It's a Maksutov with integral secondary. A 500/5.6 has a 90mm diameter
corrector. It's still possible to build a Maksutov corrector of that
small size economically. Celestron starts building Schmidt correctors
at 5" (125mm) as they've had that technology down pat since the late
60's. Maksutovs start to get very expensive very quickly once you pass
the 90mm mark. Check the price of a Questar 7" to be reminded. Finding
a good, bubble free piece of glass that large and with the required
thickness is difficult.
Chuck Norcutt
Jeff Keller wrote:
> Hmmm ... I don't remember seeing any 500/5.6 lenses before I came across the
> MTO / Rubinar. It sounds like the back end of yours is much different. Does
> it have the heavily curved front meniscus lens of a Maksutov or the
> relatively flat front lens of a Schmidt-Cassegrain?
>
> -jeff
>
> -----Original Message-----
> From: Chuck Norcutt
> Sent: Wednesday, June 21, 2006 4:50 PM
> To: olympus@xxxxxxxxxx
> Subject: [OM] Re: 500/5.6 Rubinar / MTO Catadioptric lens
>
> But the 400 was not a mirror lens. Mirror lenses are quite common in 500mm
> spotting scopes. I have one from Adorama which is the same as sold by Orion
> Telescopes. But it comes with a T adapter so that it can be used on camera
> as well. It's a 500/5.6. Not a bad spotting scope but the large secondary
> mirror (needed for f/5.6) doesn't make for much contrast.
>
> Chuck Norcutt
>
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