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Zeiss/Starlight Crayford focuser

Started by Alan Friedman, 06/22/2005 11:03AM
Posted 06/22/2005 11:03AM Opening Post
Greetings friends,

I have spoken with some of you on my project to retrofit my APQ 130 with an alternative to the Zeiss M80 helical focuser. Just yesterday I received a Starlight focuser (with 2.5" travel) made by Werner Schmidt of Starlight Instruments and outfitted with a custom adapter to mount the focuser on the unmodified rear threads of the APQ tube. I had a chance to attach the unit last night and take some pictures which I have attached below.

A detailed report will have to follow - clouds kept me from trying the focuser at infinity. Those of you who have used a Feathertouch with its dual speed pinion know that it is a very smooth functioning unit. My first tests confirm this - it moves effortlessly with no image shift whatsoever. A braking mechanism allows fine control over the resistance in both fine and coarse adjustment.

My goal in this project was to permit enough infocus to allow my Coronado solar set-up to come to focus using the Zeiss/Baader MarkV binoviewer (something I could never achieve with the original Zeiss helical.) The minimum extension of the Feathertouch (with the rotating finder ring removed) will gain about .3 inches over the minimum possible with the Zeiss helical - which should give me just enough. This unit can extend slightly longer than the Zeiss helical, but without the drawtube option it will be necessary to use an extension in some applications. I have shown the focuser with an Astro-Physics 2" compression ring extension which allowed all tested eyepieces to come to focus using the Zeiss T2 prism (I tested on a terrestrial subject 150 meters away - infinity will require less extension). Using a 2" prism, mirror diagonal or binoviewer might eliminate the need for an extension with some eyepieces.

The focuser felt fully comfortable with the weight of the binoviewer and eyepieces and added leverage of the 2" extension. That said, this solution does not have the same heft of an Astro-Physics 2.7" rack and pinion focuser. An imaging application that uses a heavy CCD camera and additional lens elements behind the focuser might require a heavier duty solution. For visual applications carryng 5 lbs or less this should be fine.

I will post additional comments once I have tested the unit more extensively under the night sky. If anyone is interested, Werner has made additional adapters which he will be selling directly. I am not sure how they will price out in production, but the adpater should run approximately $100 and the focuser with brake and compression ring fittings runs $335.

best wishes,
Alan Friedman

Attached Image:

Alan Friedman's attachment for post 25122

Alan Friedman
Posted 06/22/2005 12:12PM #1
Hello Alan,

this looks like an integral part of the Zeiss design - very well made and nice idea, design and finish!

The Zeiss helical focuser is sometimes not the best. Especially at low temperatures it becomes stiff. And the focuser travel is to much for a binoviewer - nobody wants to shorten an original Zeiss tube...

I think this would be a great focuser for my APQ100/640!

Kind regards,