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

[mrsfotografie]

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.

 

[nightbreath]

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.

 

[Standard]

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.

 

[EOBeav]

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.

 

[Juliuslepetit]

Aslo take a look at this post from CR

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

 

[cayenne]

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.

Thanks for all the replies.

I have the 5D3.

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


C

 

[Quasimodo]

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

 

[Trisal]

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.

 

[Pi]

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.

 

[Loswr]

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."

 

[kaihp]

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.

 

[Pi]

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."

You read too much into my remark.

 

[Pi]

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.

 

[Deltrus]

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!

 

[Hector1970]

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.

 

[Random Orbits]

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.

 

[cayenne]

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.

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

 

[Sharlin]

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.

 

[Loswr]

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.

+1

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

 

[Random Orbits]

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.

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

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.