The first draft of this article appeared online on 11 January 2009.
There are loads of tests online comparing slide films with a digital camera. Unfortunately most use a digital scanner to digitize the film, which opens them to the accusation that the scanner is not getting all of the detail from the film. One way to get around this is to examine the film using a microscope, and that is exactly what I have done.
In this test I compare images of the same scene taken using a digital camera and a film camera. In each case the camera was supported on a Markins M10 ball head and Gitzo GT2531EX Explorer tripod.
A Nikon 85mm F2.8 PC lens was used and photographs taken at various apertures: F5.6, F8 and F11. The aperture was set on the lens, and hence is the real aperture, not the effective one. This is one of Nikon's sharpest lenses with peak performance between F5.6 and F8.
Digital images were taken with a Nikon D200 camera set to ISO 100 and RAW with in-camera sharpening turned off to ensure optimum performance. I examined each image on the rear LCD to verify that the subject was in sharp focus. I also used mirror lock up with a cable release to reduce the effects of vibrations.
Film images were taken with a Nikon F80 camera. I chose to use Fuji Velvia 100 slide film as this is one of the finest grained colour slide films currently available. I took multiple photographs at each aperture, adjusting the focus slightly, to allow for focus errors. The shutter was triggered with a remote release cable. The film was processed by Jessops, and the slides examined with a Meiji 4300H laboratory microscope at various magnifications. I then took photographs through the microscope's photo-port of the enlarged slide image.
In both cases the exposures were about 1" in duration.
The subject consisted of a driving licence on a book case lit by natural light from an adjacent window. As the Nikon D200 has a DX sensor, it was positioned approximately 1.5x further away from the subject than the film camera to achieve the same subject framing.
Note that by virtue of the DX crop sensor, the images taken with the D200 have slightly more than 1 stop greater depth of field at a given aperture. Consequently it is slightly more difficult to achieve an accurate focus with the film camera.
Figure 1: The full frame of the scene.
Note that the above is from the digital camera, but the subject framing is the same in both cases. Note also that I have blacked out the text on my driving licence for obvious reasons.
Figure 2: A crop from the centre of the D200 image enlarged ~200%.
Figure 3: A crop from the centre of the film image viewed with a x2.5 microscope objective.
As the film image has a lot of noise, in the form of graininess, I processed it with Noise Ninja, to see if it could be improved.
Figure 4: A crop from the centre of the film image viewed with a x2.5 microscope objective, processed with Noise Ninja.
Figure 5: A crop from the edge of the D200 image enlarged ~200%.
Figure 6: A crop from the edge of the film image viewed with a x2.5 microscope objective.
Figure 7: A crop from the centre of the film image viewed with a x2.5 microscope objective, processed with Noise Ninja.
Incidentally the red fringing around the letters at the bottom of the above image is chromatic abberation originating in the lens. Many abberrations such as CA increase with distance from the image centre, and hence they are more apparent with full frame cameras.
It is pretty obvious that in terms of resolution there is no clear winner: both are providing about the same amount of detail. However, there is more to image quality than resolution, and the digital image is much smoother due to the absence of grain. Passing the film image through a noise reduction tool, in this case Noise Ninja, significantly reduces the grain.
In practice of course few photographers create a print by photographing a slide through a microscope, and then stitching the photos together. It is simply not practical. The normal approach is to either print directly, using wet chemistry, or to scan the image with a slide scanner, and then print from the digital file. For this reason this test represents an upper limit for what can be achieved using Fuji Velvia 100F slide film.
Incidentally, in case anyone wonders if there is more detail on the film than can be seen with the x2.5 microscope objective, there isn't, apart from defects and grain particles in the emulsion.
Roger Clark in an online article states that Fuji Velvia 100 slide film has a resolution equivalent to a digital SLR with between 12 and 16 MP.
A similar test - and the inspiration for the current work - was performed by Rik Littlefield who compared images taken with a Canon 300D camera (having a 6MP sensor) with images taken on a 200 ASA colour print film. In this case the author found that the 300D image showed significantly more detail than the film, but that the film had significantly greater dynamic range. Note that although the film camera did not have mirror lock up, the author has informed me that he does not believe that mirror vibrations were an issue.