Enlarging lenses best sharpness

[truls]

When are enlarging lenses most sharp? Does it follow the general rule, stopping down 2 or 3 steps? Or best if stopped down maximum? Some say stop down to f.11 as the general rule.

[Stephen]

About mid range, usually F8, using F11 is commonly quoted, but may give long exposures. Small apertures do not cause issues with Black and White. Full open is strictly for focusing.
Camera lenses may be used if four element, but most better lenses have too many glued joints, and heat from the light might damage the glue.
Cold cathode lamps do not cause heat, and many enlargers have cool lamps, depends on age of unit. Halogen lamps, reflector type are cool.
My own now uses an array of 200 LED lamps, with a glass diffuser, give excellent results, but generally is not used that much theses days.

Stephen.

[daveh]

Aug 27, 2014 12:37:02 GMT -5 truls said:

When are enlarging lenses most sharp? Does it follow the general rule, stopping down 2 or 3 steps? Or best if stopped down maximum? Some say stop down to f.11 as the general rule.

The obvious answer is run your lens tests at the different apertures available.

As regards heat generation from bulbs: I doubt any system is 100% efficient, and heat, therefore, is an inevitable by-product of the conversion from electricity to light. Cold cathode refers to the fact that the cathode isn't heated, not that it necessarily stays cold in use. Incandescent bulbs are the least efficient and give off the most heat (by a significant amount) for the same light output. Halogen bulbs get hot, very hot, but being small the heat is relatively easy to dissipate.

What is true is that more modern enlargers (and slide projectors) don't have the problem of older units with the film popping as it gets hot.

There is, of course, the added question of how flat the film is held in the projector.

[truls]

For the record the El-Nikkor is a good and widely used lens for macro photography, when reversed. A cheap lens these days.