New generation of "digital" lenses: only a commercial strategy?

Started Jun 28, 2001 | Discussions thread
Thom Hogan
Thom Hogan Forum Pro • Posts: 13,661
Re: New generation of "digital" lenses: only a commercial strategy?

No it won't - or all things working properly - then the old lenses
are still too soft for digital. The photosites work on agitation
which responds to wavelengths that are "invisible" on film and thus
the CCD records more information which has the effect of adding to
the file’s non-image forming light (on film) and effectively
softens the image.

Say what? While the response curves for CCD sensors and film (and for that matter, between any two types of film) aren't the same, They're much more alike than different.

Your assertion that a "CCD records more information" is a strange one. Depending upon the filter array used over the sensor, a digital camera may see slightly more infrared and UV energy than some film, but if so, it doesn't add information, it adds exposure. Is it your assertion that existing lenses don't properly focus those wavelengths on the correct photosite? If so, it would have to be a pretty large error, as slight color aberrations tend to fall between photosites, not on them. And frankly, I haven't seen this problem or know of anyone who has. Or is it your assertion that the extra light a photosite reacts to (compared to film) overexposes that site and overexposure looks softer than correct exposure? Again, not something I've seen in working with digital cameras.

New generation lenses need to be cut to a much finer tolerance to
eliminate these wavelengths and not to add to the vibrations and
thus not get recorded as something that gets interpolated into the
image – as was known about with film but was not recorded.

Nonsense. If a lens is made poor enough that it is focusing different wavelengths at different points (chromatic aberration), that will show up on film, too. And what the heck is "vibrations...get recorded...[as] interpolation"?

Film needs direct light to cause a reaction in a grain of silver
and an accelerator to enhance the effect. CCDs convert all light
into signal data (image/stray light/noise). These need to be
recorded at the perpendicular for the cleanest images, any
deviation cause the “purple fringing” or otherwise incorrectly know
as “CA”.

No. The purple fringing so prevalent on consumer and prosumer digital cameras in very high contrast areas is generally caused by spillover electrons from adjacent photosites and has only a little to do with the lens used. Many reviewers have automatically chalked this up to chromatic aberration, but it rarely is. Chromatic aberration has a distinct pattern to it that relates to the radius from the center of the lens, the purple spillover can occur virtually anywhere, on axis or off.

On D1, D30, S1, and other interchangeable lens digital cameras, the current range of lenses are plenty sharp enough (some built-in consumer zooms show some interesting design problems, though). Even without interpolation (in fact, especially without interpolation), digital images are slightly soft because of the inherent limitations of converting a continuous value (analog amount of light) into a highly limited value (8-bit or 12-bit digital value). Both the "pitch" of the photosites as well as the "depth" of information stored influence apparent sharpness far more than any lens flaw. As D1x users are seeing, the method of interpolation used on raw photosite data also has a tremendous visual impact (each new version of Bibble and QImage Pro seem to get slightly better at interpreting the data from the D1x, but Nikon's own interpolation scheme built into the camera for the JPEG drivers still seems to beat them).

Thom Hogan
author, The Nikon Field Guide
http://www.bythom.com

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