Were you friends using the Identical camera and lens? Complicated zooms (especially early Motion Picture lenses) used to be calibrated in T-stops instead of f/stops--T for transmission was supposed to factor in things like flare and vignetting and internal reflections rather than the theoretical f/stop--very important when matching exposures on movie stock where intercutting shots made with lenses with different transmission factors would yield a master negative roll with different negative densities as the scene was cut (a royal PITA to say the least). Two things come to mind: the Pentax engineers may have been using a calibration scheme designed to put more density on the film or your friend's cameras may have actually been producing a top speed closer to 1/500 regardless of what the dial said they were shooting (quite common before electronic shutter controls). To me 1/1000 @f/4 with proper exposure sounds much better than 1/1000 @ f/5.6 and a stop less exposure density. (I'll raise your $0.11 a dime). And regarding the original question posted, in a perfect optical world and assuming all three lenses had their field of view filled by a neutral gray background and that all three cameras had been calibrated by the same technician on the same day to the same standard you'd probably still see measurable (but acceptable) differences in the slides, prints, or whatever produced by the three systems. I am at a loss as to why this would bother anyone since photography can only interpret reality it isn't the original scene. darkroommike ---------- ----- Original Message ----- From: "Bill Wood" <bwood@cetac.com> To: "List for Photo/Imaging Educators - Professionals - Students" <photoforum@listserver.isc.rit.edu> Sent: Friday, May 02, 2003 2:35 PM Subject: Re: Question about lenses > Back in the early 70's my first camera was a Pentax Spotmatic. When everyone else was shooting at 1/1000 & f5.6 @ ISO 100, I had to shoot at 1/1000 @ f4 with the same film speed. It really irritated me at the time and I finally upgraded. > > Just my $0.11 worth. > -Bill > > >>> elgenper@telia.com 9:03:33 AM Thursday, May 01, 2003 >>> > In theory, no... and yes... ;-) > > Aside from variations in manufacture or camera calibration, lenses do > differ in actual light transmission. With today s glasses and > coatings, the differences are far smaller than they used to be, and for > "non-extreme" lenses like those three you mention, they *should* be > quite small indeed. > > In practice, I would be surprised if three different cameras did indeed > read the same without extra calibration - even if they used the same > lens... > > Per > > > torsdagen den 1 maj 2003 kl 14.53 skrev Charles Dias: > > > Hi, > > > > Another question a friend asked me and I couldn t answer perfectly. > > Imagine you placed three cameras of the same brand and model side by > > side, loaded with the same film and with the same function > > adjustments. It are pointed to the same 18% gray panel and the spot > > light meter are set. One of the cameras have a 20mm f2.8, other a 35mm > > f2.8 and the last a 135mm f2.8. > > If you set f5.6 in all lenses, will the light meters of the cameras > > indicate the same speed for all three cameras??? > > I asked him that it problably would indicate different speeds, in the > > limite of +/- 1 EV, because the lenses have different optical > > construction (different kinds, number and arrangement of optical > > elements), but I m not sure about this. > > Is my conclusion right??? > > > > > > T+ > > > > Charles > > > > "It s no better to be safe than sorry" > > In "Take on Me" song by A-Ha > > > > > > > > > > _________________________________________________________________ > > Add photos to your e-mail with MSN 8. Get 2 months FREE*. > > http://join.msn.com/?page=features/featuredemail > > >
