A question I constantly get, and I constantly see being asked online, is ‘how big a print can I get from this camera or that camera?’ Any printing expert can work this out with a pocket calculator and I’ll show you how. The trouble is, it’s wrong. Not because the figures don’t add up, but because we’re looking at this the wrong way.
So first the calculation.
The reasoning is that in order to show all the detail possible you need to print images at a resolution of 300 pixels per inch. Other figures are available, but this is the general consensus.
So let’s say you have a 24-megapixel camera where you know the images you take measure 6,000 pixels by 4,000.
The calculation is very simple. You divide the horizontal image resolution in pixels by 300 to get the width, in inches, of the largest print you can make where every scrap of detail is visible and you don’t start seeing a loss of detail creeping in from blowing up the picture too far.
For a 24-megapixel image, that would mean a print 20 inches across. I probably ought to be using metric measurements in this day and age, but most printing calculations still seem to be based around inches.
That’s not bad, right? I guess this is why the digital world seems to be settling quite happily at sensors of 24 megapixels or so.
If you go up to the 61-megapixel Sony A7R V, you get images 9,500 pixels wide and a theoretical print width of 32 inches. Or, if you’re using a 12-megapixel camera or smartphone, you’ve got images around 4,000 pixels wide and a maximum theoretical print size of around 13 inches.
There are other complications – what about the image height, what happens when you crop or rotate your photos and so on? These will affect the numbers if you’re going to be technical about it.
But let’s not get too technical because you can probably throw all this out of the window.
But why do you make big prints?
Is it so that you can go right up close to them and examine the detail? Why not? There are people (mostly technically-minded photographers) who like to do that. If you can get up close to pictures at an exhibition, you might just do that out of curiosity.
But surely the main reason people make big prints is so that they can look at them from further away. A big print is a statement piece you can admire from a distance. The impact of a big print comes from its size, its composition, its subject matter. Probably not the fine detail.
In fact, if you can’t see 300 pixels per inch of detail from the distance the picture will be viewed from, that whole calculation becomes meaningless. Viewing distance is the factor that print size calculations always leave out.