filmscanners: drum scanning services

["PAUL GRAHAM" <peegee@btinternet.com>]

Hi there, can I get some second opinions on this issue:

I've got to make a 46x33 inch highest exhibition quality Lambda or Lightjet
print from a big 5x7 inch negative. I talked to the printing Lab's and they
tell me that they output at 400 dpi for the highest quality.
Thus, if I want 400 dpi x 46" that is 18,400 pixels, from an active area of
6.25"  that gives me 2944 dpi needed. So I presumed: scan at 3000 dpi and no
problems.
This gives me a 240Mb 8-bit file, or a 480Mb 16-bit file.
I can work on that (I have a good workstation) and then hand it over.
The enlargement factor is only something like 650%, very low.

But..

Every drum scanning bureaux here  (central London) seems to think asking for
a file this big is ridiculous. One suggests 80Mb as a maximum another 120Mb.
Why? Nobody can explain to me why I would want a small file and have the
Lambda RIP invent pixels (sorry, interpolate) to make up the 400 dpi output
needed, when I have real pixels readily available on my large format
negative.
I went to the bother of shooting 5x7" precisely because I wanted the
sharpest and purest tones possible to record. Now I'm being shunted
downstream by drum operators..

Have I got something wrong here? Is there nothing wrong with a 120Mb stepped
up to 480 Mb? Or are drum operators simply too used to working to low repro
standards? Why won't anyone do a large scan for me?

pg