After reading Jostein's response to Mike I realized I shoulda been writing to Mike! My apologies, Mike! Thank *you* for the very clear explanation.
On Mar 4, 2011, at 2:13 AM, AlunFoto wrote: > 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. .... > 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. > >> 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... :-) Thanks for the very clear explanations, Jostein. I was going to try to quote extracts of it in responding, but couldn't find a word to leave out. I've flagged the message for keeping. Real understand requires practice. I'm getting hardly any practice -- neither shooting nor processing. I can imagine spending my time doing hardly anything else, but there are other things that matter that I'm loath to give up. There is not enough time for it all. Get clear about priorities, be hard-nosed about it, bite the bullet. ------------------------------------------------------------------------------------------ Eric Weir Decatur, GA USA eew...@bellsouth.net -- 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.
