Print enlargement exposure
When you change print size, exposure changes with magnification, not with paper area. Enter your dialled-in small print, then the new size.
Uses the (m+1) lens-conjugate rule. Do one confirming strip at the new size — paper and focus never lie.
About this tool
Change your print size and the light spreads over more or less paper, so the old exposure no longer holds. Enter the negative size, the old print size and its correct exposure, and the new print size. The calculator works out a new exposure time from the change in magnification, giving you a strong starting point on fresh paper.
How to use it
- Enter the negative format and the old print dimensions that were correctly exposed.
- Enter the old exposure time in seconds and the new print dimensions.
- Read the new exposure time and use it as the base for a confirming test strip.
FAQ
Why does a bigger print need more exposure?
Raising the head spreads the same light over a larger area, so intensity at the paper falls with the square of the magnification. Doubling the print dimensions can roughly quadruple the light needed, which is why the time jumps so much.
Is the calculated time ready to print at once?
Treat it as an accurate starting point, not a final value. Lens aperture, paper batch and focus all shift things slightly, so run a quick test strip at the new time before committing a full sheet.