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10-13-2010, 08:30 AM   #16
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QuoteOriginally posted by Entropy Quote
Yes. It's done pretty often with telescopes (see the above post regarding a Celestron wide angle converter).

The physical dimensions of the lens remain the same, but the focal length is shorter, so the f/d ratio drops. A way to think about it is that a certain amount of light illuminates the image circle - If you take that light and concentrate it into a smaller image circle, the illumination will be brighter.

The key issue is, however, that for many lenses (especially wider angle ones), it's simply not possible to do this without making it impossible to focus on the sensor any more. It tends to be a lot easier for long telephotos. In the above example of Celestron telescopes (and most telescope designs), they are capable of focusing WAY beyond infinity, and also capable of projecting an image on a focal plane well behind the normal mounting point of the scope. The wide angle correctors will shorten this maximum distance significantly, but not to the point where it becomes impossible to focus.

You might be able to do this with some of the mirror lenses out there, like converting the Korean 500/6.3s into 300/3.8s
But then what's the point? You'd be spending $150 on a lens, and $1000 on a converter. Just buy a DA*.

10-13-2010, 08:58 AM   #17
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I have to agree with the canadian geezers. What's the point? This "crop fixation" is a red herring. If you want to know how your 77mm ltd looks on a FF camera go out and get a film camera, you can easily find a good one for under $100.

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10-13-2010, 09:09 AM   #18
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QuoteOriginally posted by NaClH2O Quote
I have to agree with the canadian geezers. What's the point? This "crop fixation" is a red herring. If you want to know how your 77mm ltd looks on a FF camera go out and get a film camera, you can easily find a good one for under $100.

NaCl(and I'm a geezer too...and proud of it)H2O
I agree, Salty. Having at one time taking photos alternately between a Yashicamat 6x6, Minolta 16mm G, Asahi Pentax and Polaroid depending on what I wanted to do, all that is needed is to look through the viewfinder and figure it out from there. Same thing with a DSLR compared to a film SLR. Put the lens on one, have a look, put the lens on the other, have a look. If your DSLR won't take in a wide enough perspective with your 16-45, get something with a smaller first number, like 10-20 or 12-24.

BTW the Minolta 16G was really neat. Geezers will understand the comparison when I say it was about two Zippo lighters long, and a bit thicker. I think it would go into the watch pocket on some brands of jeans. Hmmm - must try that one day. It would take a regular pocket if I brought the flash along with a supply of flash bulbs. The camera itself had no electronics, just two scales, one for the ASA (now ISO), the other with pictures of sunny, cloudy, etc.
10-13-2010, 03:04 PM   #19
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Still the resulting change in aperture and depth of field could be really quite cool, and the additional light would be a bonus.

10-13-2010, 03:54 PM   #20
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Would be cool to have a SMCA 50 f 1.14 option with my f 1.7 and converter.
10-14-2010, 09:48 AM   #21
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QuoteOriginally posted by Canada_Rockies Quote
BTW the Minolta 16G was really neat. Geezers will understand the comparison when I say it was about two Zippo lighters long, and a bit thicker. I think it would go into the watch pocket on some brands of jeans. Hmmm - must try that one day. It would take a regular pocket if I brought the flash along with a supply of flash bulbs. The camera itself had no electronics, just two scales, one for the ASA (now ISO), the other with pictures of sunny, cloudy, etc.
I remember that one! I always lusted after it, thought it would make a great spy cam!

NaCl(I could pretend I was an extra on I Spy)H2O
10-14-2010, 07:26 PM   #22
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Why not buy a .66x Raynox and screw it on the front of your lens? It will negate the 1.5 crop factor.
10-14-2010, 07:49 PM   #23
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This was actually covered in a thread I started on August 23rd entitled Stupid Question or Brilliant Idea?

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/111899-stupid-...ml?src=subsct2

I pretty much got torn to shreds for even suggesting such a CRAZY idea (though I still think it's possible). Looks like this thread is a little more polite.

Don't get a Raynox HD-6600pro. I purchased one to do exactly what I wanted to do and what you are proposing. It sux...... royally. Extremely soft about 1/2 way out from center. Basically, if you don't mind the center of your image being marginally sharp and the rest being completely soft and even blurry in places, then by all means get one. I'm sending mine back to the guy who sold it to me. By the way, Raynox advises against using the DCR or HD6600pro on DSLR's. I contacted them after I used it for the first time to see if they had any input. Horrible customer service by the way. They are very rude. I will never, and I mean never buy another Raynox Product after the way I was treated. I've been coveting a DCR-150, but now I don't think I want one anymore.
If you want a wide angle conversion lens that is pretty good, just a little soft at the edges, then get an Olympus WCON-08. Only 0.8x magnification, but it's better then nothing. I own one personally and use it all the time when doing interior shots of homes. At least until I can afford a Sigma 10-20mm.
FYI to all those that have mockingly said "get a film camera" I say I SHOULDN'T HAVE TO! Either come up with something that makes my full frame lenses 'act' like their focal length says they should 'act' OR Pentax needs to come out with a full frame DSLR. That's it, end of story.

10-14-2010, 07:53 PM   #24
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QuoteOriginally posted by Canada_Rockies Quote
BTW the Minolta 16G was really neat. Geezers will understand the comparison when I say it was about two Zippo lighters long, and a bit thicker. I think it would go into the watch pocket on some brands of jeans. Hmmm - must try that one day. It would take a regular pocket if I brought the flash along with a supply of flash bulbs. The camera itself had no electronics, just two scales, one for the ASA (now ISO), the other with pictures of sunny, cloudy, etc.
That's the one that took 110, right? I think my dad still has one of those lying around.
10-15-2010, 06:37 AM   #25
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I'm more interested in the increase in light and wider aperture than in the widening of the focal length.
10-15-2010, 09:45 AM   #26
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Wouldn't the additional elements required to make the WC work properly negate the increase in light you would expect when compressing the image? It's just that usually, any time you add glass, you decrease available light. It would probably be a wash depending on the optical design of such a converter.
10-15-2010, 10:40 AM   #27
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I think it would be tough to make a "universal" WAC for all focal lengths. Especially without degradation of image. If it was possible, I don't think it would be realistic or affordable.

If Pentax was worried about making 50mm, 30mm, or something of the sort at f1.2, they would've focused on that. They are obviously going a different route and focusing on high ISO performance in an attempt at making slower lenses that are sharp usable in everyday situations.
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