Re: [ARSCLIST] Large-format scanner redux

[Don Cox <doncox@xxxxxxxxxxxxxx>]

On 14/08/08, Malcolm Smith wrote:
> A couple of thoughts with respect to copying flat originals. There is
> a reference to distortion. This common problem is caused by lenses not
> being symmetrical (front elements the same as the rear elements).
> 
It is particularly a problem with zoom lenses. Some (most?) digital
cameras correct the image for this effect automatically.

> There are lenses designed for producing color separations. They are
> known as Apochromats. They are corrected for three colors instead of
> two. If there is any way to use them, they can probably be found
> second hand at bargain prices. They were once very expensive. One name
> to look for would Artar produced by Goertz American Optics. The images
> these lenses produce from color originals are very much better than
> those produced with regular lenses.
> 
Such a lens could be used with a studio camera with a digital back. We
are talking tens of thousands of dollars here.

Neither of these problems affect scanners.

The big problem with scanners is depth of focus, or the lack of it,
especially when scanning 35mm film. The actual resolution may be well
below that stated in the specs, because part or all of the film is out
of focus. This problem would not occur if the film could be imaged with a
high resolution (say 25 Megapixel) camera with a roughly 24x36 mm ("full
frame") sensor.

It will be a couple of years before 25 Megapixel cameras in sizes
similar to traditional 35mm cameras are common. (Larger cameras such as
Hasselblads have higher resolution that that, but are very expensive.)

Regards
-- 
Don Cox
doncox@xxxxxxxxxxxxxx