Re: filmscanners: What causes this and is there any easy solution ?

[Arthur Entlich <artistic@ampsc.com>]

Karl Schulmeisters wrote:

> I don't think this is the case.  Otherwise you would have seen this
> phenomenon from enlargements made from transparencies long ago.  Consider
> this, the human eye can resolve about 1 minute of 1 degree of arc (1/60 of a
> degree) in the horizontal plane (most sensitive - less in the vertical)  So
> take a 35mm slide (which is about 1" tall) and enlarge it full frame to
> 8x10" that's an enlargement factor of about 8.  So a 4000dpi scan of a 35mm
> slide is about the same as a 500dpi scan of an 8x10.
> 
> So plugging 1/500th of an inch into the formula X = TanTheta Y where X is
> the lines/inch and Y is the eye's distance from the 8x10 enlargement, we get
> ..002 = Tan(1/60deg) Y or Y (max eye resolution) = .002/.000291 = 6.875".
> 

If human eyes actually functioned based upon a mathematical formula, 
you'd have it all solved! ;-)

Just so some people unfamiliar with the nomenclature won't get too 
confused, the symbol ["] can be used to both indicate inches as a linear 
measurement and minutes (1/60th of one degree) of an arc.  Your first 
reference (1") is one inch, your second reference (6.875") is 6.875 
minutes of a degree of an arc.

The big problem we all face in analyzing the artifacts or other 
information we see in a scan is that we are looking at the scan in a 
translated format, either via a monitor (via a software package) or a 
print (usually inkjet for most people, via a print driver program) each 
of which add other confounding factors to what is being provided by the 
scanner.  SInce none of these are purely optical in nature, we're in 
"uncharted waters", with no sextant to get us ashore, or is that a-sure? ;-)

Art


> IOW, anyone who has looked at a full frame 8x10 enlargement of a 35mm image,
> closer than 7" is in essence 'scanning' the 35mm slide at greater than
> 4000dpi.  And since we don't have reports of folks seeing this sort of
> difference in enlargements at this level (remmember folks use grain
> focussers to get even higher resolution during focussing of an
> enlargement) - I don't think there is any  'real information' there.