On Mon, Sep 8, 2014 at 10:11 AM, Darren Addy <pixelsmi...@gmail.com> wrote: > To try to find lenses that still give you that focal length and > maximum aperture becomes an expensive proposition, when it is possible > at all. > > Extreme example: DA* 200mm f2.8 can be bought for under $1K. (More > like $700, used) 300mm equiv. FOV on APS-C > Move to a full frame, now you need a 300mm f2.8 to replicate that FOV. > Price one of those lately? A Sigma is $3400. A more reasonable choice > would be a 300mm f4. You've replicated the FOV, but lost a full stop > of light.
Not really (I mean about losing the stop of light). It's true that f/4 on full frame will only produce an image half as bright on the sensor compared to f/2.8 on APS-C, but that's half as bright in the sense of photons per second _per unit area_. The full frame sensor has a little over twice the area, so it will actually be collecting slightly more photons per second _over the whole image_, which is what actually matters (or, another way to think of it is they will both get the same number of photons per second per pixel if the two sensors have the same number of pixels). And a 300 f/4 on full frame would have about the depth of field as the 200 f/2.8 on APS-C. So these two scenarios are actually very comparable. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
