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07-13-2012, 09:39 PM   #61
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Hrm, I guess I see that a little. My Tokina 500mm mirror focuses down to 4 feet, and at that distance it doesn't take particularly sharp photos. Increase to about 10 feet and they're much better, though. These are unedited, straight out of the camera shots to illustrate. All are within an inch or two of minimum focusing distance.


07-14-2012, 02:35 AM   #62
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QuoteOriginally posted by Edgar_in_Indy Quote
Yeah, she just came home and immediately set about deconstructing my carefully assembled testing lab.
Ha ha - love this story Edgar. I can just picture the scene when your wife returns and your downcast face

FWIW - I have the Tamron BB 500 (supposedly the best 500mm mirror out there) and it is certainly a very viable option for those on a very low budget but need the reach.

Couple of tests I've done here :
07-14-2012, 02:41 AM   #63
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QuoteOriginally posted by Edgar_in_Indy Quote
Those are my same feelings, but it didn't seem to be working. Unfortunately I just sold my beloved K-x, and can do no further testing. I will also not be able to do any further testing of the mighty Phoenix / Samyang 500mm until I get a K-30, but that won't happen until somebody buys my Sigma 50-150mm.
Oh what a cracking lens you're selling Edgar - someone should be all over that !
07-14-2012, 07:32 AM   #64
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A 500mm F8 lens at minimum focus distance of 1.7m has a DOF of 2.6mm.

All the focusing issues of Macro photography come to play in this setting and it is very difficult to perfectly focus without additional help.

The viewfinder will be rather dark at F8 and split screens/micro-prisms go black. Unless one uses Live View with at least 6X magnification and focusing rails, it will be next to impossible to be spot on. And if the subject is more that 2.6mm thick, the image will look soft since most of it will be out of focus.

07-14-2012, 10:00 AM   #65
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Weird topic this, its not discussing lenses at all, but 500mm mirrors.
And a rather 'great' 500mm mirror is not even discussed here !
Well, maybe better not discussed at all, because they forgot something very important on this oversized bodycap, namely a decent tripod connection.
07-14-2012, 12:51 PM   #66
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QuoteOriginally posted by Edgar_in_Indy Quote
Very sounds like you are extremely knowledgeable on the subject. Based on your experience with mirror lenses, would you say that the images I posted of the panda vase at the beginning of the thread are normal for a 500mm mirror lens shooting a subject approximately 12-15 feet away and without a lens hood? Or does it look like the lens is not performing properly?
The examples you post are exceptionally poor, I think. But I must confess, that I never used such a poor lens, so I cannot say for sure, whether this is a normal behaviour or you fell victim to sample variation. The Tokina 500(8 is really not that bad at near distances and the Russian Rubinars also, don't behave that bad (there is even a dedicated "macro" version available of the Russian 1000/10 mirrors). But if I look at the washed-out Pandas, I am also not sure, that the focus is really on the Pandas. If I look at your image, I have a slight feeling, that the focal plane lies somewhat in front of the Pandas, at least the somewhat better sharpness of the paper seems to indicate that?

You can yourself read-up on mirror lenses easily, by the way. There are several quite readable books, which cover the properties of these lenses in depth:
- "Telescope Optics - Evaluation and Design", Harrie Rutten + Martin van Venrooij - the real classical book on these subjects
- "Applied Optics and Optical Design" by A.E. Conrady - the pre-computer design must-have textbook(s), today cheaply available by Dover Publishing
- "Astrooptik" by H. Laux, but I fear it is only available in German, but great info on those more esoteric designs, like the Richer-Slevogt catadioptrics.

Also exactly the issue of the inter-mirror distance was the topic I corresponded about with the original designers of one of my telescopes, when I rebuild that a couple of years ago.


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