# Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?



## cayenne (Nov 8, 2012)

Hello all,

I've been eyeballing getting the Canon 50mm L lens, the f/1.2 one.
Reading the reviews on Amazon.com...I seen references about the lens having a problem with backfocusing.

Can someone explain this to me...what it is, why it happens?

Have others experienced this with this lens? Is it a bug through all of these lenses, or does it happen here and there?

Is this a reason to avoid this lens? If so..why hasn't Canon fixed this?

Thank you in advance,

cayenne


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## neuroanatomist (Nov 8, 2012)

Two words: focus shift.

The 50mm f/1.2L is something of a special case. That lens suffers from a particularly bad focus shift (many lenses have some focus shift, especially, fast primes, but usually not enough to notice). In the case of the 50L, the focus shift is an optical design tradeoff for the undercorrected spherical aberration that gives the lens its legendary creamy bokeh. 

Focus shift is when the focal plane of the lens changes when you change the aperture of the lens. All lenses focus with the aperture wide open, then stop down the aperture to your chosen setting as the shot is taken. In the case of the 50mm f/1.2L, if you select an aperture narrower than f/1.2, down to about f/4, focus shift means that the lens will actually focus on a point that's behind your chosen focal plane. At f/4 or a little narrower, the DoF is deep enough to mask the effect, because by then your chosen focal plane is within the DoF. At very close subject distances, the DoF is shallower, and the effect of focus shift is exaggerated (you may need f/5.6 or even f/8 to get a deep enough DoF to mask the shift).

So, what can you do? Here are some options:


Stop down to f/4 or narrower. But, I'm going to assume that shooting at f/8 is not the ideal solution... 
Shoot at f/1.2. There's no shift if you don't stop down.
Use Live View. Granted, that's not a good option with typical 50/1.2 subjects.
Manual focus with the DoF Preview button pressed. You'd almost certainly need the Eg-S focusing screen instead of the stock screen.
More complex AFMA. You could perform an AFMA at f/2, and you'd get different results than wide open - that adjustment would compensate for the focus shift at f/2, but not be applicable at f/1.6 or f/2.8, for example. So, you'd need to have a list of AFMA values, and change the setting to match the aperture you want to shoot at. Might work if you can pick an aperture for a shoot and stay there. (Side note here: the 1D X can store two AFMA settings for a zoom lens, one for the wide end and one for the long end; in theory, Canon could allow multiple, aperture-dependent AFMA settings for the 50L, which would certainly help with this issue.)
Intentionally front focus. Use an AF point over a feature that's a little bit in front of what you _really_ want to focus on.
Tweak on the fly. The 50L has full-time manual focus, so you can use AF get you close, then turn the MF ring slightly to bring the focal plane forward a little. You'd likely want to be using back-button AF for that, and it would take a fair bit of practice to get it working reliably.

The 50L can deliver amazing shots, but due to the focus shift issue it takes some work and practice to get the most from the lens.


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## Act444 (Nov 8, 2012)

Thanks for the explanation. Even though I'm not the OP, I had the same question and was wondering the same thing.

That's a bummer, really. I think it's the only weather-sealed 50mm lens for the Canon system?


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## RLPhoto (Nov 8, 2012)

cayenne said:


> Hello all,
> 
> I've been eyeballing getting the Canon 50mm L lens, the f/1.2 one.
> Reading the reviews on Amazon.com...I seen references about the lens having a problem with backfocusing.
> ...



This might Help.

http://ramonlperez.tumblr.com/post/34906285033/fast-prime-shoot-out-pt-2-50mm-1-2l-review


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## kbmelb (Nov 8, 2012)

The 50L, I consider an artist lens. Not in the sense you need to be an artist to use it or using it makes you an artist. But in the sense there isn't an exact science to using it or mastering it.

