Focus asymmetry - Canon 50mm 1.2 L

[drmikeinpdx]

A few weeks ago I picked up a Canon 50mm 1.2 L from another local photographer at a decent price, $1050. The lens appears to be in good condition and I'm using it on my 5D3.

I intend to use this lens for portraiture at about 4-6 feet, with the aperture wide open. Since this will require very accurate focus, I conducted some of my usual autofocus tests in that distance range using the various autofocus points in the viewfinder of the 5D3. All tests were done wide open, so focus shift with aperture changes would not be an issue.

The center focus point works great with no AFMA needed. Accuracy is within one inch at 5 feet and very repeatable!

Unfortunately, the peripheral focus points tend to front focus. The farthest point to the right will front focus by about 4-5 inches. The top one, about 3-4 inches. The left and bottom points front focus by about two inches. I use that farthest right point a lot since I hold the camera vertically and place that point on the subject's eye. You only have about a two inch depth of field at 5 feet, at F/1.2.

As a control, I ran the same tests with my Canon 85mm 1.8 and all points were within one inch. (Love that lens.)

I will probably send the L lens in to Canon for calibration. I'm planning to call on Monday and ask if I should also send the body with it.

Anyone run into this before or have an idea what the problem is? Anything I can do to help Canon diagnose and correct the problem?

Thanks!

 

[Mt Spokane Photography]

The lens elements might be decentered, but there is probably a lot of curvature of field.

 

[Sporgon]

There was a thread about this issue of off centre focus points about a year ago. Seems field curvature with that lens is the cause. Bit annoying really: if ever there was a lens where you needed your outer points it's a f1.2.

The link is here:

http://www.canonrumors.com/forum/index.php?topic=14675.0

 

[drmikeinpdx]

Thanks for the link Sporgon! I thought I had read a lot of articles and posts about this lens before I bought one, but by including "curvature of field" in the search terms, I'm finding even more!

Seems like front focus with the outer points is pretty common with the 50L, especially on the 5D3. Here's a link to a guy who has this problem, but says his 50L works perfectly on his 6D.

http://www.dpreview.com/forums/thread/3496264

I haven't found anyone yet who gets different amounts of front focus on the right and left sides.

And nobody can seem to explain why the curvature of field is a problem when you use an "on target" outer focus point, rather than focus and recompose.

 

[drmikeinpdx]

This is the first time I've used Canon Professional Service and so far I like it!

I called the secret number and worked my way through the menus to technical advice. I spoke with Tony and told him what the lens was doing. He says it needs calibration and to send it in. I appreciate the quick advice.

Now we will see how well the Canon service techs can adjust this expensive piece of glass!

 

[eninja]

I also recently got 50L.
And not satisfied with AF or sharpness.
I have

What is a field curvature? It sounds like a permanent problem and can not be fix?

If my center AF point nail focus, but my outer does not (front focusing for example),
does this means my lens have problem and needs calibration?
or does it means I need average AFMA on different AF Point?

I just bought Reikan Focal, I wonder what test I could use to diagnose this phenomenon? (did I use the term phenomenon right?)

 

[Mt Spokane Photography]

I also recently got 50L.
And not satisfied with AF or sharpness.
I have

What is a field curvature? It sounds like a permanent problem and can not be fix?

If my center AF point nail focus, but my outer does not (front focusing for example),
does this means my lens have problem and needs calibration?
or does it means I need average AFMA on different AF Point?

I just bought Reikan Focal, I wonder what test I could use to diagnose this phenomenon? (did I use the term phenomenon right?)

All lenses have some degree of curvature of field, google it!


Lenses like 50mm lenses with ultra wide apertures have more of it. Its possible to add a lot more lens elements to correct it, and then correct the aberrations caused by the additional elements, you can keep adding more and correcting more indefinitely, so lens manufacturers reach a point to where they feel the practical limit has been achieved.

The 50mm f/1.2 was not conceived as a flat lens as you would use for landscapes or copying, so the curvature of field is fine for portraits because it has the effect of softening the edges.

The 24-70mm f/2.8 MK I was noted for its excessive curvature of field, its original concept as a wedding lens for portraits did not cause a problem, but as DSLR's became popular and photographers wanted to use it for everything, it became a issue. The MK II fixed the issue and added more lens elements as a result.

