SNIP
Looks good. Two comments. (Oops. Make that 3.)
1. How about a 100x or so photomicrograph of the slide (and its MTF 50
value) to see what we're all missing.
That might be interesting. Although the target slide is not as sharp as it
could be, all scanners were given the same target, let's say a real life
target, with subject and lens and film limitations.
2. As a Nikon 8000 owner<g>, Bart's 5400 scan looks sharper. Why is the
background in the 5400 scan so dark? Presumably, the darkness of the
background is what makes the MTF50 value so low.
My 5400ppi scanner produces more pixels so, at same size output, it is
sharper than a 4000ppi scanner. I avoided clipping in the (paper) white. The
Nikon 8000 image had some clipping which makes the measurement less
accurate. The algorithm used is quite capable of extracting MTF of lower
contrast edges, in fact the ISO suggests a much lower target contast (to
avoid clipping).
There is a pitfall when judging per-pixel quality, especially where the 5400
ppi scan has more pixels and requires less magnification for same size
output. To illustrate:
Sample , MTF20 , 10-90% rise
===== , ===== , =========
Marty's LS8000 , 0.2762 cy/px, 2.84 px
Mike's LS-50 , 0.2490 cy/px, 2.88 px
Bart's DSE-5400 , 0.1963 cy/px, 4.04 px
If you translate that to on-film-lp/mm, you get:
Sample , MTF20 , 10-90% rise
===== , ===== , =========
Marty's LS8000 , 43.5 lp/mm, 18.0 micron
Mike's LS-50 , 39.2 lp/mm, 18.3 micron
Bart's DSE-5400 , 41.7 lp/mm, 19.0 micron (but requires 35% less
magnification, leading to 29% higher resolution at MTF20, or a 22% narrower
10-90% edge rise, than Marty's LS-8000).
As always, the devil is in the detail.
3. Hmm. Under 24 lp/mm at MTF50. Depressing. An MTF10 value would be
interesting as well. Even if only for a couple of scanners.
A few remarks.
1. The target (which as I mentioned was not as sharp as could be) tests the
combination of lens (+focus+camera shake) and film, not scanner alone. For
a relative comparison it is adequate, but it doesn't show the limit of what
these scanners can do.
2. The scans were not sharpened, which affects MTF50 a lot with a larger
radius USM.
3. An MTF20 is given in the graphs, which is much closer to the limiting
resolution. An MTF10 is sometimes difficult to evaluate accurately,
especially when only a small part of the film was measured (the readout
becomes more statistically accurate with a longer edge). An MTF10 would
correspond more to the limiting human visual resolution.
Bart
