Re: [OM] Scanner DOF

[Chuck Norcutt]

I'm really not sure I understand the question since I don't understand 
it in terms of DOF.  Some flat bed scanners have a very great DOF of 
maybe 6mm or more from the surface of the glass which is great for 
scanning 3D objects.  Others, not so much.  So, the DOF is what it is 
and you won't be able to change it.  It's not as though you can alter it 
by changing aperture or anything else except that some scanners can 
alter focus distance.  So with the right scanner it might be possible to 
do multiple scans and blend the layers.  But I don't know if scanners 
can really change focus distance enough to make that practical.

But what I read into your question is something different.  It sounds 
more like you're asking what scanning resolution you should use to 
maintain a good life-size replica of whatever you're scanning.  For 
example, you want to scan a pencil which is 15cm long and print it on 
paper at 15cm while having it look nearly as sharp as the real thing 
when viewed from a distance of about 25cm.  A resolution of 300 ppi 
should be adequate for all but Moose.  If you want to please even Moose 
go to 600.  Even he can't see better than that.  :-)  But remember to 
sharpen the final image at print size before printing.

Dr. Focus



Wayne Harridge wrote:
> Probably a question for Dr Focus.
> 
> I'm wanting to scan some 3D objects on a flatbed and wondering how much
> depth of field I need.  Assuming the resultant print is "life size" (i.e.
> ~A4) what vale of circle-of-confusion should I be using.  This should be
> related to the resolution of the human eye at a normal viewing distance I
> think - so what is that value ? 
> 
> ...Wayne
> 
> Wayne Harridge
> http://lrh.structuregraphs.com/
> 
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