Formula for bellows factor

[Bryan Fleishman]

Does anyone know what the mathematical formula is for calculating the bellows fa ctor for any given lens?

[Laura Campbell]

Hello! Here's a formula: Bellows Length2, divided by, Focal Length2 = Exposure Increase or BL2/FL2 = EI. Happy Holidays - Laura

[Mark Windom]

An easier way is to use a Quick Stik...no calculators needed.

[Charles Matter]

I strongly agree with Mark. Calumet sells an enexpensive little two piece plastic scale and square target device which I've used for years. It works perfectly and is easy and intuitive. Sinar has a little calculating "pen" which doubles as a ground glass grease pencil marker..with barrel markings to calculate bellows factor directly. Typical of Sinar..it's over priced..but equally typical it's very clever and works very well. The important point is..to ALWAYS check for bellows extension..(not just with close up work)..especially as you go towards longer fl lenses. You'll be surprised @ how far from the subject the bellows extension facrtor starts affecting your exposures.