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Focal reducer for visual?


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2 hours ago, TBRHussaR said:

Hi guys - can you use the celestron .63 focal reducer for visual work? I plan to use it on a 925. Does it have any negative effects? such as aperture loss?

A smaller scope than yours, but there was a recent discussion on using a reducer for visual on a C6 (and a C8) here: 

 

Edited by Shimrod
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8 hours ago, TBRHussaR said:

Hi guys - can you use the celestron .63 focal reducer for visual work? I plan to use it on a 925. Does it have any negative effects? such as aperture loss?

Can you?  Yes.

It improves star image quality and brightens the overall image.

It doesn't create more light, though.  So if you can use an eyepiece with a 46mm field stop at f/10, your maximum field eyepiece's field stop with the reducer is 46*0.63=29mm

That's one of the reasons it is said: " 2" eyepieces at f/10, but 1.25" eyepieces at f/6.3."

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Think of a focal reducer as an image circle compressor.  It takes that 46mm image circle and compresses it down to 29mm as Don says above.  It also flatten the field a bit.  Depending on the design, it might also correct some of the aberrations inherent in an SCT.

Thus, the amount of light per area is increased leading to a brighter image using the same eyepiece.  The trade-off is less magnification and image scale.  To get back to the same image scale and magnification would require a shorter focal length eyepiece.  However, image fidelity will suffer at some point because focal reducers tend to introduce some spherical aberration into the image at higher magnifications, much like Newtonian coma correctors and refractor field flatteners.  As such, removing the FR for critical planetary observing would probably be recommended.

Edited by Louis D
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I feel I just have to add in here, as I have both a C9.25 and a focal reducer. Don and Louis are both correct and I can add I prefer to use the reducer for deep space, then remove it for planetary. I use the reducer nearly all the time with the C9.25, because I have better for planetary. I much prefer the C9.25 with the reducer and must say, it expands options with the scope.  F10 and F6.3, two scopes for the price of one?

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My reducer lives in my C6. It only comes out when I want to use it as a photographic reducer in my Zenithstar 66, or if I want to do planetary imaging with the SCT. Visually, the reducer seems to clean up the image, and gives some more options for larger exit pupils, or wider angle eyepieces at lower magnifications.

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