[sane-devel] Epson Perfection1640: TPU focus

[ael]

I have been testing the 1640 with the TPU installed using "Positive
Film".

As I have reported earlier, the backend doesn't seem to send a focus
command, and the focus position is reported as 0x40 or 'focus on glass'.

I have now tried several scans with targets both on the glass and above.
It was actually much harder to distinguish the different cases than
I expected. I am not sure what sort of *internal* autofocus the
1640 may have.

But I think it is still "on glass" rather than above it.

To be really sure I will have to modify the code to send an explicit
command to see what difference it makes.

I have never really believed the "2.5mm" above the glass: I have just
used a micrometer screw gauge to measure the thickness of the film
holders and the result was almost precisely 1mm.

ael