35mm, Medium Format, DPI; how good is good enough?

There was a thread on a forum yesterday where a user of a Canon 20D was arguing that no one needed medium format (or for that matter anything of higher resolution) because his 20D did everything that was needed. Lots of people bandied about opinion but no one actually gave any physical reasons why what appears to be an idiotic statement was actually wrong.

Before deciding if anything is good enough, you have to define good enough for what. I did a quick search and came up with the following standard print specification in terms of DPI for different print media:

a) Web: 72dpi
b) Colour newspaper ad: 150 to 200 dpi
c) Glossy magazine: 266 to 300 dpi
d) High end printer: 300dpi
e) High-end coffee-table book using stochastic screening: up to 350 dpi.
f) human eye resolution (high contrast) : 600+dpi

Let’s take a look at what the 20D offers in terms of image. The sensor has a RAW native resolution of 3504 × 2336. If we convert this into the image size created for various print resolutions we get

72dpi - 48”x32”
200dpi - 17”x11”
300dpi - 11”x7”
350dpi - 10”x6”
600dpi - 6”x4”

So this sets the maximum image size we can achieve for any given resolution. You can see that for a good quality print the maximum size you can print is 11x7.

Let’s assume that you are going to do your own printing and have an A4 printer which will create prints of 12”x8”. We can see that we will get just under 300dpi. This is very good and anyone would be happy with that. Try A3+ at 19”x13” and you have a resolution of 184dpi which is passable if you’re not too close. If you have a larger printer such as an Epson Stylus Pro 7800 (A2) which produces 24” on the narrow side you have a resolution of 97dpi. This is well below the resolution of a newspaper colour print and I doubt if anyone would be happy with it. We are, after all, trying to produce high quality photographs.

If we bump the quality a little and go to the 5D (4368 x 2912) we get the following resolutions: A4=364, A3+=229, A2=121. This is good for A4 and A3+ but poor for larger sizes.

We now move to consider medium format film and digital. The H2D (22mp) produces a resolution of 4080x5440. This gives the DPI for our prints of A4=453, A3+=286, A2=170. We can go to 39mp (5412x7216) which gives an image that’s 24x18@300dpi. So that’s about £20000 of camera to get 300dpi at A2 (ouch).

Let’s take a look at medium format film. If you take a good film scanner you will scan at round 3200dpi which will give a scan with a resolution of 7559x7559 for a 6x6 film. This exceeds the resolution of a £20000 camera and for large prints will produce outstanding results.

So at the end of the day the 20D is a fine camera and if you only want to print small images its fine for the job. However, there is no way that it can compete with a medium format if you want to print above A4, and for a large format printer the camera would be next to useless. For the ultimate in quality you would want a fine grained film scanned at a very high resolution.

Maybe its time for me to consider a medium format film camera, a developing tank and a good scanner!

The photo is of beautiful Linx shot last month.