Canon 50L - A More Detailed Look at Focus Shift

One of the most common knocks on the 50L from its detractors is the 'focus shift' issue that this lens exhibits when stopped down. I've owned a 50L for a few years and I've never had any issue with focus shift that I could notice, even though I tend to shoot at f/2 quite a bit. I've theorized that perhaps since I don't shoot at MFD really, I stay out of the range, but since I had some time today I decided to look into this with a controlled test.

The setup is simple, 5 flat surfaces set up to allow comparison. Target #3 in the center is where the f/1.2 plane of focus lies. The other targets are #1 (leftmost) minus 1 inch, #2 - minus 1/2 inch, #4 - plus 1/2 inch and #5 - plus 1 inch.

First round of testing was done with the camera 30 inches from the target. I'll show f/1.2 and f/1.6 here in the first post to show the setup and (IMO) that f/1.6 is not definitive (I cannot clearly detect any focus shift).

I think f/2 (next post) is getting a bit more interesting. The target (#3) is still the sharpest, but to my eye #4 is sharper than #2. They should be the same, so the plane of focus has moved back a bit. Note that if #3 and #4 are equally sharp this would mean the plane of focus was halfway between them, about a 1/4 inch shift. I conclude the shift here is about 1/8th of an inch.

And at f/2.5 we have more of the same. #4 is even a bit more caught up, but it still isn't as sharp as #3. So the amount of focus shift is more than 1/8th inch but less than 1/4. Call it 3/16ths.

So what to conclude? I guess the focus shift is a real thing, but I also have some clue why I've not been bothered by it. Here we can see the plane is moving less than 1/4 inch in total, and the target never seems to really be outside a reasonable DOF.

But what about longer ranges? I moved the camera back to 5.5 feet and re-shot. I'll post that after these pictures here.

Here are the other two shots at the short distance, this time f/2 and f/2.5

OK, so I mostly shoot people and therefore I'm hardly ever down in that 0.6 - 1.0 meter range of the 50L that I think of as 'around the MFD'. I probably use this lens the most around 2 meters, so I set up the camera at 5.5 feet from the same group of targets and re-shot.

Results - The first two are f/1.2 and again, f/1.6 which doesn't show much.

At f/2 we see some shift. In this case, #4 is just about as sharp as #3. So to my mind this means that the focus shift is about 1/4 inch.

At f/2.5 we see that #4 has become the sharpest of the five, but we also see that #5 is not quite as sharp as #3. This means the plane is close to #4, but not all the way there. I'd suggest the focus shift is between 1/4 and 1/2 inch, so let's roughly call it 1/3 inch.

So what to conclude? I guess the only surprise here is that the absolute amount of shift is increasing at a longer range. But then, since the DOF is also proportionally larger the shift still never makes for a significant softening of the target.

I guess I can see why I've never felt like focus shift was affecting my shots, but I'm interested in what anyone else sees in this?

Last two shots at 5 feet. f/2 and f/2.5

Great test. This Confirms my assumption... and shows how soft this lens can be at f/1.2 . I also use mine a lot at f/2

As long as your style does not rear the "focus shift" ugliness your golden.

Since we are all unique I can see how some may not see this focus shift. I seldom ever shoot 50mm so I've lost the desire to test anymore 50L's.

Every single 50L I've tested (ALOT!!!!!) I found that virtually all of the copies i've tested (including CPS calibrated so called "perfect copies") all seemed soft. Almost like a typical ok copy of a 24-70Lmk1 wideopen. In the grand scheme of things I did think the 50L was good enough when you do not pixel peep and you put in print.

Even though I'm not a Sigma fanboy. A good ART series 50mm prime has the modern day micro contrast that the 50L does not have. This is where a stopped down 50mm ART looks much nicer overall. The Sigma USB dock can rectify any focus issues in the ART lens unlike the almost impossible calibration that is suppose to eliminate the 50L focus shift.

I found the 5 foot distance even at f/4 would have focused ears instead of tack sharp eyes with a full frame camera.

Nothing is ever perfect........ I stopped pulling the trigger for a Sigma 24-35mm ART f/2 zoom due to brutal back focus on my 5d3. I got this type of disappointment every single time I tested 50L's expecting and assuming I'd get razor tack sharp images and no back focus/focus shift issues.

Canon is long overdue for a 50Lmk2.

AlanU wrote in post #17837232
I found the 5 foot distance even at f/4 would have focused ears instead of tack sharp eyes with a full frame camera.
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A lot of statements such as this prompted me to do the test, actually. On most people, the ears are about 2.5 inches behind the eyes. If I was getting misses of 2.5 inches caused by focus shift, I would have noticed. That's what always puzzled me, the statements about focus shift ruining shots while I was not seeing it.

If you look at my test, you can see that the shift is real, but the degree that the plane of focus is shifting is happening more slowly than the DOF is increasing. I was seeing about 1/3 inch focus shift by f/2.5. I suppose if I had kept going, the lens could shift by as much as 5/8 inch or maybe even 3/4 inch at f/4 and ~5 foot subject distance.

I guess what I'm suggesting is that if you see a situation where ears are in focus and eyes are soft with the 50L, you probably have a focus-miss or backfocus problem. Not focus shift.

I'll agree with what VirtualRain said. This lens is a bit soft wide open and sharpens up by f/2. I think the focus shift issue is real, but not actually an issue. I think the focus shift issue takes the blame for missed shots and otherwise serves as a catch-all concern for people that are uneasy about this lens and it's reputation.

A+++ Writeup! This should be a sticky.

I will also agree, the focal shift does not affect photos in real-world for most users.

