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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 12 Apr 2009 (Sunday) 21:06
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are there any fisheye lens for a crop body that are not circular?

 
rdenney
Rick "who is not suited for any one title" Denney
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Apr 13, 2009 14:13 as a reply to  @ post 7721221 |  #16

This is another of the topics that I seem to write about once a week or even more often.

All fisheye lenses--all of them--produce a circular image that provides a 180-degree field of view. Why is that true? Because that's the definition of a fisheye.

To meet that requirement, the focal length of a lens with fisheye projection comes to around one-third of the diameter of the image circle when focused on infinity. Thus, if you want an image circle that is 15mm in diameter (so the whole image fits within the frame), you need a fisheye with a focal length of about 5mm. Sigma sells one.

If you want a fisheye image that the frame just fits within, so that you have (nearly) the 180-degree coverage corner to corner, you need one with a focal length of about 10mm for an APS-C sensor. Sigma sells one of those, too.

Tokina also sells a fisheye zoom that ranges from 10mm to 17mm, which is about the focal length needed to just accommodate the 24x36 format corner to corner.

So, you can buy an 8mm Peleng, and it will make an image circle 24mm in diameter. That will just fit within the 24x36 frame, making it a circular fisheye. On an APS-C sensor, that same lens won't quite reach to the corners of the sensor, so you end up with black corners.

One essential byproduct of providing a 180-degree field of view over the image circle is significant barrel distortion. It's not really distortion, because it is intentional. It is really fisheye projection. In that projection, no attempt is made to keep straight lines straight, except those that go through the center of the frame. Everything will look like it is reflected off a polished mirrored sphere.

Rectilinear lenses provide increase magnification in the corners sufficient to keep straight lines straight. They are actually harder to design than fisheye lenses. No rectillinear lens can approach 180-degree field of view.

Rick "if it doesn't say 'fisheye' it probably isn't one" Denney


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caesar2164
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Apr 13, 2009 15:02 as a reply to  @ rdenney's post |  #17

the terms for wide lenses are:

Rectilinear Ultra Wide angle = canon 10-22, sigma 10-20, tokina 11-16, etc...

Diagonal Fisheye = canon 15mm (full-frame), sigma 10mm (for aps-c), sigma 15mm (for full-frame), tokina 10-17mm (crop-full), etc...

Circular Fisheye = Sigma 8mm (full-frame), sigma 4.5mm (aps-c), peleng 8mm (full-frame), etc...

any questions? :D


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Wilt
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Apr 13, 2009 17:25 |  #18

There are multiple apects to a lens that has a very very very wide FOV...

'1. Fisheye' actually refers to the fact that any straight lines that do not intersect the CENTER of the lens will be curved

2. The second characteristic is a lens' ability to fill a rectangular frame vs. having only a circular image circle within the frame borders.

3. The third characteristic is the ability to capture a super wide 140-180 degree wide AOV within the frame.

'Circular fisheye' does #1 and #3
'rectangular fisheye' does #1 and #2 and #3
A super wide lens which is not 'fisheye' does #2 and #3, but not #1

Of course, a circular fisheye on 135/FF gets cropped off a lot by APS-C, resulting in curved edge of frame area only along one axis of the frame, and much of the 'curved' straight lines being cropped off the image by the top and bottom frame edges.


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Kruzkal
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Apr 13, 2009 17:39 |  #19

azpix wrote in post #7717623 (external link)
are there any fisheye lens for a crop body that are not circular?

Yes. There are two types of fisheye lenses on the market; circular and diagonal.

A circular fisheye creates an image circle with ~180° angle of view that fits inside the frame for the sensor it is designed for. Therefore,there will be black space in the frame with no image. Examples of this type of lens would be the Sigma 4.5mm f/2.8 EX DC HSM Circular Fisheye (external link) for the APS-C system and the 8mm f/3.5 EX DG Circular Fisheye (external link) for the FF system.

A diagonal Fisheye creates an image circle with ~180° angle of view also. However, the image fills the frame such that there is ~180° angle of view from one corner of the frame to the corner diagonally opposite to it. Hence the name diagonal fisheye. There is no empty space in the frame. The whole frame is filled with image. Examples of this type of lens would be the Sigma 10mm f/2.8 EX DC HSM Diagonal Fisheye (external link) for the APS-C system and the Sigma 15mm f/2.8 EX DG Diagonal Fisheye (external link) for the FF system.

Below is an image showing angle of view from the various focal length fisheye lenses when mounted on the APS-C system:

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
Byte size: ZERO | Content warning: NOT AN IMAGE



  
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mercury-666
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Apr 13, 2009 21:15 |  #20

rectangular:
http://www.flickr.com …in/set-72157615787501336/ (external link)

circular:
http://www.flickr.com …in/set-72157615787501336/ (external link)


settles it.