There are some 50mm lenses that have little curvature of field, macro lenses, high end 50mm lenses, those designed for photocopying or projection, or for enlargers.

 

[Viggo]

All four copies of all different manufacture years had the same issue and it couldn't be fixed. But the 50 L is so soft at the edges that using the outer points on the 5d3 and 1dx is simply hopeless.

I pushed the 50 Art, with live view, to the extreme corner beyond the outer phase AF point, and it's so sharp at 1.4 it's ridiculous.. If it only had AF like the 35 L it would be a true winner.

 

[Xyclopx]

Unfortunately, the peripheral focus points tend to front focus. The farthest point to the right will front focus by about 4-5 inches. The top one, about 3-4 inches. The left and bottom points front focus by about two inches. I use that farthest right point a lot since I hold the camera vertically and place that point on the subject's eye. You only have about a two inch depth of field at 5 feet, at F/1.2.

this is my experience as well. outer points front focus while middle is dead on. it's not just this lens though--some others do as well.

you will also note that the outer points work better on crop cameras like the 7d (at least that's my experience.) there's very little deviation from the middle to outer points on my 7d. it probably has something to do with the distortion/contrast/sharpness/field-curvature differences being exaggerated going farther out.

I found this to be true with 3 separate copies of this lens, from 2 stores.

I've basically just accepted it this way and work around it, like focusing using the center then recomposing.

no amount of sending your lens to canon will fix this--canon has had my body and lens many times and found nothing wrong. if your middle is consistently accurate, and you have no decentering problems, i'd just try to forget about this problem.

 

[drmikeinpdx]

Lens received by Canon Service in California

I will certainly be interested to see what Canon service can do for my copy. They sent me an email a few hours after they received the lens on New Year's Eve. No word on when the repair/recalibration will be complete, but they did tell me the cost. The flat fee for this kind of work is quoted at $269. I get a 20% CPS discount, then they add $18 shipping for the return, so it will cost me $238 plus what I paid to send it there.

I'm not expecting great peripheral sharpness, but I would really like the focus points to work better. I guess I am gambling on the result! Maybe I should have spent my money on lottery tickets, but that remains to be seen.

 

[Viggo]

Here you never pay for calibration as long as you have a receipt and the lens is less than 7 years old, and that's not cps. I once had to pay for a 35 L and it vas 100 usd.. 240 usd seems crazy, and specially if the issue remains unsolved.

 

[jebrady03]

Re: Lens received by Canon Service in California

A few weeks ago I picked up a Canon 50mm 1.2 L from another local photographer at a decent price, $1050.

+

so it will cost me $238 plus what I paid to send it there.

So, you're paying $1288 plus shipping to get it to CPS (so presumably over $1300 total) and you could have just purchased it brand new for $1240 here: http://www.canonpricewatch.com/product/00592/Canon-EF-50mm-f1.2L-USM-price.html. For that $1240 you'd get a one year warranty and the ability to return a decentered copy.

I'm always amazed at the price of used gear that's older than one year old. Don't get me wrong, I've sold gear over a year old and been the one benefiting from such ridiculous prices but I don't buy used gear over a year old (except one time for a 5D Mark II and I ended up selling it for a $250 profit 2 months later) and only buy gear with the original receipt. You've got to be smart and savvy when it comes to buying used gear or you can end up spending more for used than you would for new.

 

[eninja]

The first question I had if I was going to send 50L lens to canon was, will I need to pay if they did not fix the problem. I decide to buy FoCal instead.
I could not nail AFMA or justify my chosen AFMA without Reikan FoCal.
At least now I know, AF is spot on. I am quite satisfy now about 50L performance.

Let us know, what was the fix done to your lens. thanks.

 

[drmikeinpdx]

No change in status yet on my lens repair order at the Canon shop in California. It got logged in on Dec 31, but the repair tracker on the Canon site shows no change from the previous status. It just says that payment has been authorized. Hopefully that means they are doing a really good job of calibrating this lens! LOL

 

[drmikeinpdx]

Canon Service: Strike One!