I have good results with mine because I tinker. I tried to AFMA it by the book and I could NOT get a sharp shot out of it.
90% of the time I use an AF point that would line up somewhere inline with the outer third of the frame so I AFMA with one of those points. I do that on a tripod, focusing on a ruler. Then I do some test shots handheld and tinker with the AFMA little by little until I get sharp shots consistently. This may also help compensate for repetitive flaws in my technique.
I find shooting in servo can also help get sharp shots, even if you subjects are stationary.


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## 7enderbender (Nov 8, 2012)

cayenne said:


> Hello all,
> 
> I've been eyeballing getting the Canon 50mm L lens, the f/1.2 one.
> Reading the reviews on Amazon.com...I seen references about the lens having a problem with backfocusing.
> ...



neuroanatomist below - as always - has given you a great technical explanation already. Let me ad my personal experience: I always loved 50mm lenses already back in the film days. The 50 1.4 has been a reference lens for decades and rightly so. In the EF/EOS world, unfortunately, this great lens has been reduced to a consumer grade plastic lens with a stupid AF clutch design that needs to treated like a raw egg. That was the main reason for me to upgrade to the 50L. And by upgrade I first and foremost mean the build quality which to me personal is very important even though I treat this one like a raw egg as well. Go figure.
It is also an upgrade optically for my specific interests. It is much sharper wide open and the contrast is very special. It's a different lens and a different design. All this comes at a price (and I don't mean just the extra cost). My 1.4 in fact was sharper when shooting in the 2.0 or 2.8 range. Not just for brick-wall test shots but also in real life. So I kept it around for a while. I never used it while the 50L rarely is taken off my 5DII. So I sold the 1.4 even though it was a really good copy without any issues.

So despite this little difference when comparing it A to B the 50L is still the clear winner for me and I wouldn't want it changed in any way. It'll probably happen one day. Canon will come up with some (even more) plasticky new 1.4 design with IS and super sharp and everything. Doesn't interest me. I shoot wide open a lot and even stopped down to 1.6, 1.8 or 2.2 or whatever it still delivers stunning results. I've never noticed the back focus issue even though I now that by design it must be there. I've never even played around with the AF compensation settings. It's fine as it is. Just because of the narrow DOF there will be misses. So what? There will always be stunning hits also.

All the noise on various forums about how the 50L is junk because of the terrible back focus and the CA "issues", all the stupid comparisons of different manufacturing years, all the talk how the 5dII is horrid because of the AF and "banding". It's mostly irrelevant in real life. There is always something and you usually can make it work if you know what you want.

Make sure you know why you want this and then go try one out first. It's too expensive to just have it for the sake of having another hunk of glass with a red ring around it. If sharpness is your prime concern and you stop down usually a bit more the 50 1.4 may be a more reasonable choice. Or other manufacturers for that matter. Or other focal lengths such as the 35L or the 135L. "Sharper" but very different use.


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## MarkII (Nov 8, 2012)

neuroanatomist said:


> Focus shift is when the focal plane of the lens changes when you change the aperture of the lens.



Something that I have never understood is why this is not handled by the camera/lens firmware. The focus shift is a deterministic feature of the lens that depends only on aperture and focal distance.

Both of these are known by the AF system, so why is there no automatic compensation?


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## jackreacher (Nov 8, 2012)

7enderbender said:


> All the noise on various forums about how the 50L is junk because of the terrible back focus and the CA "issues", all the stupid comparisons of different manufacturing years, all the talk how the 5dII is horrid because of the AF and "banding". It's mostly irrelevant in real life. There is always something and you usually can make it work if you know what you want.
> 
> Make sure you know why you want this and then go try one out first. It's too expensive to just have it for the sake of having another hunk of glass with a red ring around it. If sharpness is your prime concern and you stop down usually a bit more the 50 1.4 may be a more reasonable choice. Or other manufacturers for that matter. Or other focal lengths such as the 35L or the 135L. "Sharper" but very different use.



I couldn't agree more, well said! I love my 50L despite all the so-called issues


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## Khristo (Nov 8, 2012)

What I don't get is _how_ this focus shift happens.

