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07-19-2007, 02:40 AM   #1
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Fish-eye versus non-fish-eye @ a similar focal length.

I'm looking for a wide angle lens.

At the time I'm considering the Pentax DA 10-17mm and the Sigma 12-24mm.

I've been told that because the DA 10-17mm is a "fish eye" the field of view (angle) at a given focal lenght is NOT the same at the field of view for a "non-fish eye" lens at the same focal length. If this is true, then I have to read up on the issue because I have always believed the opposite was true.

So, here comes a question which reveals my lack of knowledge:

Will a picture taken with the DA 10-17mm @ 12mm be similar to a picture taken with the Sigma 12-24mm @ 12mm?

I hope i don't waste to much of your time with this dum question.

Larsen.

07-19-2007, 03:33 AM   #2
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QuoteOriginally posted by Frakkas Quote
I'm looking for a wide angle lens.

At the time I'm considering the Pentax DA 10-17mm and the Sigma 12-24mm.

I've been told that because the DA 10-17mm is a "fish eye" the field of view (angle) at a given focal lenght is NOT the same at the field of view for a "non-fish eye" lens at the same focal length. If this is true, then I have to read up on the issue because I have always believed the opposite was true.

So, here comes a question which reveals my lack of knowledge:

Will a picture taken with the DA 10-17mm @ 12mm be similar to a picture taken with the Sigma 12-24mm @ 12mm?

I hope i don't waste to much of your time with this dum question.

Larsen.
Pentax also makes a DA 12-24/4 and Sigma, an EX10-20mm 4-5.6.

Yes you are right. The field of view for a fish eye is much greater at 180 whereas non fish eye ultrawides typically give around 100 degrees. However you must remember a fisheye will have very pronouced distortions. Like all the curvey lines.
07-19-2007, 03:40 AM   #3
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To compare the field of view of fish eye and non fish eye lenses you need to look at the degrees and not the mm.

The pentax 10-17mm covers 180-100 degrees
The pentax 12-24mm covers 99-61 degrees

So these two lenses actually match each other very well and do not overlap.

The fish eye has curved distortions, a lot more so at 10mm than 17mm, and it can be "corrected" with software such as ptlens to give a straight picture although not as wide as the original.
07-19-2007, 03:42 AM   #4
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In other words, in relation to your question, the 10-17 will be a tiiiiiny bit wider at 17mm than the 12-24 is at 12mm, and comparing both at 12mm will yield completely different pictures.

07-19-2007, 05:02 AM   #5
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Thank you FotoPete and and.

What a great forum this, where you get polite and informative answers - even
when asking newbie questions like mine.

I'll now start wondering which of the lenses I really want/need.

Larsen.
07-19-2007, 05:13 AM   #6
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QuoteOriginally posted by Frakkas Quote
Thank you FotoPete and and.

What a great forum this, where you get polite and informative answers - even
when asking newbie questions like mine.

I'll now start wondering which of the lenses I really want/need.

Larsen.
I own the Sigma version you referred to in the thread. It's a great lens and gets a decent amount of use. I only chose that over the Pentax because at the time it was $100 cheaper. I hear the DA12-24 is a great lens and may produce slightly better colour but I can't fault my Sigma.
I have as well thought about adding a Fish eye to the bag but don't often find situations where it would be used. Everything I've read from other users sounds like they have some fun with it but don't use them a lot. Maybe the best route is one of those 16mm Zenitar fish eye's that sell on Ebay for about $140.00. All reports are that it is a very good lens and at that price you could have both the 12-24 and a fish eye.
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