I am looking to buy a wide angle zoom to partner my 40D. I am considering the Sigma 10-20 but I am not sure whether to go for the f4-f5.6 or the f3.5. My thinking is that the extra aperture of the f3.5 over the f4-f5.6 can be addressed by upping the ISO. My reason for hesitating with the f-3.5 is that I have several P series Cokin filters and the physical diameter of the f.3.5 will result in vignetting and that I will have to buy the larger filters which is an added cost.
I would appreciate the opinions of the experts out there.
Are you trying for depth of field or motion-stopping with the wider aperture?
Because wide angle lenses already have a pretty deep depth of field at almost any aperature. Use Bob's calcluator to plug in some numbers and comapare against your needs.
Hi Angle of view is my reason for buying the wide angle and I cannot see a reason for going for the f3.5. At those focal lengths depth of field will not be an issue and I guess that at f5.6 and certainly f8 the hyperfocal distance will be 5 or 6 feet. My concern was that there might be other differences such as differences in build quality or image quality that make the f3.5 a better lens.
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