Wide open and focussed, all the rays passing through all parts of the lens focus (I think this is a pretty sharp lens?) to a sharp point on the sensor plane. Occlude some of the rays by stopping down the iris and the _unoccluded_ rays seem to have their paths changed so they focus off the sensor plane.

Don't see how that could happen - maybe there's something different going on. Can soemone educate me on that?


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## Quasimodo (Nov 8, 2012)

thank you Neuro and KBmelb for your answers. I have had this as one of my most wanted lenses for a long time. I will still get it after what you say, but not with eyes wide shut


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## neuroanatomist (Nov 8, 2012)

Khristo said:


> What I don't get is _how_ this focus shift happens.
> 
> Wide open and focussed, all the rays passing through all parts of the lens focus (I think this is a pretty sharp lens?) to a sharp point on the sensor plane. Occlude some of the rays by stopping down the iris and the _unoccluded_ rays seem to have their paths changed so they focus off the sensor plane.
> 
> Don't see how that could happen - maybe there's something different going on. Can soemone educate me on that?



http://toothwalker.org/optics/spherical.html


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## Eli (Nov 8, 2012)

Quasimodo said:


> thank you Neuro and KBmelb for your answers. I have had this as one of my most wanted lenses for a long time. I will still get it after what you say, but not with eyes wide shut



I was in the same situation, contemplating getting the lens. In the end I bought it, and absolutely LOVE it! Honestly I don't even notice a back focus issue at all when stopping down, but then again I bought the lens to shoot at f1.2, if I wanted to stop down I'd buy a 1.4. 

Just buy it!


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## Zlatko (Nov 9, 2012)

neuroanatomist said:


> Focus shift is when the focal plane of the lens changes when you change the aperture of the lens. All lenses focus with the aperture wide open, then stop down the aperture to your chosen setting as the shot is taken. In the case of the 50mm f/1.2L, if you select an aperture narrower than f/1.2, down to about f/4, focus shift means that the lens will actually focus on a point that's behind your chosen focal plane. At f/4 or a little narrower, the DoF is deep enough to mask the effect, because by then your chosen focal plane is within the DoF. At very close subject distances, the DoF is shallower, and the effect of focus shift is exaggerated (you may need f/5.6 or even f/8 to get a deep enough DoF to mask the shift).


You are correct, but I've been using the 50/1.2L almost since it was introduced and have almost forgotten about the focus shift. It's just not much of an issue. I remember testing for focus shift when I first got the lens, and confirmed that it occurred at about f/2.8 at closer distances. I often shoot at f/2.2 to f/3.5, where it _should_ be a problem, but it isn't because my subjects are usually not that close. 

I could see it being more of an issue for some photographers. I believe Canon could fix this with a floating element. Perhaps an upgrade that we'll see in version II.


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## Mt Spokane Photography (Nov 9, 2012)

Khristo said:


> What I don't get is _how_ this focus shift happens.
> 
> Wide open and focussed, all the rays passing through all parts of the lens focus (I think this is a pretty sharp lens?) to a sharp point on the sensor plane. Occlude some of the rays by stopping down the iris and the _unoccluded_ rays seem to have their paths changed so they focus off the sensor plane.
> 
> Don't see how that could happen - maybe there's something different going on. Can soemone educate me on that?


It occurrs on all lenses, but the construction of the 50mmL and the wide aperture makes it a little more apparent. You cam mitigate it once you know whats happening and why.
"*Focus shift* is a displacement of the sharp plane of focus when the lens is focused wide open, but the image is made with the lens stopped down.
Quite literally, the optimal plane of focus moves, depending on aperture! With every lens I’ve tested to date, the focus moves farther away. For example, if focus at f/1.4 is centered at 1.00 meters, then by f/2.8 it might now be centered at 1.02 meters. That apparently small difference means sparkling-sharp eyes versus not-quite-there eyes—it matters, especially with high-resolution digital cameras.
Focus shift is caused by *spherical aberration* (see vanwalree.com for an excellent technical discussion). Instead of a sharply-focused point of light a spherically aberrated lens produces a point of light with a “halo”. This is visually confusing when focusing by eye (because of the lowered contrast) making it difficult to find optimal focus. It also is confusing to autofocus systems. In spite of these issues, accurate focus can generally be obtained—but it’s no longer accurate when the lens is stopped down."
http://diglloyd.com/articles/Focus/FocusShift.html


