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016/366: Depth of Field Follies [Uncertain Principles]
I’ve been doing a lot of opining on my blogs of late, and much less science-ing that I would like. So I thought I’d try bringing a little science to the photo-a-day project, by playing around with f-numbers.
I put the camera on the tripod, with my fastest lens (a 50mm f/1.8 prime) and set up an array of SteelyKid’s Lego minifigs to be targets. Then I shot pictures of the scene at different aperture settings spanning the full range I could select. The two extremes are shown here:
Lego minifigs shot with the two extremes of my fastest lens. Top is f/22, bottom f/1.8.
I had to put it on manual focus, otherwise it went nuts trying to decide what to autofocus on, and as you can see, I didn’t get it quite dialed in on the frontmost minifigs. I kind of like the fact that it’s got that one bit of dog hair on the wagon zeroed in perfectly, though. The lens is a bit over 20cm from the table, because the tape measure I have here doesn’t have SI units on it, so I put it about 8 inches away (about the closest it would focus on). Each Lego set-up is 8 inches behind the next.
Because I’m a great big nerd, I took photos all the way through this sequence, and here’s a representative set of f-numbers (I left the exposure time on auto, which means some of the smaller apertures had rather long exposures, and a few of those pictures got some motion blur from me pushing the button; I left those out):
f/22:
f/16:
f/11:
f/8:
f/5.6:
f/4.5:
f/3.5:
f/2.8:
f/1.8:
Kind of impressive how rapidly the depth of field shrinks as you get toward the bottom. The factor-of-2 difference between f/22 and f/11 doesn’t make much difference, but going from f/3.5 to f/1.8, wow. which, you know, is not that surprising on an intellectual numbers-on-paper sort of level– it’s optical physics, after all– but it’s something else to see the effect on the images.
Anyway, there’s your highly nerdy photo-of-the-day. Next time I feel the need to do this, we’ll play with ISO values in the dark basement…
Source: http://scienceblogs.com/principles/2015/09/16/016366-depth-of-field-follies/
