Digital BW, The Print

On 07/08/2011 Lew Schwartz wrote:
> From what I've been able to read on the net, this may be due to 
> aliasing &
> not the actual grain in the film (It's much worse than I'd see in a
> traditional, gs print.). Contrary to what I've read, however, it is 
> not a
> matter of threshold iso/grain size issues, rather it's a continuum, 
> getting
> progressively worse as iso/grain increases. It may not be readily 
> noticeable
> at lower iso's, but close inspection reveals it to be there.
> 

I think I was the first to describe grain aliasing, in response to a query 
posed by Polaroid regarding a customer inquiry, on the filmscanners list 
filmscanners@... (I still operate this, but it's pretty much 
silent these days). The Photoscientia.com description of it grew out of 
this initial discussion.

Grain aliasing depends on many factors. Grain in any given emulsion is not 
a single size, but a wide range of sizes, affected by the dev used, its 
solvent action, exposure, emulsion thickness etc. Rodinal, which produces 
ferociously sharp grain and local adjacency effects, is much more likely 
to be problematic than a high-solvent-action fine grain dev like Microdol X.

The LED lightsource used by Nikon is particularly susceptible as it is 
partly collimated light which sharply renders grain topology onto the 
sensor. B&W silver films are worst, colour materials have replaced the 
silver grains with dye clouds which tend to have a softer edge.

Still if any material contains some grains sized near the Nyquist limit, 
aliasing is inevitable.

The earlier 2700ppi Nikon scanners were worse, they aliased most materials 
of ISO100 or over, expecially in areas of medium exposure, like blue sky. 
The result was often like blue sandpaper.

You aren't likely to be able to improve the Nikon's behaviour with the 
problem material by much. With some Nikon scanners it is possible to 
manually defocus the image just a little, which can help - but they 
already tend to have problems with narrow depth of focus and film 
flatness. The lens being wide aperture to cope with the fact that Nikon 
LED's are not very bright means you could end up with just a blurry mess, 
or patches of aliased and unaliased grain.

It's hard to see how a diffuser could be introduced into the optical path 
except perhaps sandwiched with the film with spacers - though attentuating 
the already dim illumination could cause underexposure.

You best bet would probably be to try a different scanner with a diffuse 
lightsource. I use a Polaroid 4000 and an Epson V700. I've only had grain 
aliasing from the Polaroid when trying to scan ISO3200 Delta and TMZ B&W, 
and not at all from the Epson, probably because I've only used it for MF 
slow emulsions.

Best materials for scanning without these issues are the chromagenic 
C41-based B&W materials, Tri Max CN and Ilford XP2.
-- 
Regards

Tony Sleep
http://tonysleep.co.uk