383L Optical Back Focus

[Dave Watson]

Hi,

With regard to the 383L+ camera Atik specify the following

      Distance from top of T-thread to focal plane: Approx 17mm
      Optical window thickness: 2mm

You would normally add 1mm to the back focus of a scopes reducer for the refractive index of the glass filters, the question is should you also add ~1mm to compensate for the cameras optical window?

QSI, for instance, don't actually quote a mechanical sensor distance from the front of the camera, they actually quote the "Optical" distance which takes the refractive index of the optical window into account.

Regards,
     Dave

[chrisjbaileyuk]

I would say yes BUT I have always found it pays to experiment with FF distances by +/- 5mm as the quoted ideal spacing has never given me iideal flatness.

Chris

[Dave Watson]

Hi,

I have just been checking the mechanical drawings for the 383L camera and I have noticed that the wording used is "Optical Backfocus = ~17.5mm".

Can someone from Atik confirm that this OPTICAL backfocus does or does not take into account the reflective index (0.68mm) of the cameras optical window.

I am using a Tak FSQ85EDX with a the Q-Reducer that needs a metal backfocus distance of 72.2mm and with the Baby-Q this distance is very critical, a tolerance of +-0.5mm had been banded around but not confirmed.

Can anyone help.....thanks.

Regards,
   Dave

[ruitripa]

Hi Dave,

Yes, it's optical distance, with both optical windows taken into account (CCD and camera's).

I find it very unlikely that a 0.5mm tolerance is required for a reducer...

[Dave Watson]

Hi Rui,

Brilliant, thanks for your answer.

I agree with you about the 0.5mm, however, Tak America say it is very very critical but won't say exactly what the tolerance is.

Regards,
   Dave