Canon EF 50mm f/1.2L USM

agphotography wrote in post #11035952
Mike,

I Have had a UV, a UX and now a UY (2010). Every copy I have tried exhibits some kind of focus shift. It's how the lens was designed. The molded rear element causes the shift, there's no escaping that. I'm not saying it's so bad that the lens is unusable, but when you use anything other than f/1.2 the shift will happen when you are within 6' of the subject. Focus shift is a very different issue from front or back focus.

Okay, so that confirms that the problem still exists, which is a shame because now we can't say for sure that they've sorted out the problem, which is how things were looking previously.

I'm well aware of the ins and outs of the focus shift problem, why it happens, how to work round it and the differences between it and simple front/back focusing, but despite the fact that the design should dictate that they all focus-shift and that it shouldn't be possible to cure, at least some of most recent date code versions of this lens don't exhibit any perceptible focus shift. I can say this with the utmost confidence in at least one case because I own one that doesn't focus-shift (UY0508 ). Others have reported the same with UY lenses, and in one case to my knowledge, UX.

I had been reading all the threads on this lens for years, in the hope of one day reading that Canon had sorted the damned things out so I could buy one. Recently it just so happened that I started reading that the later lenses (2010) didn't show any signs of this focus shift, along with reports from people that actually had one that was okay. On the strength of those reports I bought one and mine turned out to be fine too.

I can assure you that it doesn't focus-shift. I have tested it God knows how many times under normal usage, within 6' of subject distance, and I have also tested it 'properly' twice (tripod-mounted etc) at different distances within 6' (an arbitrary 60" and again at 43.5") and there is definitely no focus shift.

Unless there have always been versions of this lens that don't focus-shift, for whatever reason, then Canon must have done something to sort out the problem, otherwise non-shifting versions of this lens wouldn't exist. I have no idea what they could have done. Maybe it's down to better calibration or something. Who knows?

Mike

they need to make a mark II with fixed back focused on this

Regardless of the buggy design and the issues I had with my previous two copies. I am perfectly happy with the third. I don't want to bash this lens because it really can do some amazing things. I do agree with you Mike that my 2010 copy does seem to handle the shift BETTER than the previous two, however if I was to pixel peep (bad bad I know!) I can still find it present, but not extremely so. In most cases though It's totally fine and as I mentioned It's typically the lens always mounted on my 5DmkII and I'll only switch when I need to

I did do some micro-adjustments with mine and with a -1 on my MY 5D it is perfect. My 7D is another story, that camera is a mess lol! It's a +10 with the same 50L , a +15 with my 24L, a +7 with my 135L and totally fine at 0 with my zooms. Go figure.

agphotography wrote in post #11039191
I don't want to bash this lens because it really can do some amazing things. I do agree with you Mike that my 2010 copy does seem to handle the shift BETTER than the previous two, however if I was to pixel peep (bad bad I know!) I can still find it present, but not extremely so.

My method of inspection also involves 100% view and other fussing about, so if there was focus shift I most definitely would have found it.

A separate issue I know, but I experimented with the micro-adjustment (5D MkII) at every increment and the lens is spot-on at the zero setting. I haven't felt the need to look for faults with my other lenses, so haven't experimented with them.

Mike

Mike-DT6 wrote in post #11037999
Okay, so that confirms that the problem still exists, which is a shame because now we can't say for sure that they've sorted out the problem, which is how things were looking previously.

I can assure you that it doesn't focus-shift. I have tested it God knows how many times under normal usage, within 6' of subject distance, and I have also tested it 'properly' twice (tripod-mounted etc) at different distances within 6' (an arbitrary 60" and again at 43.5") and there is definitely no focus shift.

Unless there have always been versions of this lens that don't focus-shift, for whatever reason, then Canon must have done something to sort out the problem, otherwise non-shifting versions of this lens wouldn't exist. I have no idea what they could have done. Maybe it's down to better calibration or something. Who knows?

Mike

This is precisley why I'm so interested in this lens outside of the fact that it's on par with the 85L 1.2 in sharpness and godly bokeh for a lot less. I just dream of the 50mm focal length L hotness!!! UGHHH!!

Decisions decisions

I can agree to them fixing it. The lens i used on the pictures i posted on the previous page was a UY date code lens. Didnt have any shift focus problems at all.

I just got myself the 50mm 1.2 YAY !

but problem is... I need to get my copy of the 50mm micro-adjusted badly =(

I'll try to print out the Micro-Adjustment sheet (or whatever it's called) and see if that helps.

Hi Abram,

agphotography wrote in post #11035952
Mike,

I Have had a UV, a UX and now a UY (2010). Every copy I have tried exhibits some kind of focus shift. It's how the lens was designed. The molded rear element causes the shift, there's no escaping that. I'm not saying it's so bad that the lens is unusable, but when you use anything other than f/1.2 the shift will happen when you are within 6' of the subject. Focus shift is a very different issue from front or back focus.

Actually, the rear element has nothing to do with the focus shift, other than that it helps prevent at least part of the focus shift, as that is what aspherical lenses are designed to do.

