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03-05-2013, 08:30 PM   #1
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How Do You Know How "Fish-Eye" A Lens Is?

Can someone explain how to tell how "fish-eye" a lens is? I'm hoping to get one soon (next 6 months) and want to know what to save for. I took a look at the DA 10-17 zoom and noticed that Field of View is 180-100. Is that what I'm supposed to be looking for? Or is there something else to check for? Thanks.

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03-05-2013, 09:05 PM   #2
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Hard to tell just from the specs. I would look at the lens sample threads.
03-05-2013, 09:28 PM   #3
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Boy have you opened up a can of worms er, ah mathematics....

There really is no easy answer - and that is an actual honest truth.

In order to really know how "fishy" a fisheye really is, you need to know what type of projection the lens' optical design used. Unfortunately, the vendors don't say, the information isn't published, and if you are really interested, you need to test the lens and essentially reverse engineer it (hint - it is a lot of work, and a lot of math).

Awhile back, I asked somewhat the same question in a different way. Most fisheye lenses are 180 degrees wide (Field of View) upper corner to lower corner. I was interested in the field of view from side to side. I had asked Pentax several times and they said that they sent the request to Japan which apparently was sent into the "Office of the Obscure". Never received an answer. So, I set out to figure it out myself, and posted what I was doing. Here is the link (below). In the link you will find a number of additional links during the discussion, that get in to a lot of the technical details of fisheye lenses - probably more than what you ever wanted to know. Now, all of that was probably a lot more than what you really wanted to know. So, I'll answer with what I think you would like to know.

There are primes and a zoom. The zoom is much more versatile than the primes. I have had the 10-17 for about 5 years now, and like it very much. The 10mm end is very wide and fishy, while the 17mm end does blend out the fishiness to a fairly large extent.


Last edited by interested_observer; 03-05-2013 at 09:48 PM.
03-05-2013, 09:48 PM   #4
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Look through the images on the fisheye fever (club) thread on this site. There you will see example images of many different subjects from almost all fisheye lenses available for Pentax cameras.

https://www.pentaxforums.com/forums/lens-clubs/33549-fisheye-fever-club-flaun...ye-photos.html

One caution. There are quite a few film camera images leafed in with the digital shots, though most are well-labeled as such.


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03-05-2013, 11:17 PM   #5
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The thing that distinguishes a "fisheye" from other wide angle lenses is the barrel distortion. Usually, a fisheye has a wider field of view, approaching 180 degrees. Nikon made one with a 220 degree FOV. It was incredibly expensive. The DA 10-17 is very "fishy" at 10mm and the distortion is much less at 17mm but still there. The FOV range of 180-100 corresponds to the focal length used, obviously with 180 degrees being at 10 mm. Rather than trying to figure out math, I just consider a lens with a lot of barrel distortion a "Fisheye".
03-06-2013, 02:03 AM   #6
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QuoteOriginally posted by reivax Quote
Can someone explain how to tell how "fish-eye" a lens is? I'm hoping to get one soon (next 6 months) and want to know what to save for. I took a look at the DA 10-17 zoom and noticed that Field of View is 180-100. Is that what I'm supposed to be looking for? Or is there something else to check for? Thanks.
Although the corner to corner FOV might be 180 degrees with different fish-eye lenses, depending on the projection of the lens, what you actually get may vary







https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/172414-fisheye...ml#post1826650

Unless you really need the zoom, consider the Samyang 8mm (or a rebranded equivalent) - as good as and much cheaper than the Pentax. There are many fish-eye threads on this forum - search ?
03-06-2013, 06:07 AM   #7
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Another important question I've learned to always ask when it comes to fisheye lenses in these forums is, "Are you really wanting the fisheye lens effect or are you planning to "defish" your shots?"

If you truly want a fisheye then the Pentax 10-17mm is a GREAT choice. If are just planning to defish later while editing and actually want an ultrawide lens then there are better choices (Sigma 8-16mm, either version of the Sigma 10-20mm, Pentax 14mm f/2.8, Sigma 14mm f/2.8, or Tamron 10-24mm).
03-06-2013, 06:19 AM   #8
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I like the 10-17 because it's quite fishy at 10mm, but gradually morphs into a pseudo-rectilinear wide angle as you get closer to 17mm. If you don't need or want that capability & just want a fisheye, then the Samyang would save you some $$$.

