Archived from groups: alt.comp.periphs.scanner (
More info?)
In article <qWcve.1853$5w3.382@newssvr11.news.prodigy.com>, CSM1
<nomoremail@nomail.com> writes
>"RSD99" <rsdwla.NOSPAM@gte.net> wrote in message
>news:lc%ue.902$Uc2.403@trnddc03...
>> Emulsion Down, and 'flip' the image either in the scanning program or in
>> PhotoShop.
>>
>> Just ask yourself ... just exactly WHY should I scan *through* the film
>> base?
>>
>>
>
>Maybe because the light travels through the film base to produce the image
>on the sensor.
It certainly does, but after the light has been spatially modulated by
the image it only passes through the film base *if* the film is oriented
the wrong way. Consequently, the optical loss on the *image* only
occurs if the film is oriented with the emulsion on the side of the
light source - which *is* the wrong way.
Put it another way. The film base is not perfect - it scatters and
distorts the light to a certain degree. If the base is on the
illumination side then that scattering and distortion of the light only
serves as a diffuser. Even if the film base scattered significantly,
all that would happen would be that the light reaching the emulsion (and
hence the image) would be more diffuse. The image would still be
perfectly formed on the CCD by the scanner's primary lens. Indeed,
certain scanners have specific diffusers designed into them because
there are advantages of a diffuse source. Mount the film the wrong way
round and that built in mild diffusion on the film base affects the
*image* as well as the illumination. Mount it the correct way and only
the image is not affected.
>Either way you turn the film, the light has to travel through
>the film to get to the sensor.
In an enlarger, light has to travel through the condenser lens or the
diffuser to get to the sensor too - and the same thing happens in
scanners. In neither enlarger nor scanner does the condenser or
diffuser have the same image forming capabilities as the primary lens -
they don't need to because the light passes through them before it picks
up the image. The same is true of the film base - if it is oriented
correctly.
Conduct a simple experiment. Make a synthetically bad film base by
taping a sheet of tracing paper to one side of the slide. Hold it up to
a light source and look through it in each orientation - with the
tracing paper on the illumination side and then again with the tracing
paper on the sensor side (ie. towards your eye). In which orientation
do you see the cleanest sharpest image? Well, to a much lesser degree,
that same light scattering of the tracing paper occurs in the film base
itself.
As a result of conducting that experiment, come back and tell us which
side the non-optical graded film base should be on!
The image losses introduced by scanning the film in the wrong
orientation are minimal and in almost all cases (unless you happen to
get a rogue batch of film) there are other more significant loss
mechanisms, but they are never zero. Since they are unspecified and
variable they are best avoided by adopting the correct orientation as
the default. Only flip the film if there is no alternative.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a ah heck when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)