crop factor: using it

I wrote recently about crop factor. Well, here's an example of why you might want to be able to understand it....

There's a pic posted and it's from a Canon A720IS. That doesn't save any 35mm-equiv information in the EXIFs (that's the information saved with the file, which includes camera model, shutter speed, aperture etc.). It only saves the "real" number.

Now, I wrote that the real use of crop factors is in converting between systems. In this case, it's most definitely true as someone wanted to know what lens the "5.8mm" was with. The shortest lenses I know of are around the 8mm mark and they are fisheyes - the pic was too "real" to be really 5mm in 35mm world.

This - http://en.wikipedia.org/wiki/Image_sensor_format - tells us the crop format for the 1 2/5" sensor used is around 6, so 6 x 6 = 35mm or so.

So, I think you'll find that the field of view represented by the pic is pretty close to a 35mm on FF or 20mm on APS-C.

Couple of tips:
- at least Windows 7 has the option to show this information in fields in Explorer (try "35mm focal length")
- PhotoME is a great application to read this information from pics, including in my case the camera temperature and shutter actuations.

- Bret