Making fine prints in your digital darkroom
Scanners
by Norman Koren

---

Site map/guide to tutorials Contact | News Making fine prints in your digital darkroom Understanding image sharpness and MTF Image galleries / How to purchase prints Photographic technique Image editing with Picture Window Pro A simplified zone system Digital vs. film

View image galleries

Search WWW Search www.normankoren.com

A scanner is a device that converts prints or images on film— negatives or slides— to digital format, i.e., pixels (picture elements). A scanner consists of a fixture for holding the film or print, a light source, a CCD sensor, and associated electronics and software. Either the film or the sensor moves.

To make prints digitally from film originals you'll need to have them scanned. If you have a stock of existing film images I recommend that you purchase a scanner. Although shops can make scans, you can usually obtain the finest quality with your own scanner, and you may save money in the long run. You don't need a scanner for images made on a digital camera.

Your choice of format will be influenced by your existing equipment, your goals, your budget, and hardware availability. I now do most of my work with a digital SLR, but I have a large collection of 35mm negatives and slides dating back to the 1960s as well as a modest collection of medium format negatives. My main scanner for 35mm is the 4000 dpi Canon CanoScan FS4000US, but I still use the 2400 dpi 36 bit Hewlett-Packard PhotoSmart S20 for panoramic images. It makes decent 13 inch high (up to 33 inch long) prints. Dust can be a real pain with the HP, but the CanoScan's infrared channel dust removal is very effective. I use the Epson 3200 for medium format and larger.

We begin with a description of scanner specifications, then we discuss 35mm, medium format and large format scanners, culminating with a large Table of scanners. The use of scanners is described in a separate page, Scanning.

Film scanner specifications

• Resolution in pixels per inch (ppi), frequently called dots per inch (dpi), though pixels is more accurate. Ranges from 1200 dpi for large format flatbed scanners to 5400 dpi for the Minolta Scan Elite 5400 (higher for a few drum and "virtual drum" scanners, which are beyond the budgets of most consumers). This number specifies the maximum available optical resolution. You can usually select a lower resolution, which saves time and storage, if you don't plan to print large. Consider only optical resolution, not interpolated resolution (often a larger number), which you can obtain in image editing programs by resizing the image. True visual resolution in line pairs per inch (or mm) tends to be proportional to dpi for dedicated film scanners. More on the subject can be found in Understanding image sharpness part 2. (You might want to start with the explanation of MTF in part 1.) Inexpensive multipurpose flatbed scanners such as the Epson 3200 are not as sharp as dedicated film scanners— a bit disappointing because they're so versatile, but they are decent for medium format and have a sweet spot for 4x5. The apparent reason is that the lens has to cover a large area— usually 8.5 inches, unless the lens can be repositioned for the transparency unit. Excellent technique— fine lenses, fine film, and sturdy support— is required to take advantage of the higher resolution scanners.

• Dmax: the dynamic range, i.e., the maximum film density the scanner can respond to. Density is defined on a logarithmic scale as log₁₀(fraction of light transmitted through the film). Dmax is typically between 3 (0.001 transmitted) for basic scanners and 4.8 (0.000016 transmitted) for premium scanners like the new Nikons. Scans are often noisy in areas of slides or negatives where the density is close to Dmax. You won't find much about scanner noise in manufacturer's specifications— you'll have to read about it in reviews. With certain scanners, VueScan can scan images repeatedly and use a technique called signal averaging to reduce noise. Slides are somewhat more sensitive to Dmax than negatives: Dmax = 3.6 should be sufficient for almost any slide; Dmax = 3.2 is OK for negatives and typical (but not all) slides.

• Bit depth.  The number of bits per pixel, typically between 30 and 42. Scanners represent images in RGB format, three colors per pixel, so a 30-bit scanner has a 10-bit color depth (10 bits per color channel); a 42-bit scanner has a 14-bit color depth, etc. The number of levels n bits can represent is 2ⁿ: 10 bits represents 1024 levels; 14 bits represents 16384 levels. Most standard file formats store only 24 bits per pixel (8 bits per color channel; 256 levels), so they can't take advantage of the full color depth of a scan— information is lost when data is transferred out of the scanner. But you can retain all the scan information by saving it or transferring it to your image editor as a 48-bit file (16 bits per color channel; 65536 levels). When you do so, the scanner information (typically fewer than 48 bits) is padded with zeros to fill all 48 bits. I strongly recommend doing this if you want the richest prints with the finest tonality. You'll need an image editor that supports 48-bit files. Most don't; Photoshop (the full version, 6.0+, but not Elements) has limited 48-bit support. Picture Window Pro has full 48-bit support.

• TWAIN scanner interface.  An industry standard interface used by Windows to transfer graphic data from scanning devices (flatbed scanners, digital cameras, etc.) directly into applications such as editing programs that can use the data. If the scanner's TWAIN interface and your image editor allow it, you can manipulate and save images in 48 bit color depth. Once you're finished manipulating the image, you may save it as a 24 bit file without loss of quality.

• Infrared (IR) channel dust removal.  Some scanners acquire a separate image with an infrared light beam in order to detect the presence of dust, which responds differently to infrared than it does to visible light. Spots on the main image are filled in by interpolation. Works for all color films except Kodachrome. Does not work for B&W. This can be a very nice feature— I've spent too many hours removing dust spots from HP S20 scans with Picture Window's excellent clone tool. IR dust removal goes by the acronyms Digital ICE (Nikon and Minolta; a trademark of Applied Science Fiction) and FARE (Canon).

