Aperture, depth of field, Bokeh and learning aids

Aperture, depth of field, Bokeh and learning aids

Modern cameras are like iPads. They will do precisely what you want, fast and with precision. But you really can’t see how the cogs work. This may be one reason why so many photography courses require students to use film – and a reason why the old Zenith cameras that many of my friends had in the Seventies left their owners with a profound appreciation of technical issues. You can see the effect that aperture has on depth of field as you stop down the lens just before releasing the shutter: you can open the back and watch the shutter working.



My pictures illustrate what’s happening: the images of the Zenith with its lens wide open, stopped all the way down to f/16, and at f/5.6 show the aperture blades in use, and give a pretty graphic idea of the effect on the image – full aperture of f/2 lets a lot of light through to the film or sensor. They also show how dusty the lens is inside: I mention this because it has very little effect on performance. A bit of dust in a secondhand lens may be a reason it’s not ‘mint’ and will sell cheaper, but that simply makes it a bargain…



And the iris pictures, shot in my garden (and in my dressing gown and slippers). The one at the top is the ‘Bokeh shot’ – taken with the Helios 58mm f/2 lens from the Zenith at full aperture on a Sony Alpha 7R II. A little below it, and very little different (although maybe the out-of-focus areas are a little smoother) is a shot taken with a Samyang 45mm f/1.8 lens at full bore. Both shots are at the minimum focussing distance for the lenses.



Here is a picture with the Helios at f/5.6: the background is still well out of focus, but there’s much more of the iris sharp. At the bottom of the article, f/16 with the Helios reveals the glamorous back of the garage…



So you have a choice: use a lens wide open for those glowing and vague backgrounds – but be prepared to choose which part of your subject will be sharp. Stop down a bit to ease things, though you will need more care with backgrounds. And stop right down to bring in as much background detail as you can. The differences will all be less pronounced if you step back a bit from your minimum focus distance.



Play with it, the same way that you can with an unloaded Zenith. (And if you’ve got a Zenith, get it out and play with the controls…)