(sorry for whoring out my stuff, i couldnt be bothered looking anywhere else)


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Jman13
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Apr 13, 2009 21:26 |  #21

And there's more to a fisheye than just uncorrected distortion. They are MUCH wider. Like, 65% wider. One nice thing about the Tokina 10-17 is that it's a real diagonal fisheye on any format. It's 167 degrees at 10mm on 1.6x...it's 180 degrees at 12.5mm on 1.3x, and 180 degrees at 15mm on full frame, all without vignetting.

Here's two shots, from essentially the same area. One taken with an ultra wide (Canon 17-40), the other taken with a fisheye (Tokina 10-17 at 15mm)...both on the 1DsII:

Canon 17-40 @ 17mm (full frame):

IMAGE: http://www.jordansteele.com/forumlinks/state_leveque_uwa.jpg

Tokina 10-17 @ 15mm (full frame):
IMAGE: http://www.jordansteele.com/forumlinks/state_leveque_fe.jpg

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rdenney
Rick "who is not suited for any one title" Denney
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Apr 13, 2009 21:37 as a reply to  @ Jman13's post |  #22

You guys that are making the big distinction between circular and rectangular fisheyes are making them sound like the difference is with the lens. It is not. The difference is only the size of the image frame you put behind, compared to the focal length of the lens.

I have a 30mm full-frame fisheye for medium format. At that focal length, it provides a 180-degree coverage on an image circle about 90mm. On a 6x6 camera, it's a "full-frame" or "diagonal" fisheye. If I mounted it on my 4x5 view camera, it would be a "circular" fisheye. Same lens; different image frame.

One reason people get confused about these two different applications of fisheye lenses is because we make it sound like full-frame and circular fisheyes are fundamentally different. But I suppose I should expect it--we do the same with all focal lengths when comparing their application to different formats. How many times have I heard that a 50mm really becomes an 80mm on the small sensor? Same mistake; same confusion.

If a person wants a fisheye that doesn't leave dark corners, find one with a focal length at least one-third of the diagonal of the frame. If they want nearly the full 180-degree field of view, find one that is no longer than one-third of the diagonal of the frame. Getting nearly 180-degree coverage without leaving dark corners presents a pretty small solutions space: 10mm for APS-C and 15mm or 16mm for 24x36. (Or 30mm for 6x6 or 35mm for 6x7.)

Rick "Fisheye: a lens that projects a circular image about three times its focal length when focused on infinity, providing spherical projection and a field of view of 180 degrees" Denney


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caesar2164
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Apr 14, 2009 01:15 as a reply to  @ rdenney's post |  #23

agreed mr. denney,

but the OP was asking about fisheyes that don't make circular images on aps-c so I just listed out the terms and which lenses apply to them...


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M3Rocket
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Apr 14, 2009 04:08 |  #24

rdenney wrote in post #7724554 (external link)
You guys that are making the big distinction between circular and rectangular fisheyes are making them sound like the difference is with the lens. It is not. The difference is only the size of the image frame you put behind, compared to the focal length of the lens.

I have a 30mm full-frame fisheye for medium format. At that focal length, it provides a 180-degree coverage on an image circle about 90mm. On a 6x6 camera, it's a "full-frame" or "diagonal" fisheye. If I mounted it on my 4x5 view camera, it would be a "circular" fisheye. Same lens; different image frame.

One reason people get confused about these two different applications of fisheye lenses is because we make it sound like full-frame and circular fisheyes are fundamentally different. But I suppose I should expect it--we do the same with all focal lengths when comparing their application to different formats. How many times have I heard that a 50mm really becomes an 80mm on the small sensor? Same mistake; same confusion.

If a person wants a fisheye that doesn't leave dark corners, find one with a focal length at least one-third of the diagonal of the frame. If they want nearly the full 180-degree field of view, find one that is no longer than one-third of the diagonal of the frame. Getting nearly 180-degree coverage without leaving dark corners presents a pretty small solutions space: 10mm for APS-C and 15mm or 16mm for 24x36. (Or 30mm for 6x6 or 35mm for 6x7.)

Rick "Fisheye: a lens that projects a circular image about three times its focal length when focused on infinity, providing spherical projection and a field of view of 180 degrees" Denney

bw!

You mean there really isn't such a thing as rectilinear fisheyes??? :lol:


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Madweasel
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Apr 14, 2009 05:41 |  #25

M3Rocket wrote in post #7726063 (external link)
You mean there really isn't such a thing as rectilinear fisheyes??? :lol:

Sure there is: they're the fish-eyes that render all straight lines straight - oh wait, that's not a fish-eye is it? :lol:


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are there any fisheye lens for a crop body that are not circular?
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