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Need advice about Atmospheric Dispersion Corrector

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28 replies to this topic

#26 Peter L.

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Posted 14 July 2018 - 12:58 PM

...Indeed after it was pointed out to me that increasing the distance between ADC & camera sensor assisted in their setting/useage (at least with the common wedge variety)...

Sorry for taking this thread on an even bigger tangent, but can't help myself. I latched on to this statement, Darryl, and I'm wondering if you can elaborate because I am having issues with my ADC at the moment. In recent nights, I put the 2x shorty barlow back in my imaging train:

 

Scope --> filter wheel --> barlow inside T2 --> ZWO ADC --> 224MC

 

Sliding the barlow back as tight to the ADC as I can, I'm getting F19-20 with the F11 C14. However, with Jupiter at 28 degrees, Saturn at 20, and Mars at 18, results are all the same. I can max the ADC levers and still not quite achieve alignment. I get close with Jupiter, but not even close with Mars. Is this an indicator as to how bad my skies are or is there something I can do to help, like increase "the distance between ADC & camera sensor"? Is that a factor?

 

Thanks as always.



#27 Kokatha man

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Posted 15 July 2018 - 01:02 AM

...just got home Peter & am only just reading the later posts & thinking about them! :)

 

John is the person who pointed this out to me when we were imaging Jove & Mars earlier in their apparitions at low elevations (somewhat analogous to your own, perhaps) & after his comments we tried with the greater spacing & the improvements were very noticeable at the time!

 

As I think I said here somewhere it of course makes image scale control more problematic, but I think John would be the best person to comment re your post - I cannot remember where that thread earlier in the year is that he responded to...



#28 Tom Glenn

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Posted 15 July 2018 - 01:48 AM

Peter, if you put the barlow behind the ADC, it increases the strength of the adjustments.  So the order becomes; scope---ADC---barlow---camera.  In theory, having an F/11 light cone hit the ADC leads to more aberrations than an F/20 light cone, but in practice the amount of aberrations will be negligible in this case (and far less than uncorrected dispersion).  It sounds like it might be the only way to achieve correction for you.  This will also change your image scale when you move the barlow.....It will likely reduce your focal length because of reduced spacing between the barlow and the sensor, but you could adjust that with spacing.  


Edited by Tom Glenn, 15 July 2018 - 01:49 AM.


#29 Peter L.

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Posted 15 July 2018 - 11:08 AM

Darryl and Tom,

 

Thank you. You've both given me an option to try upon my next opportunity. I will report back on the results of each.




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