'APO' Designation-Meaningless for BW?

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Are the advantages of APO lenses confined to color film? Is there any advantage to using one for BW? Thank you.

-- Richard Fulco (calcinc@mn.rr.com), February 22, 2001

Answers

Apochromat lenses image three wavelengths of light at the same focus plane. This results in better contrast and resolution regardless of whether you're shooting color or B&W.

Godfrey

-- Godfrey DiGiorgi (ramarren@bayarea.net), February 22, 2001.


Godfrey is correct - remember you may only be sensing in monochrome on the film, but the incoming light is fully polychromatic.

-- Robin Smith (smith_robin@hotmail.com), February 22, 2001.

For non APO lenses and using black and white film with the lens shot wide open, you will see a difference but mostly when the focal length is over 120mm or so. APO would be better for that situation. It must be remembered that color correction in the non APO lenses is much better in the paraxial and zonal areas than in the marginal areas. In other words, stopping down will greatly help when using color or B&W film and non APO lenses. APO is the wide open(and expensive) alternative.

-- Steve Rasmussen (srasmuss@flash.net), February 22, 2001.

>>>In other words, stopping down will greatly help when using color or B&W film and non APO lenses. <<<

Not nessesarily. It depends on the type of chromatic abberations. This is true for longitudinal chromatic error, but not for lateral errors.

-- ochotona (telyt560@cswebmail.com), February 22, 2001.


oops... here's my real name.

-- Doug Herr (telyt560@cswebmail.com), February 22, 2001.


And stopping down also introduces unsharpness owning to diffraction, so it is still probably best to stay close to the lenses' optimum aperture when optimal sharpness is a consideration.

-- Bob Fleischman (RFXMAIL@prodigy.net), February 24, 2001.

Doug, you are right about lateral chromatic not being affected by stopping down but lateral color is way easier to correct than longitudinal and therefore lateral is not an issue with modern lenses. Stopping down even two stops from wide open will greatly reduce color fringing caused by longitudinal chromatic aberration.

-- Steve Rasmussen (srasmuss@flash.net), February 26, 2001.

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