Print Magnification / Conversion Formula!

[romie]

Enlargement Question
Having the exposure time and the lens opening of a enlargment and wanting to changing the height size of a print say from a 8x10 print @ f16 @ 00:15 exposure time to a 11x14 what is the formula to make the change from one size print to another?

[oriecat]

Well I don't know what the formula is, but according to a spreadsheet that Will gave me, I think it would be 26.75 seconds, provided I did everything right, which is no guarantee.

[romie]

Thanks Oriecat!
Somewhere I read or was told that times 10 (X10) is the formula for calculating the time needed in making a print larger timewise with the same f-stop of the original print.
I will do some test to see. :roll:
romie- Boston, MA.[/u]

[motcon]

I will do some test to see. :roll:
romie- Boston, MA.[/u]

Orie has it correct.

why bother asking if you are going to do tests anyway?

a 10x rule? u realize that takes you to nearly 3 minutes of exposure from 15 seconds? common sense should tell you to not even waste a sheet of paper on it.

[ksmattfish]

Will is right. Don't worry about crazy math. You need to be doing a whole new test print for the 11x14 anyway. When you increase enlargement, you decrease contrast, so you're basically starting over. Don't skimp on the test prints.