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11-30-2008, 12:21 PM   #1
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New Sigma Fisheye 10mm F2.8 EX DG for Pentax

This may be old news, but I thought this was interesting. With a MSRP, it will have to be phenomenal to compete with the DA 10-17mm. It is faster though.

Sigma - Lenses

There is also a 4.5mm f2.8

http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3336&navigator=6

12-01-2008, 12:49 PM   #2
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As a photonewb I have to ask. Angle of View: 180 degrees. Does that mean that you see 180 degrees? Like this? http://education.yahoo.com/homework_help/math_help/solutionimages/minigeogt/...59-23-pr-q.gif

And why is the pentax fish-eye 10-20 also 180 degrees? Do you see less or the same on the pentax?
12-01-2008, 03:38 PM   #3
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QuoteOriginally posted by Nimrad Quote
As a photonewb I have to ask. Angle of View: 180 degrees. Does that mean that you see 180 degrees? Like this? http://education.yahoo.com/homework_help/math_help/solutionimages/minigeogt/...59-23-pr-q.gif

And why is the pentax fish-eye 10-20 also 180 degrees? Do you see less or the same on the pentax?
The Pentax is actually 10-17mm and the angle of view will be greater at 10mm than 17mm. The angle of view changes with the focal length of the lens. For example, the shorter the focal length (wide angle), the wider the angle of view. Therefore, when shooting from the same position, a wide-angle lens can photograph a larger area. This also assumes that the film size or sensor stays the same since that will also affect to the angle of view. A 50mm lens on 35mm film has roughly the same angle of view as the human eye.

However, fish-eye lenses will of a given focal length will have a wider angle of view than an equivalent rectilinear lens. A good example of this would be the Sigma 14mm f2.8 rectilinear lens in comparison to the Sigma 15mm f2.8 fisheye lens.

Edit: the 14mm rectilinear lens as an angle of view of 114.2 degrees while the 15mm fisheye has 180 degrees! You can actually get your feet into the shot if you aren't careful. These angles are for 35mm film.

Last edited by Blue; 12-01-2008 at 03:48 PM.
12-01-2008, 03:50 PM   #4
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I'm not that newb, I just wanted to know how they measure mm and if 180 degrees actually IS 180 degrees angle of view. Seems so weird that I can cover everything around me with just two photos.
And why does the 10-17 mm have the same angle of view as the 4,5mm? They're both fisheye lenses. Does the 4,5 have more "normal" pics with not so much fish-eye effect?

12-01-2008, 03:57 PM   #5
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QuoteOriginally posted by Nimrad Quote
I'm not that newb, I just wanted to know how they measure mm and if 180 degrees actually IS 180 degrees angle of view. Seems so weird that I can cover everything around me with just two photos.
And why does the 10-17 mm have the same angle of view as the 4,5mm? They're both fisheye lenses. Does the 4,5 have more "normal" pics with not so much fish-eye effect?
The 180 degrees is what makes the fisheye a fisheye. The focal length and format dimensions (sensor or film) determine the angle of view for a rectilinear lens. The fisheye calculations are more complicated.

Edit: This wikepedia article does a decent job explaining it. However, they consider all ultra-wide lens fisheyes which isn't true.

http://en.wikipedia.org/wiki/Angle_of_view

Last edited by Blue; 12-01-2008 at 04:07 PM.
12-01-2008, 05:56 PM   #6
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It is 180 degrees from corner to corner. If you stand under a light bulb you can position the camera to shoot your foot in the bottom left and the light in the top right.
12-01-2008, 06:41 PM   #7
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QuoteOriginally posted by Blue Quote
This may be old news, but I thought this was interesting. With a MSRP, it will have to be phenomenal to compete with the DA 10-17mm. It is faster though.

Sigma - Lenses

There is also a 4.5mm f2.8

Sigma - Lenses
Its a year old. The good news is that it's $599 street on Amazon.
12-01-2008, 08:24 PM   #8
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QuoteOriginally posted by alohadave Quote
Its a year old. The good news is that it's $599 street on Amazon.
Post a link with one for Pentax mount.

Edit: This is the key thing:
QuoteQuote:
Now available for Sony/Minolta digital SLRs, and Pentax digital SLRs.
The Canon and Nikon version have been available since Nov 2007 but didn't do much good for Pentax. As far as I can tell, the new versions have yet to hit the shelves.


Last edited by Blue; 12-01-2008 at 08:32 PM.
12-01-2008, 09:38 PM   #9
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QuoteOriginally posted by Nimrad Quote
Seems so weird that I can cover everything around me with just two photos.
The 10mm is a diagonal fisheye, which means it sees 180 degrees from one corner to the other (but not from bottom to top or left to right). If you want to see 180 degrees all the way around, you need a circular fisheye (like the I-think-you-can't-really-get-it-for-Pentax-yet 4.5mm Sigma), which gives you a view like this:



which, as you can see, distorts the hell out of everything.

The focal length of a fisheye tells you the magnification at the center of the image; as you go away from the center the magnification decreases (so a 10mm fisheye has a wider field of view than a 10mm rectilinear lens, even though a small object at the center of the image is about the same size for both lenses).


BTW, 180 degrees isn't the limit; Nikon used to make a lens with 220 degree coverage:

Nikkor 6mm f/2.8 Fisheye Nikkor lens
12-02-2008, 08:26 AM   #10
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Also, note that the angle of view is different for different DLSRs and they have not published the coverage of the Pentax version.
12-02-2008, 09:00 AM   #11
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QuoteOriginally posted by MRRiley Quote
Also, note that the angle of view is different for different DLSRs and they have not published the coverage of the Pentax version.
I suppose we could look up the sensor dimensions on the Canon, Nikon, and Pentax and figure out the angle of view that way.

Edit: For the 10mm fisheye, the AoV for the Nikon and Sony is 180mm, Canon 167, and Sigma 154.

Last edited by Blue; 12-02-2008 at 09:56 AM.
12-02-2008, 12:45 PM   #12
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Thank you for awesome answers! I learned something. I have yet left to understand what mm means, but I'll look into it right now!
12-02-2008, 12:50 PM   #13
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QuoteOriginally posted by Nimrad Quote
Thank you for awesome answers! I learned something. I have yet left to understand what mm means, but I'll look into it right now!
You are jerking our chain!
12-02-2008, 04:40 PM   #14
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QuoteOriginally posted by Nimrad Quote
Thank you for awesome answers! I learned something. I have yet left to understand what mm means, but I'll look into it right now!
It's the system of units of linear measure that the intelligent countries use!


*ducks and runs*
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