The lens collects the same amount of light whether you put it in front of an APS-C of full frame sensor/film. Nothing has changed about the lens.
Also, I would avoid focal length equivalencies. You will only confuse yourself. A 40mm lens is 40mm no matter what camera you put it on. On Mon, Jul 2, 2012 at 5:09 AM, alban bernard <alban.bern...@yahoo.fr> wrote: > Hi folks! > > A confusing question came to me: > > To have FF equivalent focal length of a lens for our APS-C sensors, we have > to apply a factor of 1.6x: 40mm f/2.8 ltd is a 64mm FF equivalent. For the > depth of field, this factor is to be applied too: 40mm 2.8 ltd is a 64mm > f/4.5 FF equivalent. > > But, what about the amount of light? As the surface divide by 1.6x1.6 and the > sensor is placed at the same distance as a FF SLR film, the light reaching > the sensor is divided by the same amount: 2.56. Are the ISO from FF, APS-C, > m4/3, P&S all the same, or are they equivalent ones to take crop factor into > account? > > Concerning light, is the 40mm 2.8 ltd, a true f/2.8 opened lens, then? > > ~Alban. > > > -- > 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. -- David Parsons Photography http://www.davidparsonsphoto.com Aloha Photographer Photoblog http://alohaphotog.blogspot.com/ -- 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.
