


Originally Posted by KenM
D'oh! Matt already posted that. Sorry for the repeat.

Busch
Originally Posted by mark
Bruce, how goes it with the Busch?
The Bush is okay. There is significant operator error that needs to be worked out but I will PM you on those operating questions. The SK Xenar 135 seems to be a very soft contrast lens but I beleave the shutter is 'quite' accurate.

The method that I use, which is similar to the Calumet device and the QuikDisk, is to estimate or actually measure the magnification factor by comparing the width of the field of view at the plane of focus to the width of the format. If it's a still life or macro I'll put a ruler into the scene (and remove it before taking the photo), and if it's something like a portrait, I usually just estimate it. Then I have a table for converting magnification factor to exposure factor on the back of each camera.
So, for example, if I'm shooting 4x5" in horizontal mode, and the scene is 10" wide at the subject position, then the magnification is 1:2, calling for 11/3 stop additional exposure.
An attraction of this method is that it works the same way for any format, unlike the Calumet device and QuikDisk, which are only practical for large format.

Originally Posted by Bruce (Camclicker)
<snip>
BELLOWS FACTOR: From Ole Tjugen (oftjugen@online.no) on June 1, 2002.
Bellows Extension Squared Divided by Lens Length Squared = Bellows factor.
</snip>
I was researching this topic on APUG and the internet so I would like to revive it and ask a question regarding the quoted formula. Shouldn't the formula be limited to cases where the bellows extension is greater than the focal length of the lens?
If not, the formula seems to imply that when the bellows extension is less than the focal length, then the exposure factor would result in a decrease in the exposure (that is the factor would be less than 1).
Deal or No Deal?
BTW, some years ago, I was out photographing with <DropName>Cole Weston</DropName> and he had a tiny tape measure and in a small notebook he would look up on a handwritten chart to find the factor for a particular lens. I have looked around for one of these charts, but I couldn't find it. I don't want a Calumet scale because they take up way too much space. I don't want to put ruler of some scale in the image.
I think I'll reproduce one of these charts and paste to a page in my small notebook and then I'll go on a hunt for a tiny tape measure.
Maybe I will post it here if anyone is interested. I will probably cover focal lengths from 240mm to 1000mm at 1/3rd stop increments. Or, could I make a graph with x axis=bellow ext, y axis=factor and each plotted line representing a different lens?
I'm not great at math, but this seems pretty simple.
R

Originally Posted by reggie
I think I'll reproduce one of these charts and paste to a page in my small notebook and then I'll go on a hunt for a tiny tape measure.
R
Alternately, you can do all of the math calculations once , and make a scale for each lens out of paper and tape (fancier if you wish) that you attatch to the rail or bed of the camera.

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Well, what I am doing is carrying a card that I made up for my two lenses based upon the formula that Ole suggested. It seems to work, I have not had negatives using this chart that I would say were a problem.
LENS inch
135 < 4' 5" 6" 7" 8"
factor 0.9 1.3 1.7 2.3
< 4' 11" 12' 13'
factor 4.3 5.1 6
LENS <7' 5" 6" 7" 8"
240 factor .3 .4 .5 .7
<7' 11" 12' 13'
factor 1.4 1.6 1.8
I don't know how this will line up when sending.

Keeping bellows extension factor simple
I use the following formula with great success:
"Add 1/3 of a stop for every inch of bellows draw past the focal lenth of the lens."
For example, my 12 inch lens focused at 18 inches would get 2 stops extra exposure. This has worked extremely well for me. Honestly, if you're comfortable trying to be creative and doing mathmatical equations in the field, great. I'm not and this works. Best of luck. Shawn

Quick and dirty bellows exstension calculation. Use a tape measure (I keep a cloth tape in my LF case.) Convert the length of your lens to inches, a 150mm lens is 6 ". Measure the distance from the lens board to the film plane in inches, for example 11 inches. Calculate the adjustment by thinking of the two distances in terms of Fstops. In the example, what increase of exposure would you make to go from f6 to f11. (A fuzzy less than 2 stops.)

Originally Posted by rbarker
I use the $10 Calumet Exposure Calculator, #CC9201 , which consists of a small square target that is placed in the scene, and a little ruler used to measure it on the GG. Quick, easy, compact, and works with any format and focal length.
This device has been around since before dirt was invented, is totally fool proof, needs no batteries and you don't need a calculator for doing math. I have seen it in several different forms, put out by Kodak, Ansco and who ever. You cant beat it unless you are metering off the SatinSnow. As for taking up too much space, ahhh a give us a break!!!!!!! The money you save on the card and ruler device will buy several sheets of film.
Charlie.........................

Originally Posted by reggie
. . . Shouldn't the formula be limited to cases where the bellows extension is greater than the focal length of the lens?
If not, the formula seems to imply that when the bellows extension is less than the focal length, then the exposure factor would result in a decrease in the exposure (that is the factor would be less than 1).
If the bellows extension is less than the focal length, you're probably focused on a point beyond infinity, where exposure doesn't matter. There's nothing out there. Trust me. We went ther in the '60s.
[COLOR=SlateGray]"You can't depend on your eyes if your imagination is out of focus." Mark Twain[/COLOR]
Ralph Barker
Rio Rancho, NM

