It's a wonderful astrograph, each detail has taken care, but above all the optical quality is impeccable with the stars that are perfect points in the center and in the extreme edges of the 24x36 film, thanks to the correcting lenses integrated in the half of the tube. Its apochromaticy is proved by visual tests on the Full Moon and by photographic tests performed from very dark skies, where the stars, also bright, don't show any trace of halos of chromatic aberration. Excellent also the system of diaphrams, that allow to image Deneb in an angle of the field without showing any sign of reflections in other zones. The focusing system is very reliable, with a blocking ring that allow a definitive anchorage of the focuser, preventing any type of bending and focus shift.
The focal of 500mm is ideal for imaging a big number of deepsky objects, i.e. the Andromeda galaxy, California, North American, etc.
The focal ratio is not fast and is necessary 45m of exposure with 400 ISO films and dark skies, but the alternative is to spend the triple for a  100mm refractor.
The accessories are scarce: there is not an adapter for direct focus photos, and the adapter for 31,8mm eyepieces is unusable with common diagonals. The solution is not acquire the expensive Pentax diagonal but simply lathe a shorter adapter, my is only 24mm out from the focuser and allow any eyepiece or diagonal to reach focus. Also the finder is optional, and very expensive! The solution was to build an adapter for mounting the common and economic 6x30 finders.
The only useful accessory is the mounting ring for mounting on a photographic tripod or on a plate, like in my case.

Hints for autoconstruction of accessories: 1"1/4 visual adapter: this accessory allow to use standard star diagonals, while the original adaptor is too long and don't permit to reach focus using the standard star diagonal, except the expensive original Pentax one. mechanical drawing (in PDF) Images of the 1"1/4 visual adapter No vignetting photographic adapter for generic T rings: allow to get a fully illuminated 24x36mm field, without any hint of vignetting. Normally vignetting is unavoidable because of the internal diameter of the T-adapter that have a front thread of 42x0.75mm, so the photo adapter cannot have an internal diameter bigger than about 38mm. And considering that the 24x36 diagonal is 43mm, vignetting is unavoidable! This adapter allow to use only a part of the T-adapter, and to overcome the limit of the front thread. I suggest to verify your T-adaper before realizing this adapter. mechanical drawing (in PDF) Images of the no-vignetting photo adapter (on the left with the Nikon adapter) No vignetting photographic adapter for Canon EOS: the Canon EOS adapter has a free aperture of 47.4mm, bigger than the Nikon adapter and nealy all other brands. To get the maximum from this, a modification to the T-ring is necessary, removing part of the material. I've tested this adapter on my Canon EOS 5D with full frame sensor and the field is really perfectly illuminated. mechanical drawing (in PDF) Finder adapter: allow to use all the standard finders. The original Pentax finder is very expensive. mechanical drawing (in PDF) Images of the finder adapter

HTML Editing and Publishing by Lorenzo Comolli. Email me at comolli@libero.it. Back to Main Page