Forgive this foolish question...

[il barbi]

it came to me from my problem about scanning slides with a flatbed scanner
(Epson Perfection 2400 with transparency adapter in the cover) and, as
known, obtaining poor results -
Now I see my slides at best with a slide viewer, namely a small projector
that shows a slide on a 20cm x 20 cm screen - I see them with abundance of
details even in the shadowed areas. This is obviously a fully hw device -
but what if the image could be "redirected" on my PC's screen? Naturally I
don't know how... Or why the output on the viewer could not be "scanned" to
obtain a result much better than the true scanner's one, without all
mechanics & optics & electronics that make a dedicated scanner so costly?
(sure Nikon would not be glad...
il barbi

 

[Kennedy McEwen]

Now I see my slides at best with a slide viewer, namely a small projector
that shows a slide on a 20cm x 20 cm screen - I see them with abundance of
details even in the shadowed areas. This is obviously a fully hw device -
but what if the image could be "redirected" on my PC's screen? Naturally I
don't know how... Or why the output on the viewer could not be "scanned" to
obtain a result much better than the true scanner's one, without all
mechanics & optics & electronics that make a dedicated scanner so costly?

You could try shooting the screen of your projector with a digital
camera, but I don't hold out much hope for the quality of the results.
The human eye is much more forgiving of uneven illumination than a
digital camera.

 

[il barbi]

You could try shooting the screen of your projector with a digital
camera, but I don't hold out much hope for the quality of the results.
The human eye is much more forgiving of uneven illumination than a
digital camera.

I've already tried to capture the screen of my projector with a digital
camera, but it does not work, the light of the projector burns the resulting
photo
il barbi

 

[Kennedy McEwen]

I've already tried to capture the screen of my projector with a digital
camera, but it does not work, the light of the projector burns the resulting
photo

Precisely. Uneven illumination is the main problem that you have to
overcome, and the worst of this is caused by the direct line of sight to
the projector lamp. You could shoot the image at an angle to the screen
and then correct the resulting keystone distortion in software, but you
will still end up with some uneven illumination.

The difficulty you are experiencing pretty much answers your own
question - why the output of the viewer cannot be scanned.

 

[il barbi]

The difficulty you are experiencing pretty much answers your own
question - why the output of the viewer cannot be scanned.

just because you are so friendly...
has anyone thought to compare the performance of a scanner vs a digital
camera? Obviously a digital camera works worst, but why?
il barbi

 

[CSM1]

just because you are so friendly...
has anyone thought to compare the performance of a scanner vs a digital
camera? Obviously a digital camera works worst, but why?
il barbi

Two different purposes.

A digital camera is designed to take an image of the "real world" (3D). The
lens focuses at a distance from the image sensor.

A scanner is designed to create an image of a flat surface placed in close
proximity (contact)to the image sensor.

For detail a digital camera is very good when compared to the same scene
made with a film camera. Digital cameras are a lot better now, than they
were just a few years ago.

 

[Kennedy McEwen]

just because you are so friendly...
has anyone thought to compare the performance of a scanner vs a digital
camera? Obviously a digital camera works worst, but why?

There are lots of reasons why a digital camera will be worse than a
scanner for this application. As well as the issues that Carl
discussed, there is the one you have already encountered: by using
exactly the same light source at each position in the frame, the scanner
ensures even illumination, which is difficult to achieve with the same
precision in a projected system.

In addition, the scanner optic only requires to be corrected for
distortion in one axis, since the other axis is produced by a precise
mechanism. By comparison, a digital camera optic forms a two
dimensional image and it is much more difficult to achieve the same
level of distortion control over that area than it is over a single line
- especially with the other requirements that the camera lens must
deliver, such as adjustable focus over a wide range, operability at
different stops etc.

So, in at least the areas of distortion and flat illumination, the
scanner wins hands down over a digital camera for this type of
application.

Then there is resolution: not many digital cameras will give you even
close to as many samples as even a modest 2700ppi scanner. From a 35mm
full frame that produces 10Mpixels - and a 5400ppi unit produces
40Mpixels. These are real rgb pixels from the scanner, not pixels with
2/3rds of the information interpolated from adjacent pixels in a Bayer
matrix. Consequently, the resolution that a 2700ppi scanner *can*
deliver will exceed that of even a 10Mpixel camera when copying a film
image. Of course, you need an image on the film that is sharp enough to
show this benefit, but a slow Kodachrome, Velvia or Provia will do quite
nicely for that purpose.

 

[il barbi]

There are lots of reasons why a digital camera will be worse than a
scanner for this application.

thank you very much for your discussion
The reason I asked you for such comparison is because at present if I want
to have a print from a slice, I go to my favourite photo lab and I know they
photograph my slice again in order to print it (I don't know whether with a
digital camera or an analogic one)
anyway the result is far better than I can do with my scanner (I don't even
try to print, I just see the scan result on the monitor)
il barbi

 

[Kennedy McEwen]

thank you very much for your discussion
The reason I asked you for such comparison is because at present if I want
to have a print from a slice, I go to my favourite photo lab and I know they
photograph my slice again in order to print it (I don't know whether with a
digital camera or an analogic one)
anyway the result is far better than I can do with my scanner (I don't even
try to print, I just see the scan result on the monitor)

I do not know what makes you so sure that they photograph your slide to
print it, since printing direct from the slide will give far superior
results. However, even if they do photograph it, they will use a proper
slide copier unit and, probably, proper interneg film, not photographing
it from a projector screen. Even then, the results will be considerably
inferior to those obtained from a proper film scanner.

 

[CSM1]

thank you very much for your discussion
The reason I asked you for such comparison is because at present if I want
to have a print from a slice, I go to my favourite photo lab and I know they
photograph my slice again in order to print it (I don't know whether with a
digital camera or an analogic one)
anyway the result is far better than I can do with my scanner (I don't even
try to print, I just see the scan result on the monitor)
il barbi

You used the word slice, do you mean slide?
A 35mm slide is one frame of positive film mounted in a 2" x 2" mount.

Your photo lab probably uses a Film scanner or a Drum Scanner. They do not
"photograph" the slide.

Film scanners are designed to scan negatives and slides at very high
resolution, some commonly available scan at 4000 ppi.

Here are examples of very good film scanners from Nikon UK.
http://www.europe-nikon.com/category.aspx?countryid=20&languageid=22&catId=97