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## Daniel Flather (Nov 9, 2012)

It only happens when you stop down, but why pay for f1.2 and stop it down? UNLESS you're doing the ODD thing that needs some increased DOF, but at that point your probably at f8. The 50L is awesome, as Neuro said, its bokeh is smooooth.


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## cayenne (Nov 9, 2012)

Thank you all for the fantastic information. 
I think I understand most of it, but am taking to task to research more based on what I see here.

I'm planning to get two lenses here in the near future.

I'm going to first, get the 70-200 f/2.8 L IS USM II.

I think I'm going to put the 50L on my list for the next one...

I've been following on Creative Live this week, the talks by Sal Cincotta, with his excellent lectures all week on Wedding Photography, and been watching him use the 50L quite a bit, and the resulting pics he's been taking with it...well, some of them are stunning.

So, I'm going to make this my next prime. I need the zoom tele first (he also was shooting with the 70-200L a lot too)....and the next prime will be the 50L.

One question...is there rumor of a new version of the 50L in the works? I'm coming to the understanding that the current design, is getting a bit old....so, wondering if there is a new one coming out in the relatively near future?

Again, thank you all for the excellent information.

If anyone has real world reviews based on their ownership and use of the 50L, please, keep adding them onto this thread...very interesting reading, *especially* any methods or means you use to work around the focusing issues....

C


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## neuroanatomist (Nov 9, 2012)

cayenne said:


> One question...is there rumor of a new version of the 50L in the works? I'm coming to the understanding that the current design, is getting a bit old....so, wondering if there is a new one coming out in the relatively near future?



It's a 2007 lens, which is relatively quite recent. I would not expect an update anytime soon...


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## Mt Spokane Photography (Nov 9, 2012)

neuroanatomist said:


> cayenne said:
> 
> 
> > One question...is there rumor of a new version of the 50L in the works? I'm coming to the understanding that the current design, is getting a bit old....so, wondering if there is a new one coming out in the relatively near future?
> ...


 
+1 "A bit old" means ~20 years for "L" lenses. Development and tooling costs for a upgraded lens is very high, so we only see new versions more frequently for the high volume lenses where the tooling can be paid for in a reasonable time. The big whites were upgraded after 10 years, but the high cost of the re- tooling which is recovered over a relatively small number of units, was added to the price. This creates a bit of a sticker shock.


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## Daniel Flather (Nov 10, 2012)

cayenne said:


> If anyone has real world reviews based on their ownership and use of the 50L, please, keep adding them onto this thread...very interesting reading, *especially* any methods or means you use to work around the focusing issues....
> 
> C



Not much too add, but the 50L is a joy to mount and use. I don't know what body you have, but it seems to be the perfect mate to the 5D3. It's the right size and weight. I never stop the lens down, so I right any focus errors to the thin DOF and user error. I don't know why, but with all my lenses, the 50L is the only one in which never use the hood.


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## CharlieB (Nov 11, 2012)

The sad part.. is Canon could - if they wanted to - program the lens to compensate for any focus shift, based on focus distance and aperture used. Thats something Leica cannot do with their excellent Noctilux... the latter being very persnickety about the positioning of its aperture blades depending on the exact focal length of the lens thats produced - which may vary by some fraction of a mm up to nearly a full mm in focal length. They've gone so far as to use one of several helix pitches, depending on the optics of the particular lens. All that is mechanical. Canon could do it easily in lens firmware... the data flow both ways is there already, they just need to make it happen.


