From: Tony Conrad (email suppressed)
Date: Tue Nov 02 2010 - 15:47:16 PDT
Metering very long exposures is not very helpful, because of a quantum effect
called reciprocity law failure, which is different in different film emulsions.
However, a good guestimate should be possible if you use a very small pinhole and
then increase the distance between the hole and the film, relating to a test made
with a shorter time (such as your weeks-long exposure). Figuring that doubling
this distance cuts the light by a factor of four, I would take the square root of
the ratio of days and use that as the ratio of distances. This in effect changes
the f/ stop.
-------------t0ny
On Tue 11/02/10 5:14 PM , Jason Halprin email suppressed sent:
> Aditya,
>
> As I mentioned before, "metering" is not possible for this kind of
> variable. When you take a measurement of light, it is an
> instantaneous measurement. In order to figure this out you would have
> to take a series of measurements over the course of a year with
> meticulous data, and then hope that the approximate weather
> conditions were close the following year. You could do this
> measurement on one of the solstice days and extrapolate from there
> (those days being the "average" length of a day for the whole year).
> Begin a few hours before sunrise and take a measurement every 5
> minutes until a few hours after sundown, then average it out...
> However, why not just start the exposure experiment? You've already
> done 14 days, why not double it, or triple it? You already have some
> good date with which to make an educated guess.
>
> Or contact an Astronomer in your area. They may be able to direct you
> to a dataset about the amount of sunlight falling on an average day in
> your area...
>
> -Jason Halprin
> -------------------------
> FROM: Aditya Mandayam
> TO: Experimental Film Discussion List
> SENT: Tue, November 2, 2010 11:51:13 AM
> SUBJECT: Re: [Frameworks] Extremely Long Exposures - for Months and
> Years
>
> I have tested exposures of 1 day, 2 days, 1 week and a fortnight
> using
> pinhole cameras and paper.
>
> Here is an example of a week long indoor exposure:
> http://farm5.static.flickr.com/4126/5139678697_8552788b30_b.jpg
>
> The pinhole camera had an f-stop of around 250.
>
> This was performed indoors, which allows larger exposure times.
> Indoor
> long exposures allow much longer exposure times.
> I reiterate my question : how would you meter for an outdoor exposure
> over a year?
>
> On Tue, Nov 2, 2010 at 1:35 PM, Elizabeth McAlpine
> wrote:
> > Some years ago – I made a very long exposure still image not
> nearly as long
> > as you are suggesting but it was about 7 hours – I found that
> shooting on to
> > duplicating film helped lengthen the exposure – it has a very low
> IOS I also
> > used a lot of ND filters on the front of the camera which helped to
> lengthen
> > the exposure time – I was shooting in candle light – and the
> print ended up
> > having a very red cast – I was never sure if it was caused by the
> candle
> > light or the duplicating film – but it worked for my purpose
> >
> > working with pinhole aperture will defiantly increase you exposure
> times.
> >
> > best
> > Elizabeth McAlpine
> >
> >
> >
> > On 02/11/2010 12:03, "Jason Halprin" wrote:
> >
> > Well...Long story short, a very long exposure of months or years
> would be
> > very difficult or nearly impossible to meter for. When you meter
> for a shot
> > you are basing the characteristics of the film on the straight-line
> portion
> > of the characteristic curve - meaning that the film has a
> more-or-less
> > linear relationship between exposure and density.
> >
> > If you were to expose for months, you would be exposing in the
> "shoulder"
> > area of the curve, that area where an increase in exposure results
> in an
> > ever decreasing ratio of exposure to density. Essentially, you are
> working
> > with a situation where most of the possible silver-halide has been
> > activated, and the film no longer has linear, predictable results.
> >
> > Now that that's out of the way, I would propose making your own
> pin-hole
> > aperture (f64 ? smaller?) and centering this on the back of the
> lens to
> > lower the amount of light getting to the lens. Also, use a very
> slow
> > film...and test, test, test. Don't expect a doubling of exposure
> time to
> > result in a stop of increase in density (it won't be nearly that
> much). It
> > would seem the easiest option would be to rig a cable release on an
> SLR
> > camera so that you can leave it open, on a tripod, for a very long
> > time...vary your exposure, and take good notes.
> >
> > -Jason Halprin
> >
> >
> > ________________________________
> > From: Aditya Mandayam
> > To: email suppressed
> > Sent: Tue, November 2, 2010 6:40:11 AM
> > Subject: [Frameworks] Extremely Long Exposures - for Months and
> Years
> >
> > Hello, I am interested in making extremely long exposures: of the
> > order of many months, perhaps a few years.
> >
> > E.g: http://photoslaves.com/open-shutter-by-michael-wesely/
> >
> > I asked this question on photo.net as well:
> > http://photo.net/black-and-white-photo-film-processing-forum/00XKLr
>
> >
> > I would like to know how to meter for such long exposures. What
> amount
> > of light does one assume? Average brightness of a day over a year?
> >
> > Thank you.
> > _______________________________________________
> > FrameWorks mailing list
> > email suppressed
> > http://mailman-mail5.webfaction.com/listinfo/frameworks
> >
> >
> > ________________________________
> > _______________________________________________
> > FrameWorks mailing list
> > email suppressed
> > http://mailman-mail5.webfaction.com/listinfo/frameworks [1]
> >
> > _______________________________________________
> > FrameWorks mailing list
> > email suppressed
> > http://mailman-mail5.webfaction.com/listinfo/frameworks [2]
> >
> >
> _______________________________________________
> FrameWorks mailing list
> email suppressed
> http://mailman-mail5.webfaction.com/listinfo/frameworks [3]
>
>
> Links:
> ------
> [1] http://mailman-mail5.webfaction.com/listinfo/frameworks
> [2] http://mailman-mail5.webfaction.com/listinfo/frameworks
> [3] http://mailman-mail5.webfaction.com/listinfo/frameworks
>
>
_______________________________________________
FrameWorks mailing list
email suppressed
http://mailman-mail5.webfaction.com/listinfo/frameworks