I think the focus issue with the 50L has more to do with not being able to be super accurate like the 85L (it doesnt have to be). I dont recall the exact number, but he 85L has a lot more notches in the focus mechanism to be accurate. It has a much longer throw because of it. If you ever really take note of the 50L and how it precisely focuses, you can see that it can jump a bit, which would cause an OOF shot, while the 85, can get really precise.

Love my 50L, hasn't given me one iota of focus shift trouble in the past 5 years of ownership and regular use. Not the sharpest lens, but that's ok because the results it gives are awesome.

Hypothetically, let's say Canon releases the 50mm f/1.2L II with the exact same sharpness performance and "drawing" as the Sigma Art or the new 35L II... who would give up the current 50L for it? Would all of the owners who claim that they love the lens despite it's nuances jump ship for utter sharpness, clarity, no focus shift and rock-solid Canon auto focus? In exchange: no more buttery bokeh and that signature 50L rendering, and probably more size/weight.

If Canon updates the 50L this year, it's going to be fun watching how things unfold! It's hard to say what I would do, such a tough question!

Charlie wrote in post #17837849
I think the focus issue with the 50L has more to do with not being able to be super accurate like the 85L (it doesnt have to be). I dont recall the exact number, but he 85L has a lot more notches in the focus mechanism to be accurate. It has a much longer throw because of it. If you ever really take note of the 50L and how it precisely focuses, you can see that it can jump a bit, which would cause an OOF shot, while the 85, can get really precise.

Perhaps so. Ironically focus accuracy and speed is the main reason I own the 50L. I used to have the 50/1.4 and I found it to lack accuracy and hunt like crazy in low light. I'm not fond of Sigma AF performance either, so the 50L was what was left. And in general I've been quite happy with the 50L for hitting focus.

That's pretty hypothetical, but I'm not married to my 50L. I own it because 24mm and 50mm are the two focal lengths I most want to have a fast prime in, and my opinion is that the 50L is the best option in a 50mm prime mainly because it is the only EOS mount 50mm that I trust for focus performance.

I like the bokeh of the 50L, but I'm not the kind of person who buys lenses for the bokeh. I didn't sell my 50/1.4 for having bad bokeh, even though it is among Canon's worst lenses for bokeh.

^ I sold my 50 f1.4 because of its bad bokeh and I couldn't be happier with my 50L.

My focus is spot on for my needs, any OOF shots are my own user error in movements.

Here is one of my 50L doing its best to smooth out the background.

Photo from InfiniteDivide's gallery.

MatthewK wrote in post #17837882
Love my 50L, hasn't given me one iota of focus shift trouble in the past 5 years of ownership and regular use. Not the sharpest lens, but that's ok because the results it gives are awesome.

Hypothetically, let's say Canon releases the 50mm f/1.2L II with the exact same sharpness performance and "drawing" as the Sigma Art or the new 35L II... who would give up the current 50L for it? Would all of the owners who claim that they love the lens despite it's nuances jump ship for utter sharpness, clarity, no focus shift and rock-solid Canon auto focus? In exchange: no more buttery bokeh and that signature 50L rendering, and probably more size/weight.

If Canon updates the 50L this year, it's going to be fun watching how things unfold! It's hard to say what I would do, such a tough question!

that's interesting, question, and I'de hop for the new 1.2L ii for sure. I got the 50L prior sigma art era, however, I'de like the art more. We really havent seen canon updated any 1.2 lens, so it's hard to say how bad the bokeh will be. It could be good for all we know. I'm shooting the sony 55 these days, and the actual bokeh quality is quite good, better than the 50L, and the lens is razor sharp wide open, and sharper than the 50L at all apertures. I love using the lens for group shots, 50mm I can get fairly decent group shots with low distortion, and razor sharpness across the frame is very nice.

Giving up the 2/3 T-stop, amount of blur, and being slightly longer has been a tough transition TBH, but I'm learning to adopt.

Charlie,

I'm deep into Canon so I just can't jump. I would love to own a A7Rmk2 as the ultimate full frame in one package!!

As far as the 50L is concerned I have seen gorgeous photos as I do not go into pixel peeping mode.

This is where the photographer must determine to try to get extreme shallow dof effect to attempt to make magical moments.

I still think this is where style comes in. I for one may consider such a prime as long as I have a supplemental body to do the bread and butter solid shots. For events photography to assure uncle bob doesn't have soft eyes during a small group shot on a full frame can be even risky at f/5.6. No fast prime is not really necessary.

My old 50 f/1.4 that never gets love or time of day on any of my camera's. It's still a decent sharp lens but nothing like a new Sigma ART 50mm.

It's odd that so many people are into "capturing the moment" but also critical on IQ and sharpness. As of recent more are more aware of the fresh new look of high micro contrast of the new lenses.

Canon must release a new 50L to keep up with the Joneses. When I used the 50L I had to look at my monitor at least 3 feet away and absorb the "capture the moments" admire the blow out subject in bokeh of lushes cream. I am not longer a bokeh junkie like I was in the past. This is where I've really tried to shoot wide angle and do more "capture the moment" with more dof rather than hammering shots at f/1.2.

My test's I've performed cannot be micro adjusted because this is where this would harm the temper "mental" AF as the lens focus shifts. If I tried to correct a 50L with micro adjust it will not be on target when I shoot f/1.2 wideopen. This is where in my "real world" even on print I can see the back focus shift on larger prints.

I'm not a sigma guy but I think using a Docking station to help calibrate a Sigma Art 50mm is a bargain. f/1.4 can still create some nice creamy background transition into a dreamy state.

The Sony alpha series and 55 f/1.8 is such a sick envious combo!! Sony has to step up in the 50mm range!!

I use this lens frequently on a 7D2, with full body views of the model. Must be in the range of 3 meters working distance, so apparently outside MFD. At this working distance I do not see untoward focus shifts with the 50mm f/1.2L.