🚀 go-pugleaf

Bart van der Wolf wrote:
> 
> Not if the flat surface of the glass platen and a (hopefully flat) 
> mounted slide are concerned. The 0.75 mm (depending of the particular 
> mount) difference is already noticable on my 'ancient' Epson 2450 Photo. 
> One can only hope that the new 7xx models with their claimed resolution 
> have focus control.
Still, the lens can be optimized for a single object/image distance, should 
make life easier. Of course these object and image planes need to be flat 
within the DOF for the aperture used.

Regarding the focus, hard to imagine they can manufacture so precisely that 
no adjustment is ever needed.

BTW, how is chromatic aberration on your scanner? I noted that most snippets 
on that website posted earlier are near the image center, except for one from 
a corner, but that one was ill suited to spot chromatic aberration.
> 
> There is only a restriction by the combined lamp / dye colors spectum, 
> and that spectrum seems to be quite wide if one considers the 
> "Ektaspace" profile chromaticities 
> (http://www.brucelindbloom.com/index.html?WorkingSpaceInfo.html).
Ok.
 From a graph on the Epson site I gather that the blue CCD filter sensitivity 
has been shifted further towards shorter wavelengths as compared to the 
earlier model. On top of that as David Littleboy pointed out the need to 
handle IR light (what wavelength?) makes it even harder. BTW, I wonder what 
the imaging quality requirements as to this IR channel really are.
> 
> 
>> and a more sensitive CCD combined with brighter light sources could 
>> lead to a smaller aperture.
I think that if it is possible to get away with a lower aperture by 
increasing the overall sensitivity, including brighter lightsource, better 
coatings on mirrors, lenses, fewer lens surfaces, engineers will go for it. A 
lower aperture also means more tolerance with field flatness.
> 
> 
>> In principle it is also possible to illuminate with different light 
>> sources in rapid succession, eliminating the need for lateral 
>> chromatic correction.
> 
> But would increase calibration problems and component cost. It would 
> still require the optical system to have identical correction for the 
> different spectra.
No, you can correct each separately, fairly standard practice in scanning
or CCD based microscopy. You are right in that it requires a calibration step 
though.


-- Hans