Film Versus Digital: Which is Best?

Introduction

First draft: 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.

Test Summary

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 Explorer 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 Test Subject

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.

The full frame of the scene is as follows:


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.

Results

An approximately 200% crop from the centre of the D200 image is as follows:


A central crop from the film image viewed with a x2.5 microscope objective is as follows:


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. The central crop is as follows:


Here is a second crop from the edge of the digital image viewed with a x2.5 microscope objective:


Note that I have enlarged the above image to match the film crop.

The corresponding crop from the film image is as follows:


The above crop from the film image after applying Noise Ninja is as follows:


Incidentally the red fringing around the letters at the bottom of the above image are an artifact of the lens i.e. chromatic abberation. The film camera is using the full image circle of the lens, whereas the digital camera is using a crop. Many abberatons such as CA increase with distance from the image centre, and hence they are more apparent at the edges of the frame of the image recorded with a film camera.

Conclusion

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 from an aesthetic point of view the digital image is significantly better than the film image due to the graininess of the latter. Passing the film image through a noise reduction tool, Noise Ninja, significantly improves the quality, but it is still inferior to the digital image.

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.

Other Studies

According to Roger Clark in an online article Fuji Velvia 100 slide film is, in terms of resolution, equivalent to a digital SLR having 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. However the film images were take using a Pentax ZX-30 film camera which does not include mirror lock up, whilst the exposures were typically 1/15", where it is known that MLU is needed to avoid vibrations from the mirror being raised. Whether or not this was an issue is not clear.