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Does reducer or extender mpcc change the actual focal length of the newtonian telescope?

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#1 KillGit

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Posted 11 July 2024 - 01:20 AM

Hi there,

 

Recently I've been DIYing a 1200mm focal length photographic newtonian telescope, I'm having trouble designing the focuser travel distance and choosing a mpcc.

Assuming the cmos focus distance is near 1200mm when using 1x mpcc, if I use 1.1x mpcc is the focus distance near 1200mm or is it near 1200*1.1=1320?

Does an reducer or extender mpcc change the actual focal length of the newtonian telescope?

 

Looking forward to hearing from everyone's experience.

 

git



#2 GlennLeDrew

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Posted 11 July 2024 - 03:40 AM

The effective f.l. for a 1.1X corrector is indeed 1.1X longer than the 'native' f.l. Whether this means the focal surface is moved 1.1X farther from the primary mirror is another matter which depends on the thickness of the corrector and the ray paths within it. The maker of the corrector should supply information on any requirements for focuser travel while in use. For such a comparatively small amplification as 1.1X, I should think that that's the result of the design settling on this so as to require minimal focuser shift.


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#3 KillGit

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Posted 11 July 2024 - 11:43 AM

The effective f.l. for a 1.1X corrector is indeed 1.1X longer than the 'native' f.l. Whether this means the focal surface is moved 1.1X farther from the primary mirror is another matter which depends on the thickness of the corrector and the ray paths within it. The maker of the corrector should supply information on any requirements for focuser travel while in use. For such a comparatively small amplification as 1.1X, I should think that that's the result of the design settling on this so as to require minimal focuser shift.

Thanks for your reply, as you said, I looked up the manufacturer's web page and it does have data on focus shift.



#4 KBHornblower

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Posted 12 July 2024 - 08:47 AM

What is mpcc?  Please, please, pretty please, spell it out initially and perhaps follow with the abbreviation or acronym in parentheses.  Not all of us can get it from the context.



#5 GlennLeDrew

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Posted 12 July 2024 - 11:36 AM

MPCC = Multi-Purpose Coma Corrector.




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