Archived posting to the Leica Users Group, 2000/02/29

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Subject: Re: [Leica] Re: APO for B & W??
From: "Doug Herr" <Dherr@energy.state.ca.us>
Date: Tue, 29 Feb 2000 07:53:43 -0800

Christer Almqvist wrote:
>>>
>Doug's response is consistent with my understanding.  Poor correction of
>chromatic aberrations leads to color fringing.  It can be even worse in B&W
>than color because the white light coming through the negative contains all
>colors of the spectrum, whereas the color neg or slide filters some of the
>colors out, so the fringing is less noticeable.  On B&W the "color fringing"
>bears out as unsharpness or loss of acutance, rather than seeing the colors
>in the color firinging.
>
>Tom Schofield
>
Is this true for enlarger with multigrade filters above the negative?
<<<

Without having definitive information, I suspect the multigrade filter will improve the performance of enlarger lenses that aren't well corrected for chromatic errors, just because the filter will reduct the intensity of many wavelengths.

Doug Herr
Sacramento
http://ourworld.compuserve.com/homepages/telyt