Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-13-2012, 09:39 PM   #61
Veteran Member




Join Date: Jan 2010
Location: Durham, nc
Photos: Albums
Posts: 896
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.







Charles.

07-14-2012, 02:35 AM   #62
Veteran Member
Frogfish's Avatar

Join Date: Dec 2009
Location: Shanghai
Posts: 4,490
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 :

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/191036-garden-...-plus-tcs.html

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/139941-lenses-...-x1-4-etc.html

https://www.pentaxforums.com/forums/post-your-photos/133712-nature-unknown-bi...-bb-500mm.html
07-14-2012, 02:41 AM   #63
Veteran Member
Frogfish's Avatar

Join Date: Dec 2009
Location: Shanghai
Posts: 4,490
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
Veteran Member
demp10's Avatar

Join Date: Jun 2011
Location: Atlanta
Photos: Albums
Posts: 602
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
Veteran Member
glasbak's Avatar

Join Date: Apr 2009
Location: Netherlands
Posts: 346
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
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by Edgar_in_Indy Quote
Very enlightening...it 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.

Ben
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
500mm, camera, focus, image, k-mount, lens, mirror, pentax lens, phoenix, pictures, samyang, sigma, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Need lens hood for Sigma 170-500mm...same as 50-500mm and 150-500mm? Help please! Edgar_in_Indy Pentax SLR Lens Discussion 10 09-09-2011 05:32 AM
Lens shootout PGillin Pentax SLR Lens Discussion 5 02-10-2011 12:30 AM
great DSLR shootout dom777 Video and Pentax HDSLRs 1 03-25-2010 02:26 PM
Suggestion Lens shootout section Jimfear Site Suggestions and Help 11 04-23-2009 03:05 PM
Zoom Lens Shootout - Lets make some rules Lowell Goudge Pentax SLR Lens Discussion 35 12-21-2008 04:09 PM



All times are GMT -7. The time now is 11:37 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top