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## mrsfotografie (Nov 11, 2012)

Interestingly yesterday I ran into this 'focus shift' issue as well... on my Samyang 14 mm when I put an AF confirm chip in and went to micro-adjust the AF, only to find that when I calibrated it for f/2.8, all shots at smaller apertures (f/5.6) were definitely OOF. 

In the end I re-calibrated the AF confimation for use at f/5.6 (where I will use the lens most of the time anyway - I use the lens stopped down and AF confirm at f/5.6 for convenience and speed). The calibrated AF confirmation still seems valid at F/4. At larger apertures (f/2.8 ) I need to fine tune the focus by judging the DOF through my EF-S focus screen. 

At smaller apertures (f/8), the shift effect is masked and no need to manual adjust (which wouldn't work anyway because at those apertures there's no way to judge the DOF with a 14 mm lens).

So for the 50 mm I would suggest AFMA for the aperture you use when taking 'snapshots' where there's no time to manually adjust the focus. And use manual focus for the applications where you have more time and DOF is thin.


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## nightbreath (Nov 11, 2012)

mrsfotografie said:


> So for the 50 mm I would suggest AFMA for the aperture you use when taking 'snapshots' where there's no time to manually adjust the focus...


And don't forget to use the focus point you AFMAed your focus for, as 50L has curved focal plane and focus confirmation differs (in ~14 AFMA steps range) throughout focus points.


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## Standard (Nov 11, 2012)

> Is this a reason to avoid this lens? If so..why hasn't Canon fixed this?



Neuro explained it rather well. And I understand wholehearted the concern anyone would have about this lens. It seems there are always chatter about focus shift issues with this specific Canon lens. That said, I just want to say that I have no problem whatsoever with this lens. I use it with my Canon 5D Mark II and focus has never been an issue. Never. One can argued that I am either naive, don't know any better, or too dumb to know what focus shift is. Or one can simply say that I am one of the lucky few that some how got a hold of a perfect specimen. Whatever the reasons are, I can say that I am one happy 50L user...and you will find many of them around.

If you're truly interested in the 50L, my best suggestion for you is to simply purchase it from B&H as they have a great return policy. If you find problems, then simply return it. Spending any more time researching isn't gonna make it easier on your decision. If you truly want to find fault with a lens, you will.


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## EOBeav (Nov 12, 2012)

Almost everything that has been said about focus shift on the 50L could also apply to the 50mm f/1.4. It's amazingly sharp with some great bokeh (although not as creamy-smooth as the 50L), but it does have some quirks you have to work through to get the most out of it. Part of the problem I think is that when you're dealing with apertures like f/1.2 and f/1.4, the DOF is so razor thin that it would be difficult for any AF mechanism to get just right 100% of the time. I tend to have more throw-aways with mine as a result, so I take more snaps of the same comp each time just to make sure. I also make use of the Live View whenever possible. Just my 2/5 of a nickel.


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## Juliuslepetit (Nov 12, 2012)

Aslo take a look at this post from CR

http://www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/


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## cayenne (Nov 12, 2012)

Daniel Flather said:


> cayenne said:
> 
> 
> > If anyone has real world reviews based on their ownership and use of the 50L, please, keep adding them onto this thread...very interesting reading, *especially* any methods or means you use to work around the focusing issues....
> ...



Thanks for all the replies.

I have the 5D3.

I was thinking this 50mm L would also make for an excellent video lens......?


C


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## Quasimodo (Nov 12, 2012)

Juliuslepetit said:


> Aslo take a look at this post from CR
> 
> http://www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/



thanks for a good tip on an interesting article


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## Trisal (May 17, 2013)

I had Mark ii and 50mm 1.2 L lens which was otherwise excellent but very bad back focusing. I was ready to give it up. But then I bought a week ago Mark III and now everything has changed. Usually I get absolutely accurate images with this lens. I bought this new body after I read Karel Donk's blog which you should read.
Read first this:
http://blog.kareldonk.com/canon-ef-50mm-f12-l-defective-by-design/
and after that this:
http://blog.kareldonk.com/canon-eos-5d-mark-iii-review/
especially read what he says about 50 mm lens in the end part of his blog.


