2011/3/3 Eric Weir <eew...@bellsouth.net>: > Let me see if I understand some of what you say [I suspect I > don't entirely]: Absence of aperture coupling is equivalent to > using an M lens?
Worse. :-) You know, with the M series, there is a mechanical coupler that can be engaged via the Green Button. When you reverse the lens, the camera can't connect to it at all. I find that the only way to achieve accurate focus is to home in on the subject with fully open aperture and then stop down for exposure. The guy in the video seems to work with the lens already stopped down when approaching his subject. I think the viewfinder becomes too dim and focus too inaccurate working that way. > "No P-TTL" means there's no metering? > [My guess is that's not right.] Starting with the K-series DSLRs, Pentax abandoned its old TTL flash metering all together. In the *istD, there was a separate light meter for flash, measuring the incoming light onto the CCD chip and capable of quenching flash output when sufficient illumination had been provided. This system had been in use, in various incarnations, since the Pentax LX (1980). The P-TTL system no longer meters flash output during exposure, but use a preflash. For P-TTL to work, it needs aperture and focal lenght information from the lens. Thus it can only work with FA- series lenses and newer. So with a reveresed-lens-on-tubes setup, there's no flash metering at all. > I have avoided the use of flash so far, so all that's a complete > mystery to me. Would use of flash in this kind of photography > be necessary? It is absolutely necessary. To achieve at least a nominal depth of field, you need to stop down to f/11 or f/16. In addition, you lose a couple of stops worth of light through the extension tubes. However it's not as bad as it seems. A good quality flash (just avoid Sigma and you're good) will provide the same output every time when set to manual. When you work with a reversed lens, your working distance is constant. So effectively, the same combination of flash, aperture and lens setup will provide the same result every time, regardless of ambient light. You just have to work out the right combination in advance. That's a breeze with histograms, you know. I'm old enough to remember how frustrating that was with gelatine... :-) Jostein -- http://www.alunfoto.no/galleri/ http://alunfoto.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.
