On Thu, Oct 03, 2013 at 06:30:39PM +0100, Steve Cottrell wrote: > -UID: 16931 > Content-Length: 2645 > > Godders -thanks for the reminders. Re sensor crop vs DoF - D'OH!!! Of > course. Hey my excuse is my back is bad and I'm in pain - addling my brain.
Actually, the size of the sensor has nothing to do with the DoF. The size of the pixels or grain, do affect the DoF. Don't worry, this is a common circle of confusion. > > Thanks so much for that. I will do some further testing and might even > make my own set of distance markings... now where is my Dremel bwahahahahah. > > > > > > On 3/10/13, Godfrey DiGiorgi, discombobulated, unleashed: > > >One factor: > > > >Many of the less expensive mount adapters allow the lens to focus "past > >infinity", an inexpensive way to ensure that all lenses CAN focus to > >infinity by making the adapter+camera registration just a little shorter > >than nominal. The idea seems to be that since most users are likely to > >be looking TTL anyway with adapted lenses, they can set the focus > >accurately, and who cares what the focusing distance scale actually reads? > > > >This is annoying and confusing for those (like me) who like to use the > >DoF markings on the distance scales. The ONLY third-party mount adapters > >that are rigorously maintaining the proper mount register, in my > >experience with about eight different vendors' products, are Novoflex, > >Voigtländer, and Rayqual. > > > >Another factor: > > > >Remember that the DoF markings on the lens barrel for most "legacy" or > >"manual" lenses was designed to be used with 35mm film camera format, > >24x36 mm. Your Fuji, like my Ricoh, is 16x24mm format, which is cropping > >the original field of view and implicitly adding more magnification. > >More magnification == less DoF, so the markings are off. The > >magnification or crop factor for your Fuji is 1.5x, so a first order > >approximation to adjust the DoF markings is to use the set of markings > >for a one stop larger opening than what you set on the lens. That is, if > >you set the lens for 10' focus distance, and set f/8, the actual DoF > >range to include infinity will set the infinity mark at the far f/5.6 > >setting. Presuming, of course, that the distance scale index is accurate > >(meaning that the mount register is correct). > > > >A combination of these two factors is likely the cause of your > >observations. To solve the problem: > > > >- calibrate the distance scale index so you know where the true > >registration mark on the focusing ring should be. > > > >- for zone focus, use one-stop larger markings than the actual aperture > >you set. > > -- > > > Cheers, > Cotty > > > ___/\__ Broadcast, Corporate, > || (O) | Web Video Production > ---------- <www.seeingeye.tv> > _____________________________ > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRI -- Larry Colen [email protected] http://red4est.com/lrc -- 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.
