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This is similar to:

But actually, I have a different question. I have a Nikkor 16mm Fisheye lens and I was comparing it with TTArtisan 11mm in the photography shop. Both lenses give almost the same field of view. I have also an 11mm Irix lens which makes everything far in comparison to 16mm fisheye.

Here are two Fisheye lenses:

TTArtisan 11mm enter image description here

Nikkor 16mm enter image description here

16mm fisheye and 11mm Irix enter image description here

So the question is what is the use of focal length in the Fisheye lens? Is it only for marketing or does it have any meaning? Why do 11mm and 16mm Fisheye give almost the same image? Unfortunately, I was not able to test something that is far like with The church when I was comparing TTArtisan with my Nikkor in the photography shop.

I hope that my question makes sense.

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    \$\begingroup\$ The Irix isn't a fisheye, btw, it's rectilinear. \$\endgroup\$
    – Tetsujin
    Sep 15, 2023 at 12:43
  • \$\begingroup\$ @Tetsujin of course, but I was expecting to have a similar effect. I expected the 11mm Fisheye and 16mm Fisheye to have a similar difference as with 11mm Irix but with Fisheye distortion. But I don't see any difference between 11 and 16 fisheye so what is the point of having focal length at all? Is it better because it has 11 and not 16 so it's like for marketing purposes only? \$\endgroup\$
    – jcubic
    Sep 15, 2023 at 12:57
  • \$\begingroup\$ Wow, there's basically no difference in projection in your photos! I'd expect the 11mm one to have smaller objects in the center than the 16mm one has, because what's invariant in all the circularly symmetric lenses (fisheye or rectilinear or whatever) is the law dR=f·dθ in the center of the projection (it holds due to the property sin x ~ x for small x). Looks like some of the lenses is mislabeled... \$\endgroup\$
    – Ruslan
    Sep 15, 2023 at 19:50
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    \$\begingroup\$ Are 1st two images the same resolution from the camera? That is, is it possible that for the 11mm lens the camera was in, or was changed (manually or automatically) to crop/DX mode? \$\endgroup\$
    – scottbb
    Sep 15, 2023 at 21:04
  • \$\begingroup\$ @scottbb Yes they are the same resolution taken from the same spot. 16mm is an FX lens and there was no cropping in the camera and 11mm is a manual lens. \$\endgroup\$
    – jcubic
    Sep 17, 2023 at 9:27

4 Answers 4

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A few years ago, I had a similar curiosity and this is my takeaway…which may or may not be entirely accurate.

“Fisheye” is a term of art. It does not have a concrete technical meaning.

“Fisheye” generally refers to any lens explicitly designed around a spherical projection. Any spherical projection — there are at least a few and none of them are standard within photography.

This means that focal length doesn’t correlate to field of view in the way that focal length correlates for rectilinear lenses.

However, focal length will correspond to depth of field.

But because the focal length of fisheye lenses is relatively short, depth of field is rarely a primary concern for typical photographic subjects.

They are a great creative tool and not a great technical one beyond angle of view.

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I know this is a late answer but I have been looking at the TTArtisan 11mm fisheye for Nikon-F FX.

The DSLR version of this lense is actually a different optical formula than the mirrorless version. This is according to TTArtisan documentation.

The DSLR version also has 10 aperture blades as opposed to the 7 blades on the mirrorless version.

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  • \$\begingroup\$ Hi there. If you want to post a comment specifically to another answer, there is the ability to do that. If you are answering the original question, then you can post a standalone answer. Also, don't worry about how old the question is - that's irrelevant, as long as your answer is relevant and adds something new. Have a read down through the short site tour. \$\endgroup\$
    – osullic
    Mar 16 at 12:06
  • \$\begingroup\$ Thanks for the answer, but it looks more like a comment, that they are different. This doesn't answer the question. @osullic If I remember correctly you need to have some reputation to be able to comment. I think this is what Stack Overflow has. \$\endgroup\$
    – jcubic
    Mar 16 at 20:25
  • \$\begingroup\$ Indeed, it seems you need a reputation of 50 points before being allowed to comment... https://photo.stackexchange.com/help/privileges \$\endgroup\$
    – osullic
    Mar 16 at 20:52
  • \$\begingroup\$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. \$\endgroup\$
    – Community Bot
    Mar 26 at 17:48
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Focal length always correlates to the lens' field of view; even with a fisheye.

In your examples the fisheye lens images have been corrected to rectilinear, whereas the irix image has not been; because that lens is already rectilinear. When a fisheye image is corrected to rectilinear it requires cropping away the extremities of the lens' FOV.

Basically, the 11mm fisheye probably has more significant distortion, which required greater corrections to rectilinear, which equalized the output relative to the 16mm fisheye. IDK if the images were auto corrected based upon lens profiles (in camera jpegs, or in software); but if they were, you should be able to disable that.

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  • \$\begingroup\$ I did not done any correction or cropping if this what you have in mind. \$\endgroup\$
    – jcubic
    Sep 17, 2023 at 9:26
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I know what may be the reason why Nikon 16mm and TTArtisan 11mm have the same field of view. The lens was designed for Mirrorless and was adapted for the DSLR (I use a Nikon FX camera). That's probably why the field of view is narrower and the same effective focal length. Since you can't actually adapt (with an adapter) lens from Mirrorlens on DSLR (because of flange distance). And they didn't create a completely new lens. They probably keep the numbers for marketing reasons even though the focal length is probably more likely 16mm (for Full Frame DLSR).

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