Laurent Baig – The Wild Light

September 17, 2008

Focal Length Equivalents

Filed under: Photography — Laurent @ 8:48 pm

I work in a variety of formats.  I have an Olympus 4/3s DSLR. My girlfriend has a APS-C sensor DLSR. I still think in 35mm terms, and, of course, I use large format 4×5.  I sometimes want to know what focal length equates with what.  But there’s another trick.  The different formats have different aspect ratios.  To rattle off some there’s 3:2 (standard 35mm), 4:3, 4:5, 6:4.5, 6×6, 6×7, 6×8, 1:2, 1:3, … so as you see there’s a lot to think about.  So when thinking about what lens equates to what, you have to ask yourself, “In what sense?”  There’s the long side, short side, and diagonal of the image.

I’ve made a table in Excel that is actually a series of 3 tables that show 35mm focal lengths. The next column is the angle of view across the given side.  The next columns are the equivalent focal lengths of the various sensor/aspect ratios that I use, ie. Olympus 4/3s digital, APS-C digital, and 4×5 film.

Pick the image dimension you wish to compare, find in the column of the appropriate format the focal length you wish to start with and move horizontally till you get to the column of the format you are interested in. Piece of cake!

The formula for doing this was obtained from wikipedia.

You are reading a blog posting from the photographer Laurent Baig. Feel the wilderness experience at his website.

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