Re: [Leica] Enlarging lens

[Dennis Painter <dpainter@bigfoot.com>]

Joe Stephenson wrote:
> 
> Dear Martin,
> I appreciated the point you make regarding the inability of b&w paper to
> respond to red light, making an apo lens unnecessary. Therefore, I wrote to
> Rodenstock with just this question. Here is the reply I received from Don
> Nagle:
> 
> 1st - These questions should be directed to Bob Solomon @ HP Marketing
> 973-808-9010 because we are not the Photography division. We are the OEM
> division for Industrial Optics.
> 
> I can tell you that a non-chromatic corrected lens WILL CAUSE unsharpness in
> Black & White photos & color fringes in color exposures. Without getting
> into Optical theories it basically has to do with the frequency of light
> waves as they pass through various types of glass. Black is the abscence of
> color and white consists of the entire visible spectrum. Therefore it goes
> that white is the defining principal in black $ white photography and
> consists of all wavelengths. Therefore, lenses that correct for all 3
> primary wavelengths (APO) will increase sharpness in any application whether
> it be B&W or Color...
> 
> As Don suggests, I will try to follow up with Mr. Solomon and share his
> response here.
> Sincerely,
> Joe Stephenson
<snip> 

I look forward to knowing the reason and it looks to me like it will
take some theory here so let him get into the theory. It's going to take
more that saying that black and white pictures use white light which is
made up of all colours of the spectrum.

Dennis