Enlarging lens converage Question

[robc]

oops,

basic trig error.

Area of aperture for 150mm lens is 276.12 square mm. area of 75mm lens is 69.03 square mm. Which means that a 150mm lens at f8 lets through 4 times as much light as a 75mm lens at f8. Inverse square law brings this back to equality for a normal taking lens so that exposure is equal when swapping lenses and using same f stop. Arguments above still hold true when applying these figures.

[Michael Gudzinowicz]

OT:

An enlarger is nothing more than a macro camera. The effective f-stop
is (1+M) x N where M is the magnification and N is the selected aperture.

For a selected aperture and magnification, the effective aperture and
exposure are the same regardless of lens focal length. If you vary
magnification by altering print size or format, the effective aperture
and exposure will change.

The principles, formulas and physical setup are exactly the same as
those used in macro photography. However, exposure errors aren't
tolerated since paper is a high contrast (short exposure scale) medium
and exhibits reciprocity failure in its normal exposure range. The
formulas to correct for reciprocity and magnification changes are
in the r.p.d. archive.

Mike