Several essays on this blog have been concerned with the shift from film to digital. For photographers, that’s one of the key issues of the day. Digital photography offers a lot of advantages in terms of ease of use and workflow convenience, but as a relatively young and new technology, it still falls short of film in some critical areas.

One way to think about the performance of any photographic format is to consider the amount of area covered by each pixel in the photograph, either in terms of the original capture or a scanned image from film.

Right off the bat, this is a bit unfair to film in that in entails converting an analog recording of light (the exposed film) to a digital medium. But film is still able to hold its own even with that handicap.

Let’s compare the “stuff per pixel” for three photographic formats – a 6 megapixel digital capture, a 35mm film exposure, and a 6x7 cm medium format exposure.

A 6 megapixel digital camera produces an image file that is roughly 3000 x 2000 pixels in dimension. A 35mm exposure, scanned at 4000 dpi produces a file that is about 5500 x 3700 pixels in size, just over 20 megapixels. Finally, a 6x7 cm medium format frame, scanned at 3200 dpi, produces a file that is approximately 9000 x 7000 pixels in dimension, just over 62 megapixels in size.

(I picked those formats and scan resolutions simply because those are the ones I work with. I love speculation and mental experimentation as much as the next person, but ultimately count myself in the reality based population for most things and like to base comments on actual experience and tests.)

Now let’s assume that you are taking a head and shoulders portrait of person that is 2 x 3 feet in area – the portrait, that is, not the person.

With the six megapixel digital camera, each pixel in this digital capture represents a or square that is about 1/1000th of a foot, or 1/80th of an inch across. This should be more than adequate to capture fine detail in the subject.

With 35mm film, each pixel represents a square little less than 1/150th of an inch across. Even though the film grain interferes with some of this fine detail, this is clearly a leap ahead in terms of resolution.

With a 6x7cm the resolution takes another leap forward. Even scanning at a lower resolution 3200 dpi, a 6x7 exposure results in an image file where each pixel in the headshot captures a square that is 1/250th of an inch in diameter.

Despite this theoretical exercise, a lot of folks probably couldn’t see any difference between a head shot taken with the three difference cameras. Even though the medium format and 35mm exposures have the capacity to capture a lot more information, it really isn’t obvious in an 8x10 or smaller print.

The bottom line is that this kind of shot just does not have a great level of detail to record. Unless you are going to try to count individual hairs on your subject’s head, or blow the image up to billboard size, the benefits of film, even medium format film, are not obvious for this type of shot.

(That said – the one area where the difference can almost always be seen is in the smoothness of the tonal changes in the image. But this is a subtle distinction.)

On the flip side, assume you are taking a shot of a sweeping landscape, full of fine detail, and are using a wide angle lens to capture an area 100 yards across.

In this case, each pixel in the 6 megapixel digital exposure is sampling an area that is 1/10th of a foot – or 1.2 inches - square. The fine detail in this shot will clearly be compromised.

One the other hand, a 35mm film exposure scanned at 4000 dpi will result in a file where each pixel is about 2/3rds of an inch across. And a 6x7 cm medium format shot, scanned at 3200 dpi, results in a file where each pixel samples an area 0.4 inches across.

Obviously, in this kind of situation, the increased resolution of film is really an advantage. Since there is enough detail in the shot to for the viewer to see, the advantages of film for this kind of shot become clear.

Now consider the other end of the spectrum – an extreme macro, like a snow crystal shot. With snow flake photography I’m typically shooting at 4 to 8 times life sized on the film / sensor plane. That means that the projected image of the subject – in this case a snow crystal that may be 1/8th to 1/16th of an inch in size – is blown up 4 to 8 times that size.

In this case, with the 6 megapixel digital camera, each pixel represents a really minute area of the snow crystal – something on the order of a square 1/4000th to 1/8000th of an inch across! 35m film resolves even more detail, but as already noted, the interference of the film grain and lower acutance of film results in an inferior image. And so far, I’ve haven’t come up with a way to magnify a snow crystal big enough to take advantage of medium format film – so far now I’ll leave that in the ‘impractical’ column.

So what does this boil down to? If you think about your shots in terms of “stuff per pixel” you can quickly determine when you are better off shooting digital, 35mm, or medium format. You can also figure out when a lower megapixel camera will work fine, and when you need step up to a higher megapixel platform. Basically, if you think about how small the relevant details in your shot are, and how those details will relate to the total area you are exposing, it’s simple and intuitive to see when the higher resolution of film is needed, and where digital is better able to do the job.