Yes, you can use a flatbed scanner however there are some limitations.
a) most flatbed scanners cnnot match the dynamic range of drum
scanners. If your negative has a wide range of densities (many
zones) then you may not be able to capture it all with just a
single scan. You could do multiple scans, each optimized for a
different tonal region -- highlights, shadows, midtones and so
forth and then cut and paste these sections into a final image.
b) The maximum resolution of most flatbeds is lower than that of
most drum scanners. This will only be of consequence if you are
trying to enlarge your negative many times. (see answer to
your next question below).
> 2. What dpi should you scan at for a scanned neg?
If you will be using a linescreen to make the final negative (as I
recommend, as opposed to a bitmap), then I recommend that your image file
needs to be 450 dpi at the final image size.
So for example, let's say that you want to make a 16x20 print. In this
case you would need to have a resolution of 450 dpi when your image was
sized to 16x20.
If you started out with a 4x5 negative this would require an enlargement
of 4.414 times because the ACTUAL IMAGE AREA of a 4x5 negative is NOT 4x5
but 3.625 x 4.625. 16" divided by 3.625" = 4.414. Therefore to have a
450dpi resolution in the final negative at 16x20, you would need to scan
your 4x5 negative at 4.414 times 450 dpi = 1986 dpi. Since it is wise to
use a native resolution of the scanner, chances are that you would be
scanning at 2000 dpi. Obviously this is beyond the capabilities of many
flatbed scanners.
If you started with an 8x10 negative (image area 7.625 x 9.625), you
could scan at 944 dpi (or more likely 1000 dpi) which is in the range of
some moderately-priced flatbeds.
If your final image size is smaller, the enlargement factor is less and
the scanning resolution will be correspondingly lower.
Finally, you can always experiment with interpolation, which is simply
scanning at a lower resolution and then allowing a computer program, such
as Photoshop, to "add" resolution by looking at two points of data and
then adding a new point between them which is the average of the two. If
this is done to all the points (pixels) then the final resolution will be
twice as large as the original. However, it should be obvious that the
computer is not adding any new information or detail to the image, it is
just smooting out he information that is already there. For this reason,
there will be some loss of quality when using interpolated images,
HOWEVER, depending upon your image, printing medium, etc., this loss may
be insignificant. It is certainly worth trying.
> I know from the list that a number of people are using inkjet printers to
> output negs - I wanting to make slightly larger negs, and of strange
> sizes so I want to use a film bureau. So do you tell the film bureau -
> right reading emulsion down, with a 225 dot screen?
Correct. Right-reading, emulsion down, 225 dpi if the imagesetter is run
at 3600 dpi.
David Fokos