Hi David!

yes, you are right; 35mm enlarged past 12X is hard to get a "leica
standard" print quality (8 lpmm on print). That said, a lot of people are
happy with less than 8 lpmm on the print, some with older eyes (ahem) find
6 lpmm okay, others are happy at even 4 lpmm.

In a related post, I do the math for what you can expect for 35mm enlarged
8x (about what 24 MP equiv. kodak claims suggest "at least") to 13X
(maximum of 107 lpmm (which is popphoto's test result for 40 MP equiv. for
film).

The real question is why does a 6MP print look okay at 8x10" when it takes
a 24 MP film print to reach the "leica standard". First, the
smoothed/spread dots of ink jet printers don't reach the 8 lpmm leica
standard (8 lpmm * 2 dots/line * 24.5 mm/" = 392 dpi (there's about 71%
more info on the leica standard print, ignoring dot spreading issues).

The bigger issue is digital vs film print quality. 6 million pixels
spread over 80 square inches (8x10" print) would be 75,000 pixels per sq.
inch, or 273 pixels per inch or 11.2 pixels per mm, and at 2 pixels per
line, that's only 5.6 lpmm. Again, 5.6 lpmm * 2 dots/line * 24.5mm per
inch = 275 dpi. That's close enough to 300 dpi with a border.

But 392 dpi (film) vs. 275 dpi (digital) on an 8x10" print is still
comparing 392*392 (153k) against 275*275 (75.6k), which is 203% more dots
in the film based prints. So the short answer is that the film print made
from a 24 MP film equiv should be twice as good as a 6 MP (again, obvious
if you think about the area issues, 6*4=24, and 2*2=4 for area ratio).

But what isn't obvious is that the 6MP is just below (or with a border,
right at) what the 300 dpi printers can print (275 dpi full frame in our
analysis above). Conversely, what isn't obvious is that half of the film
image data is being thrown away in the digital printer.

If the 275 dpi of the 6MP camera is just sufficient to make an 8x10" print
with a border, than the 392 dpi of the 24 MP equiv. film data would have
to be reduced in HALF when printed as an equivalent 8x10".

On the other hand, we can also say that the digital print at 5.6 lpmm
falls below the 8 lpmm of the leica standard, and that "photo-realistic"
printers at 300 dpi also fall below the leica standard, and that a good
wet print at 8 lpmm will have roughly four times the info (area, or 2.04
times the linear resolution) of the 6 MP print (for 24 MP starting equiv.)

This is why wet prints look more details than so-called "photo realistic
prints" at 300 dpi, because they have higher 8 lpmm potential printing
quality. On the other hand, older eyes (ahem) often limit out at 6 lpmm or
so, so if you can't see the difference today, younger eyes or your own
eyes some years ago might have seen the difference between 6 lpmm and 8
lpmm. ;-) If you relax the printing standard to 5.6 lpmm (as in 300 dpi)
then you can get larger enlargements by a modest 2x area or so with a film
print (at 24 MP).

If you use really superb lenses, good technique, tripod, and slow 100 ISO
film, you can put circa 107 lpmm on film (as per popphoto tests, which
equates to 40 MP). In such cases, you can probably squeeze another paper
size out of your enlargement over the 80 lpmm case for 24 MP equiv. for
100 ISO films ("at least" per Kodak), i.e., 11x14" or so ;-)

Hopefully, none of this will contradict either David's or rafe's or anyone
elses considerable experience in printing and testing lenses and all that.

Digital has picked 300 dpi as photo realistic for the reasons noted; aging
eyes can't see much difference between it and the previous "leica
standard", but it means a 6 MP camera can do a nice 8x10" as all have
noted. But a 100 iso film shot can do an even nicer 8x10", with twice as
much data on the wet print, including much higher resolution and contrast
which is lost on the digital print due to the anti-aliasing filter in
DSLRs which typically limit you to around 40-50+ lpmm (42 lpmm in the 6 MP
case here).

again, my $.02 worth of electrons

bobm
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* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
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