On Sat, Jul 16, 2011 at 12:03:47PM -0500, Darren Addy wrote: > Two questions: > Forgive my ignorance, but is there a formula or table somewhere > telling me what sort of minimum focus distances can be achieved with > different Takumars with the various Pentax extension tubes, or does > one simply have to experiment? > > Seems like somewhere there should be someone who quantified it, but maybe not. > > DOF can be calculated knowing the focal length, f-stop, subject > distance and film/sensor size > http://www.dofmaster.com/dofjs.html > but is there a similar calculator that takes into account extension amount?
Not directly, no. If you think about it, there can't be a simple one; different lenses with the same focal length can have different mimimum- focussing distances. It's possible to calculate a pretty good approximation for any given lens, but in practice it's probably easy just to experiment - to get really accurate results you'd need to know how the effective focal length of the lens assembly changes with change in focussing distance, and that depends on the optical formula of the lens. -- 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.
