# Thread: Extended Bellows exposure compensation

1. ## Extended Bellows exposure compensation

I understand that is you extend the bellows beyond a certain point you will need to calculate adjustments for exposure compensation.

Is there a fast rule (to simplify using in the field) as to the compensation formula.

I have seen a quickdisk, which would work for close-ups. Is this really a significant problem for landscape work? (inifinity)

Thanks

2. ## Extended Bellows exposure compensation

This is not a significant problem for landscape photography. It only starts becoming noticable when you start making images that are .25X lifesize and progressively higher magnifications.

3. ## Extended Bellows exposure compensation

In theory, any bellows extension requires compensation to exposure, but as the previous poster says, this doesn't matter unless you are doing close-ups. To calculate the exposure, take the focal length of the lens and square it (e.g. 210(mm)x210=44100. Now take the total extension (distance from rear of lens to film) and square that (e.g. 400mm from lens to film, 400x400=160000. Now divide focal length into extension (160000/44100)=3.628. Your exposure factor is therefore 3.628, or a bit over 1 1/2 stops. If it's any help I have a D.O.F. chart that calculates this automatically, can email it if required.

4. ## Extended Bellows exposure compensation

If you work in F stops, you don't have to square anything.Divide the focal length of the lens into the total bellows extension, take away one, and that's the fraction of a stop, or number of stops, that you need to open the lens or extend the shutter speed by.For example: 150mm lens with 240 mm bellows draw. 240 divided by 150 is 1.6, minus 1 leaves 0.6. Therefore; open up 0.6 stops (2/3rds stop is close enough).

5. ## Extended Bellows exposure compensation

There's an even easier way.

If an object appears life size on the ground glass, then we know the increse in exposure is 4x or 2 stops, or PDC. To get that object at 1:1 you need 2x the focal length bellows extension (or again, PDC).

So a 10" lens at infinity has 10" of extension and therefore no exposure compensation. At 1:1 it has 20" of extension and requires 2 stops or 4X exposure compensation.

So, at 15 inches extension, it would require 1 stop increase. At 12.5 it would require 1/2 stop increase.

So, for a given lens, add 1/2 stop for every 1/4 (25%) increase in extension. Works with inches or millimeters. I carry a tiny little 36" tape measure I got as a giveaway at a hardware store for this reason in my camera case.

However as Ellis points out, Kodak and others have published the general rule that if the camera is focused NO closer than 8x (or 9x or 10x according to some sources) the lens focal length, then the increase in exposure is insignificant.

In any even Calumet and others have a nice little device that consists of a square 1" piece of plastic and a ruler that applies the above approach.

6. ## Extended Bellows exposure compensation

You don't have to do all that calculating. If the bellows is extended 1 focal length (focussed on infinity) no change in exposure is required. If the bellows is extended 1.4 focal lengths (1.5 is probably accurate enough) increase exposure by 1 stop. If the bellows is extended 2 focal lengths, increase exposure by 2 stops. Everything in between can be interpolated.

8. ## Extended Bellows exposure compensation

Or go here, download it, print it, stick it on carboard, follow the simple instructions, keep it in your camera bag and never worry about bellows compensation again! Works like a charm - make half a dozen so you won't lose em...

http://www.salzgeber.at/disc/index.html

Tim

9. ## Extended Bellows exposure compensation

Tim's right about the disc. I used it to shoot some close-ups of fallen leaves in Zion last November. The disc said to open up exactly one f-stop, my conscience told me that wasn't enough. Guess which one was right. The disc exposure was absolutely perfect!

10. ## Extended Bellows exposure compensation

Or don't worry about it much at all with landscapes. A rule of thumb is that you don't need any compensation unless the nearest object is closer than 10 times the focal length of the lens. I've also seen the rule of thumb as 8 times the focal length of the lens. With a 210 mm lens, and using the 10 times "rule," the closest object would have to be 84 nches (7 feet) or less before you became concerned. That's pretty close and I don't personally encounter that situation very often with landscape work though others might differ.

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