Back Focus

[smr]

Just trying to verify whether I have got this right if someone can help...

I have the 2600MC-Pro which has a 17.5mm back focus from the sensor to the Camera flange. Added to the Camera is the 21mm spacer, then a 16.5mm spacer (55mm) according to the diagram below I need 54.8mm of back focus with this flattener. It's the first Z73 (non adjustable) flattener. 

Is this right for back focus? If so, is it ok if I am out by 0.2mm?

Presumably the required back focus for me is 54.8mm.

 

 

 

 

Edited February 24, 2021 by smr

[Clarkey]

Assuming that the additional extension of 15.7mm is part of the flattener then 54.8 looks right. Just looking at your image, have you made any allowance for the tilt adjuster or is that part of the distance to the sensor of 17.5?

With regards to the question of whether 55mm will be OK, I would try it and see. You might need to reduce it a fraction if you are very fussy about star shapes, but equally it might be acceptable.

[smr]

25 minutes ago, Clarkey said:

Assuming that the additional extension of 15.7mm is part of the flattener then 54.8 looks right. Just looking at your image, have you made any allowance for the tilt adjuster or is that part of the distance to the sensor of 17.5?

With regards to the question of whether 55mm will be OK, I would try it and see. You might need to reduce it a fraction if you are very fussy about star shapes, but equally it might be acceptable.

I don't know, I'm confused. That 15.70mm part is a spacing ring, which does come with the flattener, but the glass in the flattener ends here:

 

 

[Budgie1]

I cleaned up the WO Back Focus diagram to make it a bit clearer.

It looks like you've got it correct, you're just 0.2mm long and the 15.70mm is part of the train.

[smr]

15 hours ago, Budgie1 said:

I cleaned up the WO Back Focus diagram to make it a bit clearer.

It looks like you've got it correct, you're just 0.2mm long and the 15.70mm is part of the train.

Thank you Martin.