Interesting - but LX literature does not mention it - maybe the response of the SBC is indeed close to the average film characteristics and that is why I have never encountered reciprocity effects. But you should still filter for correct colour balance, whatever that is. Adams´ book is very old now but the basics still apply, of course. All the best! Raimo Personal photography homepage at http://personal.inet.fi/private/raimo.korhonen -----Alkuperäinen viesti----- Lähettäjä: PAUL STENQUIST <[EMAIL PROTECTED]> Vastaanottaja: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Päivä: 06. tammikuuta 2001 21:02 Aihe: Re: Vs: Vs: Macro Metering & Exposure Compensation >Hi Raimo, >Different films do exhibit different characteristics in regard to >exposure requirements at longer shutter speeds, but are these >differences truly significant? If so, why do so many sources publish >charts to correct for reciprocity failure? For example, on page 45 of >the paper-bound version of Ansel Adams "The Negative," you can find just >such a chart. Ansel's chart, like every other one I've seen, prescribes >a one stop increase at 1 second, two stops at ten seconds, and three >stops at 100 seconds. (Ansel also recommends development adjustment to >account for changes in contrast with BW film, and notes that color shift >may occur with color films, which is in keeping with what you have >said.) When using my meterless cameras I've relied on this chart and >others like it with consistently good results. So these values are >apparently somewhat constant, even if they vary a bit from one film >stock to another. That makes me wonder if these values aren't programmed >into some of the more advanced TTL meters for long aperture priority exposures. > I conducted a little test this afternoon with my Pentax analog >spotmeter and my LX. The spotmeter was recently calibrated by Light >Metrics, a company that specializes in photographic meter repair and >calibration. The LX was recently calibrated at Pentax USA, and it >delivers very good exposures with transparency film. I mounted a 200mm >lens on the LX, loaded it with Ektachrome 100VS, and positioned a gray >card in a dim room. With the asa set at 100, and the lens stopped down >to f11, the LX exposed the film for 21 seconds. The ambient light >reading on the spotmeter indicated an exposure of 6 seconds, about 1 1/2 >stops less. This is in keeping with the values on the Adams chart. Of >course the spotmeter cannot be calibrated to correct for reciprocity, >because it doesn't know what aperture I'm going to choose. After writing >down these values, I moved the gray card to an area with more light, >changed the LX meter to 1600asa and made another exposure. The LX meter >indicated 1/30 second at f11, and the audible results of an aperture >priority exposure seemed to confirm it (although I obviously can't be >certain that it was exactly 1/30 second). The spotmeter indicated >exactly the same exposure f11 at 1/30 second for 1600 asa. Based on this >single experiment, I suspect that the LX meter is programmed to correct >for reciprocity failure when making long exposures in aperture priority mode. > > >Raimo Korhonen wrote: >> >> Reciprocity failure is not taken into account because of different characteristics >of the photocell and films - and all films are different. Actually even different >layers of film react differently so reciprocity failure affects colour balance - and >this cannot be taken into account by TTL metering. Actually today´s films are so good >and the amount of variables so large that it is impossible for an amateur to >establish the effects of reciprocity failure. >> All the best! >> Raimo >> Personal photography homepage at http://personal.inet.fi/private/raimo.korhonen >> This message is from the Pentax-Discuss Mail List. To unsubscribe, visit http://www.pdml.net and follow the directions. Don't forget to visit the PUG at http://pug.komkon.org
