7D single point AF issue. Advice needed.

[tmac965626]

  I'm having a focusing issue with my 7D, and I was hoping someone out there might be able to provide some insight. The focus with the single point Af is vastly inconsistent, even with the center point and on a tripod. I recently tried using a calibration tool to see if my lens was going one way or the other, but the focus seems to be inline (when it hits the mark). If I manually focus the camera it does come out much sharper though, and if I use the zone AF, the results appear to be consistently in focus, albeit not as sharp as a manual focus. The single point AF, on the other hand, will register as being in focus if the image is blurry, near sharp, or somewhere in between. The focus is slow, even with optimal lighting. If I put the camera on a tripod and take three consecutive shots, I will get three different levels of focus. This is becoming very frustrating. I shoot with a 28-70 2.8L lens, and my cheap travel camera (a NIkon D3200 with a kit lens) is focusing faster and sharper, even in low light situations. If anyone could provide me with some insight as to what the problem might be, or how to fix it, it would be greatly appreciated. I also removed both batteries for a hard reset, but I did not see any improvement. 

[ebiggs1]

"I also removed both batteries for a hard reset, but I did not see any improvement."

You had to reset the date when you turned it back on?  If you didn't it did not reset.

Second I would get a ruler, like a yard stick, and place it some distance from the camera/lens on a tripod. The ruler needs to be at a 45 degree, give or take, angle so you can see if it is hitting the desired focus point. Focus right at a center point on the ruler. Use just the center focus point on the 7D.

BTW, exactly what lens are you trying to use?

[Waddizzle]

You can do AFMA with a ruler, a couple of red bricks, and a yardstick or tape measure.

[tmac965626]

Yeah, I had to reset the date. I left the batteries out for quite some time. The calibration tool I used was a pop-up card with a target and a ruler set at 45 degrees. Not the largest or most expensive system by any means. I'll try it with a larger ruler, but results thus far didn't indicate a need for adjustment. My lens is a Canon 28-70mm f/2.8L USM. I've had it for quite some time and never had any problems with it. I was going to test to see if it was decentered, but that's out of frustration. I don't see anything that would actually indicate that. 

[TCampbell]

When I focus-test lenses, I run the focus all the way "in" and force the camera to focus out and repeat that a dozen times.  Then I focus all the way "out" and force the camera to focus in ... and repeat that a dozen times.

Then I compare to see if either direction of travel gets consistent results.

The lens may have developed excessive gear backlash ... to where the camera thinks it has adjusted focus well-enough to nail to the subject, but slop in the lens is causing it to miss focus anyway.

Does it only happen with this lens?

[tmac965626]

So, as suggested, I tried to calibrate the lens with a ruler instead of my dinky pop-up card. The ruler did provide a much easier guide. I made some adjustments, but unfortunately, on the 7D you can only make a single adjustment per lens and I could not get consistent results. This was due to two reasons: the adjustment changes with the focal length, and I am still getting an inconsistent focus. I settled on a generalized -2, and this appears to have narrowed the degree of variance, but a consistent focus just isn't there. 

I also tried focusing inwards and outwards repeatedly to see whether one way focused more consistently than the other, but that was a wash. It's about even. So no excessive backlash, that I can tell. How would one repair that if that were the case? One of the reasons I stayed with an APS-C sensor is that my 28-70 works perfectly for what I need, due to the magnification factor. I don't have any other lenses with me, but I do have my 20D, which I can put the lens on. Should I just consider the lens to be generally worn out and in need of rejuvenation or replacement?

I also used a Zeiss Star Chart to see if the lens was decentered...it was not. 

I'm running the firmware version 2.0.3 on the camera. I saw that a 2.0.6 update was released to correct issues with two lenses. While that particular update may not help, does anyone know if there was anything in between that might be of relevance? Is there any other way to recalibrate the autofocus inside the camera itself?

[Waddizzle]

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@tmac965626 wrote:

So, as suggested, I tried to calibrate the lens with a ruler instead of my dinky pop-up card. The ruler did provide a much easier guide. I made some adjustments, but unfortunately, on the 7D you can only make a single adjustment per lens and I could not get consistent results.

This was due to two reasons: the adjustment changes with the focal length, and I am still getting an inconsistent focus. I settled on a generalized -2, and this appears to have narrowed the degree of variance, but a consistent focus just isn't there. 

