Two weeks back I wrote about the gradual demise of dedicated film scanners and how, in the future, that is going to make it increasingly difficult, if not impossible, to conveniently scan film positives and negatives for digital printing. Many readers expressed interest in the idea of using a good digital camera in lieu of a dedicated film scanner; a few had even tried.
This is not an impossible approach. Doing it well requires knowledge and skill. I think it may prove an entirely workable alternative to film scanners in the future, so long as people remember it is a skilled craft, very much the same way good enlarging in the darkroom is. It's something you can do well and reliably with the right equipment and with practice, not without.
Now, if you don't care about doing it really well, and many of you don't (for good reasons; I do understand) then don't even bother with this approach. A flatbed scanner, even one a generation old, is going to do this better and a lot more conveniently. Alternatively, there are plenty of mail-order outfits that charge circa a dollar a scan that will easily beat a thrown-together rig.
That's my most basic recommendation—either do camera captures well or don't do them at all.
(A slight pause, while half the class gets up and leaves the room.)
First, uniformity of illumination is important. It's not as easy to achieve as one might imagine. The best way to get a really uniform and controllable light source with good off-axis characteristics is to buy a used diffusion color enlarger head. They're cheap these days. Turn it upside down and it becomes your light table. Problem solved.
Color accuracy and tonal range are not major problems if you're working from negatives. Even a very contrasty color or black and white negative rarely hits a density range of 2.4 (8 stops). Any digital camera you have that you consider of high enough quality for this work will have more than sufficient exposure range at its base ISO.
Slides are a more difficult problem. At a minimum you're dealing with density ranges of 3.0 and the most contrasty of them go above 4.0 (10–13 stops). At the low end of that scale, quite a few cameras are satisfactory; at the high-end, very few. HDR might be the solution, but it's rarely invoked to produce a perfectly linear tone scale, and that's an absolute must for accurate film scanning (in case it's not obvious, you better be working in Raw when you scan film). I don't know if the HDR converters out there are capable of doing this, but I'll bet one of our readers does.
Then there's resolution. That's the real hard part. There are four major components to that: film flatness, camera/lens/film alignment, camera resolution, and lens quality. I'll talk about the first two now; the second two will have to wait until next week.
No matter how good your camera and lens are, they aren't going to perform very well if the film isn't actually in the plane of focus. Film flatness is the first issue. At 2400 PPI, 1:1 magnification, your depth of field is really, really tiny. A tenth of a millimeter matters. Film usually doesn't stay that flat without some kind of tensioning mount or glass mount. Anyone who's done film scanning knows how much difference in sharpness there is between a scan done using a glass carrier versus an open one. The same thing is going to happen on your copy rig.
That 0.1 mm tolerance doesn't apply just to film flexure, it also applies to the alignment of the film plane. Your camera's sensor, the lens, and the film need to be really, really parallel. I mean really parallel. You've got about a quarter degree of slop, that's it. Any more than that and you're going to notice in your photos that one side of the frame or the other, or both, are less sharp than the center.
So how do you tell if you've got an alignment problem, as opposed to a curvature of field or edge sharpness problem in your lens? If it's a problem with the lens, the lack of sharpness will be roughly radially symmetric; all four corners will be similarly unsharp. If your unsharpness is caused by your film plane being tilted, there will be a line at some angle where the image is uniformly sharp, edge to edge, and it will be maximally unsharp at the edges at right angles to that.
Next week I'll wrap this up with the camera and lens discussion.
Ctein's weekly photo-tech column appears on TOP on Wednesdays.
ADDENDUM from Ctein: OK, I thought my position on this was pretty clear from my articles and comments over the last two columns. Apparently not. So here it is, with no minced words:
I think digitizing film positives and negatives by photographing them with a digital camera is a bad idea. Most people will get worse results than they would with a reasonably-priced flatbed scanner. Ninety-nine-plus percent of them will get worse results than they would with a decent film scanner or with sending their film to a dollar-a-scan service. I have not been encouraging anyone to do this. Quite the opposite. My hope is to discourage people from wasting their time even trying.
I'm writing this two-part article because (a) a lot of people seemed interested in trying this approach and (b) I want to let them know exactly what they're in for and how much work they'll have. I am hoping this will dissuade many from even trying. For the rest, I'm hoping it will dispel any illusions that (to be blunt) half-assed results can compare in any way to doing this with a scanner or a service.
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Original contents copyright 2011 by Michael C. Johnston and/or the bylined author. All Rights Reserved.
