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Old 26-11-2015, 09:37 AM
apaulo (Paul)
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Qhy9m to WO P-Flat 4 correct distance

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
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Old 26-11-2015, 10:07 AM
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rustigsmed (Russell)
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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
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Old 26-11-2015, 04:12 PM
HarryD (Greg)
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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
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Old 27-11-2015, 04:45 PM
apaulo (Paul)
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Tnx

Thank you for your help
Paul

Last edited by apaulo; 28-11-2015 at 10:17 AM.
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Old 27-11-2015, 05:47 PM
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Atmos (Colin)
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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.
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Old 28-11-2015, 08:17 AM
cfranks (Charles)
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You also have to take the filter thickness into consideration. Increase the physical distance by 1/3 filter thickness.

Charles
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Old 28-11-2015, 10:17 AM
apaulo (Paul)
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Distances

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
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Old 28-11-2015, 11:38 AM
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Atmos (Colin)
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Quote:
Originally Posted by apaulo View Post
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
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.
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