03-06-2013, 09:33 AM   #9
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QuoteOriginally posted by GibbyTheMole Quote
I like the 10-17 because it's quite fishy at 10mm, but gradually morphs into a pseudo-rectilinear wide angle as you get closer to 17mm. If you don't need or want that capability & just want a fisheye, then the Samyang would save you some $$$.
I bought my 10-17 in the Marketplace because the previous owner was very upset that the results he got from "de-fishing" were not good. The DA 10-17 is (or at least was 4 years ago) considerably cheaper than the 12-24, Sigma 10-20 or other rectilinear wide angle lenses offered in K mount (just slightly over $300 new). Yes, you can crop some shots and the effect isn't visible but you can't count on removing the distortion in most shots so if you don't like the distorted view of the fisheye, don't buy one. I get really annoyed at lens reviews that list barrel distortion as a con. It's made that way. That's why it's called a fisheye.
03-06-2013, 10:27 AM   #10
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The Sammy 8mm (and it's rebadged variants) has a near stereographic projection which means there's a lot less "squeezing/compressing" near the edges. This makes it much more useful for defishing and composition and 360 VR panoramas. You can see it in the pics posted above by kh123.. For the price, it's a no-brainer!

The math involved is quite interesting ~!
Stereographic Projection -- from Wolfram MathWorld
Stereographic projection - Wikipedia, the free encyclopedia
03-06-2013, 01:59 PM   #11
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The trouble is that the 10-17mm fisheye is not all that good - even the kit 18-55mm is sharper at 18mm than the 10-17mm at 17mm - you'd be buying it mainly for the fisheye effect capability. And for that the Samyang 8mm is as good as and cheaper. The lack of autofocus is usually not a problem, given the huge depth of field at these focal lengths. If you have the cash, get the Samyang 8mm and the DA15 Ltd for when you get bored with fisheyeing and still want something very wide
03-06-2013, 07:11 PM   #12
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QuoteOriginally posted by kh1234567890 Quote
The trouble is that the 10-17mm fisheye is not all that good - even the kit 18-55mm is sharper at 18mm than the 10-17mm at 17mm - you'd be buying it mainly for the fisheye effect capability. And for that the Samyang 8mm is as good as and cheaper. The lack of autofocus is usually not a problem, given the huge depth of field at these focal lengths. If you have the cash, get the Samyang 8mm and the DA15 Ltd for when you get bored with fisheyeing and still want something very wide
Comparing the 10-17 @17 to the 18-55 @18 is comparing apples and oranges. You really can not compare sharpness of the lenses, even at apparent equal focal lengths. The 18-55 @18 has a field of view of 74 degrees, while the 10-17 @17 has a field of view of 100 degrees. That is a 24 degrees of difference, representing about a 30% increase in the area each pixel is representing. There is no expectation that the sharpness should be the same. You really can not compare equivalent focal lengths of a rectilinear lens against a fisheye, since the field of view is no where the same.

Also, you would have to expect that the sharpness of a prime fisheye would be better than the sharpness of a zoom.

Overall, the short focal length lenses are going to have a very deep depth of field around the focal plane. That is just part and parcel of wide angle lenses.

I do not disagree that the prime would be better and cheaper, however the zoom does provide more versatility. The trade is certainly based on cost and how you expect to use the lens.

03-07-2013, 08:41 AM   #13
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QuoteOriginally posted by reivax Quote
Can someone explain how to tell how "fish-eye" a lens is? I'm hoping to get one soon (next 6 months) and want to know what to save for. I took a look at the DA 10-17 zoom and noticed that Field of View is 180-100. Is that what I'm supposed to be looking for? Or is there something else to check for? Thanks.
from what is listed here, nothing at all.

what would be interesting, but I am not sure each software maker is consistent in the use of controls, is the barrel distortion correction required to "defish" a fisheye.

that would tell you something.

as for the question of FOV, 180 degrees is corner to corner at 10 mm, and 100 degrees is corner to corner at 17 mm, both on APS-C sensors.

if you compare, for example, a sigma 10-20 mm rectalinear zoom, the FOV at 10 mm is 109 degrees.

what you can see from this is that the 10-17 has almost the same FOV at 17 mm as a rectalinear lens at 10mm. so even at 17 mm this lens would be quite "fishy"

maybe, without a distortion indication, taking a comparison of the fisheye FOV compared to a rectalinear lens is the best way to judge the amount of distortion.
03-07-2013, 10:43 AM   #14
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QuoteOriginally posted by reeftool Quote
I get really annoyed at lens reviews that list barrel distortion as a con. It's made that way. That's why it's called a fisheye.
Now that is funny!
03-07-2013, 10:54 AM   #15
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QuoteOriginally posted by kh1234567890 Quote
The trouble is that the 10-17mm fisheye is not all that good - even the kit 18-55mm is sharper at 18mm than the 10-17mm at 17mm - you'd be buying it mainly for the fisheye effect capability. And for that the Samyang 8mm is as good as and cheaper. The lack of autofocus is usually not a problem, given the huge depth of field at these focal lengths. If you have the cash, get the Samyang 8mm and the DA15 Ltd for when you get bored with fisheyeing and still want something very wide
I haven't noticed any sharpness issues with my DA 10-17. I will admit to not shooting much wide open with this lens if at all because almost all my shooting is daytime/outdoors but my copy is very sharp and far better than my 18-55 kit lens and at least equal to or better than my DA 15. I use it often for closeups of flowers with excellent results.
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