Bellows Extension calculation

[Bill Glickman]

Don, you are totally right. I should have noted this simplified method is "almost exact" but not truly exact as you point out. In the end, you are usually dealing with a difference of .1 stops, something very difficult to even set a lens for, hence the reason I usually advise people to keep it simple and get close to the 1/3 stop settings the lenses are marked for.

In reality, I no longer use any of these methods. I determine the distance I need to focus to acheive the required DOF I am seeking. I use a laser rangefinder to find something at this distance, then focus on it. My DOF chart contains the exp. compensation required for focussing at that distance. It's just one less thing to think about. Of course, since its on a cheat sheet, I use the formual to do the exact math.

[S Ratzlaff]

Guess I should have mentioned ...

T H I S I S F R E E

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

Just print it out and paste it onto heavy paper. I have one in each camera case. Even use it with my 35mm macro stuff. If you can print a PDF file, or postscript you'll take maybe 15 minutes to make one.

Much less time than writing down a bunch of numbers.

This guy has done a great service. The only limitation is that it's only designed to be used up to life-size. If you want something higher than 1:1, then you'll have to calculate bellows extension via your method.

[S Ratzlaff]

Hmm ... extraneous white space seems to get deleted. Must ne to save bandwidth.

Anyhow, I meant to say bellows factor.

[corgan4321]

Is this equation: [ log(bellows extension) - log(focal length) ]/ log(sqrt(2))

written for extension and focal length in millimeters?

[aduncanson]

millimeters or inches, doesn't matter - just be consistent

[Lachlan 717]

If you have an iPhone, try "PhotoBuddy". Type in FL of lens, format & draw, and there you have it: bellow factor in 5 seconds.

It has myriad other good stuff (all the DoF, CoC, hylerfocal etc) as well.

No affiliation with makers of this; just a good, handy product.