Digital BW, The Print

Ernst Dinkla wrote:

> I think a true optical resolution 
> above 3000 PPI for 4x5 and smaller isn't impossible. 

Doing the maths again and starting from the 2000 PPI true
optical resolution estimation of Rafe's 4990.

A straight 6400/4800 x 2000 PPI (true optical resolution as 
estimated by Rafe for his 4990) would give 2666 PPI true 
optical resolution. But the max scan area for high resolution 
is 150 x 247 mm ( Effective pixels data) which probably means 
the windows of the twin 4x5 holder are not in the length. The 
216 x 297 mm area for the lower resolution used means that if 
there's 2000 PPI true optical resolution on the total width of 
the bed ( Rafe's estimation for his 4990) the high resolution 
should be about 2880 PPI true optical resolution (216/150 x 
2000). The smaller angle of the lens and the less DOF needed 
with the dual lens system may get it over the 3000 PPI mark. 
If the twin 4x5 holder had the windows lengthwise then the 
stroke of the lens for higher resolution doesn't have to be 
wider than 95 mm (4 inch minus the unexposed borders). That 
could have brought the resolution near 4500 PPI. All based on 
one axis calculation. There are probably other (optical) 
limitations though that make this wishful thinking.

Ernst


                    --
           Ernst Dinkla


www.pigment-print.com
(         unvollendet         )