display and set the SCOPE option to either EP
(Equatorial Perfect) or GP (German Perfect). If you
cant polar-align the telescope, set the SCOPE
option to EQ or GQ.
(I would have thought
that the "P" in EP and GP stood for
"Polar" but the JMI book insists that it stands
for "Perfect." Oh well
JMI designed the
box so its got the right to call the shots.)
Which way is up?
Here we make a quick
test to ensure that the NGC-MAX knows how the declination
axis encoder reports motion as the telescope is moved.
In each of the alignment
options youll need to make sure that the NGC-MAX
knows which way the declination encoders move to
represent motion of the telescopes declination
axis. The problem occurs when you set up the telescope:
there are two ways that the declination axis on a German
mount can be positioned to look at any place in the sky
except at the two points exactly in line with its RA
axis.
The test is not necessary
if you always set up the telescope so that the first (or
only) alignment star is viewed from the same side of the
telescope, but this can often be uncomfortable, and
isnt necessary if you make a quick test each time
you set up the mount. The test doesnt require
careful adjustment to the telescopes position.
Start by deciding how
youre going to align the telescope and the NGC-MAX.
Turn the NGC-MAX off and select one of the procedures
below:
If your telescope is
roughly polar-aligned:
- Turn the NGC-MAX on.
If you selected non-polar-aligned mode
youll see the instruction SET DEC=0; in
this case set the declination to zero (you can
use the setting circle for this) and press ENTER.
- If the mount has
been set up somewhere within shouting distance of
polar alignment the test is extremely quick;
its quickest if the star is one of the 30
stars listed under MODE ALIGN STAR. (Do not
choose Polaris!) If this is the case, point the
telescope somewhere near the star, select MODE
ALIGN STAR, select the star name from the list,
press ENTER, and skip to step 4.
- If the star is not
in the list under MODE ALIGN STAR or youre
using some non-stellar object, use MODE CATALOG
function to select the star, planet, or whatever
youve chosen, point the telescope at the
object, then go to MODE ALIGN and press ENTER.
The NGC-MAX will display the identifier of the
object youve chosen; press ENTER again. Go
to step 4.
- Now press the MODE
key and UP or DOWN until the NGC-MAX displays
MODE RA DEC. Press ENTER; the RA and DEC of the
object you selected will be displayed. Finally,
swing the telescope on its DEC axis in the
direction of Polaris. If the DEC value increases
(or becomes less negative) the DEC axis is
correctly configured. If the DEC value decreases
(or becomes more negative) you need to change the
sign of the DEC calibration value (see step 5
below). The displayed DEC value should be near
+90° when the telescope is pointed in the
direction of Polaris.
- To change the sign
of the DEC calibration, press MODE, then press UP
or DOWN until the NGC-MAX displays the message
MODE SETUP. Press the ENTER key ten times; the
display should now show the letters AL on the
left, a blinking plus or minus sign, and five
decimal digits. Press the UP or DOWN key once to
change the plus to a minus, or the minus to a
plus, then press ENTER six times. The NGC-MAX
will now display MODE SETUP again; youve
completed this procedure. Turn the NGC-MAX off
and proceed to the appropriate alignment
procedure below.
If your telescope is not
polar-aligned:
- Turn the NGC-MAX on.
If you selected non-polar-aligned mode
youll see the instruction SET DEC=0; in
this case set the declination to zero (you can
use the setting circle for this) and press ENTER.
- You need to do a
rough alignment using the two stars youve
chosen to align the NGC-MAX. Point the telescope
to the first of your two objects, then use MODE
ALIGN STAR (if the object is a star in the MODE
ALIGN STAR list) or use MODE CATALOG and MODE
ALIGN if it isnt. See steps 2 and 3 in the
procedure (above) for a polar-aligned mount for
details.
- Repeat the previous
step for the second object.
- Go to step 4 in the
procedure (above) for a polar-aligned mount.
