What is a Drum Scan?
A drum scanner uses photomultiplier tube (PMT) technology to convert the light passing through the film into very sensitive electric signals. These RGB signals are then "multiplied" and converted to a digital file resulting in sharp, geometrically accurate, colourful scans devoid of digital noise and flare. They scan a single pixel at a time, thus avoiding the common problems associated with other scanners while bringing out the full dynamic range of the film and can "see" details at the grain level. Since there are no lens or mirrors forming a picture in the optical path, the images are very clean with a three-dimensional filmic feel. And isn't that why you are shooting film in the first place?
Lens-based scanners like the CCD and CMOS capture devices currently available, introduce certain artifacts like chromatic aberration (commonly known as colour fringing or purple fringing), digital noise in the shadows, low highlight retention and overall softer scans. With good care you can still get quite usable files, but you must understand the given limitations of such systems and set out to ensure you are getting the most you can from it. Drum scanners demand good technique as well, but by nature of design, they will typically churn out better, and larger scans due to the inherent technology built into them.
The drum scanners that seemed to be getting the best overall, consistent performance time and again were those made by Heidelberg/Linotype-Hell in Kiel, Germany. These units dominated the commercial prepress printing industry at one time. Quality books and magazines like National Geographic entrusted them. Museums still use them for proper archival work. Wouldn't you want to treat your best films to this same level of respect?
That is why I decided to purchase a Heidelberg Primescan D7100 from Hudson Grafik Services.
Built tough and precise, weighing in at 550 lbs, it can scan film all the way up to 12"x16" and comes with two drums for increased productivity.
How does it work?
1) Films are wet-mounted in fluid onto a clear acrylic drum on a mounting station outside of the scanner.
2) The film becomes sandwiched between the drum and a clear piece of optical grade mylar, resulting in perfect edge to edge sharpness.
3) The drum is placed into the scanner where it spins upwards of 2000 rpm depending on the quality settings of the final scan.
3) Each pixel is recorded separately by the scanning head via a set of analog PMTs in Red, Green and Blue channels.
4) The PMT information is converted to a digital file.
5) The film is removed from the drum, drying almost instantly without any residue, and returned to its original sleeve or mount.
At left is the full-frame reception photo I took for my brother's wedding. It was shot on Kodak Ektar 100 with a Pentax 67II.
Below are two detail crops at 100%. This is from a 4K scan which yields a 30"x37" print. Look at the stitch detail in the jacket fabric, the metal zipper, the velcro, her fine strands of hair, the skin of her hand, the ring. You can almost count the diamonds!
I can spend all day re-visiting details that went un-noticed before. This is the mark of a good drum scan. They also happen to be very unforgiving scans. So be sure that you are representing your best work. In fact, once you get your first drum scan you'll see that you'll quickly be paying more attention to your technique out in the field. A good drum scan deserves it.
For comparison a scan from the Epson V850 is below. This is the best I can muster but at some point the limitations of the hardware get in the way. Fine detail is rubbed out and it feels like someone put a heavy diffusion filter over the lens.