Getting my flange distance right

[Space Oddities]

Hello!

Before I purchase yet another adapter, I just wanted to check with you guys that my calculations are correct.

Basically, I'm trying to attach my Baader UFC filter system to a Canon EF lens (Samyang 135/2 and Canon 200/2.8) and a cooled ASI1600. The lens has a 44mm flange distance.

The imaging train I'm putting together to do this:

• ASI1600 > 6.5mm
• ZWO's T2 to T2 spacer > 11mm
• Baader UFC filter slider (M48 to T2) > 16mm
• TS Optics EOS to M48 adapter > 10mm 

Which makes a total of 43.5mm. However, since I'm going to use filters, with up to 2mm thickness, I believe I need to take this into account in the optical path. 

So my question is: from your experience, is 45.5mm close enough to reach infinity focus? Or should I try looking for a smaller camera spacer (9 or 10mm) ?

Thanks for you feedback  

[teoria_del_big_bang]

From my understanding you add a third of the filter thickness to the train to allow for refraction inside the filter. So the distance would be 43.5 + 0.67 mm, so would be more like 44 mm.

Also I think you need to put your filters as close to the camera as possible to prevent vignetting, not have the spacer in between but have the spacer the other side between the filters and the optics.  At 2" probably fine where they are sorry.

 

Like I say this is my understanding but I am sure I will be corrected if I am wrong. 🙂 

Steve

Edited October 14, 2019 by teoria_del_big_bang

[Jkulin]

What is the recommended back focus? For CCD's it is usually 55mm from the CCD to the flattener shoulder.

[Space Oddities]

44 minutes ago, teoria_del_big_bang said:

From my understanding you add a third of the filter thickness to the train to allow for refraction inside the filter. So the distance would be 43.5 + 0.67 mm, so would be more like 44 mm.

Also I think you need to put your filters as close to the camera as possible to prevent vignetting, not have the spacer in between but have the spacer the other side between the filters and the optics.  At 2" probably fine where they are sorry.

 

Like I say this is my understanding but I am sure I will be corrected if I am wrong. 🙂 

Steve

Thank you Steve! Indeed I'm using 2" filters, so I should be fine regarding vignetting  

[Space Oddities]

18 minutes ago, Jkulin said:

What is the recommended back focus? For CCD's it is usually 55mm from the CCD to the flattener shoulder.

I believe the back focus depends on the lens or telescope you're using. In that case (Canon lens), it's 44mm