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Re: [APML] Meade/Celestron focal reducers
The 10" F6.3 has a 40% obstruction vs 37% for the F10 scope. That's
about all I know about the differences between the 2 scopes.
cheers
Duncan
Lane, Jason R wrote:
>Hi Ray,
>
>Good point about the longer SCT. I agree that a longer tube variant would typically have better field correction, but it may also be possible with the more compact scopes. Although compactness is definitely a trade-off, one perk of designing for photography vs. visual is that your performance requirements are different and in some ways more relaxed. For example, while you want a flat field, you can sacrifice sharpness since you don't require diffraction limited performance (ie Airy discs)..only that point sources image to grain size or less (ie. less than, say, 25um). I don't know if you could do it with spherical mirrors and keep a short tube, but using aspheric mirrors you probably could. I wonder if the f/6.3 has the same size secondary mirror or a larger one, since a photographic SCT doesn't need as small a secondary as a visual scope does.
>
>Can't wait to see Duncan's results.
>
>Cheers,
>Jason
>
>
>-----Original Message-----
>From: astro-photo-bounces@seds.org
>[mailto:astro-photo-bounces@seds.org]On Behalf Of Ray Butler
>Sent: Monday, October 18, 2004 9:40 AM
>To: Discussion of Film Astrophotography
>Subject: Re: [APML] Meade/Celestron focal reducers
>
>
>
> > One thing to remember about f/6.3 SCTs like yours is that these were
> > designed more for astrophotography vs. visual use, so it was likely
> > designed with a fairly flat field to begin with.
>
>I kinda doubt that the dedicated f/6.3 SCTs have off-axis performance
>which is any better than the f/10 versions. In choosing to use such an
>extremely short-tube variant of the SCT design, both Meade and Celestron
>opted for compactness, over the better field correction which could have
>delivered by a longer design with wider-spaced optics & a slower primary
>mirror. Can't remember which book I saw this in...might have been Wallis
>& Provin's book.
>
>Ray "who's possibly falling into the trap which goes 'I don't know what
>I'm talking about, but I'm going to say something anyway' " Butler
>
>
>
>Lane, Jason R wrote:
>
>
>
>>Hi Duncan,
>>
>>>From what I've seen on Meade's site and from folks testing out the reducer, it'd likely be a pair of positive achromatic doublets with an effective focal length of about +230 mm. Since the lenses have been designed to work together and the whole thing has been designed to work with the SCT, you won't be able to break it down into a separate reducing lens and a field flattener.
>>
>>One thing to remember about f/6.3 SCTs like yours is that these were designed more for astrophotography vs. visual use, so it was likely designed with a fairly flat field to begin with. How do your stars look at the corners of an image vs. the center? That'd be the best way to tell.
>>
>>Cheers,
>>Jason
>>
>>-----Original Message-----
>>From: astro-photo-bounces@seds.org
>>[mailto:astro-photo-bounces@seds.org]On Behalf Of Duncan Munro
>>Sent: Saturday, October 16, 2004 11:39 AM
>>To: Discussion of Film Astrophotography
>>Subject: Re: [APML] Meade/Celestron focal reducers
>>
>>
>>I am interested in adapting a field flattener for a Meade 10" F6.3 SCT
>>OTA. I 'm curious about the design of the f6.3 reducer corrector as
>>well. I'm wondering if it is a combo of a doublet reducing lens and a
>>zero power doublet field flattener? If so it might be possible to remove
>>the reducing elements and use it as a zero power field flattener (with a
>>consequent reduction in vignetting).
>>
>>I'm also interested in calculating the radius of curvature of the f6.3
>>OTA to see if any existing flatteners will work with it.
>>
>>cheers
>>
>>Duncan
>>
>>Lane, Jason R wrote:
>>
>>
>>
>>
>>>Hi Duncan,
>>>
>>>Didn't think of Vixen. I'm curious because I'd like to include the focal reducer in my telescope's Zemax model (optical CAD package), and want to know if what I think it might be is actually on the right track. Really nothing more than idle curiosity.
>>>
>>>Cheers,
>>>Jason
>>>
>>>
>>>-----Original Message-----
>>>From: astro-photo-bounces@seds.org
>>>[mailto:astro-photo-bounces@seds.org]On Behalf Of Duncan Munro
>>>Sent: Friday, October 15, 2004 10:53 PM
>>>To: Discussion of Film Astrophotography
>>>Subject: Re: [APML] Meade/Celestron focal reducers
>>>
>>>
>>>I suspect that they are the same as well. I'll bet Vixen might have had
>>>a hand in the design but that is just a guess based upon Vixen's past
>>>ties with Celestron. Why are you interested?
>>>
>>>cheers
>>>
>>>Duncan
>>>
>>>Radu Corlan wrote:
>>>
>>>
>>>
>>>
>>>
>>>
>>>>On Fri, 15 Oct 2004, Lane, Jason R wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>Hi all,
>>>>>
>>>>>I've heard rumor that the 0.63x reducers from Meade and Celestron are
>>>>>both made by the same optical house in Japan. Whether they are or not,
>>>>>does anybody know who makes the optics?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>Mine are marked "Made in Japan", true. And i don't think i ever heared
>>>>anybody saying that there is any difference between the two. Can't help
>>>>you with the name of the maker unfortunately.
>>>>
>>>>Radu
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>Cheers,
>>>>>Jason
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>>
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>
>
>
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