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11-04-2010, 02:38 AM   #16
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QuoteOriginally posted by interested_observer Quote
The field of view of some of the lenses are...
  • 12-24 - 99 to 60 degrees
  • 10-20 - 104 - 63 degrees
  • 8-16 - 114-75 degrees
You seemed to have gotten the FOV figures for the Sigma lenses from the Sigma website. Sigma bases the FOV values on their own sensor size which is a bit smaller than Pentax sensor sizes.

Assuming a crop factor of 1.54 (i.e., K-7) the FOV values are as follows:
  • 12-24: 99 to 60.6 degrees
  • 10-20: 109 - 70 degrees
  • 8-16: 120.6 - 82.5 degrees


11-04-2010, 08:45 PM   #17
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QuoteOriginally posted by sevenarrow Quote
As a real estate photographer, I take hundreds of pics every day and so live and breath ultra-wide angle.

I have the Pentax 12-24, Sigma 10-20 f4-5.6, and Tamron 10-24. Generally speaking all three are good lenses but I think the Pentax is the best. It has the least barrel distortion of the three and clearest and sharpest pics edge to edge.

However, sometimes the Pentax 12-24 is not quite wide enough. That extra 2mm that comes with the Sigma and Tamron lenses is very significant in SOME situations. Most of the time the 12-24 is sufficient though.

My least favorite of the three is the Tamron. The further away you get from the center of the image, the more fuzziness you see. I've compared images side by side between the Tamron and Pentax (pics of the exact same scene) and the Pentax wins hands down.

Both the Tamron and Sigma lenses has a little more barrel distortion than than the Pentax but that is easily corrected in Photoshop. That extra 2mm width might be contributing to that extra barrel distortion.

A sample photo for each lens is below. No obvious winner from these photos which just means that any of these lenses will do a good job for you.

Tamron 12-24




Pentax 12-24




Sigma 10-20 f4-5.6
Thank you for the photo samples, sevenarrow.
Those are really helpful samples. Since no obvious winner, I think I should go with the widest & cheapest one then
The shot from Pentax 12-24mm looks very good. Too bad it only goes up to 12mm.
But I like the constant aperture, sigh..
11-07-2010, 11:54 AM   #18
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QuoteOriginally posted by Class A Quote
You seemed to have gotten the FOV figures for the Sigma lenses from the Sigma website. Sigma bases the FOV values on their own sensor size which is a bit smaller than Pentax sensor sizes.

Assuming a crop factor of 1.54 (i.e., K-7) the FOV values are as follows:
  • 12-24: 99 to 60.6 degrees
  • 10-20: 109 - 70 degrees
  • 8-16: 120.6 - 82.5 degrees
Yes, I pulled the Sigma numbers from the Sigma website.....

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