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Overview of some accessories for your scope
Vibration absorbers (IV) You have certainly experimented one day the adverse effects of vibrations looking at the eyepiece of your scope or recording a long exposure at high resolution. Ouch, ouch, ouch ! Sometimes, you don't perceive them and you only notice them on photographic enlargements. These vibrations have several origins : cars and heavy trucks circulating on a very close road or motorway, the passage of the train or subway, as well as wind gusts, without forgetting unconscient knocks on the mount... If the ground is made of concrete, paving stones or flagstones, and even macadam, it offers the disadvantage to be very compact and transmit very easily vibrations, even when the source is located at a distance of several tens of meters. Except earthquakes, we can prevent these effects in installing vibration absorber blocks under the tripod or under the base of the mount. For example, here are two animations created by Kazuyuki Tanaka (190 KB .AVI files) showing the image of a star, without vibration absorbers (the tripod is put down directly on the concrete surface of the balconery) and with vibration absorbers. This is not the panacea yet, but this is already much better. These blocks are constituted of simple rubber-foam disks very dense, 10 cm wide for 2 cm thick placed below each pod. This is a temporary solution. If we usually think to rubber, sometimes to polyester foam or frigolite (expanded polyester) to absorb vibrations, this is first of all for economy reasons and convenience, these products being easily available. However, at least four materials have been specially designed to absorb shocks and vibrations : 1°. Alpha-gel. A thickness of 2 cm is able to amortize the falling of an egg from a heigth of 18m ! "High-tech" product, it supports temperatures between -40 and +200°C et is not affected by ultraviolet rays. Depending on models, it tolerates a tensile strength between 0.03 and 2.3 MPa and an elongation ratio between 73% and more than 700% and comes back to its original shape. Steve Fujii Shinji from the japanese Geltec company sells various models (disk, bush, sheet, etc) that you can easily adapt to your scope (below the tripod or the base of your mount) or to isolate a sensitive device from vibrations, specially Alpha-gel sheets (SN15 or SN30) of 10x10cm (37 € per sheet). Geltec is represented in Germany to KITAGAWA GmbH and in various other european countries. 2°. The rubber or polyurethan silicon, from the elastomer family. Also called "gummi". It is more expensive than Alpha-gel and shows mecanical performance slightly lower. The Swiss company TYP represented in the U.K and other european countries sells this isolator in form of disks of various thicknesses and diameters. They only work at request from a blueprint or an sketch. 3°. Sorbothan. Sold since the 1970s by Edmund Scientific, this is also a polymer sold in sheet of 30 cm (12") and 3 mm (1/8") thick ($16). This material cuts out at any size with simple scissors. It shows the same texture as rubber. According to the manufacturer, it absorbs up to 94.7% of the impact energy and comes back to its original shape. 4°. RockStable. This is a visco-elastic material used to create anti-vibration pads. There are sold by set of three to Orion Telescope & Binoculars ($49 or 72.79 € and 50 € to Optique-Unterlinden for a Kepler model), to Celestron dealers ($44.95 on Amazon or 79.58 € to Amazon.fr), or to Médas (82 €). A picture of this item is displayed on top right of this page and below left. Note that we found on Amazon, so-called vibration supressors from $5 but they are first of all used to isolate a device from the gound and they are not dedictated to remove vibrations.