• Light source.  This important aspect of scanners is rarely mentioned in the specs. As with enlargers (illustrated on the right), there are two essential types: collimated, i.e., beamed (shown on the left for a condenser enlarger) and diffuse (coming from all directions; shown on the right for a diffusion enlarger). All flatbed scanners have diffuse light sources; most dedicated film scanners have collimated light sources, though they differ in the degree of collimation. A "point source" would be 100% collimated.

.
Collimated light sources have higher contrast when used to scan (or enlarge) Black & White film because silver grains scatter light. Since most of the light entering the film is pointed towards the enlarging lens, scattering causes a loss of light, hence an increase in contrast. This contrast increase is known as the Callier effect. With diffusion light sources, light is entering the film from all directions; as much light is scattered towards the enlarging lens as is lost; hence there is no increase in contrast. Collimated light sources tend to block highlights; diffuse light sources have a longer tonal scale— they are generally preferred for fine B&W printing. The light source has little effect of the contrast of color images because color dyes don't scatter light.
.
There a persistent myth that diffusion light sources produce less sharp and less grainy images than condenser light sources. Not so! In my wet darkroom days I used a condenser enlarger for 35mm Black & White and a diffusion enlarger (a color head) for medium format and color images. The diffusion enlarger was every bit as sharp. If images from diffusion light sources seem less grainy, it is because they are less contrasty. Nevertheless, the myth may persist a while because inexpensive flatbed scanners, which have diffusion light sources, tend to be less sharp than dedicated film scanners. This is due to their optical systems: lenses on inexpensive  flatbed scanners must cover an 8½ wide field; 35mm camera lenses only need to cover a 1.71 inch diagonal. The problem is not the light source.
.
One indisputable advantage of diffusion light sources is that they are less sensitive to film scratches and defects— small bumps and irregularities— on the film surface (usually the backing). That is because scratches and irregularities bend light; as much light is gained from a diffuse light source as is lost. The price of this advantage is rather modest: diffusion light sources are inefficient; only a small fraction of the light reaches the enlarger lens (or the CCD).

Erik de Goederen of the Netherlands markets, the Scanhancer, a device made of a special polymer resembling an ultrafine groundglass screen, that diffuses the highly collimated light source in the Minolta DiMAGE Scan Multi Pro. He claims significant advantages— lower grain and smoother tonal gradations— even with color film. Check the site for availability with newer scanners. I'd like to try one with my CanoScan FS4000US. The Minolta Scan Elite 5400 has a diffuser option, which could be more of an advantage than its high scan PPI.

In the discussion that follows I omit some of the technical details of individual scanners. You can find them in the scanner table, below.

View image galleries . . An excellent opportunity to collect high quality photographic prints and support this website .

Scanner types

35mm film scanners

In July 2001 I purchased the 4000 dpi Canon CanoScan FS4000US 35mm/APS film scanner. Scans have 42 bit precision with Dmax = 3.4 (4.2 in 42-bit mode). Its highly effective FARE infrared channel dust removal (Canon's version of ICE) has minimal effect on image sharpness. It scans more slowly than the other 4000 dpi scanners, but its superior dust removal is likely to make the total scan process faster than the Polaroid. Reviewed by Imaging-resource (6/26/2001), Steves-Digicams (6/23/2001) and Taylor Hively. Unfortunately the hardware doesn't support panoramic scans. According to a photo.net post, there were numerous manufacturing defects (excessive noise, black dots, or "sootiness") in early samples. I heard less about defects in 2002. As of 2005 the FS4000US has been discontinued. Today I'd choose one of the Nikon or Minolta scanners listed in the scanner table, below.

Multipurpose flatbed scanners for 35mm, medium format, and 4x5 (inexpensive)

Dedicated medium format film scanners (expensive)

Heavy metal

Scanner table

All the scanners I've mentioned provide excellent results when used properly. It's more important to learn to use your scanner well than to purchase the latest, greatest model. (This is true of most other equipment, as well.) I discuss the use of scanners— how to get the most out of them— in Making fine prints Part 2: Scanning.

Film scanner links

---

• Imaging Resource scanner reviews   The best overall source of scanner reviews with excellent tutorials. Kept up-to-date.
• Ken Rockwell's Scanner Recommendations — a nice list, with opinions.
• Popular Photography has some scanner reviews, well worth reading. This page also includes links to film, printer and software reviews. Since it's hard to tell if they'll keep it up, here are links to the Canon FS4000US, 7 film scanners and 10 flatbed scanners.
• Tony Sleep's Film Scanner Reviews   More than you wanted to know, but may not be up-to-date. His Filmscanners List archive can be accessed by Thread, Subject or Search. It gets a huge number of posts. Well worth looking at, but don't sign up for the e-mail list unless you want an average of 40 e-mails a day.
• Steve Hoffman's Nature and Scenic Photography   Good information on HP and Nikon scanners.
• VueScan   Highly regarded inexpensive scanner software which works on most film scanners. Updated frequently. I use it for panoramic scans with the HP S20. This photo.net post has some tips and a comparison with SilverFast.
• SilverFast  Scanning software. More professional, flexible and expensive than VueScan.
• Scanning tips by Wayne Fulton. Covers flatbed and film scanners.
• A Primer on Image Histograms and Curves— How to scan by Dane Kosaka.
• Photo.net's forum on scanning (a geek's delight with over 400 threads) and scanner reviews.
• Filmscanner.info  Extremely informative site, in Deutsch. Worth translating.

Scanning film

Images and text copyright (C) 2000-2013 by Norman Koren. Norman Koren lives in Boulder, Colorado, where he worked in developing magnetic recording technology for high capacity data storage systems until 2001. Since 2003 most of his time has been devoted to the development of Imatest. He has been involved with photography since 1964.