[APML]: Scanner Flatness

[Chuck Vaughn <aa6g@aa6g.org>]

Some threads ago mention was made that film scanners may not
be even if you do enough contrast stretching.

I took a blank piece of 0.6D Tech Pan and scanned it. I performed
an average contrast stretch in the pre-scan, like I would for a
typical astrophoto and then performed an extreme contrast stretch
in Photoshop.

The typical stretch looked completely even. The extreme stretch,
a mere 20 gray level stretched across the entire range from blcak 
to white, was dominated by uneven film development. To verify this
I flipped the negative and scanned it exactly the same. The pattern
was inverted. There were some very minor variations on the order
of a few gray levels. Most of what I saw was sprocket marks and
higher density at the edges than in the middle and a couple of
streaks.

None of this would be visible on an astrophoto using the a normal
amount of contrast stretching. What I did here would have made any
object on a negative totally white.

Whatever uneveness there is from the SprintScan 35 itself is very
small and does not make any noticable contribution to the image.
I have to say I'm still pleased with this scanner's performance.

Chuck  <aa6g@aa6g.org>