How to calculate bellows extension from the bellows factor?

[Cor]

Hi Ken,

A blast from the past ! I still use a Palm Pilot, mostly as a timer for processing film..my original thread made me remember a project I never really finished: using a 480 lens on my 8*10 for portraiture ! I'll give it a try, thanks for the reminder !

Best,

Cor

Cor...
I just came across this a 'question' couple of days ago after having recently 'resurrecting' my Palm Pilot that had gone into 'hiding' after a house-move a number of year ago'.
When I was a 'working "Biological Photographer' my Palm with Photographer's Vade mecum was used on a daily basis... I don't know how I could have survived without it since close-up images of specimens were requested with an "I need this done NOW". I managed to find the Vade mecum programme on line and have just reloaded it to my Palm 505... all that I now need is to 're-learn' proper use of the stylus for entering the information required to give me the required 'corrections'

Ken

[Daniel Casper Lohenstein]

In this chart you see the bellows factor on the right side of the upper chart. On the left side you find the bellows extensions sorted by focal length. Cut it out, stick it on your camera.

Regards

[Drew Bedo]

So this is not a camera-in-hand exercise: Yeah . . .I can't play chess in my head. I measure from the front of the lens board to the film plane and do the math. For the lens you mention, each 3 inches of extension beyond infinity requires about a third of a stop extra exposure. I did that pretty quick and that's an approximation, but should work.

On this board the pool of knowledge and experiences both deep and wide. Someone will tell you how to do this calculation to several significant figures . . . .I respect them.

Cheers

[Jerry Bodine]

It's just a simple calculation using algebra. The formula for calculating the bellows FACTOR is:
Extension squared divided by lens focal length squared. So if you already know the bellows factor, then solving the formula for bellows extension you get:

bellows extension = square root of [bellows factor times focal length squared].

I've never owned a Palm Pilot, but an inexpensive pocket calculator can do this calculation easily.