Tak Sky90 ll and a PlayerOne Poseidon-c IMX571

[Laszlo]

Hi yAll, I'm having a little problem trying to get the proper back focus on this set up. I think I have it at 56mm, when it is supposed to be 55mm. Also, I don't believe the way I've achieved that is even a good idea. It's a t 2.7 focuser with a camera angle adjuster, then the focal reducer/flattener. After that is an adapter and an 2" eye piece holder. I then slip the camera nose piece into that. It is snug, but I'm worried about flex. Here's a photo of my image train.... any help is appreciated. 

[ollypenrice]

I think this will be a case of 'try it and see.' Being 1mm out might not matter since Tak claim a 45mm image circle for your system and your chip diagonal is only 28mm. This is a very good margin. It is on chips exploiting the outer part of the image circle that chip spacing becomes ultra critical.

While you are right to prefer an all-threaded set of connections between scope and camera, push-fit can work fine. I've had several push-fit systems giving perfectly good results.

The original Sky 90 was notorious for being prone to mis-collimation. (This affects other Tak scopes as well, particularly the FSQ range.) I don't know if the later version has been improved. If you do get distorted stars, therefore, don't assume automatically that it is chip tilt. Rotate the camera through 90 degrees and take another test shot. If the distortion remains in the same oriention on the sky, it will be collimation. If the distortion follows the camera angle, it will be tilt.

Olly

[Laszlo]

Thanks Olly... I believe my Sky 90ll NSV is the latest model. The original one I received was the older version and I sent it back because of pinched optics. The new one they sent me, was a shorter version hence the NSV(new short version). I'd rather not have to send it in for collimation if I don't have to, so I'll check it next time out. However, I did contact Takahashi in Texas and they said when using the Tak focal reducer/flattener you need 56.2mm back focus... 55mm is the norm on my camera. So, I guess I'll have to get some very thin spacers..? Thanks again for your input Olly.

Les