[filmscanners] RE: HP PhotsSmart - questions

["Laurie Solomon" <laurie@advancenet.net>]

It is very possible that I have oversimplified things greatly as you
suggest; but not being an engineer that is the way I tend to grasp the
basic general gist of what is being said.  :-)

While I think I understand the gist of your argument along with the what
you are showing in the two animations; I am in the unenviable position
of not knowing enough of the technical information well enough to
comfortably disagree with what you are saying or to comfortably agree
with the position in its entirety.  :-)  I guess my main problem is that
my point of reference is with scanners that do not have variable optical
resolutions or variable focusing, which leaves me uncomfortable when
trying to conceptualize such a scanner and the relationship between
optical resolution and effective optical resolutions (I am not talking
at all about interpolation or resampling upward or downward)in such a
scanner.

> Any scanner can downsample to achieve lower resolution than
> optical, thats why optical resolution is so important.
> Refocusing to capture a wider strip is NOT the same as downsampling.

Yes and any scanner can upsample to achieve higher resolutions than
optical(but both of these types of resampling are not hardware functions
but software functions external to the scanner and its operation).  For
my arguments, I was not in any way referring to any form of resampling
when I was referring tot effective optical resolution.  What I was
referring to was to a fixed number of pixels that the sensor can capture
in terms of its maximum limit in which one varies the size of the strip
that is being covered by that sensor.  This changes the effective
optical resolution of the scanner in terms of the number of pixels per
inch that one can achieve.  I am not sure how this relates to focus or
depth of field which is what I think your discussion revolves around,
although I do think it does impact on it as you suggest.

As I have come to realize, we may be in agreement with respect to the
general thesis, although the specifics are what leave me uncomfortable
at this stage - maybe because I am having some trouble visualizing and
comprehending the details when it comes to variable focus and resolution
scanners.  The camera analogy does not help me; in fact it only confuses
me. :-)  Unlike the camera one can change the both the field of coverage
and depth of field by changing lenses from telephoto to normal to wide
angle as well as by moving closer and further away from the subject and
in addition to any focusing that one might do by turning the focusing
ring on the lens which will move the lens elements in relation to each
other or any manipulation in the lens' aperture.  I do not conceive of
scanners as allowing for changing sensors from those which can capture x
number of pixels within a given configuration to those which can capture
y number of pixels in the same or a different configuration; nor do I
understand scanners as allowing one to change apertures on either the
lenses or the sensors (or what would be the equivalent).



----Original Message----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk] On Behalf Of
wbgilloolyjr@charter.net
Sent: Monday, August 08, 2005 4:53 PM
To: laurie@advancenet.net
Subject: [filmscanners] Re: HP PhotsSmart - questions

> You are not wrong, but you have very much oversimplified things.
>
> Basically, the optical resolution of a scanner is determined
> by how many pixels the sensor (CCD,CMOS) captures and how
> wide a strip the scanner scans.
>
> So, a scanner with a 5,000 element (pixel) sensor that
> covered a strip 1" wide would be a 5,000ppi scanner
> (5,000pixels/1"=5,000pixels/inch).
> If the same 5,000 element sensor covered an 8.5" wide
> (full-bed) strip, you'd have an 588ppi scanner
> (5,000pixels/8.5"=588.25pixels/inch).
>
> There is, of course a lens between the artwork/flatbed and
> the sensor and the lens-sensor assembly is very much like a
> camera.  Just as you can move closer or farther away from a
> subject refocusing the lens to make sure everything is sharp
> a scanner can move the sensor-lens assembly closer (for
> higher resolution) or farther away (to cover a wider area).
> It must refocus to achieve maximum sharpness.  Not all
> scanners do this (in fact pretty few), but some can.
>
> Any scanner can downsample to achieve lower resolution than
> optical, thats why optical resolution is so important.
> Refocusing to capture a wider strip is NOT the same as downsampling.
>
> My original description is the most accurate way of
> describing the focusing procedure for any optical assembly (including
> your camera). Your lens to film (or CCD/CMOS) distance that you set
> while "focusing" is actually setting the magnification ratio.  Your
> distance
> from the subject sets what's in focus.  This isn't obvious
> for large distances (greater than about 2'), you can move
> your self then "focus" the lens.
> But anyone that does a lot of macro photography knows that
> moving the camera-lens assembly forward and back to achieve
> focusing after setting the lens is much easier and more
> straightforward.  This is why a scanner with variable optical
> resolution sets the lens to sensor distance first (to achieve
> magnification ratio/strip width/optical resolution - they can
> be used interchangeably here) then moves the lens-sensor
> assembly to achieve focus.  Scanners work at macro distances
> as your reproduction ratio is usually about 1:1.
>
> Mr. Bill
>
>
> Laurie Solomon wrote:
>>> If the optical resolution is variable and YES there are scanners
>>> that can do it
>>
>>
>> I will take your word for it; but according to my understanding, the
>> optical resolution has little to do with the distance between the
>> lens and the sensor and more to do with the size and capacity of the
>> sensor.  The effective resolution may change with the changes in the
>> distances between the lens and the sensor; but the actual native
>> hardware optical resolution remains the same.  But I could be wrong
>> in my understanding; I am not an engineer.
>
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