When we enlarge an image with a high-quality enlarging lens, how much visual "data" is lost ?
Can this be expressed as a percentage ? Can this be compared to what is lost by scanning ?
Can the difference (between scanning and enlarging) be expressed or estimated ?
I ask, because I stumbled across some older Silver prints that I made from medium format and 4x5 - and was surprised how natural and analog things look, when no Unsharp Mask and other "corrections" have been applied.
Ken, this comparison, while not numerical, gives some idea. Compare contact print to enlargement and digital prints:
http://www.custom-digital.com/
MTF charts would be a good measure for what you ask.
If you've got top quality optics, including precise negative carrier glass, and have
everything aligned and tuned in, and flare under control, you can typically enlarge a large format original with no visible loss whatsoever to the naked eye, say up to
four or six times the original. Of course, higher contrast prints will appear sharper than lower contrast ones, and the nature of the film itself and paper surface are also factors in perceived sharpness. This can certainly never be said for digital prints. No doubt someone will want to interject some motheaten hogwash about "normal" viewing distances - "the bigger the print, the farther away people will view it." Bull. For a billboard the normal viewing distance is about fifty to a hundred yards, if that's what they mean; but much closer and it's sheer mush. I personally like to be nose to
nose with prints no matter what size they are, even if a soft-focus lens was used.
Well, you said "visual data" rather than just "data", which opens a can of worms.Originally Posted by Ken Lee
One question is whether you lose information from a negative as you enlarge and projection-print. The answer is, of course, the process is always lossy, but with impeccable technique you can keep that loss to a minimum.
The next issue is, what can you see? Here the waters get muddier. As you enlarge, up to a point you actually see more spatial information in the picture - more visible detail - but at the price of tonal subtlety. Turn it around: when you contact print, some details in the negative become too small to discern by the naked eye even at grain-sniffing distance. But the rendering of what you can see is exquisite, both tonally and spatially.
Appropriate caveats apply re printing technique, paper surfaces, etc., as mentioned by Drew.
Last edited by Oren Grad; 26-Dec-2008 at 22:29.
And this is a different point. "Natural" doesn't necessarily require "more information". But it is about the kind of information.
I doubt that there's much loss at all due solely to the enlarging lens, assuming a high quality lens. It's always been my understanding that the principal loss (of detail and tonal gradations) in traditional prints is due to the fact that paper isn't capable of resolving the same degree of detail and tonal gradations as film. I vaguely recall that Ctein's book contained a chapter about the limitations of photographic paper but I no longer have the book so I can't check.
Tyler Boley's article that Ron cited is interesting but as big an admirer as I am of Tyler's wonderful photography and his technical knowledge, for me comparisons based on degrees of enlargement so massive that all you see are big blobs of some unknown something aren't very useful as a practical matter.
Brian Ellis
Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
a mile away and you'll have their shoes.
Ken, I think most people here will answer you based on their visual perception experience. That will not be quantifiable in any sense but just intuitive based on someones experience.
OTOH I believe that one could quantify the difference between an enlarging lens and a scanned image by examining a print produce both ways using a scanning microdensitometer of sufficiently small aperture. That densitometer data could then be compared to densitometer data from the original negative. After some considerable thought and observation of the results one would need to come up with a set of standards in order to tabulate the results in an intelligible fashion. Come to think about it I think that the prints might want to be a positive on film for the purposes of microdensitometer scans.
The scanned print is a bit more complicated owing to effects that can be introduced by the printer. I suppose extraneous artifacts could be largely eliminated by turning off or minimizing arcane software functions but I'm not a digital savvy person; (my body is totally analog).
Nate Potter, Austin TX.
Ctein's tests established that with proper contact printing technique - and that's not a trivial matter - black and white silver gelatin printing papers are capable of recording information far beyond what the unaided eye can discern.
In general terms, it sounds like there is negligible "noise" introduced by enlarging.
Ignoring grain altogether, it sounds like whatever "data" we lose, can be attributed to magnification of the original, which merely reveals the flaws that are already there: the performance of the lens, limited depth of field, etc.
If we consider the influence of grain, then again, enlargement is merely revealing the "noise" inherent in the graininess of the film/developer combination.
Some of Ctein's evaluations of the potential of contact prints were based upon looking at things through a microscope, literally. His personal enlarging equipment is
not really sophisticated enough to make a truly objective comparision, even though
he acquired or borrowed a range of top enlarging optics for those studies. His actual
darkroom setup is fairly primitive. But those of us who attempt to optimize enlarging technique do essentially the same thing when we view the projected image
through a high-quality grain magnifier. A ten power magnifer on just a 20X24 print
is equivalent to a nose to nose look at the print sixteen feet wide! No paper is capable of this level of resolution, although color polyester base comes the closest.
So at this level we're really talking about science, not about ordinary visual perception. Most truly modern enlarging lenses at correct magnification ratios will
give excellent results. I'd be a lot more concerned about questions of tonality, and
actual visible nuances. Of course, little things add up; so I personally use the finest
enlarging lenses and carrier glass, etc, that I can afford. But as nitpicky as I am
about all this, the esthetic issues far more important. And for me personally, digital
prints never look truly photographic. They might be nice in other respects, if well
done, but seem to belong to a different category altogether.
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