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I would like to open this thread because since about a year I am looking for an alternative for the focuser of my TAK E130. The focuser has at least two problems. One is that the drawtube is not parallel to the axis of the outer tube by a large amount. Therefore one needs to recollimate primary and secondary mirror for every rotation of the focuser. Secondly, when I reverse the direction of the focuser movement during focusing, the image shifts and rotates by about 7 degrees. TAK has already replaced the focuser once, with no significant change. My naive idea was that in the age when people send helicopers flying on Mars it should be possible to construct a focuser which just works precisely enough. However, in my case, a solution seems to be impossible to find, because I would like to continue to use my ASIAIR. With the ASIAIR, I am right now stuck with their EAF focuser motor. This means that I am also bound to use a mechanical focuser to attach the EAF. Unfortunatelly I havent found any alternative mechanical focusers for the Epsilons on the market. All products are integrated motorized solutions. Even Moonlite, which produced a very nice mechanical focuser especially for the E130, stopped production in favor of a motorized solution. (At this point usually the discussion starts that ZWO is so bad to not support other focusers working with the ASCOM standard or why I dont use NINA instead of ASIAIR. I already talked to ZWO about this and also looked into NINA, but this would be a topic for another thread.) |
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Hi, I have an TAK E160 and use the standard focuser with EAF and ASIAIR. I can confirm that a rotation of the focuser leads to a shift of the optical axis and thus the instrument goes out of collimation. The focuser has 2 set screws which can be thightened such that the inner tube will not shake around. But this is not sufficient to adjust the drawtube w.r.t. optical axis. So I decided to not rotate the focuser but keep one position for which I collimate the instrument. I do not experience a field rotation w.r.t. focuser direction, autofocus with EAF works nice once the backlash is set correctly in ASIAIR. As I use a full frame sensor I hope to get away in most cases with cropping the image instead of rotating the focuser. Another option could be to put an extra field rotator into the optical train, but I didn't try so far. My main problem with the standard focuser is that it is not light tight. As I image from a light polluted area (being directly exposed to street light) the light leaking through the focuser is an issue. I could mitigate this with the help of a 3D printer but would be interested to know if there are alternative focusers which are light tight. Kind regards, Thorsten |
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Thorsten Glebe: Hi Thorsten, your mention of the light leak is quite a revelation to me. It finally explains the strange artifacts in some of my images during moonlight. So I say "wow" and "thank you" ! Götz |
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Hi Götz, this is a worst case example for the light leak of the focuser, 180s exposure taken during daytime.  I constructed a simple 3D printed collar which fits over the drawtube https://www.thingiverse.com/thing:5402209. Focusing works with the collar in place and light leakage is reduced to a level where it is not relevant anymore. However I would not take FlatDarks in daylight environment.... Kind regards, Thorsten |
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I made a similar test image this afternoon with 300sec exposure. This is how it looks like with may E130 and optical train. When I try to image during moonlight I indeed see the bright area on the left side and the bright spot on the center right side - and was always wondering why flat fielding doesnt remove these artifacts. So thanks again for the hint. |
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| My 160ed has exactly same light leak issue. I now have to take flat in very early morning just finish light frame with a light panel, and then take flatdark after it. Since it is still dark outside, the exposure time is just around 10 seconds, the light leak is not a big problem for now. |
