question about angle of view on two 17-50mm lenses


TPF Noob!
Nov 4, 2011
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I have been spending way too much time comparing two different lenses,

Sigma 17-50mm f/2.8 (600$)
Tamaron 17-50mm f/2.8.(400-450$ without VC).

Its tough because although they get nearly identical reviews i have seen some terrible test images for the tamarons auto-focus, which makes me wonder if the sigma is worth the extra 150.00 (if you have any personal recommendation feel free to share)

While comparing all their specs on B&H i noticed their "angles of view" are different:

Sigma: 72.4° - 27.9°
Tamaron: 78° - 31°

what does this mean? how can they be different if they are both "17-50mm" ?
Focal length is but one measurement of the optics. It does not always mean the same FOV.

You're also speaking of two different manufacturers. One may measure from side to side of the image, the other may be corner to corner.
... and often focal lengths are rounded to common values.

However, I always found good reviews of the Tamron, which in fact will be sooner or later my upgrade for the kit lens. If you have to share a link to what you found, I'm glad to read it.
I used the Tamron (non VC) for several years and it was a great lens. The AF was slower and louder than I would have liked (it's no Canon USM) but I never had an issue with AF accuracy like he's showing in that review.

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