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Thread started 25 Jul 2010 (Sunday) 12:45
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7D focus - Please advise on these examples.

 
Ross_Curtis
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Jul 25, 2010 12:45 |  #1

I've had my 7D for a few months now, so I've had the time to get used to it's complicated AF system/setup. Having seen various posts of user error I wanted to give myself time to learn it properly.

The problem is I just can't seem to get consistent shots.

I've just got the camera and lens back from Canon. Canon have apparently adjusted both camera and lens (24L II).

All these shots were taken at F1.4 in AV mode, single focus, centre focus, tripod etc. In most I turned the ISO up to 400 to achieve a fast shutter. Each photo was taken 4 times, the first 3 all with these settings, the 4th shot was taken using live view zoomed in at 10X (live view is always bottom right).

As you can see all examples using live view are spot-on (I understand live view works on different principles, so although I'm not comparing them I've used live view as a good reference shot). However the other 3 are all inconsistent. Some in focus some out. My initial thoughts were that the camera may need some Microadjustment, however, the shot of the shoe shows focus is pretty much spot on (although finer inspection shows some small variations even in this high contrast black/white focus point).

I didn't want to use test charts so all the shots are real taken in real life situations.

http://i267.photobucke​t.com …tis/7D%20tests/​bottle.jpg (external link)

http://i267.photobucke​t.com …tis/7D%20tests/​cooker.jpg (external link)

http://i267.photobucke​t.com …D%20tests/garde​nlight.jpg (external link)

http://i267.photobucke​t.com …s/7D%20tests/ma​gazine.jpg (external link)

http://i267.photobucke​t.com …rtis/7D%20tests​/screw.jpg (external link)

http://i267.photobucke​t.com …urtis/7D%20test​s/shed.jpg (external link)

http://i267.photobucke​t.com …urtis/7D%20test​s/shoe.jpg (external link)

http://i267.photobucke​t.com …tis/7D%20tests/​stones.jpg (external link)

http://i267.photobucke​t.com …D%20tests/tapem​easure.jpg (external link)

Is this normal or am I expecting too much from the camera/lens?

Thanks
Ross


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stsva
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Jul 25, 2010 13:52 |  #2

It's hard to tell - some of the samples seem to have all four in good focus, while others don't. Here are a few thoughts - study where the focus point was for each of your samples using DPP. Consider that the actual focus sensors are considerably larger than the focus square in the viewfinder, and whether that could have resulted in focus on something outside the focus square but still within the area of the sensors. Consider also that the focus system is looking for a high-contrast edge. Those factors may largely account for the differences in focus in at least the majority of your samples.


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Ross_Curtis
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Jul 25, 2010 14:11 |  #3

That makes sense but it doesn't explain the inconsistency.


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tinyrobot
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Jul 25, 2010 14:33 |  #4

Did you shoot from a tripod? Also, use the timer to shoot. Actually, when I was checking my lens for focus consistency, I shot a few off, but normally I could just AF and check against a live view manual focus on a tripod.




  
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jwcdds
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Jul 25, 2010 14:44 |  #5

Ross_Curtis wrote in post #10600587 (external link)
That makes sense but it doesn't explain the inconsistency.

But it would and does explain the inconsistency. For example, your shoe and tape measure shots are clear examples of giving the camera high-contrast to focus on. And for those 2, you get the sharpest best AF from the camera.

I'm assuming these are all 100% crops? If these are 100% crops, then you're expecting WAAAY too much if you think the camera can see that garden light amongst the surrounding plants (offering distracting contrasts).

You noted "single focus", was this "single" or "spot"? Because the focus cross hair for "single" is quite large, nearly double the size of the actual rectangle. Even "spot" focus, the cross hair will venture slightly beyond the borders of the outer focus square.

If you didn't use spot, that will most certainly contribute to your problem.


