Now we see what your real definition of "perfect" exposure is, just make everything you point the camera at medium gray regardless of what it is in a real life scene. Absurd.
Look at what you said below. Even assuming "100%" accuracy in METERS AND SHUTTERS which is definitely not true, but just the tolerance errors YOU listed (unproven and which I still disagree with): pro slide film : 1/6 stop pentax apertures : 1/10 stop processing : 1/6 stop Just WHAT YOU LISTED will not allow you to always stay within 1/3 stop of "perfect", let alone add in the errors of the shutter and the meter. You are obviously not a math wizard. These errors may sometimes cancel, but they may also ADD UP, that's what random tolerances do. As for velvia, being "screaming obvious" different to a 1/3 stop exposure difference, I don't use it but if it was that sensitive, it would have an exposure latitude of something like +/- 1/6 stops which would be so narrow to make it unworthy of my consideration. I doubt FUJI would even market a film that prone to disaster. JCO > -----Original Message----- > From: Pål Jensen [mailto:[EMAIL PROTECTED] > Sent: Thursday, June 12, 2003 9:56 AM > To: [EMAIL PROTECTED] > Subject: Re: Exposure > > > From: "J. C. O'Connell" <[EMAIL PROTECTED]> > Subject: RE: Exposure (WAS: Re: OK Survey time) > > > Weve been down this road before, unless your > aiming your camera at a full screen 18% reflectance > subject the meter will over or under expose > the subject. the only way you could be accurate > is if you manually compensated the meter reading > based on the KNOWN reflectance of the subject and > that is nearly always UNKNOWN. > > > REPLY: > > Arrgh! This is not about autoexposure but metering which > something entirely different. It is about being able to set > metering within 1/3 of a stop. Known reflectance has nothing to > do with it. What matter for a photographer is tonality on FILM. > Ansel Adams didn't worry about known reflectance but the tonality > of the various part of the scene on film. It is exactly the same > principle with slidefim just the difference that developing for > all practical purposes is a constant and not something that can > be used to adjust the contrast range. Have you seen an Ansel > Adams print. Do you really think that whats medium toned on the > print was medium toned in real life? Maybe maybe not (most likely > not) but who cares and does it matter? > If I meter a medium toned piece of rock it is totally unimportant > if the rock is medium toned or not in reality. If I want it > medium toned I expose it as such, which is 0, it doesn't matter > if the rock is really white or black - it will be medium toned on > the film. If I want it + 1/3 I do that. If I want it as > silhouttte I expose it at -2. I don't care if the green grass > over there is really 0, -1/3, +1/3, -0.5 or whatever. What I do > want is to render it on film at +1/3 (with Velvia) because thats > nice in my opinion, and I get that with precision every damed time. > I also want to asses the contrast range of the scene fast and > with precision. I can do that as well. This will tell me how all > parts of the scene falls in the tonality range if I expose for > this or that. Say theres a patch of snow in the picture I don't > want to burn out. I need to expose it at +1,7. How then will the > tonality of the snow-free foreground turn out? Is the image > possible at all? I can figure this out in seconds because I have > that tool to nail it. If I expose snow at +1,7 it always get +1,7 > on film; never +2 which ruins the shot. I can promptly figure out > the contrast range between the forground and the sky. Do I need a > graduated Nd filter? How many stops? > These are the reasons why I want ot be able to nail exposure > within 1/3 of a stop fast and efficiently. > > - Pro slide film are within 1/6s tolerance. That is a worst case > scenario; they are practically speaking dead on. > Amateur slide film are within 1/3s but in reality amateur film is > exactly the same film as the pro version but is released earlier > to the store so that the manufacturer cannot guarantee its > history. Whatever differences this may make it is usually in > subtle colour balance, not exposure. > - Pro Labs are within 1/6 stops > - Modern Pentax lenses have apertures calibrated within 1/10s > accuracy. Canon claim 1/12s for the L lenses. > - All slr camera made after approximately 1985 have 100% shutter > accuracy. This have made the once common camera shutter tests > redundant. Even on older, less precise cameras the errors are > usually only significant in the real short speeds. > - All Pentax cameras I've bought since the 90's have 100% correct > calibrated meters right out of the box. In the old days, pre > 1990, a how to photography books would tell you to calibrate you > meter. They don't anymore as new camera bodies are usually dead > on. This usually no real problem as this is usually a constant > and any erors can be calibrated away. > > All the errors above don't really add up to anything significant > unless faulty equipment is at play or an accident happens. They > are too small to be of any concern and they are more likely to > cancel each other out than to add to each other. > I've shot several side by side test images where I compare > various Pentax 645 lenses. I shoot at various apertures and > varios zoom setting with various lenses. There are no exposure > differences regardless on Velvia. On this film 1/3s is screaming > obvious. Whats annoying with this futile discussion is that some > in reality are claiming that those of us who do nail the exposure > we want within 1/3s are lying bastards. It is somehow not > surpising that these allegation comes from people who use very > old equipment. That probably explains it all. I cannot nail > exposure this accurat with my older cameras. > Life is really too short for these futile discussions. > > Pål >
