Calculating new exposure for new print size

[walter23]

I thought you'd just take the area of the new size divided by the area of the old size to get an exposure factor.

E.g. going from 8x10 to 11x14:

11 * 14 = 154 square inches
8 * 10 = 80 square inches

154 / 80 = 1.925

So if your original exposure was 15 seconds for an 8x10, you'd have 15 * 1.925 = 28.875 seconds for the new exposure. Ideally you'd correct it for the aspect ratio differences and cropping (so for 8x10 you'd actually use 11.2 x 14 as your enlarged size to keep the ratio the same).

[Greg Lockrey]

I hate shortcuts, they never seem to work.

I call this the Calibrate Your Center Column Method.

If your negatives are "properly exposed" a quick trick would be to mark exposure times on the center column of your enlarger for each print size and/or crop position. Then in the future once you have the correct exposure/f-stop combonation for your given size, moving up or down the column would be a mere adjustment of the time holding the f-stop as the standard. Bare in mind that exposures are affected by lag time that the light comes on/off from the timer and the voltage of the light source. But usually it's close enough if you adjust your development times....and that's another issue too.

A good way to set your standard time is use your Zone II calibration negative and set the times for each print size from that negative developing them the same amount of time to match the Dmax. Don't have a meter? Use a bright light.