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07-24-2008, 05:22 PM   #31
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Here's a decent article about them,
Mirror Lenses

07-24-2008, 06:28 PM   #32
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That looks like a nice one!
07-24-2008, 06:54 PM   #33
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Thanks, peter.
07-24-2008, 07:14 PM   #34
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QuoteOriginally posted by Miserere Quote
Damn it, Peter, I'm almost regreting not bidding on that auction! I would'a had a fast 28 and a slow 1000

You were complaining about no focus confirmation due to lack of Pentax contrast, but I think that on a cloudy day, and at f/10, it's more a matter of lack of light as you did get confirmation when it was bright and sunny.

Hey, now you should be able to get some icebergs on the horizon next time you're in Newfoundland.
Mis, if either of had really realized what was in that auction I think we would have had to make a deal to split it or risk a bidding war. I like this long slow old gal a lot more than I though I might. Poor man's FA* 1200mm.

I just finally spent an hour with it this evening and the shots are here:

https://www.pentaxforums.com/forums/post-your-photos/32992-sometimes-little-l...tml#post300491

07-24-2008, 09:19 PM   #35
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Peter, fantastic shots!

You just reminded me of a little gem I have had in my closet for a couple of decades, from back in my Canon AE-1p days... Basically, this same lens in white.

Did yours come with the adapter or did you purchase one? I have been looking for one on and off (I have the Canon FD adapter on it and it's removable from the t-mount). I don't know if I can just buy the mounting portion of it or if I need to give up on it and buy a whole new mount assembly.

I used to do some astrophotography and birding with it, and even have some Meade eyepieces to boost up the power. After seeing your shots, I'm going to have to get the Pentax adapter and clean this baby up, see what it can do for me!

FYI - there are some photos of my version at this astrophotography board, though that one is missing the rubber from the focusing ring:
Astromart Classifieds - Filters, Finders, Guide Scopes - Meade 1000mm f/11 Mirror Lens REDUCED AGAIN
07-24-2008, 09:41 PM   #36
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Frogroast, Yours looks much nicer than mine and is different in a few ways Yours says D=90mm and mine says D=102mm whatever those mean. Of course yours is f11 and mine f10 but that's not much. I think you can just get a T-2 adapter and get shooting. It has the thread for the tube which I think is universal. These T-2's with K mount are pretty cheap on Ebay (I found one for around $10 +S/H).

it's fun and a whole new learning experience. I was out today see: https://www.pentaxforums.com/forums/post-your-photos/32992-sometimes-little-luck-also-helps.html
It was fun! Like shooting with my old K1000 (35mm) again. All manual.

Here's another I just took a few minutes ago. I tried a 2x TC and it was quite good but the moon doesn't fit in the frame!

Name:  IMGP2901 moon shot.jpg
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Last edited by Peter Zack; 07-25-2008 at 05:43 AM.
07-24-2008, 10:00 PM   #37
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i really like that moonshot. might have to hunt down one of these just for that purpose!!
07-24-2008, 10:14 PM   #38
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Wow.. that's some moon shot!

I assumed 90mm was the filter diameter, but it's actually the diameter of the inside of the front (which might also be the diameter of the mirror. I think I remember this being more of a telescope measurement, not sure anymore.

I'll have to start hunting for that adapter on ebay!

07-24-2008, 11:23 PM   #39
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QuoteOriginally posted by Peter Zack Quote
Yours says D=90mm and mine says D=102mm whatever those mean. Of course ours is f11 and mine f10 but that's not much.
D is the diameter of the main mirror.Knowing that and the focal length you can easily calculate the aperture:
102/1000 = ~1:10
07-25-2008, 12:13 AM   #40
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Well, this is one time I have to say "Mine is definitely not as big as yours!"
07-25-2008, 02:01 AM   #41
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QuoteOriginally posted by Frogroast Quote
Wow.. that's some moon shot!

I assumed 90mm was the filter diameter, but it's actually the diameter of the inside of the front (which might also be the diameter of the mirror. I think I remember this being more of a telescope measurement, not sure anymore.
You are quite correct. Telescopes usually quote the open diameter first, followed by the focal length: 90/1000 or 102/1000.

In complex scopes, like the Schmidt and Maksutovs you may find three number, like 100/110/1000, where the 100 is the open diameter = diameter of the Schmidt or Maksutov corrector, the 110 would be the diametr of the slightly oversized main mirror nd 1000 the focal length. If for any reason (mostly convenience) there are only two numbers quoted, they usually refer to the corrrector's diameter and the focal length.

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07-25-2008, 02:06 AM   #42
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QuoteOriginally posted by Peter Zack Quote
Frogroast, Yours looks much nicer than mine and is different in a few ways Yours says D=90mm and mine says D=102mm whatever those mean. Of course ours is f11 and mine f10 but that's not much. I think you can just get a T-2 adapter and get shooting. It has the thread for the tube which I think is universal. These T-2's with K mount are pretty cheap on Ebay (I found one for around $10 +S/H).

it's fun and a whole new learning experience. I was out today see: https://www.pentaxforums.com/forums/post-your-photos/32992-sometimes-little-luck-also-helps.html
It was fun! Like shooting with my old K1000 (35mm) again. All manual.

Here's another I just took a few minutes ago. I tried a 2x TC and it was quite good but the moon doesn't fit in the frame![/ATTACH]
This is a very good moonshot - one of the best I have seen recently with purly photographic equipment (aka: without a mounted telescope).

You will find, that the moon and sun increase 1mm in size on the sensor plane for every 100mm focal length. So at fl=1000mm the image on the sensor (or film) is 10mm in diameter. The APS-C sensor would be filled with 1500mm fl and anything longer than that will only show parts of the disk. For a 36mm x 24mm full-frame the max. fl to image the full disk is just above 2000mm, the standar focal length of the most popular telescops class on the market (the 8-inch Schmidt-Cassegrains by Celestron and Meade).

Ben
07-25-2008, 02:06 AM   #43
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I shot all my birds shots this way - with an astro scope.

But I use a refractor.

If your interested take a look at my gallery shots.

All were taken with a variety of refractors.
07-25-2008, 02:13 AM   #44
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QuoteOriginally posted by Peter Zack Quote
The focus ring is around the back tube right at the back of the body of the lens. It's not a knob style.
This sounds like IF (internal focusing), which would also explain the additional lens group inside. Very convenient and I have never seen one of these lenses.

The article at B&H you linked is not bad. But iit is only valid for dedicated mirror lenses. If one (mis)uses a telescope for photography, you won't find (for example) the rear lens. This rear lens is usually only a field flattener, as the Schmidt-Cassegrains and Maksutov-Cassegrains have a fairly spherical image plain, which needs to be flattend for photographic use. In a standard telescope you would add a separate field flattener for that purpose, if you intend to use the 36mm x 24mm full frame format.

The silver coating on your mirrors very probably have an additional protective coating to prevent corrosion. I don't know off any Meade or Celestron mirror/catadioptric, that hasn't got this protective layer. That has been standard for the last 30 years. So you need not to worry too much about storage, unless you live in a very humid area.

Ben
07-25-2008, 02:32 AM   #45
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Peter, nice thread and some good shots. You might want to check the brief wikipedia article on Schmidt-Cassegrain telescopes, which will tell you that you bought into one of the best-corrected reflex mirror designs among smaller modern telescopes. Good score on that one!

The corrector element in the center of a Schmidt-Cassegrain design reduces spherical aberrations; as noted elsewhere in this thread by procyon, CA isn't much of an issue with (properly ground and aligned) mirror reflex lenses. CA is more endemic to refractive optics, such as our ordinary camera lenses.
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