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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 25 Mar 2010 (Thursday) 19:28
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50L focus shift / back focus

 
David ­ S
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Mar 25, 2010 19:28 |  #1

I just received my 50L and knowing the focus shift issue associated with the lens design, I went ahead and did some tests.

First thing I notice is the lens is back focusing on my 1ds2.

My question to all 50L owners, is the focus shift in the pics below good or bad as I don't really have a reference point? I am thinking it is not too bad and looks to be within the DOF. So the focus shift would not really be noticed in real world shots.

Also, should I return the lens for an exchange or should I just send this copy in to Canon to get the back focus fixed. I assume when Canon fixes the back focus, the focus shift can't get worse. I am worried exchanging this lens can mean getting a much worse focus shift 50L.

Two sets of test shots.

The first set is around 3 ft back and focused on the 2nd "m" of "50mm".

f/1.2

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f/1.4
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f/2.0
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f/2.8
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f/4.0
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f/5.6
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f/8.0
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David ­ S
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Mar 25, 2010 19:37 |  #2

Second set is about 1.5 feet away focused on the 2nd hump of the 2nd "m" of "50mm".

f/1.2

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f/1.4
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f/2.0
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f/2.8
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f/4.0
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f/5.6
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f/8.0
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nicksan
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Mar 25, 2010 20:26 |  #3

I would have to say that this is quite typical of this lens.

I notice a slight back focus problem wide open. Since you have a non-micro adjusting body, you are pretty much SOL with this. Chances of you getting a spot on (at f1.2) lens isn't great to begin with. You can either send it back to Adorama, and try another one, or send it to Irvine, CA. It really depends on whether you intend to keep this lens or not b/c I am assuming once you send it to Irvine, CA, it's good as yours. If you return it to Adorama, get another "bad" copy, then you can make a decision right then and there whether you actually want to pursue this lens or not.

As far as focus shift, you can see some. Not sure if it's absolutely terrible. It would probably be even better if the regular back focusing was corrected.

However, I say again, this looks all too familar. From the looks at f1.2 to the shifting. That's the 50L for ya! :)




  
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Rendition
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Mar 25, 2010 20:56 |  #4

It's sad to say this but... you have to get used to it - focusing is lousier than the 1.4. Sent to Canon Singapore to fix only the back focusing issue but focus shifting seems to be something they can not fix. I also realised that focus shifting will tend to occur when you're close to the MFD.

Thank gawd I don't fancy using it very wide open.


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David ­ S
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Mar 25, 2010 21:00 |  #5

Thanks for the input Nick.

After looking at the pics again, I see a little focus shift from f/1.4 to f/2.0. After that the DOF looks to be concealing it. Or maybe my eyes are playing tricks on me after staring at the pics too long. :)

I do want to keep this lens because I like this focal length. I am still debating on sending this to Canon or exchanging for a new one due to the back focus.


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David ­ S
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Mar 25, 2010 21:04 |  #6

Rendition wrote in post #9872099 (external link)
It's sad to say this but... you have to get used to it - focusing is lousier than the 1.4. Sent to Canon Singapore to fix only the back focusing issue but focus shifting seems to be something they can not fix. I also realised that focus shifting will tend to occur when you're close to the MFD.

Thank gawd I don't fancy using it very wide open.

I was definitely aware of the shortcomings of the 50L before purchasing. When Canon fixed your back focus, did it affect the focus shift? I know there is no fix for the shift but I don't want to get my lens fixed for back focusing and the shift coming back worse.


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nicksan
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Mar 25, 2010 21:09 |  #7

It's up to you. As you mentioned, what if you get a copy that's worse?
The fact that both your bodies don't have MFA is adding to the issue here. :(

Knowing what I know now about the 50L, if I was in your shoes, I'd send it back, get a new one, then deal with that one. Or if you have the funds, maybe buy from another place with a great return policy and pick out the best of the 2?

The lens acts like a totally different lens beyond 5-6ft. Are you going to shoot close to MFD? If not, I wouldn't get fixated on the shift.

Also, have you checked for regular back focus further away from the target?




  
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David ­ S
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Mar 25, 2010 21:18 |  #8

I do like shooting in the "danger zone". I haven't tried shooting further out yet as I got it today but I will try that to see if the back focus is still there.

The focus shift on my copy is definitely not as bad as I was expecting. I can probably live with that as long as I don't see it in real life shots. The back focus is definitely my number 1 concern. I did have some issues with Canon Irvine before, so I am a little hesitant even sending it there.

I think I will just flip a coin to determine my next step. :)


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toxic
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Mar 25, 2010 22:09 |  #9

The focus shift is pretty minimal, so I would just send it to Canon to correct the backfocus.




  
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Rendition
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Mar 26, 2010 01:35 |  #10

David S wrote in post #9872133 (external link)
I was definitely aware of the shortcomings of the 50L before purchasing. When Canon fixed your back focus, did it affect the focus shift? I know there is no fix for the shift but I don't want to get my lens fixed for back focusing and the shift coming back worse.

I don't think it'll be worse. Neither did mine get worse - just that it's still happening once awhile and I am used to it.

I actually went back Canon twice. When I sent for the first time, got it back, it was still back focusing... whether or not it was because of consistent focusing shifting I don't know but the technician claimed they have brought it back to 'factory settings'.

Second time, I tested it in their testing room... it was still happening but when he tried it in front of me... for some reason, spot on. It stroked me that it could be due to the way I shoot... maybe my body weight is causing camera to be moved forward. I do know people who tend to move backwards due to body weight too. So... I simply told them to force adjust the focusing more forward by a fraction. Since then, it has been OK. or rather I am getting more 'correct' focus.


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David ­ S
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Mar 26, 2010 14:51 |  #11

I did quite a few more test shots. The back focus is there even out of the danger zone. Also, I can't really see the focus shift as most of it is concealed by the DOF. I will be doing some real shooting over the weekend.

toxic wrote in post #9872517 (external link)
The focus shift is pretty minimal, so I would just send it to Canon to correct the backfocus.

That is what I am leaning towards. I will see after shooting over the weekend.

Rendition wrote in post #9873307 (external link)
I don't think it'll be worse. Neither did mine get worse - just that it's still happening once awhile and I am used to it.

I actually went back Canon twice. When I sent for the first time, got it back, it was still back focusing... whether or not it was because of consistent focusing shifting I don't know but the technician claimed they have brought it back to 'factory settings'.

Second time, I tested it in their testing room... it was still happening but when he tried it in front of me... for some reason, spot on. It stroked me that it could be due to the way I shoot... maybe my body weight is causing camera to be moved forward. I do know people who tend to move backwards due to body weight too. So... I simply told them to force adjust the focusing more forward by a fraction. Since then, it has been OK. or rather I am getting more 'correct' focus.

I have to agree. I think some people hold the shutter down half way too long and then the focus point is no longer valid, especially with larger apertures. For my back focus, I have to lean a little back.:)

Focus chart definitely shows back focus, and the "20mm" on the left side of the chart looks to be what's in focus at f/1.2. That "20mm" never goes out of focus up to f/8. I can see the focus shift, but fortunately the "20mm" is within the expanding DOF for each increasing aperture.

f/1.2

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f/1.4
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f/2.0
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f/2.8
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f/4.0
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f/5.6
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f/8.0
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50L focus shift / back focus
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