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[OM] Re: More comparisons [was Comparison shots]

Subject: [OM] Re: More comparisons [was Comparison shots]
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Mon, 03 Nov 2008 09:59:44 -0500
I think I may have answered my own question now that I've put it into 
words and cogitated on it for a moment.  Statements about good depth of 
field over a range of 1/2" above the surface of the glass have to do 
with scanning solid objects resting on the glass... things like pencils 
for example.  But these objects are being scanned at modest resolutions 
since the scan of the object is already life size.  300 ppi could make a 
good life size print.  Scanning film, on the other hand, may be done at 
3-4000 ppi or even higher which would place a much more severe 
constraint on depth of field.  Anyhow, that's my guess.

Chuck Norcutt

Chuck Norcutt wrote:
> I think you must have meant "aren't held flat against the glass".  I 
> think the answer is that they can't be and also be held in a frame.  The 
> frame has to have some thickness and in the case of the V700 it's 2.5mm 
> from bottom of frame to film surface.  But another more interesting 
> question is why adjustment of +/- 1/2mm is significant.  It's my 
> understanding that flat beds typically have good depth of field over 
> about 1/2" above the surface of the glass.  I don't know why the V700 is 
> any different.
> 
> Chuck Norcutt
> 
> Ken Norton wrote:
>>> Stick a small 2-3mm thick support near the center of the frame.  Scan
>>> once, move the support and scan again.  Then combine the images in PS.  :-)
>>
>> I am at a loss as to why the negs are held flat against the glass?
>>
>> AG
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