800x3200 vs 1200x2400 vs 1180 -- Scanner Resolution???

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How do I compare a scanner with resolution of 800x3200 (Epson 800) vs one with 1200x2400 (Umax PowerlookIII)? Is it just a matter of multiplying the two numbers to get the total maximum amount of resolution per square inch? It would seem so, but often the data I've seen only lists the first number (or do they use the square root of the product?) For example, the two scanners listed above give a __x__ resolution spec, whereas the Minolta scan multi just lists it's medium format resolution as 1180. I know Dmax is also important. Which is the more critical measurement, resolution or Dmax?

FYI, I am buying a scanner to use for medium/large format film scanning plus the occasional print. Thanks in advance for your help.jj

-- Joe Johnson (joseph.johnson_85@gsbalum.uchicago.edu), October 21, 1999

Answers

Well the Epson 800 has true 800dpi Optical capability. Obviously the scanner has a finite resolution in the horizontal direction since the scanner moves vertically to scan the document. 800dpi is the horizontal resolution. 3200dpi in the vertical direction is achieved through Microstepping the carriage 4 times every inch, this effectively provides 4 times the resolution ( hence 3200dpi ) in the vertical direction. Umax halfsteps the carriage to provide double the resolution vertically as opposed to Epson using the 4 times stepping motor. Like all things in life there is a hitch, when you scan at 3200dpi optical, the vertical scan is optical but a good portion of the horizontal is interpolated ( yuck!) . Honestly, you will never scan a print at anywhere near that resolution but a negative is another story. The transparency adapters need all the resolution they can get since the film has lots of detail and is very small. At that point I would do a 2400dpi or 3200dpi scan and experiment for the best results. With scanner like the Epson 800 or Umax Powerlook your getting better quality optics and 36bit output more than anything. My Epson 636U scans at 36bit but the scanner and software truncate the 36bits to 24bits. Not great for the most pristine work. Do most people even care or miss that feature? No since almost nothing short of Photoshop can handle over 24bit images. Also the optics are just flat out better in the more expensive units. For web sites, and anything else not demanding absolute professional results, the current batch of $250 scanners work fine. Hey, the newest $250 scanners would put to shame some high end units costing 5 times as much only a year or two ago. Buy one and don't wait forever since there will be better ones coming out all the time. That goes out to all you digicam people too, if you keep waiting for the perfect camera, you'll be in your casket before you buy one, so stop spending your life deliberating the digicam purchase, go buy one and have fun.

-- Cris Daniels (danfla@gte.net), October 22, 1999.

Any optical resolution around 600x1200 is okay. The problem is, you could not work with a file that you could scan at the maximum resolution anyway. File sizes that work well with good resolution for print, etc are in the 25MB range. This is what a 35mm slide scanned at 2500dpi would come to. The most important thing is to think of what you're going to do with the file. Are you going to print? what size? What media? a scan resampled to 150-200dpi will print well and be of a manageable file size.

-- Tony Reynolds (treynold@gte.net), November 06, 1999.

Tony:

You forgot to mention that a 25MB file in Photoshop would require at least 256MB of memory in the PC or Mac to handle the image and do anything with it. ;-)

-- Jim Martin (jfmartin@infi.net), November 28, 1999.


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