Atik 4000 Back Focus...

[fatwoul]

The technican drawing for the Atik 4000 shows a backfocus of 17mm, but the FAQ states it is 18mm.  Which is it?  I'm wondering if the 3mm optical window's refractive index is what increases the backfocus from 17mm to 18mm.

I want to use my 4000 with an f/2.8 system, so focus and back focus are critical, but I need to get an adapter made to fit to fill the distance accurately.

Thanks all

[ruitripa]

Hi,

The Atik 4000 has a backfocus of 17mm, not counting window thickness.

[fatwoul]

Thanks Rui,

So including the 3mm glass window, the backfocus I should allow when constructing my adapter will be...18mm?  Is that correct?  Is that where the 18mm listed backfocus comes from?

Thanks again

[ruitripa]

Hi,

There was a mistake and actually some incosistency in the information. I've just updated the information on the mechanical drawing to reflect the correct optical backfocus distance. In any case, please note that there may be slight variations from camera to camera.

I hope this helps, and sorry for the confusion generated.

Rui

[fatwoul]

Thanks Rui, that's a big help.

Understood that there might be variations, but I wanted to make sure I had the factory specs correct before I have an adapter made.

Best wishes

[fatwoul]

...Ah OK I've had a look.  So the physical distance is 16.5mm, and there is 4mm glass, so the effective backfocus is 17.8mm, so pretty much 18mm.  Got it.  Thanks.

[stephensmith]

I have just came to know about this can you tell what should I initially start with?

[Konihlav]

based that the User's Manual is updated:
http://www.atik-cameras.com/downloads/manuals/Atik400011000Manual.pdf

I'd guess 18mm.

[Andi]

The optical back focus is shown as 16.5mm, this distance takes into account the refractive index of the glass and should therefore be taken as this number. A filter of 3mm thickness should then be taken to add another 1 mm of back focus.

So, for example, my takahashi reducer needs 72mm of back focus. I can subtract 16.5mm and, 1mm for the filters in the filter wheel, so I need 56.5mm of extension.