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Jul 25, 2010 14:52 as a reply to  @ jwcdds's post |  #6

Here (external link)are a few examples, taken today, of what the 7D can accomplish focuswise. These are highly dynamic, of course, and taken using Servo AF.
It doesn't help the OP at all, but I wanted to give some reference for those who get the impression that the 7D always fails.


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Ross_Curtis
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Jul 25, 2010 15:15 |  #7

jwcdds wrote in post #10600719 (external link)
But it would and does explain the inconsistency. For example, your shoe and tape measure shots are clear examples of giving the camera high-contrast to focus on. And for those 2, you get the sharpest best AF from the camera.

I'm assuming these are all 100% crops? If these are 100% crops, then you're expecting WAAAY too much if you think the camera can see that garden light amongst the surrounding plants (offering distracting contrasts).

You noted "single focus", was this "single" or "spot"? Because the focus cross hair for "single" is quite large, nearly double the size of the actual rectangle. Even "spot" focus, the cross hair will venture slightly beyond the borders of the outer focus square.

If you didn't use spot, that will most certainly contribute to your problem.


Yes all 100% crops.

They were taken with a combination of single and spot on a tripod.

Are you saying the focus point in the viewfinder is actually twice the size of the rectangle in the viewfinder?
That certainly might contribute.

Maybe the garden light was a bad example.

Surely a flat surface with good contrast like a road sign when there is no chance of the focus catching another object should give you consistent focus?


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jwcdds
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Jul 25, 2010 15:36 |  #8

Well... I'm guessing you haven't looked up previous 7D AF complaint threads and never came across this image.

I must first give credit where credit is due assuming The-Digital-Picture.com is the originator of this image: http://www.the-digital-picture.com …al-SLR-Camera-Review.aspx (external link)

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: NOT FOUND | MIME changed to 'binary/octet-stream'


As you can see, this image shows how the AF cross hairs are with regards to single vs. spot. Both of which extend beyond the outer rectangle seen on the LCD.

And the following (again from the digital picture.com) shows how it appears with all 19-points:

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: NOT FOUND | MIME changed to 'binary/octet-stream'



*edit* and from your samples above, I didn't see any "road signs" that you were referring to.

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Ross_Curtis
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Jul 25, 2010 16:34 as a reply to  @ jwcdds's post |  #9

While testing the camera recently in a controlled enviroment, tripod, remote release etc against a test chart I was getting only 70% in focus. OK it was minimal, but at 100% it was clearly miss focusing. As a test I set the camera to AI servo, I found the focus was constantly jumping around, you could clearly see the focus markings on the lens moving back and forth a couple of mm, with the lens set at 1.4 this was enough to send the whole photo out of focus.

Why should a focus change when nothing else has, this still doesn't make sense to me?

I now understand the focus points a little better from those pictures, thanks Julian.

Maybe I am expecting alittle too much.......?


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Jul 25, 2010 17:19 |  #10

If there are various points of contrast that fall within the AF sensor cross hair, then once it finds the contrast, it will assume focus has been achieved, giving you a focus confirmation when it might not be where you want it to be.

If there is only one point/area of contrast that falls within the AF sensor cross hair, then you will get consistent results (like the shoe, and the tape measure).

IMO, it seems your expectations of the autofocus system is unrealistic. As much as everyone would like the AF to be perfect and accurate all the time, it is still an imperfect system, unable to read your mind. One can only hope that Canon and Nikon will continue to develop improvements to the system, but in the mean time, understanding its capabilities (along with accepting its limitations) allows us to adapt to the existing AF system, to make it work for us and improve keeper rates.

If focus is absolutely critical, nothing beats live view MF at 10x magnification. Whether the situation allows for it or not... well, that's another story.


