Newbie scanner questions

Not too long ago, I bought a Konica-Minolta DiMAGE 2 scanner to
digitize my slides and print negatives. After a small learning curve,
I'm very happy with the scanner and the results, but have a question
I hope someone here can help with.

With an optical resolution of 5400 dpi and a dynamic range of 4.8, it
should be able to capture essentially all the information on either a
slide or a negative. (Correct me if I'm wrong.) So, when I scan,
should I use automatic exposure and possibly manual over-rides on
exposure or (as it now seems to me) is it better to use fixed exposure
and correct exposure digitally afterward, for example in PhotoShop
Elements?

I'm finding that, even with automatic exposure (which I'm now
doubting I should use), PSE significantly improves many scans. For
example, using Auto Levels often turns a so-so scan into a great one.
Of course, many of PS's tools only work after converting the 16 bit
per channel scan into an 8 bit one, so at that point I've got much
less dynamic range than advertised. (I'm using PSE 3.0 if that
affects things. I could upgrade if it would make a big enough
difference.)

Also, if anyone wants to critique it (again, I'm learning), I've
been scanning at 2700 dpi which produces about 9 megapixel scans. But
each of those is 50 MB in size in TIFF format. I might use the higher
5400 dpi setting on a few, very special photos, but 2700 seems to
provide excellent results, allowing significant cropping or zooming
with great detail. And 5400 dpi would produce 200 MB TIFFs that I
suspect would be slow to open even on my 2 GHz G5 iMac. Along these
lines, I'm really glad I waited til now to start scanning. A few
years ago, even if the scanners were as good (which I doubt), the
storage and computing requirements would have made the process a real
pain. Today, at 9 megapixels per scan, the speed is reasonable.

Thanks for any help.

Martin

Stephen Henning wrote:
> You basically answered your own question. You want to use an exposure
> that will keep the most important part of the picture in the center of
> the dynamic range. If you want to bring out highlights or shadow areas,
> you have to choose exposures that will permit this. You need to have
> the most important information where it won't be truncated when your
> photo program reduces the dynamic range. I feel a fixed exposure is
> completely wrong except for groups of similar slides. Auto exposure is
> the best place to start with sometimes manual over-ride used to move the
> dynamic range.

Thanks for the response. In between this and my earlier post, I
discovered that KM's stated Dynamic Range of 4.8 with "theoretical" in
parenthesis is almost surely an overstatement. Apparently, some scanner
makers started giving a "theoretical" DR based merely on the number of
bits output by the scanner, with no regard to the actual DR of the
sensor. Really useless information, and misleading to call it
"theoretical." But according to what I found, once one maker started
doing this, others almost had to follow suit to avoid looking worse.
Does anyone have an idea of the actual DR of my KM DiMAGE 5400-2 and
similar scanners?