Digital BW, The Print

"lgrrrb@..." <lgrrrb@...> wrote:
>
> Sharp-cut filters (when shooting in color OR black & white) definitely improve image sharpness because they eliminates chromatic aberrations that blur images and produce colored fringes. 

The sharpest on-film image I ever saw in my resolution testing of lenses and B&W films used a B+W red filter on a Nikon 50 mm lens, using Agfa 25 film.  On film I could readily separate 200 lp/mm.

(I think that red filter would probably be considered within the definition of "sharp cut" filters at http://www.hoyaoptics.com/color_filter/sharp_cut.htm .)


> Green filters usually work better than red or blue since most lenses are corrected chromatically for green. 

Yes, and that was a setback for B&W photography, in my view.  Some of my older very good optics, for example the Zeiss optics for the Rollei SL66, were better with a red filter than the newer versions of the lenses.  My hypothesis is that as color film started to dominate, the lens companies adjusted their optical formulas to stress green more, giving up some resolution at the old red and blue points that used to be used in optical design.

Our digital sensors also usually have 2 green pixels.  I suspect that could make for lower noise there. 

I usually find in digital that the blue channel is the noisiest.  Green and red are very close.  Blue is a higher energy light, going toward UV.  So, I can see where even for color work or B&W, those sharp cut off filters might be useful.  I'm waiting for a "sky light" filter for one optic and will see if that has any impact.  I'm hesitant to cut off too much blue, because I also find it can sometimes reach into shadows better.  Even noisy detail might be better than none.


>Apochromatic lenses are the exception. 

Expensive exception...

As a Canon rep. once told me, the trick is not to be able to make the absolute best optics, but to make the best ones possible at price points that are appropriate for the target markets.    


Paul
www.PaulRoark.com