# Thread: lens factor with movements ?

1. ## lens factor with movements ?

Can someone help me to do the math on the following:
When I use a 47mm lens and extend the film format (49,1x36,8mm) by movements to the max of 89,1mm x 66,8mm (cropped to 3x4 image format)... what is the resulting equivalent "focal length", i.e. the "lens factor"?

2. ## Re: lens factor with movements ?

got it... just have to divide the diagonals

Bingo

4. ## Re: lens factor with movements ?

Yes, lens factor is "normal" equal the diagonal of the format. (So a normal lens on a 24x36 sensor would be ~~ 43mm.) From there, you can simply compare diagonals to the common focal lengths you are used to.

In fact, at one time I had so many differing formats, I put them all into an excel spreadsheet and had it do all the relative calcs for me . It's crude, but works and you're welcome to it if you want. Should be easy to add any custom formats or focal lengths you want. Also, there's an automatic diagonal calculator at the bottom of the chart -- just enter your sensor width and height:

5. ## Re: lens factor with movements ?

Jack - thank you very much! That is very useful!