Hey everyone. This post is something I’ve wanted to do for a while. I will be demonstrating the effect of changing aperture on depth of field. Because of the many big pictures in the post, I will be ending the summary right here. Be sure to click through to see the demonstration!
When I first got Zeke (Canon EOS 20D), I learned the basics of exposing images by playing with the numbers in the “exposure triangle;” I’d be changing up ISO, shutter speed, and aperture to make the camera’s meter happy. Unfortunately, depth of field would generally only get quick blurbs in the “how to’s” I read, so at first, I didn’t understand why having a smaller/larger f-number would be such a big deal. This, coincidentally, explains why I initially didn’t understand the appeal of, say, Canon’s f/2.8 L zooms or why a prime lens with f/1.4 could make blurred backgrounds easier. Eventually, I wound up getting a Carl Zeiss 50mm ZF Planar f/1.4 for a good price and was blown away by the bokeh (word I didn’t know at the time). Soon, I read more and found toys like depth of field calculators online, like this one:
http://www.dofmaster.com/dofjs.html
However, seeing numbers didn’t really give me an experience…or “sense of scale.” A bit like doing theoretical designs in my chemical engineering classes and THEN seeing a picture of what the equipment would look like. I’d attach some bad-ass pictures of a process flow diagram with a 10,000 gpm light key flow distillation column with a picture of one in real life compared to a person, but I have neither. Slash, I’m not willing to look up stock photos for that stuff.
Regardless, I thought I’d show some pictures that demonstrate how depth of field changes with aperture size for a given focal length. These pictures will ignore composition, shutter speed, ISO, whatever, just so you can see what happens. I purposely picked a busy background/foreground to further emphasize the point being made.
EXIF data for all the photos:
Cameras: Canon EOS 5D Mark II (Taya) and Canon EOS 20D (Zeke)
Lens: Minolta MC Rokkor-PG 58mm f/1.2 adapted for Canon EOS (biggest aperture lens I’ve got)
We’ll keep it to one camera for now and stay with the 5D Mark II. Definitely feel free to plug in the focal length, f-numbers, and camera type into a DoF calculator. The distance to the focal point was like 4 or 5 feet, probably.
f/1.2:
Sorry this isn’t a Leica lens that’s razor sharp when wide open. What we can see here, though, is that the depth of field is quite small. The “WM” in Bowmore was the focal point, and little else is legible besides that label. The sugar canister is passably legible and the Chinese label behind it is sufficiently readable, but both are within 3-5 inches of the focal point (if I had to guess, didn’t measure). What happens when we stop down?
f/2:
More is in focus. The Chinese label is now sharp, and the sugar can is legible. Notice the big yellow text on the red bag in the background can be read, as can the Halls bag in the foreground…if one doesn’t mind pretending they don’t have glasses on. Let’s go to f/2.8.
f/2.8:
Ah yes, that is fuzzily-clearly a Halls bag. The red bag also has words one can figure out. Biggest difference for me is the word “charcoal” that is now visible. Also, in the near foreground, the white box has words and not just blue blurs. Next?
f/4:
Beginning to make out the biggest word on the white box in the foreground, sugar can is definitely sharp now, more on the red bag is clear.
f/5.6
Oh hey, one can start making out the clock in the background! And look, the white box looks like it says “Great Value” on it…I think.
f/8:
Yeah, white box definitely says “Great Value.” Salt shaker and oil spray can in the background are coming into focus. Clock has a decently legible time and the company logo on the stove fan is getting clearer.
f/11:
I’d say pretty much everything in the kitchen is in focus now. Foreground is sharp enough, time is fully legible (but not sharp) and the fan logo is clear enough to read (NuTone), but let’s do the last stop:
f/16
Yeah, everything is in focus…or in focus enough to be distracting.
Ok, let’s switch to the Canon APS-C size sensor on the EOS 20D. Same lens, same f-numbers, but now the distance to subject is different. Plug in 20D, 58mm, the f-numbers, and ~7-8 feet for the distance. Apologies for not nailing the composition to make everything “appear” the same, kinda just eyeballed it. No commentary this time, I’ll just show the results.
f/1.2:
f/2:
f/2.8:
f/4:
f/5.6:
f/8:
f/11:
f/16:
You may be wondering why I did this twice. Well, I know not everyone has a full frame sensor, so I thought it’d be better for people to visualize/utilize the effect if they saw it was done on similar hardware. Plus, it allows me to show the comparison in depth of field for the same lens, similar enough composition, but different sensors! I’ll save my commentary for the very end of these comparison shots.
f/1.2:
f/2:
f/2.8:
f/4:
f/5.6:
f/8:
f/11:
f/16:
Notice anything? If I had perfectly placed Zeke, one SHOULD have seen that, with the same lens and aperture, the crop sensor shows more in focus! If I had to guess, I’d say f/1.2 on the APS-C sensor in Zeke looks more like f/2.8 or f/4 on Taya’s full frame sensor.
Interesting stuff right? Wish I had a comparison like this when I started out. Later I’ll make a post on one reason why manual focus lenses are still awesome. It will also be related to depth of field.
