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Focusing Question

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#1 Jmax


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Posted 31 January 2013 - 10:16 AM

I have never been able to image with my 8" Newt because I cannot get the sensor of my camera to the focal point. Infocus is not sufficient. I know I can move the mirror up in the tube slightly, but I don't really like the idea of doing surgery on my tube. I know another alternative is to use a barlow to move the focal point back, but I have read that this is not optimal. So my question is, if I get a coma corrector (which I need anyway), would this accomplish the same thing as a barlow? would I then be able to reach focus? I am thinking that, logically, if the coma corrector is like an eyepiece, and therefore, it is working kind of like eyepiece projection then it should work. But then again, sometimes logic escapes me.

#2 Alex McConahay

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Posted 31 January 2013 - 10:59 AM

My Coma corrector requires even more infocus.

Have you tried extending the collimation bolts (or leaving them at their extreme end--as far out as they will go and still collimate.

And then there is the low profile focuser.

And, by the way--the surgery on the news is really not much in most tubes.

#3 Phil Sherman

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Posted 31 January 2013 - 11:45 AM

Try a Baader MPCC. It adds around 25mm of back focuus and makes no changes to the focal ratio. It'll also help eliminate coma.


#4 Gray


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Posted 02 February 2013 - 07:54 PM

Yep, lower the profile of the focuser. And the Baader mpcc works great. I've done the same to mine. CS, especially in Al.

#5 dugpatrick


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Posted 02 February 2013 - 08:33 PM

Does the focuser on the 200N have a screw-on attachment? I ask because my Celestron 8" newt had a similar problem reaching focus when using the stock attachment. In my case I picked up the #FAGA attachment from scopestuff and now I can reach focus.


#6 Jeff2011



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Posted 04 February 2013 - 12:30 AM

You can move the primary mirror without cutting the tube by replacing the collimation screws with longer ones. I replaced the 1 inch screws that came with my scope with 2 inch. It only took me an afternoon to do it. Check out this guys web site for details on how to do it.

The other nice thing about this method is that you can easily reverse it if it does not workout.

I do have a baader mpcc on the way but I don't think it would have solved my infocus issue.

I did have to get an extender to use my eyepieces after moving the mirror.

(The URL above has been corrected)

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