There are two common crops for dSLRs as compared to FF SLR, 1.5 (Nikon and Pentax) and 1.6 (Canon).
Canon has a 1.3 crop on some of their pro bodies. P&S sensors are a whole other barrel of fish and there are many sizes, but they don't correlate because the lenses are not interchangeable. On Mon, Apr 12, 2010 at 3:00 PM, Keith Whaley <[email protected]> wrote: > P N Stenquist wrote: >> >> On Apr 12, 2010, at 8:48 AM, Keith Whaley wrote: >> >>> Bong Manayon wrote: >>>> >>>> Thinking of ... >>>> 1. Pentax DA 12-24 >>>> 2. Sigma 10-20 >>>> 3. Tamron 10-24 >>>> Am not into fish-eyes so those options are out. Any votes for or >>>> against any of those listed above? >>>> Thanks! >>>> Bong > >>> I don't think those focal lengths are 35mm-equivalent numbers. I suspect >>> they're double ~ such as the Pentax DA 12-24 is really like a 35mm lens of >>> 24-48mm focal length. >>> Nice wide angle-to-normal lens, but hardly a fish-eye... > >> First, the conversion factor for angle of view is 1.5. > > Was Bong talking about a specific camera? I know we were talking digitals, > but, I thought each camera had it's own conversion camera. In my limited > experience, which does NOT include DSLRs, most cameras differ a little as to > what their 35mm equivalent is. > I avoid the uncertainty by referring to the owner's manual for each camera. > They always mention it... > >> So the 12-24 has the same _angle of view_ on an APS-C DSLR >> as an 18-36 would have on a conventional 35 mm frame. > > Cropping factor, or what I call the telephoto effect, brought on by the size > of the sensor. In other words, the ratio derives from how much smaller the > DSLR's sensor is compared to 35mm film size. > See: > > http://www.minasi.com/photos/dslrmag/ > >> However, the focal length is 12-24. That doesn't change, regardless of the >> format. Furthermore, it's not a fisheye on any format. It's a rectilinear >> lens. In other words, the optics make the verticals as true as possible >> given the size of the elements and the constraints of physical science. >> Paul > > Quite so. Thanks Paul. > > keith whaley > > > -- > 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. > -- Aloha Photographer Photoblog http://alohaphotog.blogspot.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.
