# Good or lucky copy of the 50L?



## VitorMachado (Oct 18, 2013)

Today I received my copy of the 50L and I was very impressed with it's sharpness. Like all of you may know, this lens has a reputation for back-focusing. Fortunately for me though, my copy seems to be tack sharp. Something I'd like to know is: Does Canon fix issues as they go and continue to make production of that same exact lens with these improvements or do they leave it alone until a new model undergoes production? I'm very satisfied with the fact that I received a good copy, or Canon has fixed this problem.

Also, this is my first f/1.2 lens and the DOF is indeed extremely delicate, but not as tough to shoot as many say.


----------



## chilledXpress (Oct 18, 2013)

Many like to complain about this lens but on the 5D3 or 1DX, at least for me, it's razor sharp and always impressive.




Lovers at Filoli… [/url] by David.K.M, on SmugMug


----------



## Pi (Oct 18, 2013)

It is hard to say what Canon does. I have experience with two copies, the second one was slightly sharper but they both focused well. The focus shift is much more pronounced when focusing very close. Since I never do that (wide open), no problems, even with the outer AF points on the lowly 5D2.


----------



## Mt Spokane Photography (Oct 18, 2013)

I have not heard of a reputation for back focusing. Its a special lens and requires some knowledge as to how to use it. Most of the complaints come from users who try to focus and recompose at wide apertures.

It is not the sharpest lens around, but its not bad either.


----------



## mememe (Oct 18, 2013)

When used at 1.2 focus is fine. Stop it down and work at close distance. 

Or mount your cam on a tripod. Focus in close distance. Set to MF and take some images at different apertures. You will see how the sharpness is moving away. And if it's bad it will move so far that your first focussed spot is out of focus.


----------



## BL (Oct 18, 2013)

VitorMachado said:


> Today I received my copy of the 50L and I was very impressed with it's sharpness. Like all of you may know, this lens has a reputation for back-focusing.



back focussing was something others have experienced when stopped down, not wide open


----------



## florianbieler.de (Oct 18, 2013)

I owned a 2012 copy of that lens which did not front or back focus at any distance or aperture, but I just wasn't satisfied with the image quality for the price tag the lens wears, it is just not worth four digits, especially when you peek at the Sigma 35 1.4 and how sharp that is wide open. Despite it's great build quality, haptics and bokehlicious look, I would _not_ recommend the 50L to anyone, only if you got the money and don't know where to put it.


----------



## neuroanatomist (Oct 18, 2013)

Pi said:


> The focus shift is much more pronounced when focusing very close. Since I never do that (*wide open*)



To clarify, focus shift does not occur if the aperture is wide open, it only occurs when the lens is stopped down.




mememe said:


> When used at 1.2 focus is fine. Stop it down and work at close distance.
> 
> Or mount your cam on a tripod. Focus in close distance. Set to MF and take some images at different apertures. You will see how the sharpness is moving away. And if it's bad it will move so far that your first focussed spot is out of focus.



Exactly - that's focus shift. It occurs in the 50L due to the optical design of the lens, it's not something that Canon can 'fix' without updating the lens....and even then, it's questionable if some would call it a fix. Lens design is always about tradeoffs, and in the case of the 50L, Canon's design intentionally undercorrects the spherical aberration to produce the creamy bokeh for which the lens is renowned, but focus shift is one consequence of that design.


----------



## Pi (Oct 19, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > The focus shift is much more pronounced when focusing very close. Since I never do that (*wide open*)
> ...



Correct.

EDIT: To be even more precise, the lens is focused at f/2.8 with the high precision sensors, probably calibrated (or MA'd) to focus well wide open, and then shifts from there.


----------



## neuroanatomist (Oct 19, 2013)

Pi said:


> EDIT: To be even more precise, the lens is focused at f/2.8 with the high precision sensors, probably calibrated (or MA'd) to focus well wide open, and then shifts from there.



To be even more precisely and accurately precise, AF is performed wide open at f/1.2, even though the sensor lines are spaced for f/2.8 (assuming a high-precision point is in use). Assuming the calibration is correct, accurate focus is achieved (with the specified precision of 1/3 of the depth of focus with the lens at max aperture, or within 1 depth of focus for a standard precision AF point). Then, if an aperture narrower than f/1.2 is selected, just before the exposure begins, the iris diaphragm closes down to the selected aperture, blocking the light rays further from the center of the optical axis. That shifts the plane of focus progressively, the more the aperture is closed down. However, DoF is also getting deeper as the aperture is narrowed, and the deeper DoF eventually overcomes the focus shift, masking the backfocus by bringing the shifted focal plane within the DoF. Focus shift still occurs with distant subjects, but there again, it's masked by deeper DoF. Since the DoF is thinner with close subjects, that's where the effect of focus shift is observed.


----------



## drmikeinpdx (Oct 19, 2013)

My Sigma 50mm 1.4 has a bit of focus shift. That makes it a bit tricky to do micro adjustments. Do I set it for accurate focus wide open or one stop down where I usually use it? Hmmm.....

The only shift I could find was between 1.4 and 2.0, after that the depth of field overwhelmed it. Pretty much what Neuro said.


----------



## Pi (Oct 19, 2013)

neuroanatomist said:


> Pi said:
> 
> 
> > EDIT: To be even more precise, the lens is focused at f/2.8 with the high precision sensors, probably calibrated (or MA'd) to focus well wide open, and then shifts from there.
> ...



That is what I meant.


----------



## alexturton (Oct 19, 2013)

in respect of focus shift comments.... who buys a f1.2 lens to stop down?


----------



## neuroanatomist (Oct 19, 2013)

alexturton said:


> in respect of focus shift comments.... who buys a f1.2 lens to stop down?



Sometimes it's desirable to have more than three eyelashes in focus. I usually shoot my 85/1.2L II at f/1.6-2.2 (although I did shoot wide open on my 7D).


----------



## wsgroves (Oct 19, 2013)

I have been contemplating picking one of these up.
You are saying if you plan to use it stopped down (for various reasons), do not?


----------



## neuroanatomist (Oct 19, 2013)

wsgroves said:


> I have been contemplating picking one of these up.
> You are saying if you plan to use it stopped down (for various reasons), do not?



With very close subjects (near MFD), you can learn to manually tweak focus to compensate. With more distant subjects, it's not much of an issue.


----------



## wsgroves (Oct 19, 2013)

Ah ok thanks. I probably wouldnt be at MFD anyways.


----------



## Dylan777 (Oct 20, 2013)

Congrats on your new toy.

My 50L is good at f1.2, but MUCH MUCH better at f1.6


----------

