I think I agree with your disagreement. After my last post on the
subject, I opened the Kodak Darkroom Dataguide for BW film and noticed
that their reciprocity correction factors for the newer films like T-Max
100 and 400 are much smaller than those in the Adams chart, closer to
what you cite here for the Fuji color films. I think your final point is
an excellent one. Contemporary cameras could easily be programmed with
response curves for current films. If you load a film for which the
camera is not programmed, it could advise you that there is no
reciprocity curve for that particular film.
I did conduct a little experiment with my LX and an analog spotmeter
to see if the LX had any built in correction for long exposures in auto
aperture mode. In my test, it appeared that it did. However, my methods
were far from scientific, and while my spotmeter was recently
calibrated, it may well be that it is not completely accurate at very
low light levels.
Kevin Thornsberry wrote:
>
> Paul,
>
> By way of disagreement I'll point out that in "The Negative" Adams quotes Kodak's
>recommendation of adding 1 stop of aperature adjustment for exposures of 1 second. I
>like to use Fuji Reala 100 print film. The Reala data sheet states that 1 stop of
>adjustment should be used for exposures of 16 seconds. While I don't use Fuji
>Superia 100 it is supposed to be very similar to the Reala. The Superia 100 data
>sheet suggest adding 1 stop of adjustment for exposures of 64 seconds. Superia 200
>suggests adding 1 stop at 16 seconds while Superia 400 is back to adding 1 stop at 64
>seconds. Similar examples can be made from Kodak films.
>
> Perhaps, with all of these new features and electronics we put into our camera's
>these days should be the ability to load a reciprocity response curve for each film
>we will use with that camera.
>
> Kevin
>
> -----Original Message-----
> From: PAUL STENQUIST [SMTP:[EMAIL PROTECTED]]
> Sent: Saturday, January 06, 2001 10:13 AM
> To: [EMAIL PROTECTED]
> Subject: Re: Vs: Macro Metering & Exposure Compensation
>
>
> Thanks Bill,
> I stand corrected. My opinion was based on an assumption that film
> responded in a linear way. That is not the case. The reciprocity failure
> is indeed caused by the inability of film to continue to respond to
> light in a linear way when exposures are long. And you are also correct
> in saying that different films require different correction. However,
> that being said, It should also be pointed out that the variation
> between film stocks is minor. The curves tend to fall off in a very
> similar fashion. Consider that numerous charts have been published that
> will bring you darn close for almost any film. They always call for one
> stop at one second, two stops at ten seconds, and three stops at 100
> seconds. You can find one in Ansel Adams' book "The Negative."
> Now if those charts can serve well for most purposes, I would think
> that this factor might be built into more advanced metering systems. I
> know I've shot exposures as long as two minutes with my LX and no
> correction with good results. I'm curious about this, so later today,
> I'll try checking the LX aperture priority exposure time against my
> recently calibrated Pentax spotmeter in low light with the LX stopped
> down for a long exposure.
> Paul
>
> William Robb wrote:
> >
> > Paul, I think you might be misunderstanding reciprocity failure.
> > At some point, the film's response to light goes non linear.
> > Effectively, what happens is that at (example only) a one minute
> > exposure, your 100 speed film is still a 100 speed film, but at
> > a 5 minute exposure, it is suddenly a 25 speed film. No meter
> > can account for that, because it is an individual film
> > characteristic.
> > William Robb
> > ----- Original Message -----
> > From: "PAUL STENQUIST" <[EMAIL PROTECTED]>
> > To: <[EMAIL PROTECTED]>
> > Sent: Saturday, January 06, 2001 7:44 AM
> > Subject: Re: Vs: Macro Metering & Exposure Compensation
> >
> > > A TTL light meter will correct for any exposure variation that
> > involves
> > > loss of light through the lens and shutter, including
> > reciprocity
> > > failure. (Or perhaps I should say that since a TTL meter
> > measures the
> > > light reaching the film/sensors inside the camera, it goes to
> > follow
> > > that it does not have the same problems with long and short
> > exposures
> > > that a meter measuring ambient light encounters.) Compare the
> > readings
> > > of your TTL meter to a handheld meter for an exposure of ten
> > seconds or
> > > so, and you'll see exactly what I mean. The ability to correct
> > for
> > > reciprocity and extensions was one of the principle benefits
> > of SLR/TTL
> > > cameras. And it is a huge benefits with a camera like the LX
> > that will
> > > measure very low levels of light. No heacache invoking
> > calculations
> > > necessary for those two minute exposures.
> > > Paul
> >
> > 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
>
> This message is from the Pentax-Discuss Mail List. To unsubscribe, visit
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