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Coma in binotrons

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#1 alexvh

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Posted 23 September 2021 - 05:21 AM

Hi guys, 

Anyone using the binotron in Fast scopes (F4 perhaps?) What can you do to fight coma?

A



#2 Jeff B

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Posted 23 September 2021 - 09:15 AM

I assume you are referring to use in a newtonian.  If so, I hope you are using the A45 OCS element.  How much do you see and where in the FOV does it become noticeable?   

 

Russ has told me in the past that his OCS system has some coma reduction associated with it, not as much as a TV Paracor, but it is there.  However, he never really quantified it.  My own subjective assessment is that the coma ends up being similar to the resulting focal ratio with that particular switch position.  For example, with an F4 and the 1.3X switch position, it's similar to a native F5.2 system in monovision.  With the 1.8X switch position it's similar to that of an F7.2 system and so forth.  My fastest newtonian is F7, so for me and my scopes, coma has been basically eliminated.  

 

This all assumes your system is well collimated, which, at F4, is very important.

 

Jeff



#3 alexvh

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Posted 23 September 2021 - 09:51 AM

I assume you are referring to use in a newtonian.  If so, I hope you are using the A45 OCS element.  How much do you see and where in the FOV does it become noticeable?   

 

Russ has told me in the past that his OCS system has some coma reduction associated with it, not as much as a TV Paracor, but it is there.  However, he never really quantified it.  My own subjective assessment is that the coma ends up being similar to the resulting focal ratio with that particular switch position.  For example, with an F4 and the 1.3X switch position, it's similar to a native F5.2 system in monovision.  With the 1.8X switch position it's similar to that of an F7.2 system and so forth.  My fastest newtonian is F7, so for me and my scopes, coma has been basically eliminated.  

 

This all assumes your system is well collimated, which, at F4, is very important.

 

Jeff

Yes i have the A45 OCS - however this does not reduce Coma, only the FOV... the coma is still there on the edges



#4 Jeff B

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Posted 23 September 2021 - 12:27 PM

Yes i have the A45 OCS - however this does not reduce Coma, only the FOV... the coma is still there on the edges

What power switch settings do you see the coma at and how close to the edges?  Also, it is easy to confuse coma with eyepiece off-axis astigmatism, especially as they co-occur in fast newtonians.

 

Jeff



#5 alexvh

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Posted 23 September 2021 - 07:03 PM

Does anyone ever use a paracor with a binotron?

#6 scarubia

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Posted 23 September 2021 - 07:48 PM

Does anyone ever use a paracor with a binotron?

Can't be done with the Binotron. The only bino system I know of that does accommodate serious coma correction is the TV Binovue used with the TV Paracor 2. See here: https://www.televue....id=63&Tab=_pcor

 

I use this set up on my 18" and it works beautifully.




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