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06-16-2013, 02:00 AM   #1
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Question about Fisheye vs. Ultra-Wide Angle

Is there a certain mm it goes past to become classified as a fish eye? Or There's still a difference between the glass is shaped?

For example, hypothetically, 8mm Fish Eye vs. 8mm Ultra-Wide. Would there be a difference?

Such as the fish eye has extended top and bottom view, and the ultra-wide is just left and right ?

06-16-2013, 02:05 AM   #2
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A fish-eye, by definition, has extreme barrel distortion; straight lines at the edges appear as convex curves.
A 10mm fish-eye give a much larger diagonal angle of view than a 10mm rectilinear UWA.
06-16-2013, 02:16 AM   #3
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Thanks! Oh, another question. Off topic, but.. what's it mean by the elements in groups ? The Rokinon 8mm has "10 elements in 7 groups"
06-16-2013, 02:59 AM   #4
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QuoteOriginally posted by steezylistic Quote
Thanks! Oh, another question. Off topic, but.. what's it mean by the elements in groups ? The Rokinon 8mm has "10 elements in 7 groups"
For those of us who just like taking photos, I don't think it means anything. Essentially, it is borne from a desire to satisfy the patent clerk. Optical engineers will no doubt disagree.

06-16-2013, 03:52 AM   #5
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An important thing about comparing a 10mm fisheye and a 10mm normal lens.

The edges of the fisheye curve. So a person on the edge of the photo appears like a small part of a circle.

A 10mm normal lens does what occurs on a flat world map. It spreads out the edges. The person on the edge of the photo may be standing straight but the corners are pulled out the person looks like their head belongs to an alien.

I actually find a 10mm fisheye less dangerous or the distortion is easier to take advantage of compared with a 10mm lens. I keep my 10 mm lens away from any jobs.

A 10 mm fisheye is 180degrees along the diagonal. the are other fisheyes that are even fewer degrees and the image comes out as a circle.

All the these lenses tend to have issues with keeping your feet out of the photo.
06-16-2013, 04:38 AM   #6
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QuoteOriginally posted by steezylistic Quote
Thanks! Oh, another question. Off topic, but.. what's it mean by the elements in groups ? The Rokinon 8mm has "10 elements in 7 groups"
10 individual lenses (lens elements); 7 places in the whole lens where one or more elements are placed to do something. Eg. a focus group, zoom group etc.
06-16-2013, 07:57 AM   #7
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I thought that it might be interesting to compare both - a fisheye and a normal lens together, apples to apples - i.e., when the fisheye is defished into a normal image. This way, you can actually see what the differences are between the two types of lenses.
06-17-2013, 12:26 AM   #8
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QuoteOriginally posted by interested_observer Quote
I thought that it might be interesting to compare both - a fisheye and a normal lens together, apples to apples - i.e., when the fisheye is defished into a normal image. This way, you can actually see what the differences are between the two types of lenses.
oh, wow . thanks! So.. this Rokinon 8mm states it's an "ultra-wide angle fish eye"

What is it really..? A fish eye then ?

06-17-2013, 05:01 AM   #9
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QuoteOriginally posted by steezylistic Quote
Thanks! Oh, another question. Off topic, but.. what's it mean by the elements in groups ? The Rokinon 8mm has "10 elements in 7 groups"
The number of elements is the number of pieces of 'glass' in the lens. They are groups if they are cemented together.
06-17-2013, 08:09 AM   #10
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QuoteOriginally posted by steezylistic Quote
oh, wow . thanks! So.. this Rokinon 8mm states it's an "ultra-wide angle fish eye"

What is it really..? A fish eye then ?
It's a fisheye. Both fisheye and wide-angle rectilinear lenses use distortion to get a really wide field of view. They stretch and pull in different ways. Rectilinear lenses distort in a way that looks less unusual at first. Fisheye distortion allows a lot more field of view to be crammed into the frame.

Bob mentioned the world map analogy and it makes a lot of sense to me. Paper world maps always distort the shapes of land masses to get a round world on a flat piece of paper, and lenses do the same thing.

The fisheye lenses are rated in millimeters like all lenses but this is somewhat misleading. If you look at fields of view, the DA 10-17mm fisheye zoom has the same field of view at 17mm as the DA 12-24mm rectilinear zoom does at 12mm.

Look at the Lens Club threads to see a lot of examples of either type.
06-17-2013, 06:45 PM   #11
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Evening, A while back I created a thread on the 10-17's field of view (side to side, rather than corner to corner). There is probably way more information in there than what you may be looking for, but it may be an interesting read. Each fisheye lens, tends to use a different projection, so they differ even if they have the same focal length. Anyway - for your reading enjoyment - if it strikes your fancy....
06-17-2013, 07:59 PM   #12
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Sorry I did not do the fisheye at 10mm.

06-19-2013, 05:37 AM   #13
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An element in a camera lens refers to a single piece of optical glass or plastic. The group in a lens description refer to either single elements, or two or more elements that are in contact over the whole of their surfaces. So a lens with four elements in contact in one lump and two elements that don't touch any other has six elements in three groups. This web page has some lens diagrams which might make this clear:

Four Thirds | Micro Four Thirds | Products(Lenses)

All straight lines on a photo taken with a rectilinear wide angle lens will be shown as straight. This ensures that photos of buildings and other things with straight lines do not appear distorted. With a fisheye lens, only straight lines that go through the exact centre of the photo will be shown as straight. All others will be curved.

Now consider a rectilinear, very wide angle lens set up to take a photo of a building. The camera is set up so that the sensor is parallel to the face of the building. The middle of the building is perhaps 30 feet in front of, and also 30 feet away from the lens, but the ends of the building, still 30 feet in front of the lens, are (diagonally) 42 feet away. Yet the photo shows the ends of the building to the same scale as the middle; they do not diminish in size due to perspective.

There's a snag. Although buildings look alright, three dimensional, roughly spherical objects that we are familiar with do not. Here I mean people's faces and bodies. Look at this page, and scroll down to the 'Complement your wide-angle lens' section at the bottom. Click on the before and after buttons below the wedding photo:

Features | www.dxo.com

It's most noticeable on faces but can make people look very fat. The further from the centre, the worse the effect. Any lens wider than about 19mm on a Pentax DSLR will show this effect at the edges and especially the corners to an unflattering degree.

Fisheye lenses don't seem to me to show this effect to anywhere near the same degree, but I'm still experimenting with my lens. If you change lenses from the very wideangle lens in the building shot above to a fisheye lens, the ends of the building will look smaller in line with the laws of perspective. Any straight lines in the building will be curved, unless they go though the exact centre of the lens.

Scenes without any clues to distortion like buildings or people in them can be taken with a fisheye lens without the fisheye effect being noticeable.

Rectilinear very wideangle lenses usually have a very small, almost unnoticeable amount of barrel distortion; it's very difficult to get rid of it altogether. Barrel distortion is what fisheye lenses have in abundance.
06-21-2013, 03:17 PM   #14
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QuoteOriginally posted by steezylistic Quote
oh, wow . thanks! So.. this Rokinon 8mm states it's an "ultra-wide angle fish eye"

What is it really..? A fish eye then ?
The Rokinon 8mm is really the Samyang 8mm. Not all fisheyes are equal - the projection (how the picture is squeezed) varies. The Rokinon/Samyang 8mm is approximates 'stereographic' projection, which is good. You can 'de-fish' shots taken with fish-eye lenses in post-processing to make them look something like those taken with a rectilinear lens, with varying degrees of success. As others have said, there are many examples and threads on the forum. In the end it depends on what effect you are trying to achieve (and how much you want to spend).
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