exposures longer than 1 second?

[ki6mf]

What you are getting into is reciprocity failure. This happens for all exposures beyond 1 second and faster than 1/1000 of a second. The spec sheet for the film, check the manufacturers web site on line, should have recommendations. Search this web site for answers as its been covered here before this post.

To compensate use a reciprocity chart and a stop watch. As always your mileage may vary and testing may be in order.

Steve Simmons recommends this for HP5 1=2, 2=4, 4=7, 8=19, 12=33, 16=50, 24=93, 32=145

[Preston]

I have used the multiple exposure method many times. However, one must be careful. Look to see if there are objects in the scene that may move between one exposure and the next. Also, allow time for any vibrations that occur as a result of recocking the shutter to damp out before releasing the shutter the second time. Using the multiple exposure method is a bit of gamble, as Kev says, but counting a two-second exposure is quite error-prone, in my opinion.

If you practice counting with a metronome, or a clock, before going into the field, you will be able to get very accurate longer exposures.

-Preston

[Jim Rice]

In terms of measuring long exposures I've found an electronic metronome (cheap) to be the best solution.

[Robert Hughes]

a thousand ONE, a thousand TWO... it's close enough...

[dh003i]

I use my Olympus E-3 DSLR to meter exposures. It serves a dual role -- scouting out shots and allowing me to be creative, if I find something I really like, I take it with my 4x5.

[Brian Ellis]

I use a wrist watch just because it's always there. But once you get past 5 or 10 seconds you can count "mississippis" or whatever just as well, a few seconds off here and there isn't going to matter once you get into the longer exposures.

All films don't exhibit reciprocity failure at 1 second. Different films have different reciprocity characteristics. I use one reciprocity table for TMax films and another one for HP5+ (the only two b&w films I use) since TMax has different reciprocity characteristics than other films (or at least different than HP5+).

[BetterSense]

You can never trust manufacturer's reciprocity tables anyway, IME. They usually exaggerate the effect, erring on the side of overexposure.

I feel that counting one thousand ONE one thousand TWO... is plenty accurate for negative film exposure starting at one second. I'm sure I can do +- 1/3 stop which is insignificant to me and probably better than my shutters are anyway.

[MIke Sherck]

The "B" setting on your shutter stands for "Bulb": when you press the shutter release the shutter opens and when you release the shutter button the shutter closes. If your shutter has a "T" setting, it stands for "Time": the shutter opens when you press the shutter release and closes when you press it again.

I usually time exposures up to three seconds by counting; over three seconds I use the stopwatch function on my wristwatch (these days, shooting LF is the only time I wear a wristwatch!) I use B&W film pretty much always and in longer exposures (say, seven or eight seconds or more,) a second one way or another doesn't seem to make much difference so sub-second accuracy isn't necessary. If you're shooting chromes you may have a different experience.

Mike

[evan clarke]

At 2 seconds exposure, an error of 1/10 second is 1/20th of a stop....don't worry about it, close is pretty good...Evan Clarke

[ic-racer]

One more vote here for "one-one thousand, two-one thousand..." (B&W Negative film)