4x5 ISO 100 long exposure

[Hughjb]

Thanks everybody for taking the time, I will start experimenting this weekend.

Hugh

[Deckled Edge]

Need some enlightment or at least an educated guess!

I want to start doing some long exposures (5 minutes +).


Any ideas or advise for a 5-7 minutes exposure, or what do I need to add to my ND 3.0 to get there.

Thanks

Hugh

To paraphrase an old photo-journalist quote "f256, and be there".
That's 10 stops from f8 (3.0 ND).
For tiny film (4x5), your lens should handle f32 without much diffraction, so with a 1.4 reciprocity factor a 5 min. exposure should require that you stack a 0.6 ND and a 3.0 ND and shoot at f32.3. As David points out, any other film than T-Max will require a more heroic reciprocity factor, up to 2.0--that would be 5 min. at f22.6 down to f22.

[2F/2F]

Fuji Neopan also has excellent maintenance of reciprocity during long exposures. So does Provia, if you want a color film.

The first thing you do, in lieu of doing your own tests, is to look at the film's data sheet. Read the section on reciprocity characteristics. Look for the exposure which you need to expose 5 minutes to replicate. For sake of this example, let us say that your data sheet says to expose 5 minutes when your desired exposure calls for a 4 minute shutter speed. So you want to calculate your effective f/stop based on a 4 minute shutter speed (in this hypothetical example). When aiming for a particular shutter speed, you come at it backwards like this, because the desired shutter speed of 5 minutes is your fixed factor.

Assuming a bright, sunny day, you would use this film at approx. f/16-2/3 at '60, assuming that box speed matches your personal EI, which it probably does not. To get '60 down to 4 minutes, you need to go, let's see...'30, '15, '8, '4, '2, 1, 2, 4, 8, 15, 30 sec., 1 min., 2, 4. So you need to cut 14 stops from your BDE (basic daylight exposure, AKA sunny 16 rule). Go to f/32-2/3 and you only need to cut 12 stops, or add 3.60 total ND. So, you need to stack a 0.60 ND filter on top of your 3.0 ND filter, assuming shots in bright sun on a clear day.

Of course, you can use wider apertures by using more ND. If I was going to make a pastime out of this, I would have 6.0, 3.0, 1.20, a few 0.60s, and a few 0.30s.

In this case, you may, in fact, be better off using a film that suffers from bad reciprocity loss during long exposures. You just need to test for it first to get a handle on things.

2F/2F