Sorry Bruce, P.J. - I misattributed your post, P.J., to Bruce. stan
On Oct 7, 2014, at 12:32 AM, Stanley Halpin <s...@stans-photography.info> wrote: > > On Oct 6, 2014, at 10:38 PM, P.J. Alling <webstertwenty...@gmail.com> wrote: > >> On 10/6/2014 9:33 PM, Bruce Walker wrote: >>> On Mon, Oct 6, 2014 at 9:23 PM, Stanley Halpin >>> <s...@stans-photography.info> wrote: >>>> On Oct 6, 2014, at 4:26 PM, Larry Colen <l...@red4est.com> wrote: >>>>> P.J. Alling wrote: >>>>>> and wonder of wonders it's got some interesting information for free. >>>>>> >>>>>> http://www.luminous-landscape.com/techniques/pentax_645z_astrophotography.shtml >>>>> Excellent link, though I'm afraid that if I were to spend $10K on a 645Z, >>>>> I wouldn't have any money left over for the $500 astro mount. >>>>> >>>>> I was surprised to find that there don't seem any lenses faster than >>>>> f/2.8 available for the 645. Doing some quick web search, there don't >>>>> even seem to be any manual focus lenses faster than f/2.8 available. >>>>> >>>> There are adapters that support the use of Hassleblad etc. on the 645. >>>> Maybe you can find the faster glass you need by going that route? >>> I always assumed that there isn't faster glass because there doesn't >>> need to be. The DoF on medium format is already razor thin compared to >>> 35mm and APS-C and perhaps a 1.4 on a 645z would create a serious >>> focusing problem? Or ridiculously OOF portraits? >>> >>> In other words, we have what's practical to sell, as with other >>> formats. Or am I way off base? >>> >> Not just DOF, but an f2.0 135mm would be quite large and heavy if built to >> cover the 645 format, yet it would be the equivalent of a Portrait lens say >> 85mm on 35mm, (75mm actually). Fast glass makes in any focal length on 645 >> need a tripod, whereas Pentax build a system to be equally good as a hand >> held field camera, as well as at home on a tripod in a studio. Traditionally >> medium format lenses have been fairly slow. There are exceptions, but they >> are exceptions. >> > > Bruce, not to disagree with your point at all, but FYI a 645 135mm lens on > the 645z would have an effective field of view equivalent to a 110mm lens on > a 35mm film camera. The “crop factor” is 0.8. So taking (many of) the actual > lenses available, the 645z has: > > X 645 lens => equivalent to Ymm focal length on 35mm > > 25 => 20mm > 35 => 28mm > 45 => 35mm > 55 => 44mm > 75 => 60mm > 90 => 72mm > 120 => 96mm > 150 => 120mm > 200 => 160mm > > I think you were basing your comparison on actual 6x4.5 film vs. 35mm film. > > One other point about lens speed: the importance of wide apertures has > seriously diminished (except for very specialized niche applications that > call for shallow DOF) - the ability to shoot clean shots at ISO6400 or 12800 > really makes “fast” lenses a relic of the good old days when we had a choice > of either Kodachrome as God intended it to be at ISO 25 or of that new > Kodachrome 64 that was a serious compromise in quality. > > Though I must admit that I prefer a fast lens to a slower one for the simple > reason that I have a brighter image to focus and compose. > > Stan > > > -- > 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. -- 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.