Featured Comment by Hugh Crawford: "The dead simple way to align an SLR camera and the work is to put a mirror where the work is. If the reflection of the camera lens is in the center of the image, then the work, lens, and camera are aligned. (Assuming that the lens and sensor are aligned. View cameras have a whole other layer of stuff to mess with.) Perhaps the reflection of the lens in the film or carrier glass might serve as well as a reflection in the mirror ?
"The mirror thing always seemed obvious to me but some people I do copy work for seem surprised.
"Additionally, I find that longer focal length lenses are much more forgiving of issues of film flatness.
"If you live in the big city, you have the choice of mounting your copy rig on something really heavy like say a cubic yard of concrete or using strobes as the light source. I find that no matter how rigid I have things, strobe lighting is sharper, and a little short-duration shoe flash is sharper than a long-duration studio flash.
"Also, you should consider that an older color head dissipates a lot of heat either by convection or with fans, usually through vents on the top. A lot of the old color heads used gravity to keep the mixing box in place, or to make the filters follow the cams. I don't think old Beseler Dicro head would work upside down, and I'm pretty sure my Durst would catch on fire if I left it on for more than a half hour upside down. For what it's worth, I tried using an old Aristo Graphlarger cold light head as a light source for copying negatives, but the tubes flicker at 120Hz and as a result I got stripes if I was shooting faster than 1/60th of a second.
"The little Omega and Beseler enlargers for 120 film were both advertised as being suitable for turning into copy cameras*. I even have an attachment to bolt a T adapter in place of the negative carrier on a B66 around here somewhere, so maybe their heads would work."
[*Several of the Saunders/LPLs, too —Mike]
Featured Comment by Bob Rosinsky: "I use a 39-MP multi-shot back, a 26mm tube, a 120mm macro lens, and a backlit film stage (illuminated with an Elinchrom Quadra) for copy work. At ƒ/16, I am able to see sharp grain across the field (35mm up to 4x5-inch negs). I use negative carriers from an ancient Omega enlarger to hold the film in place. I avoid glass. I think it introduces too many problems."
Featured Comment by Andrew Molitor: "I use the monitor of my iMac as a light source. Set the desktop background to pure white, clear the icons off a sufficiently large area of it, and go from there. I make sure it's well back from the focal plane, which should cover any minor variations (I hope). The results are at least OK, probably pretty close to the camera limits (which isn't saying much—it's crop sensor, and I use a medium good macro lens)."
Featured Comment by jz: "Your column might end up being the inspiration I needed to get out the old Beseler slide duplicator with a Rodenstock Apo-Rodagon R 75mm lens. I should have figured this out a long time ago."
Featured Comment by Aaron Campbell: "For 35mm scans simply get a Plustek 7600 and forget about do-it-yourself solutions. [Plustek in introducing a new 120 scanner too, according to this link (supplied by mani in an earlier comment). —Ed.] It also doesn't make sense to complain about film scanners disappearing and then not even buying one that is in production and delivering pretty good results. [The question was just, 'IF you were going to do that, how would you?' It's not a recommended technique per se. —Ed.] I recommend the Plustek 7600 for any 35mm photographer. (The only thing that sucks about it is manual frame advance. But then, also one less part to break so maybe a good thing in the end....)"
Featured Comment by Sara Piazza: "I recently was able to get my (15 year-old) Nikon CoolScan up and running again via a special Firewire I had to purchase to replace the original SCSI connection, and by installing VueScan (which makes the scanner compatible with newer OSs). I'm excited to be scanning old B&W negs, some of which I never got around to making contact sheets for, seeing some of these images for the first time—many great B&Ws of my young family. Very interesting post. Thank you."
Featured Comment by Kristian: "Here is my solution for scanning 6x6:
"I have since then flipped the box up, and put the negatives between glass to obtain a flat negative. So what is it? Cardboard box coated inside with a sort of glossy white paper, and a flash attached. Tried regular paper at first, but then the papers fibers would shine through and transfer to the inage in some way. It may not be perfect, but works fine for those few times I develop meduim format. Here's an example:
Question from davide: "Can anyone recommend a resource to explain the relationship between density range and dynamic range? Ctein said that B&W/color negatives had a density range of around 8 stops while slides were 10–13. I had been of the impression that negatives had a wider dynamic range than slides in general and that some had a much wider dynamic range than 8 stops in particular. Any explanation would be appreciated."
Ctein replies: Density range is the brightness range in the film. It is usually expressed in log units—a density range of 1.0 equals a factor of ten. A density range of 0.3 equals a factor of two. The camera's exposure range, usually expressed in stops (factors of two) has to be large enough to be able to capture the density range of the film. The exposure range of the film (the range of subject brightnesses it can record) has nothing to do with its density range, so you don't have to worry about that. Hope this cleared things up.