Finding a scanner's "sweet spot"

[PixelMover]

Originally posted by jeaniesa
Hmmm - given that you just posted a question about Linux drivers for a Scitex, I think that perhaps you DO have a high-end scanner!
Jeanie

My flatbed scanner is a Heidelberg/Linotype Hell Jade. Ok, ppl see this as a high-end scanner, but this is actually the cheapest, most basic one they have (600x1200dpi, 24bits SCSI). That's why I was interested to try this 'sweet spot' thing. I thought some parts of the scanner gave better results than others and thought this was a good way to check it...
Got it secondhand for $200 including transparency adapter. (At the dutch equivalent of E-bay).

As for the Scitex, I swapped it for a used Nikon F4 and lens

Hmm...anyone here who wants to swap a Sony 24" TFT screen for a 1986 Honda Civic? Only 128.000km !!

[Stephen M]

As noted, different substrates may show different levels when equalized. Perhaps try different types of white paper, as well as black. Matte or less glossy may work better.

Two good links on consumer scanning can be found here:

http://digitaldog.net/files/Scanningtutorial.pdf

http://www.thelawlers.com/FTP/B&W%20Scanning.pdf.sit

The fine detail test suggested by Andrew Rodney using currency is a good approach too (legalities though). GAFT and other print based organisations would have dedicated scanning targets, for both colour/tone and detail.

A Umax 'prepress' scanner I used to use had a 'zero' point marked on the ruler at the front of the scanner - this spot was where the manual suggested the best focus was obtained, tests also showed this...so tranny scanning was done one at a time, while reflective was done with more originals and batching so that more productivity could be gained.

This sweet spot issue can be critical when you are attempting to batch scan many originals. Some scanners let you set separate scan crop frames and apply separate endpoints/gradation etc to each scan frame and save the files off to disk or live to Photoshop for post processing. This is a huge productivity bonus, but if the flatbed has serious probems over the entire scanning area - quality may be sacrificed or the batch may be smaller than you would like if you try to stay within the better area.

I used to use a CreoScitex EverSmart Supreme high end flatbed (US40K) - which had patented XY positioning...the scanner head moved both vertically and horizontally to focus in on parts of each image, then it would stich the strips into one final scan. Sounds scary, but I never saw any issues from this technique. With this line of scanners you can use the full surface of the bed and the biggest plus is the batch scanning workflow. Prescan the whole bed, set your scan crops, adjust your first scan and then send to the scan qeue, adjust the next prescan crop while the first is scanning/writing to disk etc.

I currently work for a publisher who uses a drum - I am not sure that a high end flatbed could match the pace/productivity of a good drum and operator.

Now I just use a humble Microtek flatbed and SilverFast software - since the drum does most of the work (I am not a drum operator and scanning is not the focus of my job).

Scanning is such a deep area to go into - and any discussion involving scanning should include this link:

http://www.scantips.com

Have fun.

Sincerely,

Stephen Marsh.

[G. Couch]

I think BigAL is on the right track with his explanation. I did some more research and found this in one of my books, Scanning the Professional Way-

"The fluorescent lamps used in most flatbed scanners are susceptible to fall-off, a phenomenon that produces better illumination near the center and less at the outer edges of an original."

Obviously higher end devices have better light sources, higher quality CCDs, A/D converters, etc... I think electronic noise plays a part as well. Certain areas in the scanner are more susceptible than other areas to interference.

[WideAngle]

I am using a Microtek 6100pro with silverfast which I guess is sort of midrange (about 400CAN dollars). see the pic for the sweet spot after applying equalization, I assume an even gray is good? There is some noise on the edges though.
Wide angle

[kaulike]

Posted below are before and after shots of my Epson 3170. The first was by laying a sheet of heavyweight matte paper and hitting the button. The second was augmented by pressing down on the lid while scanning, as I noticed the first time that the dark spot was caused by a slight warp in the paper. I thought the difference was remarkable.

[raniday]

Hmmm, maybe scanners have improved since this thread was begun. I scanned a sheet of white paper on several settings and just got a completely white sheet of paper. Sweet.

[kaulike]

Try loading the result into Photoshop and use the Equalize command. I think you may be surprised at the results.

If you are still getting a completely blank document, make sure you don't have the scanner set to scan with a transparency adapter. *Any* scanner will have varying results across its scan area.

hope this helps!