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02-21-2011, 11:54 AM   #1
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Fish Eye Lens

Looking for advice on what fish eye lens to purchase for K20D. Differences in diagonal and circular fish eye lens, not sure on the effect of each. If I understand the circular lens gives you a actual circular image on paper with dark areas on all sides, where diagonal lens fills the whole film area with the image. What or how much distortion do either of these give you. Please help, Jerry

02-21-2011, 12:22 PM   #2
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QuoteOriginally posted by firstshot Quote
Differences in diagonal and circular fish eye lens, not sure on the effect of each. y
Fisheye lens - Wikipedia, the free encyclopedia
02-21-2011, 12:46 PM   #3
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Just about right mate. Circulars tend to be wider focal length lenses as well as a result of this effect.
02-21-2011, 01:31 PM   #4
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Make sure to buy a fish eye that is designed for APS-C sensor

02-21-2011, 01:52 PM   #5
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I'll just do what everyone else does and suggest the stuff I own...
To consider: Except for the Samyang I now own I haven't ever used a fisheye lens.

But the Samyang (rectilinear) is a great lens and pretty much the cheapest option (2nd to 16mm Zenitar).
I'd rate it 9 out of 10 fish - -1 fish because I doesn't focus very close (30cm).
02-22-2011, 01:58 AM   #6
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Most 'fisheye' camera lenses are frame-filling (of various projections), not full-circle. AFAIK no native full-circle lenses exist for APS-C size sensors -- that requires a focal length of around 5mm. Some VERY expensive full-circle FE's exist for 135/FF cameras. (A Sony A850 would be Nice To Have.) Frame-filling fisheyes might be rated as 180 degrees corner-to-corner, the diagonal FOV. The DA10-17 at 10mm is such -- while at 16mm it's maybe 100 degrees and less fishy, rather like the Zenitar 16/2.8 but slower.

I have a big old Kenko 180 Degree Fisheye adapter, also branded as Vivitar, Spiratone, etc. I usually mount it on a 28-80 or 35-70 zoom. It's full-circle at around 40mm, frame-filling from 60mm on up, and an interesting way to test various FE projections. But it's not super-duper sharp, especially around the edges. Except in bright light, a tripod is required.

Any very wide lens will have considerable distortion. Rectilinear ultra-wides stretch lines and angles. Fisheyes render them in circular projections, less distorted really but they're not what our eyes are used to so they look pretty odd. Shooting a forest, all the trees are falling on me, HELP!!

I'll guess that you could approximate a full-circle FE with a very short C-mount cine / video / surveillance lens. Just dremel a hole into a one-buck PK body cap and glue the lens in. But that would be VERY close focus, macro almost, and the image circle would probably be rather smaller than the camera's frame height. But it would be pretty cheap. Hmmm, I'll have to try that...

Another option: CHEAT! Stitch some images together and use your photo editor to render them in a full-circle projection. You'll get much sharper results than with a Kenko-type adapter. The how-to varies with editors, so RTFM.

Oh yeah, with full-circle FE, exposure can be tricky because of the big black spaces. This is easily adjusted on dSLRs, and not so easily handled on 135/FF film SLRs with only center-weighted metering. I've wasted some film that way. Bother.

Last edited by RioRico; 02-22-2011 at 02:14 AM.
02-22-2011, 05:00 AM   #7
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Sigma does make a 4.5mm fish-eye lens specifically for the APS-C that produces a circular image. I have found though that my K10 and K20 don't register the focal length because it's smaller than what the camera recognizes and as such I have found that the pictures are clearer when I turn shake reduction off when using that lens.

Another option would be to get an add on adapter like RioRico suggested. I have used several of those and they seem to work pretty well for what they do and the cost is definitely less than buying a dedicated circular fish-eye.
02-22-2011, 05:40 AM   #8
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Check the fisheye club in the lens club forum

I have the samyang fisheye and like it. It OS 180. degrees corner to corner and very good against flare which is important because it is almost impossible to keep the sun (or your feet) out of the frame

Only drawback is it is manual focus

02-22-2011, 05:43 AM   #9
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I've tried a bunch of different fisheyes for pentax digital cameras, and my favorite by far is the pro optic 8mm It's also marketed under the Bower, Rokinon and most likely other brands as well (Samyang?). In any event it has a full 180degree FOV on 1.5 crop sensors. It is a rectangular projection rather than circular, which I prefer. You can always crop if you want circular. It is a manual focus lens, not a big deal at 8mm, the DOF is HUGE! One of the biggest benefits of this lens is it's very very very good flare resistance. It's kinda hard to eliminate the sun when you've got a 180 FOV! Yet I have yet to have any flare problems with it. I'm at work and don't have access to some sample shots, I'll try to remember to post them tonight.

edit: looks like Lowell beat me to it. But we like exactly the same things about this lens.

NaCl(good crop sensor fisheye, check it out)H2O

Last edited by NaClH2O; 02-22-2011 at 05:45 AM. Reason: added the 'edit'
02-22-2011, 06:21 AM   #10
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Yes, the Pro Optic/Opteka/... is the Samyang lens. Congratulations on owning a great lens.
02-22-2011, 06:38 AM   #11
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Thank you Everyone, I'm on the research. Jerry

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