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2" diagonal and f 6.3 focal reducer on my 8" LX

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#1 davidpitre

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Posted 21 October 2005 - 07:35 PM

I've put a f6.3 focal reducer on my LX90 (8").
No I can't reach Zenith when used with the 2" diagonal.
I haven't had a chance to use it yet, but I'm wondering , will my U.O. 40 MK70 vignette worse with the reducer than it does without the reducer?
Anyone else used a similar superwide field combo with an 8" SCT?
Anyone else had clearance problems with the 2" diagonal and focal reducer? My diagonal is a W.O.. I was wondering if other diagonals might be more low profile.
Could I get an adapter and use the reducer on the eyepiece side of the diagonal?
Thanks for your suggestions.

#2 Lew Zealand

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Posted 21 October 2005 - 11:10 PM

I don't have that same setup but your 40mm 70° EP will definitely vignette with the focal reducer. An SCT can only get so much of a wide field - they're not designed to do that. Actually I'm curious how much you will notice it, please let us know!

My 2" Antares diag just barely clears the base of my 8" LX90 (no focal reducer) so I'd guess that with the extra length of the focal reducer, you will probably not be able to reach the zenith with any 2" diagonal.

#3 Jeff Young

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Posted 22 October 2005 - 07:44 PM

David --

I'm also curious how much the vignetting is noticable. A 40mm 70° occular will vignette even at f/10 (although I'm hard pressed to notice it). I'd expect the outside edges to be either noticably darker or completely black at f/6.3 -- but I don't have a focal reducer to try it.

-- Jeff.

#4 davidpitre

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Posted 23 October 2005 - 08:52 AM

Well. The U.O. 40MK 70 is not a pretty sight with a focal reducer. I'm wondering if it would preform that badly in other f/6 scopes.
As for vignetting, it wasn't as bad as I thought. The star images started to flatten out terribly from 50% out, though.
I am a big fan of this eyepiece at f/10. It has small amount of vignetting, but I never notice it. You'd have to be studying the edge to see it. Tremendous view.
Surprisingly, though, the 40mm ultima (1 1\4") was stunning with the reducer. I could fit the entire Pliades! That's considerably more than is encompassed with the 40MK 70 ,which gives the max FOV at f/10.
If someone wanted either a 2" diagonal or an f/6.3 reducer, I'd say go with the reducer if you have the eyepieces to work with it.

#5 John_Gillies

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Posted 26 October 2005 - 07:48 AM

Hi David,

Are you familiar with the Denkmeier #S1 Power x Switch Star Diagonal? It is a WO 2" diagonal (Silver enhanced or Dielectric) with a Denkmeier Power x Switch mounted on it. It provides .66 focal reduction, normal power (1X), and 2X magnification, all with one eyepiece. For an 8" SCT, you get a supplied "shorty" version SCT adapter and nosepiece with the diagonal and it does clear the forks for viewing the Zenith. To change powers, you merely slide one or the other arm into the light path, or leave both arms out for normal power. Focusing is no different from a seperate focal reducer or barlow in that you have to re-focus for whatever mode you are in. The beauty of it is, you don't have to remove or swap out anything to change powers. I like to find my targets in reduced mode, and increase power to match the target I'm looking at. You don't get the light loss that you experience with most barlows either. I have 3 of these....the #S1 for my 8" LX10, #S2 (for binoviewing and single eyepiece) for my 12" LX200, and the #R1 (single eyepiece and binoviewing) for my ST102 refractor. I find I'm never changing eyepieces anymore.

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  • 657889-Small Copy of #S1 for single eyepieces.jpg



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