Let's specify that if these products are appropriate to isolate your instrument from vibrations going up from the ground, contrary to what state some dealers, in any case these pads and other absorbers will help you to reduce vibrations generated by a shock on the OTA or by wind gusts. In this latter case, only a wind-cutter or a true shelter will help you. As for a light shock onthe OTA, on the mount or the tripod, you must learn to keep the arms close to your body and to move away from the scope during a long exposure... But after have missed some beautiful pictures because of vibrations, one learns quickly the lesson! Fortunately, at the time of CCD and instantaneous snapshots (1/10-1/500th of second), these vibrations extending over several seconds pass often unperceived. Remain to find a solution if the exposure exceeds a fraction of second. This is here that the choice of an observing site as well as the stability and the quality of your mount are very important factors to consider if you want to get good results in long exposure astrophotography. CCD and digital astronomical cameras Many manufacturers designed CCD cameras for all kind of users and resolutions (from 31000 pixels to 16 megapixels), of various photosite sizes (from 9 to 25 microns) and in a very wide range of prices ($500-13000). We can easily understand why amateurs are interested in such devices : they get in 5 minutes of acquisition the same amount of light as if they exposed an argentic film 30 minutes long. More, as the image is saved in electronic form, it can be upload into a computer and "improved" using any image processing software (see the Image gallery for some masterpieces). To read : Don't be afraid of CCD
But using a CCD needs some practice and to understand how the light is recorded by a pixel. A CCD camera requires a very accurate focusing, much accurate than an argentic film, and in some low-end models, the image size is quite small. Nowadays, several models include an autofocus system while other are color built-in. Some sensors provide an optional anti-blooming gate to avoid the pixel saturation by an overflow of light, and recent or high-end models are equipped with a regulated cooling system down to -40°Cor are even water-cooled. You have also to "optimize" your scope f/ratio to your CCD detector and use a sturdy and accurate equatorial mount as the tracking cannot shift more than a few dozen microns on the chip surface. Then once the images acquired, you have to understand the process of image processing and its functions as explained in the above page. While there are constraints in using a CCD or a digital astronomy camera, results are amazing, doing the fierty of their author. At last, remind that with the revolution of compact digicams and DSLRs, many amateurs have replaced their CCD camera with a reflex, most of them (Canon EOS series, Nikon D series, etc) being today suited to astrophotography, including to deepsky photography as explained in this article written in French. PS. Read also the "To buy or not from oversea ?" report if you consider to import some material from abroad. Image Intensifier For some years, ITT Night Vision and Ceoptics (Collins Electro Optics) gives the amateurs the opportunity to gain 2 magnitudes while observing the sky. Your Nexstar 5" reaches easily the 14th magnitude, just enough to see Pluto (if you know where to search it) ! The magic tool is an image intensifier of 3d generation called I3 intensifier ($1995). Available in 1.25" and 2" barrel, the 25mm model yields better images, with a less pronounced field curvature than the 15mm. Only counterpoint except the price, at high gain the green phosphor display of the "eyepiece" yields snowy images as on old TV-screen due to the electronic noise amplification. But both monochromatic image and noise cannot convince me to not buy it. Today it counts among my accessories...
This device is based on the same principle as a CCD but with a major difference. The I3 intensifier is able to display on-line images like an ordinary eyepiece where the CCD needs an integration time to acquire an image. Only counterpoint you cannot process your raw-images like you should do it with a CCD camera. Good to know in regards of the quality of this device, NASA choosed the I3 system for its 120" infrared telescope. Read my review (in French) for more detail (using the translation module at left if needed). Binocular If you have never observed the sky through a binocular, you could not imagine what is the effect of looking at a rich stars field or a planetary landscape through such a optics... An amazing and magic impression of deep, like a diving into the real three dimensional deep space. But read my report for more details. Due to its rarity and its price, this accessory is considered with respect by amateurs. A binocular like Tele Vue "BinoVue" or the Lichtenknecker Optics model is useless alone. They cost about 1300 € or $1300, but you have to add it two eyepieces, for example two Tele Vue 19 mm Panoptic ($1478). Your bill reaches crazy heights ! A cheaper solution is buying the Lumicon BinoViewer that presents 91% of transmission ($800) but you have always to add two eyepieces.
Note that the low cost Celestron and University Optics SCT models are unsuited for astronomy purposes. These binoculars present an angle of 120°, very uncomfortable to use. Whatever your decision, I wish you to use it at least once. Binoculars are impressive optics that will give you stunning feeling of deep looking at both terrestrial or astronomical objects. Manufacturers & dealers (My 1001 links, letter M) |
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