Most mid-day outdoor photography includes areas illuminated by direct sunlight. If you have elements in your picture that have direct sun falling on them the correct exposure is really a foregone conclusion.

If you find the BDE formula in an old photographic technique book it reads like “The reciprocal of the film speed at f16” a terse and potentially confusing statement of a simple calculation.

If you set the film speed, E.I., as the shutter speed and put the lens on f16 you will have the correct exposure for bright sunlight. With film speed (E.I.) 125 the BDE is 1/125th at f16, E.I. 400 is 1/400th at f16.

But you use your light meter and it gives many different readings in the same situation.

Which is right?

Only one… The BDE.

Your camera is averaging the values together and calculating the exposure. If you have direct sunlit areas in your picture they will be over or underexposed by an averaging meter.

If I want good exposure in bright sunlight I calculate the exposure, set it and forget it. I ignore the meter because it will lead me away from the path of righteous exposure.

Many famous pictures were shot using this methodology including “Moonrise over Hernandez N.M.” by Ansel Adams. In the case of that image he used the known standard amount of light on the moon to calculate the exposure. He frequently used this as it is always correct if you have direct sun on some part of your scene.

This method won't work for sunrises or sunsets but... for the rest of the day it is rock solid and dependable. Try it... It will free your mind to concentrate on the picture rather then getting the correct exposure.

Tags: exposure,daylight,basic

Knowing the film speeds can be useful in applying filter factors and making general exposure calculations. Following is a listing of the film speeds (E.I.'s) in 1/3 of a stop increments.

To calculate the exposure correction for a filter simply take the amount of in stops and subtract that from the E.I. using the table below and then use that re-calculated film speed to make your exposure calculations.

To convert from filter factor to stops is a little less clear. A factor of 2 is a one stop increase, 3 is 1.5 stops and 4 is 2 stops. As it goes on 6 is 2.5 stops and 8 is 3 stops.

I always calculate the correction values of my filters in 1/3's of a stop not factors. Filter factors are the construct of a warped mind and are an unnecessary level of distraction and indirection.

No, no attitude… I really do love filter factors. /snark

It is just more direct to make a correction without having to calculate the factors difference in stops prior to making the correction.

Mark the correction amount on the filters case or some tape on your filter pouch. I call the thirds .3 and .6 so that a correction of 1.3 is an increase in exposure of 1 1/3 stops, 1.6 is an increase of 1 2/3 stops. Using this method a P1 circular polarizer has a correction of 1.6 stops.

Tags: iso,ei,filter,factor,film,speed

For years I have calculated my bellows comp in my head for large format. I always enjoyed using my RB-67 partially because of the bully bellows comp scale which made the bellows factor calculation into a non-issue.

I wanted to improve my large format production rate as overall it is a notoriously slow process. This was one of the points where I saw that it could be better, not that it took me that long to figure out the factor but just having to go into math mode detracted from the experience of vision and visualization.

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I have carried a legal size xerox of a ruler which I coated with packing tape on two sides for years. When backpacking a 4x5 I try to keep the kit light.

I decided to make a scale that was like the RB-67 scale which covered the lenses in my kit while giving me an inch ruler as well.

I immediately noticed that there were not many simple calculators for bellows extension on line so I fixed that...

While I can't use the online version in the field it will certainly did enable me to make an excellent paper ruler.

I first made a 2 inch tall version and hindsight being 20:20 I decided I wanted it even smaller so I transformed it to make a 1 inch version. My Zone VI field camera has a 300 mm maximum bellows draw so my ruler ends in that range. The ruler is around 14 inches long.

Here are links to the two rulers, the 2 inch and the slightly more compressed 1 inch version.

Tags: lf,bellows,extension,compensation,ruler