Aligning the
telescope using the NGC-MAX
If you chose EP or GP
mode and can see Polaris, the NGC-MAX can assist you in
correctly aligning the telescope. Skip this section if
you didnt select EP or GP mode, or if you are using
some other means to polar-align your telescope mount.
The best way to align an
equatorial mount (either German or fork) is the so-called
drift method, but using it can take a lot of time. See
any good book on using amateur telescopes for information
on using this procedure.
Other methods involve the
use of special guides on the mount (such as the boresight
device available with Losmandy mounts). If you dont
use these methods to align the telescope you can use the
alignment feature in the NGC-MAX if you can see Polaris
and at least one of the other bright stars.
Polar-aligning with
the NGC-MAX
The POLAR mode of the
NGC-MAX guides you in aligning the mount with the NCP. It
also calibrates the digital setting circles.
This procedure
requires that Polaris is visible. The NGC-MAX cannot
assist you in polar-aligning the telescopes mount
if you cannot sight Polaris. In addition to Polaris, you
must have a good view of one of the 29 other stars in the
MODE POLAR or MODE ALIGN STAR lists.
Start by orienting the
telescope as closely as you can to the NCP when you set
it up. Once you have tried to move the tripod of a
fully-loaded telescope because the NCP is beyond the
limits of the vernier adjustments youll appreciate
the need to make a good initial orientation.
Select a visible star
other than Polaris from the thirty that are available in
the MODE POLAR or MODE ALIGN STAR lists. To complete the
alignment using the NGC-MAX:
- Turn the NGC-MAX
off, wait five seconds, and turn it on. If the
unit displays the message:
SET DEC=0
then you have forgotten to configure the NGC-MAX
setup option for polar mode. Go to the MODE SETUP
options and change it to read SCOPE EP or SCOPE
GP, then start this step again.
- Press the MODE
button if necessary to display one of the mode
names, then press UP or DOWN until the display
reads MODE POLAR. Press ENTER. The display should
now read SIGHT and display the name of a star.
- Press the UP and/or
DOWN buttons to find a star that you can see (do
not choose Polaris). The best stars will be
within about 30 degrees of the celestial equator.
Do not press ENTER yet.
- Swing your telescope
on its RA and DEC axes to center the named star
in the eyepiece. Use a high-power eyepiece here
since the closer you get to pointing exactly at a
star the better your alignment will be. When the
selected star is exactly in the center of the
eyepiece, press ENTER. The display may flash a
short message, then display a message telling you
to move the telescope to where the NGC-MAX
expects Polaris to be. If you chose Deneb as your
star the message will look like this:
POLARIS 87¬ 44
This is the same type of display that we saw a
few pages ago while demonstrating the guide mode.
- Move the telescope
using the RA and DEC axes until both of the
numbers in the display have become zero. At this
point the telescope should be pointing directly
at Polaris, but unless the mount is already
aligned the telescope will be pointing somewhere
else in the sky (hopefully not too far
from Polaris!). Lock the RA and DEC clutches.
- Without moving
the RA or DEC axes of the telescope, adjust
the azimuth and/or altitude axes of the mount
until Polaris is in the center of the eyepiece.
The display should still show zeros. Press ENTER;
the display will briefly display the message
ADJUST ALT AZM
And will again display SIGHT and the name of the
star youre using.
- Repeat steps 4, 5,
and 6 until in step 5 you see Polaris centered in
the field of view when you swing the telescope to
make the display show zeros. Your telescope is
now well-aligned with the NCP and the NGC-MAX is
ready to go to work.
Note that the NGC-MAX has
taken into account the fact that Polaris is not exactly
at the NCP. You can see this by centering Polaris in the
eyepiece, then selecting MODE RA DEC on the NGC-MAX and
pressing ENTER. The display should show that youve
aimed the telescope at RA 2h34, DEC 89°
17.
Now would be a good time
to adjust the mechanical setting circles on the mount;
point at any known object in the sky (preferably one
close to the celestial equator) and adjust the setting
circles to make them show that objects RA and DEC
values.