Dear CPS Service,

My EF 50 1.2 L still has the same problem as when I sent it in. I would like you to authorize a shipping label for me to send it back again. I will describe the problem here and again in a letter that I will enclose with the lens when I send it back.

1. The focus points on the far right side of the viewfinder have severe front focus, approx 10 inches at 6-7 feet when the camera is held vertically and about 6 inches when held horizontally.

2. The upper focus points have a mild front focus problem. The center, left and lower points work fine with zero AFMA.

3. All points work fine using live view.

4. I repeated my tests using my Canon EF 85mm 1.8 lens and all points worked perfectly, so I don't think the camera is at fault.

5. The camera is a Canon 5D Mark 3, firmware version: 1.2.1

6. I use the camera a lot in a vertical orientation for portraits and I put the farthest right focus point (now at the top) on the eye of my subject. I really need that focus point to work well, especially with an aperture of F/1.2!

7. I would appreciate it if you would test the lens on a 5D3 after any adjustments and make sure the right side focus points are working.

Thanks,

Mike

 

[privatebydesign]

I appreciate your frustration, but they will not test it on a camera, let alone a specified 5D MkIII.

They test lens and body performance on test benches and a tested item is either within spec, or it is not. I have done the Canon repair dance enough times to know they don't look at images you send along with the body or lens demonstrating the issues you have either, they just put it on their test equipment and go from there. It can be a frustratingly repetitive exercise on occasions but bare with them, they normally sort the actual issue out in the end, despite themselves.

Don't deal with the regular reps either, once they have missed one opportunity then just ask to speak to the supervisor, they have more clout (though not much) and have the authority for up to 10% discount just because, so talk nicely to them if you can!

 

[drmikeinpdx]

Hi privatebydesign! I appreciate your input.

A few years ago I had to do the Canon service dance three times to get a zoom lens working right, so I know what you mean about that.

I would appreciate hearing more about the testing procedures they use. I understand optical benches of course. However, I have seen forum posts that mention Canon service techs testing lenses on, if I recall correctly, "reference" bodies.

I'm not sure how sophisticated the optical benches are, but I wonder if they have the capability to test the electronic functions of the lens?

Anybody know?

 

[privatebydesign]

I'm not sure how sophisticated the optical benches are, but I wonder if they have the capability to test the electronic functions of the lens?

Anybody know?

They do, but it is a different piece of equipment. I claim no insider knowledge of this but a couple of years ago there was a big stink between Canon and a large Californian parts and service center that had authorised Canon repair status.

In their business they had several of the lens test machines, one of which was pictured (it looked like an innocuous box with a lens mount on it! And could well have been a reference body, it certainly tested lenses), well they sold it for $35,000 and Canon said they didn't have the right to sell it, the business argued, successfully, that as Canon had made them buy it from them in the first place it was theirs to sell, so the sale went through. But Canon subsequently stripped them of their authourised status saying that even thought the sale had been deemed legal, the conditions of the official Canon authourisation were breached because the equipment was considered proprietary and should not have been offered for general sale.

 

[drmikeinpdx]

Well, the lens in question is now on it's way to Southern California for another little vacation at the Canon Spa. I boxed up my 5D3 and sent it along at the suggestion of the service rep who I exchanged email with. Canon sent me a Fedex overnight shipping label, so it isn't costing me anything but time. I will have to use my 7D for several days, which will be interesting.

Before I boxed up the 50L I did a boudoir photoshoot with it. I used the center focus point and the ones on the left and bottom that had been working well. It felt funny sometimes holding the camera opposite to how I normally hold for vertical shots. However, I have to say that the lens focuses really well with those points that were functional. :

I'd share photos, but they are too naughty for this forum.

I think I'm going to like this lens if/when the focus problem is fixed.

 

[Hjalmarg1]

I also recently got 50L.
And not satisfied with AF or sharpness.
I have

What is a field curvature? It sounds like a permanent problem and can not be fix?

If my center AF point nail focus, but my outer does not (front focusing for example),
does this means my lens have problem and needs calibration?
or does it means I need average AFMA on different AF Point?

I just bought Reikan Focal, I wonder what test I could use to diagnose this phenomenon? (did I use the term phenomenon right?)

Those were partially the reason why I sold my 50L