Digital Darkroom Basics, Part 3: Scanners
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Last month we learned how to calculate the resolution required from our input device in order to print the highest possible quality prints on our printer. Please take a moment to review that column, since we will use the same example this month. Let's Get Serious Slide scanners are serious contenders. The Microtek ScanMaker 35t Plus scans 35mm images at 1950 dpi optical, or 7300 dpi with software interpolation (in other words, it cheats). At $750, this would meet my example requirements. However, I also work with the 2-1/4" format so I kept looking. (Slide scanners jump from 35mm up to 4x5, which is too expensive for me.) Flatbed scanners are most popular for scanning reflective material. If you make color prints, you could then scan them using a flatbed scanner. Some flatbeds have special tops that allow you to scan transparencies. These tops are usually optional, but the Agfa Arcus II comes with one built-in. Most of these scanners offer resolutions of 4800 dpi or more, using software interpolation. Any of these would meet my requirements for the previous example. FREE ADVICE: If you only work with 35mm images, buy a 35mm scanner. The Microtek, Minolta and Nikon ones are supposed to be good. If you work with larger formats or also want to scan color prints, get a flatbed scanner with a transparency adapter. Before you do, however, I have another trade secret for you. Don't Be As Dense As Your Slide There are actually three things to consider when picking a scanner: color capability, scan resolution and optical density. Since almost all color devices support 16.7 million colors these days, I haven't mentioned that. We have just covered scanner resolution. So what the heck is optical density, and why haven't any computer magazines mentioned it when they review scanners? Density relates to the opacity of transparent or reflective materials, but is way too complicated to explain. If you really must know, read "An Introduction To Digital Scanning," by Agfa. Anyway, it seems transparencies have a maximum density of about 3.3 and a minimum density of about 0.3, giving a density range of 3.0. Reflective materials have a density range of about 2.0. But wait, it isn't linear. It's proportional to the logarithm of the opacity. So a transparency has a tonal range ten times greater than a print! Computer magazines write for the business world. Scanners are used by business to scan reflective materials. Even the cheapest scanners on the market will handle the minimal density requirements of printed matter. That's why they don't even know about optical density. I expected graphics art-type magazines to include optical density in their product reviews. Luckily, I didn't hold my breath. Most slide scanners have a density range of at least 3.0. That's really why they are so expensive, not because of the resolution capabilities. For example, the Polaroid Sprintscan 35 Plus boasts an optical density range of 3.4, which Agfa would have to admit was greater than the range of any color film they make! Most flatbed scanners are optimized for reflective scanning. Even with a transparency adapter, the results are ten times worse than you need. This is where mid-level flatbed scanners enter the picture. They cost from $2000 to $3000, but offer a density range almost as good as a slide scanner. I bought an Agfa Arcus II, which features a density range of 3.0, and has a built-in transparency hood, instead of an add-on attachment. I am 100% satisfied with it. And yes, the Agfa is capable of meeting the requirements of my example, using software interpolation. Get whatever type of scanner meets your requirements. Next, get a copy of "Make Your Scanner A Great Design & Production Tool," by Michael J. Sullivan. [Next month we learn how to select photo-editing software.]
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