how to calculate long exposure?

[stradibarrius]

Is there a simple method to calculate a long exposure?

[Kevin Crisp]

Are you asking how to compensate for reciprocity failure after you have a meter reading? Or how to get a meter reading in the first place?

[r.e.]

Is there a simple method to calculate a long exposure?

You will find it helpful to do a search on the forum for the phrase reciprocity failure. There are lots of threads specifically on this subject, so it is perhaps best/more efficient to search for the phrase in titles only rather than posts.

[Pawlowski6132]

Its film dependent.

[evan clarke]

Don't be afraid of giving enoigh exposure. I make lots of 10-20 minute exposures and you can't give it too much..EC

[r.e.]

Don't be afraid of giving enoigh exposure. I make lots of 10-20 minute exposures and you can't give it too much..EC

That reminds me that Seattle photographer Chris Jordan, who at one time participated in this forum, made his early 8x10 photographs by exposing colour film for hours. None of that work appears to be on the internet anymore, but it looked rather different from his current work: http://www.chrisjordan.com/gallery/rtn/#car-keys

[Robbie Shymanski]

Experience.

[atlcruiser]

Hi Barry,
Seems like you did not get many good replies :)

I am not sure what factors are in question for you.

I figure the base exposure and, more often than not, add .5 to 1 stop to that. I then add in filter factor then bellows extension if needed. I have a small printed table to figure reciprocity. I take the above determined exposure to my table and figure final exposure from there. Usually 1-10 seconds or so i go with the table. over that I might double or even triple those times.

I almost never have an issue with overexposure but I have had many issues with underexposure.

[ic-racer]

If you are using Kodak film, the table provided by Kodak is pretty clear. For example "If the [meter] indicated exposure is 100 (seconds), Use this lens-aperture adjustment (+1 stop) or [use] this adjusted exposure time (200 seconds)."

[stradibarrius]

Maybe I should ask this question. If I want to take a shot on a city sidewalk, at night, that has some street lights would I just take a meter reading as normal.
I am asking this as the first part of the question... reciprocity would be part two.

[atlcruiser]

If your meter will read that low. Some wont and some will read lower than they should. I would pick an area that is lit and meter my hand from there then decide what zone that should be in. from there you can figure the rest.

[ki6mf]

Maybe I should ask this question. If I want to take a shot on a city sidewalk, at night, that has some street lights would I just take a meter reading as normal.
I am asking this as the first part of the question... reciprocity would be part two.

For night shooting most don't bother to calculate the exposure. Rather bracket using multiple exposures, taking good notes, and remembering what the ambient light is in your notes will allow you to develop a sense of what the correct exposure time will be.

I personally start with 5 Minutes @ f22 and then do 10 minutes at f22, and 20 minutes @22 etc. Because the highlights are relatively easy to bring out i would suggest compensation developer to get shadow detail. In my case my preference is D76 diluted 1/3 developer to 2/3 water with gentle agitation every 2 minutes. I use two cameras one for the longer exposures and one for the shorter times.

Most important gear after the camera is a folding beach chair to sit in for those long long long exposures on very day nights. Though its mostly digital check out the Nocturnes web site too for suggestions on technique.

[neil poulsen]

A good place to start is with the technical paper for the film that can be found on the film's website. IIford gives a graph for each film with metered time on the horizontal axis and what you use as the exposure time on the vertical axis. The exposure time is enough longer than the metered time to adjust for reciprocity failure.

[Matus Kalisky]

A good start could be to use a digital camera to estimate the exposure and scale it to your film speed and f/stop, then apply the factor for reciprocity failure for given film and exposure time. The first part is easy, the second requires not only the film data, but also some experience.

[Joseph Dickerson]

There are a number of night exposure calculators available, including an excellent one in Kodak's Professional Data Guide. (publication number R-28). I'm sure it's long out of print but it shouldn't be too hard to find a used one somewhere.

The Professional Data Guide also has reciprocity data for both black and white and color films (only Kodak of course). It contains tons of other useful stuff by the way.

Exposure charts are frequently more accurate than light meters for extreme low light situations. After some experience, and accurate record keeping, you'll be able to go on instinct alone, as many do.

If you google Basic Daylight Exposure (BDE), which is what Brooks Institute calls the Sunny Sixteen rule, you'll probably find another good chart. If you don't, PM me and I'll email the one that I share with my students.

JD

[Steve Smith]

If I want to take a shot on a city sidewalk, at night, that has some street lights would I just take a meter reading as normal.

If you take a meter reading at night, assuming your meter can read light that low, it will give you an exposure suggestion based on a 'normal' 18% grey scene - i.e. try to make it look like a normal daylight scene.

This will be too much exposure as you will want to make the image appear to be night time. In this case, you will probably want to reduce it by one to two stops.

However...


I am asking this as the first part of the question... reciprocity would be part two.

As has already been suggested, for a long exposure, you will need to add a stop or two to allow for reciprocity.

So it is possible that your straight meter reading will give you the right exposure!


Steve.