Qhy9m to WO P-Flat 4 correct distance

[apaulo]

Hello Everyone

I need to confirm if my thinking is right regarding the spacing between my qhy9m ccd face and the WO P-flat 4 focal reducer/ flattener.
The distance from CCD face to the Filter wheel M42 screw is 39.3mm
Wo suggests a distance of 73.5 so i need to insert an spacer measuring 34.2mm or 35mm rounded up.
The question I have, is the total distance of 73.5 mm from the m42 thread of the ccd end of the p-flat 4 to the CCD face
or is it the variable setting on the P flat 4?
I think its the spacing between the M42 thread to ccd face, but can't seem to find any documentation.
Regards Paul

[rustigsmed]

Hi Paul,
Without knowing your specific example - usually with spacers its the distance to the sensor as this distance varies from camera to camera.

Cheers

Rusty

[HarryD]

Hi Paul

I have a WO FLT132 and a WO "adjustable" PFlat4 to go with my QSI683.
I went to the expense of ordering an adaptor from Precise Parts in the US after careful consideration of the distances given by WO.
However I did find that the recommendations from WO, for my system, didn't work straight away. It was only after much testing and adjusting that I can achieve round stars to the edge. You may find that worrying about 0.5 mm or 1 or 2mm is not going to make any difference. You may still have to play with it to get it to work.
Good luck.
Greg

[apaulo]

Thank you for your help
Paul

[Atmos]

What calculation have you used for the QHY9 back focus distance? The QHY9 manual mentions 15mm, I have read of others using 17mm and then others saying that it is 16.2mm when taking the CCD chamber glass plate into the equation.

[cfranks]

You also have to take the filter thickness into consideration. Increase the physical distance by 1/3 filter thickness.

Charles

[apaulo]

Atmos

The correct distance of the qhy9m is 17.3mm and you have to add the back focus of the filter wheel also, which measures 20.6mm so a total of 38mm

The WO website suggests the distance required is 73.5mm for the WO P-flat 4 and the WO flt110.

Hence 73.5mm - 38mm is close to a 35mm spacer required.

The question is still un answered though
"Is the total distance of 73.5 mm from the end of the p-flat 4 to the CCD face or is it the variable setting on the P flat 4?

AS for the thinkness of the filters themselves, not to sure about that one...

Regards Paul

[Atmos]

Haha so now I have four figures from numerous different locations across the web!

As for the filters, it is correct that you add a third. So with a set of Astrodons I had to add another 1mm to the calculation. Do my flattener effectively went from 54.8mm to 55.8mm.