Scanner focus

[iancc]

I have used three Epson scanners - 3200 photo, 750 photo and one which was called 4950? (i'm not sure about the name of the last one, and it is long gone so I can't check)
All of them have been out of focus when scanning transparencies! The 750 has adjustable feet to raise the transparency carrier, but the others I have had to resort to bits of card under the corners of the carrier. The 3200 that I still use at home needs approx 750 microns under it (about 10 sheets of paper) The 750 needs nearly 2mm!
This seems to true of epson scanners - I wonder if it is true of other brands?
I've attached an image showing the before and after using the 3200. These images were scanned at 1000 percent from a colour negative and have not been adjusted or sharpened at all.
The difference in the Epson 750 was much, much worse (I will try and upload a before and after from that soon) hence the need for 2mm of adjustment.
I would be interested to know if this has happened to others.