Archived posting to the Leica Users Group, 2001/01/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Jesse Hellman wrote: > does this mean that there would be little use for an > apo lens in black and white printing on variable contrast papers, where > red does not register and the emulsions are sensitive to green and blue? Jesse, B&W film is most sensitive to the blue end of the spectrum and our eyes are most responsive to the yellow-green part of the spectrum and that is why achromatic lenses are corrected for those two colors, and not primarily for the reds. With regard to printing b&w images, from b&w negatives, with the lens stopped down by 2-3 stops, your theory is correct and there will be little advantage to buying an apochromatic enlarging lens. Also, most modern enlarging lenses are symmetrical designs and they are very well corrected for chromatic aberrations anyway. When used at their optimum aperture of f5.6-f8.0, you'd be hard-pressed to tell the difference between the current top-of-the-line enlarging lenses and their more expensive apochromatic cousins. There are other factors about the apochromatic lens design that should influence your decision on what to buy and use. I use an Apo-Rodagon on my Valoy II and love it, mostly because the lens design allows for sharper prints in the f2.8-f4.0 range. With a big enlargement, or when trying to burn in a highlight from a dense negative, a lens that is almost as sharp at f2.8, as it is at f5.6, allows you to open up the lens without fear of much image quality loss. That is where the apo lens shines. Normal (non-apo) enlarging lenses were optically designed to be used at between f5.6-f8.0 for optimum performance, and are a bit soft if you try to use them at f2.8. While looking through a grain magnifier, you can actually see the sharpness difference between f2.8 and f5.6 Regards, Rob McElroy Buffalo, NY