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Your results as you changed focal length may have been misleading.  You should be adjusting the distance to the focus target as you adjust focal length.  The recommended distance is 50x the focal length of the lens.  When you start to get into super telephoto lenses, that can drop to 25x the focal length.

Performing a lens AFMA is deceptively difficult.  It can challenge your skills as a photographer.  You can take nothing for granted.  Dot every “I”, and cross every “T”.  You need a fully charged battery.  If you are using a tripod, I recommend lowering the center column as far as is practical.  Take the time to adjust the camera height by adjusting the legs, and record the positions and extensions, so that you can come back again and repeat the same test.

Your ambient lighting can dramatically affect the results that you get, especially artificial lighting.  For example, I was getting inconsistent results in my hallway one evening.  The next morning, I tested outdoors in bright sunshine, and got very consistent results.  I was still using Av mode and a fixed ISO 100, both indoors and out.

I recommend trying the Dot-Tune Method, on YouTube.

https://m.youtube.com/watch?feature=youtu.be&v=7zE50jCUPhM

This method is the most objective approach I have seen.  Instead of you judging when the focus is correct, the camera tells you when it thinks it is correct.  This is the only effective method that I know of that accurately adjusts AFMA with a vertical focus chart, parallel to the place of focus.  Otherwise, you really need an inclined scale so that you can measure DoF.

As far as having only one focus adjustment for all lenses, this is a distinct disadvantage.  Newer Canon DSLRs allow two adjustments for zooms, and one for a prime lens.  You seem to be on the right track by calculating an average between the short and long ends of the zoom range.  But, even that approach has its’ limitations, and for some lenses it is of no help at all.

[tmac965626]

So, as an update: This morning, I went outside with my camera to take shots of pretty much anything that crossed my path. It was a VERY bright day, and the camera was operating with the speed that it should, which had me wondering if it was a problem with the sensor reading low light? The focus was grabbing quickly, but it was still somewhat off the mark.

When I got back I found a reply to a request I had sent Canon several days ago. I feel the details are worth posting for anyone else who may come across this problem.

"In this situation it is difficult to tell if there is an issue with the camera or lens. For this type of issue I recommend performing a complete reset on the camera, and a reset on the lens, for further testing. Please follow the instructions below." 

Settings Reset

1. While the camera is on turn the mode dial to "P" (Program mode), which allows all menu options to become available, then press the menu button.

2. Move across the top of the menu to the last wrench tab. (Yellow tabs)

3. Go down the menu list to "Clear Settings" and press the Set button.

4. Choose "Clear all Camera Settings", and press the Set button.

5. To complete the reset highlight "OK" and press the Set button again.

6. Next, move over to the Custom Functions menu list.

7. Reset the "Clear all Custom Func." settings as well.

Power Reset

1. Make sure the camera is off, and then remove the battery, memory card, and lens.

2. Close the battery/memory card doors.

3. Turn the power switch to the "ON" position, and then press and hold down the shutter button for 10 seconds.

4. Release the shutter button, turn the power switch to the "OFF" position, then reinsert the battery and memory card.

5. Before attaching the lens set the focus switch to MF. Rotate the focus and zoom rings back and forth through the range of motion a couple of times, and then set the lens back to AF.

6. I would then use a clean, dry, soft cloth the gently wipe the gold colored contacts on the mount end of the lens to ensure the camera and lens have a good connection.

7. Now mount the lens on the camera and power the camera on for testing.

I then followed these directions. As a result, the camera is no longer slow to focus in lower light conditions. I went around my house and re-took photographs that the camera was previously struggling with. For whatever the reason, the problems are no more. The focus was properly dead-on in very few shots, but not in any way as far off as before. I then went to my dinky pop-up calibration card and target. I have not done a proper re-test as of yet. But, I did focus in and out of that target multiple times, just to test the AF. While the range of focus has consistently narrowed closer to the target and the speed of focus has increased, there still remains an inconsistent variation off of the center.

I will attempt the dot-tune method tonight. Hopefully that will close the gap further. I did forget to adjust the distance between the target and the camera when changing focal lengths in my previous testing. Thank you for pointing that out. 

[CaliforniaDream]

tmac965626 really good information, thanks for shairing.  It would be good to know if this works on other canon cameras.