metering and lenses.

Hi all. I'm about to venture into deep darkness of photography and need some guidance. I'm taking on a project to build a large 6 feet

cube camera that will shoot 16 20 paper negatives. It's going to be equipped with 15 inch lens and will house me and needed stuff. My

question is about the metering. I have shot paper negatives before with graflex camera and got good results but here I'm using 15 inch

lens and I assume that at its infinity the exposure will not need adjustment from what the meter tells me, am I correct? As I get closer in

focus I will just apply bellows compensation. Am I safe to assume that at infinity there is no need to compensate for exposure? No matter

the lens used?

<p>As long as the lens aperture and meter are correctly calibrated there's no need for compensation at infinity focus, or down to around 12 feet subject distance. You'll need an extra 1/3rd of stop at around 11.5 feet. This increases to 1 whole stop at just over 4ft subject-to-lens.</p>

<p>The whole point of relative aperture numbers (f/4, f/5.6 etc.) is that they're independent of the lens used. And an easy way to calculate the exposure compensation is to simply multiply the f-number by the total bellows length divided by their length at infinity.</p>

<p>BTW, how are you going to recess a 15" lens into a 6' cube box? That's one heck of a lenshood. Unless it's basically a darkroom with a camera on the front.</p>

It's a tent like room with lens mounted in the front.

Focus is done by means of portable plywood on a stand.

The paper will be attached to that plywood. For infinity

the stand will be at 15 inches, but for closer focusing

dust and will be moved back. I'm planning to do portraits

with this setup, so infinity focusing will be rearly used

Auto spell is messing things up for me. I'm using my

phone to type.

<p>The quick and easy way to calculate the exposure compensation on a set up like this is to use a tape measure. </p>

<p>Assume you meter the scene and determine you need a one second exposure. You have a 15 inch lens. Think of that as f15 (close enough to f16 that f'16 will work.) Measure the distance from the lens to the paper. Suppose it is 22 inches. Translate the inches into stops, so the paper is at f22. The difference between f16 and f22 is one stop, so give one more stop exposure, or a two second exposure. </p>

<p>If the paper is at 40 inches, then it becomes f40. The difference between f16 and f40 is about 2 1/2 stops, so give it 6 seconds exposure. <br>

If you were using film, you'd have to calculate reciprocity failure, but unless you get very long exposures, paper shouldn't require it. </p>

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