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Severe focus issues on EdgeHD 1100

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#1 dragneg

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Posted 24 August 2019 - 03:38 AM

Hello everyone...

 

A Celestron EdgeHD 1100 arrived this week together with the Celestron f7 Reducer Lens. It saw first light Wednesday night, but not very clear...

 

I have previously used my ASI294 with my EdgeHD 800, and the combination to the right in the photo below is 133.5mm from the SC-adapter ( B ) to the sensor. That is the correct distance for imaging with the 8” EdgeHD at f10. With the f7-reducer installed I just switch to adapter A and get the required 105.0mm.

 

The EdgeHD 1100 require 146.05mm, regardless of f7 or f10.

 

The included step-down adapter ( C ) for the 11” Edge has a working back focus distance of 12.7mm and together with the 133.5mm-kit it equals the required 146mm almost perfectly. However, I am not able to reach focus. With the focus knob at max anti-clockwise to the stop, I need more. Infinity is not enough!

I desperately tried adapter A instead and found focus at a couple of turns clockwise, but the working back focus distance was then 117.7mm and the stars did not look very good.

 

For visual observation, with the included diagonal installed on the step-down adapter and the 23mm Luminos eyepiece, I cannot reach focus together with the reducer lens. Once again infinity is not enough. Without the reducer lens however, I find focus at about seven full turns clockwise. (I have yet to try the camera at f10)

 

 

Full focus travel on my Edge11 is 29.5 turns and it seems to me a bit strange that focus is so far off to one side. On my Edge8 the full travel is 44 turns and focus is found approximately in the middle.

 

 

Is there any 11" EdgeHD-owner out there, who can confirm that focus is found very close to infinity?
Has anyone any idea of what could be wrong in my setup?

 

 

 

/anders

 

Backfocus EdgeHD 11.jpg



#2 jdupton

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Posted 24 August 2019 - 05:31 AM

Anders,

 

   Does anything in this thread from last year help any? You are not the first to encounter this problem.

 

https://www.cloudynights.com/topic/540822-c11-edge-focus-issue/

 

   Ignore all the side topic discussion in that thread about how to measure the back-focus point from the reducer. My reducer came with an old instruction sheet. There was a revised sheet included with later shipments of the reducer.

 

   The net of that thread was that most users get about 39 to 44 turns of the focus knob to go from full stop to full stop of the focus range. The OP in that thread only got about 30 turns and was unable to reach proper focus. Count the turns for you focuser and if it is less than about 39 turns see the solution in the above thread at Post #51.

 

 

John


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#3 dragneg

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Posted 24 August 2019 - 06:42 AM

Brilliant John! Thanks big time for pointing me to that thread.

 

My full focus travel is 29.5 turns. I understand Ettu changed a screw and got two or three turns more, which was sufficient, but there are still about seven full turns missing to the more normal ~40. Do you, by any chance, know what the real problem is? 

 

 

/anders



#4 petert913

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Posted 24 August 2019 - 07:40 AM

Sounds like a warranty discussion with Celestron is in order. 



#5 dragneg

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Posted 02 September 2019 - 09:56 AM

Chris at Celestron support was very helpful and provided me with a fix. It arrived today and now I have 34 complete turns of focus travel, instead of 29.5 before. I have yet to confirm it's enough, but it seems promising...

 

/anders

 

 

IMG_20190902_164940.jpg


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