- Using the NGC-MAX
Weve finally
finished with orientation and setup. At long last we can
do something with it!
After all of the
preceding work weve finally gotten the telescope
and NGC-MAX set up so that we can use them. At this point
there are four functions that the NGC-MAX can perform for
us (not counting the ability to tell a computer where the
telescope is pointing), so lets step through them:
OK, where is the
telescope pointing?
Select MODE RA DEC and
press ENTER. The display will show the RA and declination
where the telescope is pointing; it will look like this:
R=12h36 D=+26° 42
to tell you that the
telescope is pointing to 12h36 RA and
+26° 42¢ declination. The declination value is given in
degrees and minutes, not degrees and fractions of
a degree.
Swing the telescope on
its axes; if the NGC-MAX is in polar mode moving the RA
or declination shaft will affect only the corresponding
part of the display; if the NGC-MAX is not in polar mode
and the telescope isnt polar-aligned, moving one of
the shafts on the mount will cause both the RA and
declination values to change.
As an extra bonus, if you
are using either the Sky Atlas 2000 or Uranometria
charts, press the ENTER key and the NGC-MAX will identify
the chart which contains the area of the sky to which the
telescope is currently pointing. (See the instructions
for MODE SETUP on page * for the procedure to specify
which map you are using.) Pressing the ENTER key a second
time will cause the display to again show RA and
declination values.
OK, where do I
point it to see a particular object?
To find a particular
object in the sky, we use the built-in catalog and the
GUIDE mode.
Selecting a particular object from the built-in catalog
was described and demonstrated in the section titled
"Introducing the NGC-MAX controls" beginning on
page *; using the GUIDE mode to point the telescope at
the selected object was covered in the section
"Aiming at a specific object" on page *.
Although it may take several steps to select the desired
object from the catalog, once thats done all you
need to do in GUIDE mode is to move the telescopes
axes until the NGC-MAX display shows zeros.
Im looking at
something. What is it?
If youve pointed
the telescope at something in the sky but arent too
sure just what youve found, select MODE IDENTIFY on
the NGC-MAX. The first time you do this the display will
show:
IDENTIFY ANY MAG 10
with the word "ANY" blinking. If you want to
restrict the search to a particular type of object (such
as red star, galaxy, nebula, etc.) press the UP and/or
DOWN key to make the selection. See page 9 of the
JMI-provided operators manual for the NGC-MAX for a
list of the available object types.
Press ENTER and the
number 10 will begin blinking; this field allows you to
select the faintest object that can be found by the
search of the built-in data base, with the ability to
select any magnitude from 1 to 17. Dont go
overboard with this limit; if youve got lousy
seeing conditions with a magnitude limit of 6 its
not going to buy you anything to tell the NGC-MAX to
return an object with magnitude 17.
Press ENTER to perform
the search. When the search is complete the identity of
the object that meets your search criteria (type of
object and limiting magnitude) closest to where the
telescope is pointed will be displayed; press ENTER again
to see information about that object.
Note: whatever object is
found by the IDENTIFY function becomes the
"selected" object in the catalog, replacing
whatever you had previously selected.
Timing an activity
The last function that the NGC-MAX can perform for us in
the field is to act as a very expensive stopwatch. Select
MODE TIMER and press ENTER; the display will show:
00 00 00.0
representing hours,
minutes, seconds, and tenths of seconds. Pressing the
ENTER key successively starts, stops, and resets the
timer.
Note that when starting the timer the word
"START" will appear for a short time before the
timer begins to count. If youll watch closely
youll see that the elapsed time displayed by the
NGC-MAX jumps from 00.0 seconds to 00.7 seconds when the
word START disappears, so its actually running as
soon as you press the ENTER key to start it.
Once started the timer continues to run even if you go to
a different mode; when you return to the MODE TIMER
display the time displayed will represent the elapsed
time from the instant you pressed the ENTER key to start
the timer.
|