[jfsavage]

Checking the specifications of various ultrawide zooms, I notice that Pentax claim that their 12-24 has a FOV of 99-61 and the Sigma is 102-63. Is the Sigma specification for a different sensor size?

I've also seen a comment on the web claiming the Pentax is actually a 13mm at the wide end not 12. Anyone find a test to back that up?

[Lowell Goudge]

Checking the specifications of various ultrawide zooms, I notice that Pentax claim that their 12-24 has a FOV of 99-61 and the Sigma is 102-63. Is the Sigma specification for a different sensor size?

and what is odd about this? the sigma is a wider lens hence the wider FOV, or were you expecting more?

I've also seen a comment on the web claiming the Pentax is actually a 13mm at the wide end not 12. Anyone find a test to back that up?

you could easily do a test.

at infinity (or big distances) image size = subject size * focal length / subject distance.

go out and shoot a known subject from a known distance then measure the image size and do the math.

[jfsavage]

the lenses are 20% difference in focal length (10mm/12mm), but the FOV are only ~3% different.

I would expect more of a difference:

Distortions and FOV Photo Gallery by lightrules at pbase.com
Tokina 12-24mm f4 DX Review - Complete "Hands-on" Lens Test

[Blue]

Checking the specifications of various ultrawide zooms, I notice that Pentax claim that their 12-24 has a FOV of 99-61 and the Sigma is 102-63. Is the Sigma specification for a different sensor size?

I've also seen a comment on the web claiming the Pentax is actually a 13mm at the wide end not 12. Anyone find a test to back that up?

The sigma angle of view listed is for SIGMA, CANON, NIKON, SONY/MINOLTA, PENTAX, and FOUR THIRDS. There is likely some differences among those. I would especially expect the Sigma, Canon and Nikon ones to be different. Angle of view depends on the focal length and sensor size (or film). For example, they list the angle of view as 94.5 - 56.8 degrees for the Four Thirds.

Edit: The Sigma SD format is 102.4 - 63.8 degrees http://www.fredmiranda.com/reviews/showproduct.php?product=298&sort=7&cat=37&page=1

For Pentax and Minolta it is 109.4 to 70.5[ Go here> http://www.livingroom.org.au/photolog/lenses/sigma_1020mm_f456_ex_dc_konica_...tax_mounts.php and here > http://www.letsgodigital.org/en/news/articles/story_5354.html

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Last edited by Blue; 12-02-2008 at 02:43 PM.

[jfsavage]

Edit: The Sigma SD format is 102.4 - 63.8 degrees FM Reviews - 10-20mm F4-5.6 EX DC HSM

For Pentax and Minolta it is 109.4 to 70.5[ Go here> Sigma 10-20mm F4-5.6 EX DC (Konica Minolta and Pentax mounts) and here > Sigma 10-20mm F4-5.6 EX DC for Minolta & Pentax

Many thanks - that was the data I was looking for and had not found. So the Tamron/Sigma have a FOV about 10% greater than the Pentax.