Anyway, here is an explanation I gave on focus shift a while ago:
https://photography-on-the.net …hp?p=10916460&p​ostcount=4

Kind regards, Wim

HemisFear wrote in post #11040061
This is precisley why I'm so interested in this lens outside of the fact that it's on par with the 85L 1.2 in sharpness and godly bokeh for a lot less. I just dream of the 50mm focal length L hotness!!! UGHHH!!

Decisions decisions

Make that better bokeh, both in front at behind of the DoF plane, and some corner softness at F/1.2.

Kind regards, Wim

wimg wrote in post #11040947
Hi Abram,

Actually, the rear element has nothing to do with the focus shift, other than that it helps prevent at least part of the focus shift, as that is what aspherical lenses are designed to do.

Anyway, here is an explanation I gave on focus shift a while ago:
https://photography-on-the.net …hp?p=10916460&p​ostcount=4

Kind regards, Wim

Oh thanks for the correction Wim, I always thought it was the molded rear element that was causing the problem since it was not a floating rear element like the 35L and 85L.

agphotography wrote in post #11041014
Oh thanks for the correction Wim, I always thought it was the molded rear element that was causing the problem since it was not a floating rear element like the 35L and 85L.

Another correction, if you don't mind too much, about which I wrote many times already (as this is a typical internet myth, which I have been trying to correct singlehandedly so far ): the rear element of the 85L is not the floating element. I assume the 35L has a similar design, but don't know for sure as at the time when I tested a 35L I didn't pay attention to the optical construction .

Anyway, the rear element of the 85L actually is a static element. The 85L design incorporates floating elements, emphasis on the plural s here. What this means in the case of the 85L is that all elements move when focusing, bar the last one, the static one which is closest to the sensor. This is also the reason why AF even with the tank engine USM AF motor of the 85L is still slow. If the rear element was the floating one, I can assure you AF would have been lightning fast.

Kind regards, Wim

^ I really like that pic.

wimg wrote in post #11041144


Another correction, if you don't mind too much, about which I wrote many times already (as this is a typical internet myth, which I have been trying to correct singlehandedly so far ): the rear element of the 85L is not the floating element. I assume the 35L has a similar design, but don't know for sure as at the time when I tested a 35L I didn't pay attention to the optical construction .

Anyway, the rear element of the 85L actually is a static element. The 85L design incorporates floating elements, emphasis on the plural s here. What this means in the case of the 85L is that all elements move when focusing, bar the last one, the static one which is closest to the sensor. This is also the reason why AF even with the tank engine USM AF motor of the 85L is still slow. If the rear element was the floating one, I can assure you AF would have been lightning fast.

Kind regards, Wim

Don't mind a bit, I'd rather be informed correctly! I've always heard it called a "Floating Rear Element" for as long as I can remember and I never investigated any further. Admittedly I don't study Lens Diagrams or MTF charts, I just find what works for me. But I am always willing to learn new things if someone is offering the information!

- Abram

agphotography wrote in post #11042148
Don't mind a bit, I'd rather be informed correctly! I've always heard it called a "Floating Rear Element" for as long as I can remember and I never investigated any further. Admittedly I don't study Lens Diagrams or MTF charts, I just find what works for me. But I am always willing to learn new things if someone is offering the information!

- Abram

Thanks!

Anyway, when you do get a chance, have a look at an 85L, caps removed, first focused at infinity, and then at MFD. You may be able to just see that although the rear element doesn't move, all the other elements have moved.

From this page,http://www.canon.com …06_ef_85_f1.2lI​I_usm.html :
"Employing large, high-precision aspherical lenses in combination with a floating construction that suppresses aberrations during focusing,..."

It doesn't mention the rear element , and neither does it mention spherical aberrations, BTW, only aberrations.

However, for the older version:
http://www.canon.com …andard/ef_85_12​l_usm.html
"The floating system corrects coma for high image quality. " As we all know, the optical construction is the same... .

Even the notion that a floating construction fixes focus shift likely isn't true. AFAIK, that is taken care of by the aspherical lens, because it precisely is the function of an aspherical lens (or more than one) to correct spherical aberrations first and foremost, to make sure all light rays including the edge ones focus in a single point or plane.

In short, I do think that the 50L still is a design just over the bleeding edge for assembly line production runs rather than single item laboratory production runs with regard to spherical aberrations to create great bokeh, notably both in front and behind the DoF plane. This latter combination is really contradictory when it comes to spherical aberration correction, as under normal conditions good bokeh in front of the DoF plane precludes good bokeh behind the DoF plane, and vice versa. I really do admire that Canon did manage this, despite the fact that this means it is hard to find a specimen without appreciable focus shift close to MFD at large apertures just beyond F/1.2, even though their current production runs seem to mitigate this most of the time.

As you know well yourself, anybody prepared to invest the time to work with the 50L, either to get a good specimen, or work around the problems, or both, tends to be rather pleased with the results this lens provides. And that, IMO, is what it is all about .

Kind regards, Wim