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Is this a backfocus problem?

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9 replies to this topic

#1 Hugo52

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Posted 05 June 2020 - 03:34 PM

I have a C11 and focal reduser.

My bacfofus is 146.5 mm, it should be 146.05 +-0.5 mm

I measure it from the latest boint of the FR to the sensor.

Pls look at this picture and advice if the eggs in the corners are caused by a backfocus problem?

Regards Hugo

https://drive.google...iew?usp=sharing

 

 

afbeelding(1).png


Edited by Hugo52, 05 June 2020 - 03:35 PM.


#2 rgsalinger

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Posted 05 June 2020 - 03:44 PM

No. The lower right corner is almost perfect. CCD Insprector shows considerable tilt as well as the need for better collimation. 



#3 Hugo52

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Posted 06 June 2020 - 08:19 AM

Wilh a level device laser I found 2 rings who are wobbling.

Thank you for analysing.

Regards Hugo



#4 Hugo52

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Posted 06 June 2020 - 08:38 AM

Now I see it also with a micrometer that these rings are not good



#5 f430

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Posted 06 June 2020 - 11:36 AM

 For your backfocus measurement, you did measure from the correct location; the flat at the end of the threads.



#6 Hugo52

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Posted 06 June 2020 - 03:20 PM

f430, tks



#7 Hugo52

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Posted 10 June 2020 - 05:01 PM

Latest update.

With the laser I found out that using a 2 inch filter, Baader or Hutech a tilt causes

I put the focal reducer with all stuff on a stable table and at the end no camera but a big ring.

I put the laser on top of this ring and mark it the spot on the wall a few meters ahead and start turning.

Only using this 2 inch filters I get a swing of 2 cm.

If I do not use a filter, the laser stays exact on this marked spot.

Is this a known problem that filters are causing this problem?

Regards Hugo



#8 Hugo52

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Posted 11 June 2020 - 05:02 PM

This wil solve all tthe problems.

https://www.ganymede....is-instelbaar/

https://www.teleskop....nge-15-mm.html



#9 Hugo52

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Posted 18 June 2020 - 06:20 AM

Assembled today:
https://www.teleskop...enge-15-mm.html
There is now absolutely no measurable tilt anymore. (Method, see photo)
The back focus is now perfectly set with:
https://www.ganymede...uis-instelbaar/
Now it is time for a clear sky.
Hugo

IMG-6107_crop.jpg


Edited by Hugo52, 18 June 2020 - 06:23 AM.


#10 Hugo52

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Posted 18 June 2020 - 08:34 AM

The problem was reported by Baader, they say that is is not good to use it like I did:

 

There is no standard for 2" filter threads, so we have designed our filter threads to be compatible with as many manufacturers as possible. A part of this solution is a short filter thread, and in combination with the necessary tolerances, this seems to introduce enough play into the optical path.

A filter cell is usually not designed to be a part of the mechanical adaptation, but only to carry more or less its own weight. To be honest, this is the first time that I've heard of someone integrating a filter cell like this into the adaptation.




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