How to make an eight hour exposure...

[David]

Because you're dealing with severe reciprocity you may find that somewhere in the middle of these you end up with a lith negative (ie areas which have had light above a certain threshold are completely exposed and anything below are completely unexposed).
Roger.

When I was doing the really long Cathedral exposures I couldn't find anything in the way of good information. The times were just too far out of the norm. You just learn by doing. What I did find through experimentation was that with the really long exposures it was almost impossible to blow out the highlights - something that was both unexpected and counter-intuitive. I develop by inspection but the decelopment times were pretty close to normal (whatever that is).

[c6h6o3]

I want to make the exposure 8 hours. Why? Because that will eliminate all traces of movement.

You don't need anywhere near 8 hours to do that. Way, way less time is needed. Take a look at Storrow Drive by David Fokos. (Scroll down. It's at the very end.)

8 hours is a little like going after a squirrel with a .458 Winchester Magnum.

[David A. Goldfarb]

You've discussed this with the Station Master at GCT? It's not hard to get a tripod permit for GCT, but they will limit where you can set up (no stairways, as I recall), and not during rush hour in general. Maybe if you can shoot on a weekend, you can find an 8-hour window in which to shoot, if you decide that you really need 8 hours.

I'd definitely do some testing. If you've got more than one camera, you could also set up a range of exposures. With two cameras, for instance, you could try 8, 5, and 3 hours.

Have you considered doing this as a pinhole shot? That and an ND filter will extend your exposure time pretty far. Finney probably makes a pinhole cap for your Leica. Calumet sells them.

[Jim Jones]

. . . Have you considered doing this as a pinhole shot? That and an ND filter will extend your exposure time pretty far. Finney probably makes a pinhole cap for your Leica. Calumet sells them.

A 35mm pinhole shot with a 12mm focal length will produce sharp billfold size prints. The goal for such an investment in time could be larger images than that.

The formula I used for determining pinhole exposures of an hour or more with several common films of a few decades ago was:

actual exposure = (metered exposure / .6) raised to the 1.4 power.

A light meter and a cheap cientific calculator saved a lot of tests. However, even back then, some films departed considerably from this reciprocity failure calculation. Astrophotographers may have experience with long exposures on Ilford SFX. A google search for astrophotography may show much better information. Perhaps your ND filter reduces the light to about the level of the night sky. If so, your range of test shots will be narrowed. Remember, the relative IR content of the light may vary from day to night in Grand Central Station.

[Claire Senft]

I think David id givinhg good advice in sugessting a test. If GST is close to you got there and take a light reading. Duplicate that light level at home and test and bracket some exposures. If you wish a view with no people take your photo at 2-3 am Monday monning. Granted I have never been to GST but I am guessing that the traffic at time is light enough that you could take several exposures of 2 minutes each without any people in them. With your camera on a tripod 5 feet from the floor I would guess that you can set your focus to have everything thing sharp @ f8 At f22 on a 12mm lens you have a diameter of about 1/2mm. This is a very small aperture and will mosy likely cause a good deal of diffraction. Leitz has. in the past stated that any physical aperture smaller than 4mm will lead to increasing losses thru diffraction. F22 would allow. at a medum green wavelength apprix 64lpm.
F8 would allow 200lpm. Obviously, you will not get either level of resolution because of film characteristics etc. If an exposure that is not corrected for reciprocity is 64 seconds on one hand at f22 it will be 8 seconds at f8. I have not used the film in question but I doubt that more than 45 seconds would be required at f8 when correctiing for recprocity.

Good luck with your photo.

[Claire Senft]

Mr Jones It is not often that I get to rural Mo. What do you charge for Koolaid..I am dieing to know?

[Gerald Koch]

Are you sure that an 8 hour exposure is needed to eliminate people. I seem to remember some photos doing the same with an exposure of 40 min.

[George Papantoniou]

I finally found the time to make some tests and here are the results:

Shot Fortepan 200 with an IR filter (the one that is too dark to see anything but the sun through it) at f8 and an exposure of 3.25 hours gave excellent results (rodinal 1+50, 11 min).

Shot Ilford Ortho with a deep red filter and f32 for 30 minutes and the results were OK too. Developed it toghether with the Forte, but it actually needed less time in the soup (8 minutes would have given great highlight detail, now they are dense).

All tests were made at bright sunlight, outside.

I guess that if you want to shoot indoors, you should make some trial exposures, but I am sure you're going to find a way to expose for the right time. My guess is that 30 minutes are more than enough in order to avoid any moving object from appearing on the film.

[ras351]

When I was doing the really long Cathedral exposures I couldn't find anything in the way of good information. The times were just too far out of the norm. You just learn by doing. What I did find through experimentation was that with the really long exposures it was almost impossible to blow out the highlights - something that was both unexpected and counter-intuitive. I develop by inspection but the decelopment times were pretty close to normal (whatever that is).

Hi David,

Different films have different reciprocity curves and I hope you'll accept that there is a point with all films at which no amount of reciprocity failure can offset the lack of light. On a graph of time against negative density this would show as flat. At the other 'normal' end we have the usual nicely graduated S curve ranging in density from fb+fog up to the dmax of the film/developer combination. As we approach an infinite reciprocity factor we tend towards the former and at some point the threshold becomes more critical and we lose the ability to distinguish between anything but either the exposed or unexposed clumps - ie we lose tonality. This is the point I was trying to make however I admit it didn't exactly come out as such (and may still be somewhat confusing). A similar situation occurs when you overrate film to near its limits.

I agree that with some films an eight hour exposure is viable and you can end up with a negative with reasonable/good tonality. Ilford doesn't appear to publish any reciprocity information on SFX so it may or may not suffer badly from this type of failure.

Roger.

[Lee L]

Sorry that I didn't think to post this earlier. I had forgotten that SFX was in a test group of potential astrophoto films. Robert Reeves has tested SFX along with other B&W films for reciprocity failure and use for astrophotography. See: http://www.robertreeves.com/b&w.htm for the full scoop. He has the Schwarzschild formula and the Schwarzschild factor for SFX posted there, so you can do some calculations. SFX loses 2.67 stops in a two minute exposure when adjusted from a short exposure with no reciprocity allowance, so you can think of the ISO as dropping to about 32 in a two minute exposure, and even lower for longer times.

There are several threads on APUG on reciprocity failure that will give you a few formulae and references on how to use them. Those formulae and the Schwarzschild exponent from Reeves' test might help you do a better estimate of where you reach the point of total failure. However, I'd bet you'll still have to test to be certain of usable results. Look at his testing setup to get ideas of how to make some long exposure tests of your own.

Hope this helps.

Lee