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High Point Scientific 2 inch Coma Corrector-Imaging

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#1 Astrohoven

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Posted 11 October 2018 - 05:48 AM

Hello!

 

I bought the HPS 2 inch coma corrector https://www.highpoin...r-photo-visual  and I thought it would at least come with it's own manual showing the correct spacing etc.. but apparently it doesn't.

 

I checked some forums, and they are comparing it to the GSO CC on which I found a huge thread and it requires 75mm of spacing. The problem is that I haven't had success with 75mm spacing and I don't have enough spacers to try different spacings.

 

So is there anyone using this specific CC with good results? and what's the spacing you're using? 

 

Edit: I'm using an 8 inch F5 newtonian.

 

Thanks!

Anthony


Edited by Astrohoven, 11 October 2018 - 06:25 AM.


#2 evan9162

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Posted 11 October 2018 - 06:03 AM

I think the correct spacing is going to vary, and may depend on the focal ratio of the telescope.

 

I've been playing with my TPO CC (same GSO made CC as your HPS), with an F/4 newt.  Last night, I found the best spacing was 90mm from the shoulder (with the 2" eyepiece holder removed) to the focal plane.  Keep in mind, with a DSLR, typically there's 55mm from the front edge of the T-adapter to the focal plane.   So I ended up with 35mm of spacing between the shoulder of the CC with the 2" holder removed, to the front edge of the T-adapter on my DSLR.



#3 Astrohoven

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Posted 11 October 2018 - 06:25 AM

I think the correct spacing is going to vary, and may depend on the focal ratio of the telescope.

 

I've been playing with my TPO CC (same GSO made CC as your HPS), with an F/4 newt.  Last night, I found the best spacing was 90mm from the shoulder (with the 2" eyepiece holder removed) to the focal plane.  Keep in mind, with a DSLR, typically there's 55mm from the front edge of the T-adapter to the focal plane.   So I ended up with 35mm of spacing between the shoulder of the CC with the 2" holder removed, to the front edge of the T-adapter on my DSLR.

Ok thanks but I would like someone with the exact same CC to give me the spacing they've been having good results in since the spacing seems to vary a lot between one CC and the other. I really can't currently afford to buy additional spacers or a variable spacer without making sure that it would work. My scope is F5 and I think the spacing between different focal ratios would differ by a slight amount so at least I'd get in the ballpark but I don't think it would differ by 20 mm or more. Would it?



#4 happylimpet

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Posted 11 October 2018 - 08:15 AM

Ok thanks but I would like someone with the exact same CC to give me the spacing they've been having good results in since the spacing seems to vary a lot between one CC and the other. I really can't currently afford to buy additional spacers or a variable spacer without making sure that it would work. My scope is F5 and I think the spacing between different focal ratios would differ by a slight amount so at least I'd get in the ballpark but I don't think it would differ by 20 mm or more. Would it?

I would expect the difference in spacing for different f/ratios would be of the order of 1-2mm. I have an ASA 2korr coma corrector, and I think its about that for me going from f4 to f6...but its been a while since i checked it.



#5 Astrohoven

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Posted 11 October 2018 - 08:26 AM

I would expect the difference in spacing for different f/ratios would be of the order of 1-2mm. I have an ASA 2korr coma corrector, and I think its about that for me going from f4 to f6...but its been a while since i checked it.

Ye that's what I would expect, not a difference of 20mm. So I just can't find any info on whether or not the HPS coma corrector should have a 75 mm or not.



#6 MitchAlsup

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Posted 11 October 2018 - 09:27 AM

I think the correct spacing is going to vary, and may depend on the focal ratio of the telescope.

The "criticality" of spacing does depend on the focal ratio.

The point of optimum correction does not.


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