# Inconsistent focusing with new Canon 50mm and 85mm F1.8 lenses. A distressing problem



## JonHornsby (Mar 14, 2009)

My daughter has a Canon Rebel XT and recently purchased a Canon 50mm F1.8 and a Canon 85mm F1.8 lens for this camera. She had two reasons for wanting these lenses: (a) to take pictures when ambient light levels are low without having to use flash and (b) to use the shallow depth of field of these lenses at large apertures to separate the subject from the background. The two lenses are quite sharp but unfortunately, 64% of the images taken at a wide aperture (F2) are out of focus regardless of the focusing mode used. We took a series of photos of a stationary object with the camera/lens mounted on a tripod, using the self timer to eliminate vibration caused by mirror slap. We photographed the subject using Manual Focus override, AI mode, and One-Shot mode.

The overall result was that 64% of the time, the camera focused in front of the subject  far enough in front to create an unacceptably blurry picture of the subject. (To be precise, only 20% of the images were sharply focused in AI mode, only 40% in One-shot mode, and only 50% in the manual tweaking mode) This is very annoying. Actually its more than annoying, its downright unsatisfactory. The problem does not occur with the standard 18-55mm zoom kit lens because the maximum lens opening is only F3.5-F5.6 (greater depth of field) with the kit lens. which takes amazingly sharp pictures.


The problem is apparently caused by the camera's sensor and/or mirror alignment or positioning, and could presumably be corrected by Canon for a "mere" $210. But is it worthwhile to have this camera repaired, or should my daughter get an upgraded Canon camera with more megapixels and the stabilized kit zoom lens? Also, what is the likelihood that Canon would fix the camera free, since this appears (maybe it is, maybe it isn't) similar to the problem that prompted the technical advisory and free repair for EOS-1D cameras which experienced focus tracking problems?


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## 250Gimp (Mar 15, 2009)

How old is the Xt?

If it is out of warranty I doubt that Canon will fix it for free.

If you send it in you should probably send the lenses in as well so they calibrated with the body.


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## JonHornsby (Mar 15, 2009)

*Thanks, 250Gimp.*

A quick follow up.  My daughter has sent the new Canon lens back and will sell her Canon XT, which is a couple of years old and out of warranty.  She will get a Nikon D300 with 18-135mm lens and a Nikon 85mm F1.8 lens.


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## Jaszek (Mar 15, 2009)

can you post some sample shots? maybe you should've checked where the focusing point was set to.


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## AlexColeman (Mar 15, 2009)

She will be much happier with the Nikon.


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## JonHornsby (Mar 16, 2009)

The vertical type was 1 inch in front of the horizontal type (the thickness of two gum wrapper boxes). Hopefully, the effect will show up at the resolution of the photos in this reply. I'm very new at doing this and had to get help in placing an image in the message.


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## JonHornsby (Mar 16, 2009)

Thanks, *Alex*.  I am certainly not condemning Canon products as a result of this one "glitch."  Canon makes fine cameras and lenses.  But I think you are right. She will be very happy with the Nikon.


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## 250Gimp (Mar 17, 2009)

Were these shots taken with a tripod?

The DOF is very thin at f2, so if you lean into the shot the least little bit after aquiring focus you will get an out of focus shot.

To do this test properly you need to use a tripod, or at least put the camera on something solid so it doesn't move at all.

Cheers


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## JonHornsby (Mar 17, 2009)

Yes, the photos were taken with a tripod, using the self timer to eliminate vibration caused by mirror slap.


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## Flash Harry (Mar 17, 2009)

The money spent on these cameras/lens there should be no such issues and if there is whether in or out of warranty should be corrected free, its time these mega rich companies were brought to book a camera that can't focus is about as much use as a chocolate fireguard. 

Canon have had focus issues for years now on some models, I first read of such issues in 2001, my Niks however work with all nikon lens perfectly, the d300 even have a built in calibrator just for this reason, not that I've had to use it yet, so I think another nikon convert will be very happy with the new tool. H


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## JonHornsby (Mar 17, 2009)

Most interesting.  I had no idea the D300 had such a feature.  My daughter will be glad to hear that.


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## JerryPH (Mar 17, 2009)

D700 and D3 also have this feature... though I am happy to say that none of my lenses need any adjustments, even my 85mm F/1.4 is spot on set at F/1.4 and minimal focus distance.

Before I blame any lens, my first is to blame the person behind the camera.  At F/1.8, as mentioned, a tiny lean in or out after teh focus is locked in can cause this effect.  Set it on a tripod, and I think we will see that 1 of 2 things will happen:

- Lens will be consistently perfectly focused
- Lens will be consistently out of focus

If it is consistently out of focus, sending it to Canon for adjustment is the answer, if its not out of focus... user technique needs work.


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## JonHornsby (Mar 17, 2009)

*JerryPH* - I also would have thought that on a tripod the lens would have been consistently in (or consistently out of) focus. However, the tests we conducted showed that it was out of focus a certain percentage of the time, and in focus the remainder of the time. Those percentages were enumerated in my opening post. So given those observations, I could only conclude that focusing was "inconsistent." It couldn't have been user error, because the camera was on a sturdy tripod and the self timer was employed.


