Formula to calculate plane of sharp focus?

[Robot]

What is the formula to calculate the plane of sharp focus given focal length and bellows extension?

I just purchased a 305mm Repro-Claron and learned the limits of my camera. The closest I was able to focus was 15' away with my bellows cranked all the way out (about 310mm). Do those figures sound correct? Is there a formula that will corroborate those numbers?

I wanted to use the lens for tight portraits but it appears as though that is not going to be possible with my current camera (Toyo 45AX).

[ic-racer]

1/p + 1/q = 1/f Where, p= image distance and q= subject distance and f= focal length. Here is a web page with a calculator to solve it:
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html


Yes your results seem correct. You can easily memorize that at infinity you need the same bellows length as the focal length of the lens and at 1:1 macro level you need DOUBLE the bellows extension.

Using a bigger camera (5x7 or 8x10) with a 4x5 reducing back is one solution. Another is to get a telephoto 300mm. Top-hat lens board is another solution.

[Robot]

In that equation would the image distance be bellows extension?

[Dan Fromm]

Image distance is the distance from the lens' rear node to the film plane. For lenses that are neither telephoto nor retrofocus, this is approximately the distance from the lens' diaphragm to the film plane. The diaphragm usually sits a bit in front of the front standard.

[sun of sand]

why would you need a formula to check your real life findings

everything pushed out to the max gives your answer
for a formula youd need exact measurements of everything and since nobody is taking off your bellows or measuring the bed or the exact focal length of your lens

[domaz]

why would you need a formula to check your real life findings

everything pushed out to the max gives your answer
for a formula youd need exact measurements of everything and since nobody is taking off your bellows or measuring the bed or the exact focal length of your lens

Maybe he wants a formula so he can calculate how close he can focus given his camera's bellows extension. That way he won't buy a lens again that doesn't focus close enough.

[Robot]

Correct. Also just like to know that math behind the visuals.