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## Pi (May 17, 2013)

The focus shift can only be a problem if you focus too close. I have used two copies of he 50L, and I have never noticed any focus shift problems.


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## neuroanatomist (May 17, 2013)

Pi said:


> The focus shift can only be a problem if you focus too close. I have used two copies of he 50L, and I have never noticed any focus shift problems.



Yes, the problem is more evident at or close to the MFD. But just because that's "too close" for you, doesn't mean that's true for everyone who uses the lens. One could also say, it's only a problem if you shoot too stopped down - Someone who always shoots wide open would also "never notice a problem."


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## kaihp (May 17, 2013)

neuroanatomist said:


> http://toothwalker.org/optics/spherical.html



Thanks for the link, neuro, that explained it so even I could understand it 

This might also explain why I see my 70-200IS MkI needs different AFMA at 200mm MFD than at "reasonable" distance. IIRC, there were 6 AFMA points between the best MFD setting and the "normal" setting.


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## Pi (May 18, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > The focus shift can only be a problem if you focus too close. I have used two copies of he 50L, and I have never noticed any focus shift problems.
> ...



You read too much into my remark.


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## Pi (May 18, 2013)

Dave_NYC said:


> I've seen the phrase "as long as you aren't too close" a few times (or variations of it), and neuro mentioned it is most evident at/near MFD.
> 
> Which for me kind of begs the question: at what distance to subject would the problem become less of an issue (or a total non issue)? Asking, because I frequently have to change from wide open to about f/4~5.6 with subjects about six feet away (3 or more times MFD). I shoot full frame, if that matters.



In my experience, 6 ft is fine. I can focus with my 5D2 with the outer AF points (!) in AI servo, no problems.


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## Deltrus (Jan 8, 2017)

Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!


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## Hector1970 (Jan 9, 2017)

I love my 50 1.2. I don't find the focus shift an issue in reality.
The shallow depth of field is more of an issue but even at that my copy focusses really well.
To The last poster, if the lens is new send it back if you are not happy with it. Make sure you are doing your test with a tripod.


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## Random Orbits (Jan 9, 2017)

Deltrus said:


> Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...
> 
> I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!



AFMA. It should be set to hit the target accurately wide open using the center point. Some camera bodies don't have AFMA, at which point the lens and body should be sent in to be recalibrated.


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## cayenne (Jan 9, 2017)

Random Orbits said:


> Deltrus said:
> 
> 
> > Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...
> ...



Where and to whom at Canon do you send your camera and lenses in to be calibrated?
How much does it cost and how long does it take?

TIA,

cayenne


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## Sharlin (Jan 9, 2017)

cayenne said:


> Where and to whom at Canon do you send your camera and lenses in to be calibrated?
> How much does it cost and how long does it take?



Depends on your country. Not necessarily to "Canon" per se but to a local licensed service shop.


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## neuroanatomist (Jan 9, 2017)

Random Orbits said:


> Deltrus said:
> 
> 
> > Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...
> ...



+1

If backfocus is seen wide open, AFMA is the answer.


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## Random Orbits (Jan 9, 2017)

cayenne said:


> Random Orbits said:
> 
> 
> > Deltrus said:
> ...



Canon. I've never done it personally, although I came close. I had a 24L II that wasn't focusing right, and they fixed it (under warranty). If that didn't work, then I would have had to send in the body as well. I'm guessing that the cost would be a couple hundred USD or more, which is one reason why I avoid bodies that don't have AFMA. It also explained why my 20D + 17-55 f/2.8 IS never was quite right. There was no AFMA on the 20D, so I took more shots to compensate for it. Then I tried a friend's 7D with AFMA dialed in, and I suddenly, the 17-55 shots looked a lot better.


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