Who says you can't review lenses that you don't own? This episode of Scientography is brought to you in part by the madness of a photographer with gear lust.
So, depth of field is defined as the portion of an image that is within tolerances enough to be considered "in focus". This is a questionable definition, as everyone's tolerances are different. Maybe you're very picky, maybe you could care less. Either way, as long as we base all of our calculations on the same Circle of Confusion, we should be fine for scientific purposes.
Oh, I didn't say what this is all about? I'm going to be comparing every full-frame lens that Canon has on their website to rank them in terms of how thin the DoF is (and, arguably, the amount of bokeh).
So, I set off on a quest to learn more about lenses.
It's easy to say that a 200mm f/2.8 lens will provide a thinner DoF than a 100mm f/2.8 lens, provided you're standing in the same spot. This is because your lens' magnification increases when you increase the focal length but not the distance between you and the subject.
After looking up a few formulas and punching in a few numbers, I wound up with an excel spreadsheet that compares every current Canon lens' DoF at Minimum Focusing Distance, 3 Meters, and at 1:20 Magnification.
The 1:20 Magnification column was the one I was most interested in, since an equal magnification means as equal of an image as you're going to get, regardless of focal length. In order to find the 1:20 magnification DoF, I had to first calculate how far away from the subject you'd have to be in order to achieve this, then I calculated DoF from there. Anyways, I'll get down to the results:
I'll be breaking these down into categories.
1:20 Magnification, Open Class (Any Lens):
- 85mm f/1.2L II USM - 2.9233cm @ 5.856 feet
- 50mm f/1.2L II USM - 2.9237cm @ 3.444 feet
- 50mm f/1.4 USM - 3.4112cm @ 3.444 feet
- 35mm f/1.4L USM - 3.4122cm @ 2.411 feet
- 24mm f/1.4L II USM - 3.4143cm @ 1.653 feet
Wow, so the 50mm f/1.4 USM has the #3 thinnest DoF of any of Canon's current lenses @ 1:20 magnification. Talk about bang for your buck! The 50/1.4 is the ONLY lens in the top 5 that costs less than $1000. BANG!
MFD, Primes (Non-Macro)
- 24mm f/1.4L II USM - 0.5mm @ 0.077m (77mm)
- 135mm f/2L USM - 4.3mm @ 0.9m
- 300mm f/4L IS USM - 4.64mm @ 1.5m
- 35mm f/2 IS USM - 4.65mm @ 0.24m
- 50mm f/1.2L USM - 5.0mm @ 0.45m
Anyone want to point out why the 85mm isn't on this list with it's super thin DoF? It's because the 85mm f/1.2L II has a MFD of 0.95 meters. That's a long way away!
Anyways, here's my findings as neatly as I can put them for some of the more considered lenses for bokeh:
35mm f/1.4L USM:
MFD: 5.27mm @ 0.3m
3m: 59.53cm @ 3m
1:20 Mag: 3.41cm @ 2.411'
50mm f/1.2L USM:
MFD: 5.0mm @ 0.45m
3m: 24.68cm @ 3m
1:20 Mag: 2.92cm @ 3.444'
85mm f/1.2L II USM:
MFD: 7.91mm @ 0.95m
3m: 8.425cm @ 3m
1:20 Mag: 2.92cm @ 5.856'
135mm f/2L USM:
MFD: 4.38mm @ 0.9m
3m: 5.471cm @ 3m
1:20 Mag: 4.87cm @ 9.301'
I'll upload the spreadsheet to Google Docs when I get a chance so everyone can check out the findings themselves!
In the meantime, if you'd like to know about the results of a specific lens, let me know in the comments and I'll give you the info. I didn't include zooms in the top 5 lists because Canon only publishes the lowest minimum focusing distance, which changes as you zoom in, which adequately shat on my formulas. I'm sorry, but I don't think that the 28-135mm f/3.5-5.6 does 3.2mm DoF @ 135mm, f/5.6, 0.5 meters. It just doesn't. That's thinner than the fastest primes out there. Sorry, but I don't buy it.