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## tsaraleksi (Mar 17, 2009)

If it's always off by the same amount, that is probably the lens or camera. If it's off by varying amounts, in very low light, then chances are pretty good it's just the particulars of the situation or the fact that the XT does not have particularly good low-light focus (it's an older model, entry level camera after all). 

Also, just to double check, which focusing point were you using?

What sort of problems was she having with it in the real world that led you to this testing?


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## JonHornsby (Mar 17, 2009)

Although not stated in my opening post, the lighting during our tests was very adequate so the lens did not have to search for a focus in the tests. The camera was programmed to focus on the central square in the focusing screen, and as indicated in the pictures (hopefully they show up on your monitor - one reader indicated they were "X'd" out on his screen), the D in the horizontally printed word "Dork" was where the central square was centered.

In the real world the problem was that with the new lenses, she only got 6 or 8 acceptably sharp pictures out of a "bazillion" exposures. Most of the images were exceedingly out of focus and blurry in bright daylight with the lens at or near maximum aperture (F1.8 or thereabouts). Of course the shutter speeds were quite high so long exposure was not the "culprit."

My daughter has two years of experience using the camera and had never had such a plethora of out of focus images. We decided to use the tripod test to determine if the problem was: (a) "her" (b) the lenses or (c) the camera body. Since the problem of inconsistent focus occurred with both lenses, the conclusion (after consultation with a camera technician on a web site) was that the problem was in the camera, not the lenses. It would have been very unlikely for two brand new lenses to exhibit the same problem.

I certainly acknowledge it is harder to get a tack sharp image with an aperture of F1.8 than it would be at F5.6 due to the shallow depth of field. That was the very reason we conducted those tests - to determine just exactly what was going on. Again, the test procedure is described in my opening post, with additional details given in the pictures. Also, I have tried to clarify what I did in various responses above.

Thanks for your interest and comments.


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## 250Gimp (Mar 17, 2009)

Just so you know...you have to use mirror lock up along with thte timer or remote shutter release to prevent mirror slap. This is in the Custom Function menu.

Probably not making a difference in this case, but letting you know.


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## JonHornsby (Mar 17, 2009)

Uh, oh.  

We failed to lock the mirror - never occurred to me to do that.  So that was a flaw in our test procedure.

As you say, it may not have biased our test results but I sure wish we HAD done that.

Thanks.


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## JerryPH (Mar 17, 2009)

I bet that, considering all that was done, that this would not have changed things much. If you have the camera still, you can give it a go, its not that long to do, but if you have already gone to another camera, don't bother and just move on.

Personally, I am the curious type and would try it, just for the sake of the fun of testing.

Out of curiosity, how many shutter actuations are on the camera in question?  That could also be a factor... a well used unit would have wear issues that could cause just that.


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## Mike_E (Mar 17, 2009)

One of my favorite lenses is a Tokina 28-80mm f/2.8.  Most Canon shooters I've ever heard disliked the lens but practically every Nikon shooter loved it.  (of those who used it of course)

Focus was always the complaint among the Canon shooters.


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## JonHornsby (Mar 17, 2009)

*JerryPH and Mike E* ---  Insofar as I know there is only one button to physically actuate the shutter, the "regular" button you push to take a picture.  This same button activates the self timer.  Hopefully, I have not misunderstood your question.

And that's interesting ("suggestive") about the focus complaints with the Tokina lens on the Canon.


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## JerryPH (Mar 18, 2009)

Mike_E said:


> One of my favorite lenses is a Tokina 28-80mm f/2.8. Most Canon shooters I've ever heard disliked the lens but practically every Nikon shooter loved it. (of those who used it of course)
> 
> Focus was always the complaint among the Canon shooters.


 
Well to be honest, Sigma has some issues with consistency and quality control.  When they get something right, it is incredibly right... reverse is true too.  They have a bit of a bad track record with some lenses and QC.

Honestly, I sincerely doubt that mirror slap was so bad that it would cause this level of blur.  That would have to be a seriously instable tripod... lol

The fact that this happens on more than 1 lens also points the finger at the camera.  That is why I was asking about actuations.  A well used camera would have a lot of loose parts and could cause these fluctuations in focus.  XT or XTi's are not really made to go much over 50,000 actuations without issues.


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## Dao (Mar 18, 2009)

If you are still interested in doing more testing, this site is pretty helpful.


Nikon D70 Focus Chart


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## JonHornsby (Mar 18, 2009)

Oh, excuse me, *JerryPH*.  I didn't realize what you meant by actuations.  I would guess the shutter had been pressed maybe a couple of thousand times over the past two years.

And thanks, *Dao*, that looks very useful.  But since Jenny has now sold the camera, I won't be pursuing testing for the Rebel Xt.  However, I will save this on my hard drive for future tests, should the need arise.


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