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Ross_Curtis
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Jul 26, 2010 02:00 |  #11

“If there are various points of contrast that fall within the AF sensor cross hair, then once it finds the contrast, it will assume focus has been achieved, giving you a focus confirmation when it might not be where you want it to be

If there is only one point/area of contrast that falls within the AF sensor cross hair, then you will get consistent results (like the shoe, and the tape measure)”
*
That makes sense.
*
But, to add more fuel to my fire, I set up my 40D (same settings), against a white box with a black barcode.* I made sure the centre focus markings were covered by the barcode.
The 40D showed, VERY slight variations (even the bad ones are useable).* Same situations and settings the 7D showed massive variations, out of the 10 shots only 2 were perfect.
*
It seems the 7D performs well in well lit high contrast situations, reduce the lighting slightly (say daylight through a window) its performance drops off dramatically in line with above, whereas the 40D still performs admirably.
*
These types of results are not what I would have expected from a camera in this price bracket.*
*

“If focus is absolutely critical, nothing beats live view MF at 10x magnification. Whether the situation allows for it or not... well, that's another story.”
*
Absolutely, it’s a wonderful tool in the right circumstances.
*
*
*
*


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jwcdds
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Jul 26, 2010 02:29 |  #12

Ross_Curtis wrote in post #10603501 (external link)
But, to add more fuel to my fire, I set up my 40D (same settings), against a white box with a black barcode.* I made sure the centre focus markings were covered by the barcode.
The 40D showed, VERY slight variations (even the bad ones are useable).* Same situations and settings the 7D showed massive variations, out of the 10 shots only 2 were perfect.
*
It seems the 7D performs well in well lit high contrast situations, reduce the lighting slightly (say daylight through a window) its performance drops off dramatically in line with above, whereas the 40D still performs admirably.
*
These types of results are not what I would have expected from a camera in this price bracket.*

If you want to compare the 7D vs. the 40D, then do this:

First, reduce your 7D image from 5184x3456 to 3888x2592 (10mp of 40D).

Then, view both images at the new 100% and compare them side by side. If the 40D is still much sharper than the 7D, then perhaps your 7D is faulty.

If the newly resized(downsized) 7D image matches sharpness with the 40D and it seems that your keeper rate goes up, then what you need to do is stop pixel-peeping at 100%. What you are seeing is the "bad" that comes with greater pixel density. The greater the image is magnified, the more likely you'll see the imperfections.

And lastly... (at the risk of offending you), are these the types of photos you take on a daily basis? Some garden light, some tape measurer, some cooker, etc...? Do you blow up such images to 20x30 or greater prints?


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Ross_Curtis
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Jul 26, 2010 03:14 |  #13

Don’t worry you can’t offend me, I appreciate your input and feedback.
Of course these images are not typical of my photography.
*
You are right, people and I include myself here do become a little obsessed with pixel peeping.* I rarely blow my images up. I guess that is the ironic thing, so why should I care what the image looks like at 100%?* I’m never going to distinguish a slightly out of focus image when printed at 7x5.* For me it is all about getting the perfect shot and if the focus is slightly out, I’m not happy.
*
I will try reducing the image size down to 3888x2592 to match the 40D.* Although I’m 90% sure it will not resolve this (but I’m willing to try).
*
Whenever I have tested both the 40 and 7D I have always taken a control shot using live view and 10x magnification.* I’m not directly comparing the images between the 40 and 7D, I am comparing them to the control shot.* By doing this I can see what an in focus image should be.* When I run a series of say 10 shots and only 2 are close to being in focus, compared to 8 on the 40D (compared to the control shot of the relevant camera) naturally I begin to question the camera.
*
*
*
*


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Jul 26, 2010 03:28 |  #14

Well, your copy of the 7D certainly could be faulty. But in order to make that determination, you'll have to try other lenses and see if the 7D gives you the same low-keeper rate as it does with your 24.

I'm assuming in your tests, you've been racking the focus out to infinity and then re-acquiring focus between each take?


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Ross_Curtis
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Jul 26, 2010 04:00 |  #15

I have been focusing on infinity between shots, I’ve also tried leaving it and just re-focusing with similar results.
*
Tonight I will try another series, this time using both the 24L and 135L on both the 40D and 7D.
*
I’ll post some examples later, but be warned they’ll be incredibly boring.

How are you enjoying the 85 F1.2?


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