Larry Colen wrote: >I've been thinking, for low light work, about the Sigma 18-35/1.8 versus >the Pentax/Tamron 24-70/2.8. > >With the crop factor of 1.5x, in their native modes, the two lenses have >approximately the same angle of view. > >My understanding of depth of field is that you get approximately the >same depth of field at 27 mm at f/2.8 as you do at 18mm at f/2.0. > >In other words, to a first order approximation, with a "one stop larger >sensor", and stopped down by a stop the 24-70 will have *close* to the >same angle of view and depth of field as the 18-35. > >In order to shoot at the same shutter speed, stopped down by a stop, you >will need to increase the ISO sensitivity by a stop. When you do this, >your per pixel noise increases by about a stop (3dB) and your per pixel >dynamic range decreases by about a stop. However, you have twice the >number of pixels (area of silicon) to use, so that when you process your >photo to the final size, your effective noise and dynamic range will be >approximately the same. > >In short, when the dust settles, and you look at the final images, my >guess is that the results with the two lenses will be very close,
Well, that is, after all, the reason Sigma made that lens. -- Mark Roberts - Photography & Multimedia www.robertstech.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
