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difference between 8mm fisheye and 16mm fisheye?

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BrianSayler View Drop Down
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Post Options Post Options   Quote BrianSayler Quote  Post ReplyReply Direct Link To This Post Topic: difference between 8mm fisheye and 16mm fisheye?
    Posted: 16 March 2007 at 22:01
what's the difference between an 8mm versus a 16mm fisheye? Apparently both are available for the A100 (sigma makes both, I think, and sony makes the 16). Will the 8mm just capture a bigger field of view?

Sample images would be nice, if anyone has them.

Also, opinions about the usefulness of one versus the other would be helpful.
 



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groovyone View Drop Down
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Post Options Post Options   Quote groovyone Quote  Post ReplyReply Direct Link To This Post Posted: 17 March 2007 at 01:06
About 8mm.


Sorry, couldn't resist. It looks like the 16mm looses the fisheye effect to some degree on the crop sensor A100. The 8mm is a 12mm with the crop factor and will give more of a fisheye effect on the crop sensor.
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Blind Boy View Drop Down
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Post Options Post Options   Quote Blind Boy Quote  Post ReplyReply Direct Link To This Post Posted: 17 March 2007 at 04:01
AFAIK the 8 mm is circular while the 16 mm is diagonal which means from what I've understood that the 16 mm will give you a 180 degree viewing angle diagonally on a full-frame imager, be it film or digital. The 8 mm however is circular and will put the whole image circle inside the edges of a full-frame imager, meaning you'll have a circle centered in the frame with completely black parts around it. This means you'll have a 180 degree viewing angle in all directions, not just diagonally.

As far as APS-C is concerned, an 8 mm will still be a lot more pure fish-eye than a 16. The 8 mm will still give you black corners on an aps sensor while the 16 mm will only be a bendy wide angle lens. It'll give you a wider view than a 16 mm rectilinear lens but it won't really be a fish-eye anymore as you're not getting the 180 degree view.
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polossatik View Drop Down
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Post Options Post Options   Quote polossatik Quote  Post ReplyReply Direct Link To This Post Posted: 17 March 2007 at 14:27
This is a picture from a 16mm Zenitar



This is a picture from a 8mm Peleng ( a entry of mine for the DPC#29 "Going Wide" (there are other fisheye pictures in the DPC)linky)



Review of 8mm Peleng

This thread has also some more info, discussions and pictures about fisheyes linky

Edited by polossatik - 17 March 2007 at 14:29
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MostlyHarmless View Drop Down
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Post Options Post Options   Quote MostlyHarmless Quote  Post ReplyReply Direct Link To This Post Posted: 21 March 2007 at 01:40
Originally posted by groovyone groovyone wrote:

The 8mm is a 12mm with the crop factor and will give more of a fisheye effect on the crop sensor.


Actually, that FOV multiplier doesn't work the same way for fisheye lenses. As Blind Boy said, the 8mm is what's called a "circular fisheye" while the 15/16/17mm are "diagonal fisheye".

Someone did the math once and figured out that an image from a diagonal fisheye, when projected rectilinearly, is equivalent to a 10.6mm rectilinear lens.

http://www.fredmiranda.com/A9_rico/

The same math is a bit... more difficult on a circular fisheye. On a crop sensor, you're cutting off more from the top and bottom than you are from the sides so you no longer have this. I don't think anyone has done the math as to what the FOV is once you project the image rectilinearly but it's a good deal greater than what you'll get from a diagonal fisheye.

Edited by MostlyHarmless - 21 March 2007 at 01:42
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