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Celestron f/6.3 reducer and 31mm Nagler

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#1 AlienRatDog

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Posted 31 December 2012 - 09:11 AM

Can anyone tell me how that combination works? A lot of vignetting or would I have a wider field of view with better edge performance?

#2 rmollise

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Posted 31 December 2012 - 09:50 AM

There will be vignetting aplenty. There is certainly plenty with my 35mm Pan and the 6.3...but a couple of observations...

You might still like the results. Yes, the vignetting is severe as such things go, but I can overlook that for the reward of seeing most of the Pleiads in a C8.

A combination like this is not something I often want/need. Magnification that low is not something I normally use even at my semi-light polluted semi-dark site.

In other words: It's what you can tolerate and what you need. If you are one of those folks who obsesses about slightly misshapen stars at the edge of he field, fuhgedabout it. If you are like me, who mainly looks at what's in the center of the field, you might occasionally like the results.

:gramps:

#3 Patrick

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Posted 02 January 2013 - 10:59 PM

Well, one of the reasons Celestron developed the EdgeHD SCT's was to improve the edge of field performance with wide field eyepieces like the Naglers. I don't think they would have brought out a new line of scopes if the existing scopes performed will with the large AFOV eyepieces.

I've personally found that my C11 performs at it's best with the Panoptic 68° eyepieces.

Patrick

#4 Eddgie

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Posted 02 January 2013 - 11:16 PM

This has been my own message for several years. Panoptics and similar 68 degree AFOV eyepices are a far better choice for the standard SCT than wider apparent field types, and the larger the SCT, the more benefit there is to using 68 degree AFOV eyepiecs over 82 degree types for the same true field size. It simply reduces the effects of coma and field curvature inherent in the standard SCT design.

There is also this. For a given true field size, the lower magnifiction of the Panoptic will mitigate the bloating that is often seen when using larger apertures at higher powers. SCTs are often slammed for soft or fuzzy stars, but this is the natural consequence of using a big aperture at high powers.

Lowering the power (for a given true field size) simply reduces the blur diameter of stars that are abberated by seeing so that the abberation is harder to resolve.

Bottom line... Stars look sharper in standard SCTs when using Pans or similar eyepiecs when compared to SCTs using Naglers and similar eyepeices providing the same true field size, and the larger the SCT the more benefit to be had.

I can't stand to use Naglers in my C14. The Panoptics give far sharper fields.

But in my EdgeHD, the Naglers ofter the same pinpoint performance that refractors offer. Side by side with my 6" APO, the sharpness across the field is every bit as good as the AP 152. This is the first reflector that I have ever used that I can say this about.

#5 Rick Woods

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Posted 03 January 2013 - 01:10 AM

That's funny that you guys both feel that way about Naglers. The 31mm Nagler is a terrific performer in my Meade SCT, with almost no edge distortion at all. Is there some difference in the way the mirrors are ground that would account for this?

I don't think the results of an f/6.3 reducer coupled with a 31mm Nagler are going to be good. The Nagler alone gives almost the maximum possible FOV for a 2" eyepiece anyway; gilding the lily rarely improves it. (That was my experience, anyway.) The doc for my FR/FF was specific about its being intended for use with non-WA eyepieces.

#6 Eddgie

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Posted 03 January 2013 - 07:01 AM

The stars are unsharp in my C14 when using the 31mm Nagler because of the field curvature and coma of the Telescope.

When I use the 31mm Nagler in my EdgeHD 8" or 6" APO, the stars are very sharp right out to the edge.

Some people are less sensitive to off axis abberations than others I guess. No big deal. But once you get used to seeeing pinpoint stars across the field, you start noticing when they aren't pinpoint.

#7 AlienRatDog

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Posted 04 January 2013 - 12:29 AM

Hmmm you guys kind of make me want to get an Edge version of my CPC...

#8 rmollise

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Posted 04 January 2013 - 09:03 AM

This has been my own message for several years. Panoptics and similar 68 degree AFOV eyepices are a far better choice


So I guess my 13 Ethos isn't REALLY as good as it looks to me. Sigh. Guess I'd better go back to the Panoptics. NOT. ;)

#9 rflinn68

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Posted 04 January 2013 - 11:10 AM

This has been my own message for several years. Panoptics and similar 68 degree AFOV eyepices are a far better choice


So I guess my 13 Ethos isn't REALLY as good as it looks to me. Sigh. Guess I'd better go back to the Panoptics. NOT. ;)


Call me when you're ready and I'll order you up a brand new shiny Panoptic for that used Ethos Rod. You'll be much better off then :grin:

#10 rmollise

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Posted 04 January 2013 - 11:40 AM


Call me when you're ready and I'll order you up a brand new shiny Panoptic for that used Ethos Rod. You'll be much better off then :grin:


Maybe a nice 40-degree Ramsden would be better still... :lol:

#11 Patrick

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Posted 04 January 2013 - 12:12 PM

So I guess my 13 Ethos isn't REALLY as good as it looks to me. Sigh. Guess I'd better go back to the Panoptics.



If you send me your 13 Ethos I can do a direct comparison and let you know what I really think. :grin:

Patrick

#12 JoeR

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Posted 04 January 2013 - 12:46 PM

I tried that reducer with a 40mm SWA 68° and the vignetting was ridiculous a very pronounced black ring around the edge. However the Astro-Physics CCDT67 telecompressor has a larger clear aperture of 44mm and all the eyepieces I've used works well with it, even the 30mm 82° It won't correct the standard SCT but it will allow your 12" LX200GPS to have a wider FOV. With my EdgeHD optics it is a perfect match.

TeleVue lists the field stop diameters for all their eyepieces on their web site so that's a good reference point what sizes work well with focal reducers.

#13 Rick Woods

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Posted 04 January 2013 - 01:56 PM

It won't correct the standard SCT but it will allow your 12" LX200GPS to have a wider FOV.


Is this really true?

Isn't an SCT of a given size only capable of a certain size FOV, which can be obtained without the reducer by using the appropriate eyepiece? I mean, the baffle tube size hasn't changed; and the max FOV of a 1.25" or 2" eyepiece doesn't change.
Doesn't the reducer only increase the FOV of some eyepieces that are below the widest FOV in the first place? The Meade FR came with doc that said it was only meant for smaller FOV eyepieces such as the 26mm Super Plossl, and that using it on a WA eyepiece would vignette the view.

I really don't know the answer here. I remember when Meade came out with the UHTC coatings, people misunderstood the advertising hype ("It's like adding an extra inch or aperture!") and said things like their 14" SCT was the equivalent to a 15" scope, which is of course ridiculous.

So, I'm wondering if people are expecting the same sort of impossible performance from the f/6.3 reducer? I mean, you can't beat the physics, right?

#14 Rick Woods

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Posted 04 January 2013 - 01:57 PM

JoeR:

What in the world is your avatar? It looks like a piece of toast farting?

#15 neotesla

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Posted 04 January 2013 - 02:19 PM

JoeR:

What in the world is your avatar? It looks like a piece of toast farting?


http://en.wikipedia....wiki/Domo_(NHK)

http://www.bing.com/...omo&FORM=HDRSC2

#16 JoeR

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Posted 04 January 2013 - 03:27 PM

It gives an apparent wider FOV with the lower magnification, but you are still limited to the SCT design. You can only go so low before the secondary obstruction shadow begins to emerge. The widest I can go on my EdgeHD 11 is 1.3° with the telecompressor. That is the same with the standard C8 using the Panoptic 41mm or Plossl 55mm at native resolution. Same AFOV but different magnifications.






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