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Re: [OM] Best FILM for lens testing?

Subject: Re: [OM] Best FILM for lens testing?
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 2 Jul 2009 17:10:36 -0500
>
> I don't understand shooting B&W and B&W, high contrast test charts if
> you're ultimately going to be shooting color film and real world scenes.
>  You could probably save on film by first filtering the duds with the
> digital.  If the lens doesn't cut it in the center it's unlikely to do
> much good in the corners.
>


Shooting the test charts in color is really only beneficial if you want to
see the color aberations.

If shooting in color, it would be preferable to use slide film for loupe
analysis and the only current choices that I would consider for
high-contrast tests is Ektachrome 64T, Kodachrome 64, or Fujichrome Astia
100F.

The key to picking a film for lens testing is looking at the film's MTF
Curves.  Examine the 50% response point and see that it exceeds 30
cycles/mm.  (30 cycles/mm is about halfway between the 20 cycles/mm line and
50 cycles/mm line).

If your tests are limited in contrast, Fujichrome Velvai 100 (not 50 or
100F) is the current leader with a MTF at 50% of around 50 cycles/mm,
otherwise lateral halation will be the limiting factor. Portra 100F is among
the worse films for lens testing because of this.  If your contrast is
reasonable in the test-chart, Fujichrome Velvia 100 would beat all.

If color negative films would work, I'd use Kodak Portra 160NC or the newest
Fuji 160S without hesitation. These are the finest-grain, highest resolution
color print films on the market--with 160S being slightly higher
resolutioned, but 160NC having less grain.

We shoot res charts instead of "real world scenes" for lens tests because of
controlled lighting and repeatability. It's too easy to be fooled by changes
in exposure or contrast when shooting trees like Ken Rockwell does.  You
don't want to be a "Rockwell" now, do you?

USAF line-pair charts may be "old school" but they existed for a reason and
I personally haven't found anything more consistant and reliable for
comparison testing.

AG
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