Is it the body or the lens?

[tmorgan]

Hi, anybody recognize this one?

 

I just did a shoot using a 24 2.8 with a 7D body in tighter quarters than usual.

 

I noticed that the images were very soft, so I did a bunch of test shots with the 7D body

and this lens and a few others I had.

 

The 24 2.8 *and only* the 24 2.8 seems to back focus by about 6 inches for shots out to

six feet or so.

 

I can manual focus the thing fine.

 

-So, what does this sound like? The body? The lens? The body with this lens?

 

-What's it like to deal with KM on this sort of thing (I've never had occasion to talk to them

about anything).

 

Thanks.

 

...Tom M

[clinton_abe]

Can you clarify what you're talking about? What exactly do you mean the 24 "seems to back focus by about 6 inches for shots out to six feet or so."?

 

And what do you mean "I can manual focus the thing fine."? Are you saying the pictures are soft only when you auto-focus?

 

What other lens did you test?

[tmorgan]

Clinton,

 

Clarifications:

 

If I use auto focus, I was getting a soft image.

 

To investigate, I put some large type text down on a table top, at various distances from

the camera, to give me targets that are easy to judge for sharpness.

 

-Using spot auto focus, I find that items which are about 6" *behind* the indicated auto

focus point are sharp; items *at* the auto focus distance are soft.

 

-If I turn off auto focus and use my Mark-I eyeballs, the point I am focusing on is sharp.

 

-These symptoms only occur for the 24mm f2.8 lens; other lenses appear sharp at the

auto focus point, as you'd expect.

 

Thanks for thinking about this. I am trying to figure out whether I need to complain about

the lens, the body, or the combination.

 

...Tom M

[bob_gentile]

If you're having that problem <em>only</em> with <em>that</em> lens... and if there's no problem with <em>any</em> of your <em>other</em> lenses... then, the problem is with the lens.

[dw fletcher]

I've had the same problems with both a 24/f2.8 and a 50/1.4. Shooting wide open, the camera would not focus correctly at all. The problems do seem worse at the distances you describe.

 

I sent my 7D in last tuesday for the second time. The first time they didn't fix it (I'm wondering if they even looked at it). I expect it'll be back tomorrow...I'll come back and let you know if they actually fixed it this time.

 

In the meantime, try using one of the corner AF sensors and see if they're more accurate than the central one. That was the case with mine. I could get pretty good autofocus using the lower-left sensor only. The central one -- the one you'd like to use in most cases -- was way, way off.

 

KM knows about the 7D's problem. When I called in, they knew exactly what I was talking about and told me to send it in. They'll pay for the shipping, but you may have to ask them to do it. Don't be surprised if you have to send it more than once. Also, my KM contact told me that they're starting to get more and more cameras in, to the point that service is beginning to slow down. The first time I sent my 7D in, the turn around was extremely fast. This last time, it was signinficantly slower.

 

The backfocusing problem is very common.

[tmorgan]

Telemachus,

<br><br>

Ahh, thanks, so I am not seeing things.

<br><br>

I took a bunch more pictures of rulers pointing away from me, at various distances away

from the camera.

<br><br>

I did a pretty careful exploration of the variables I could think of. The trouble for me

seems to be concentrated on:

<br><br>

<ol>

<li>This particular wide lens (24mm)

<li>Wide aperature (below 4) (although the increasing DOF muddies things up)

<li>A distance to target of 6 to 8 feet(*)

</ol>

<br><br>

I always used the center focus point.

<br><br>

Item 3 seems like a clue to me. This is the distance on the 24mm where very small

motion of the distance scale has a big effect on the focus distance. It's much touchier

than, for example, the 24-50mm f4 set at 24mm.

<br><br>

I did a bunch of manual focusing in this range, watching the in focus dot as it went on and

off. It looked to me like the 7D was a little 'careless'; the in focus dot would stay on thru a

pretty big range (in feet) in this range of 6 feet on out. In the camera's opinion, 6 feet and

infiinity were both okay as set points for an object at 6 feet.

<br><br>

==

<br><br>

Did KM give you any idea what they were doing to the bodies?

<br><br>

It would seem to me that this could be a firmware fixable thing. Given that it's possible to

focus manually, I'd expect that working on the autofocus algorithms would fix things.

<br><br>

Thanks for the offer to let us know how you make out with your second (ugh) go around.

<br><br>

...Tom M

<br><br>

(*)For reference, the other lenses that I tried, all of which autofocused okay at all the

distances I

tried were:

<ul>

<li>85mm f1.4 (the old one)

<li> 24-50mm f4

<li>70-210mm f4

<li> 35-80 f4-5.6

</ul>

[dw fletcher]

Yours may not have the same problem that mine does. It doesn't matter what lens I use. I do have a 70-210 f4 that doesn't backfocus, but at f4 all my other lenses are okay, too, so I don't consider that.

 

Anyway, on mine they're calibrating the AF sensors. It's not a firmware problem.

[dw fletcher]

My weird 7D saga continues. My contact at KM called me today and said my center AF sensor is fine but my corners are off. This is totally bizarre as far as I'm concerned.

 

First, none of the sensors should be off at all since they have had the camera before for that very issue. Second, I shot dozens of shots with that center AF sensor and just about all of them are out of focus. I've shot dozens of similar shots with the lower-left corner sensor and most of them were in PERFECT focus.

 

So, Thomas, I don't know what to tell you.

[tmorgan]

Telemachus,

<br><br>

It sounds to me like there is Something Really Wrong with respect to 7D autofocus at

wide apertures.

<br><br>

When I hear 'bizarre symptoms' I immediately think 'computer'.

<br><br>

I wonder how the processing of the AF sensors is done on the 7D. I found a <a

href="http://konicaminolta.com/products/consumer/camera-pus/slr/maxxum7/

ope01b.html">page</a> that describes the AF sensor operation for the 7, but nothing for

the 7D.

<br><br>

Good luck with your repairs, please let me know what the resolution turns out to be.

<br><br>

Makes me glad that mostly I shoot with a range finder :-)

...Tom M

[bob_gentile]

<p><em>"... Makes me glad that mostly I shoot with a range finder..."</em></p>

 

<p>-----------------------------------</p>

 

<p>That's what I was thinking. Not a rangefinder, but all-mechanical SRTs. </p>

 

<p>Are problems like these common with AF cameras/lenses? Just the newer models... until

all the bugs get worked out? Rare? </p>

[dw fletcher]

There was a similar problem with the 10D came out, I think. For some reason I never heard about it on SLR's, although it may have happened then, too.

 

Thomas, my camera should be back tomorrow and I'll let you know. I won't have anything better to do as it's supposed to rain.

[dw fletcher]

Well, my camera came back today. They said there was nothing wrong with the center AF sensor, but it sure is focusing a lot better now than when I sent it in. I have no idea why.

[tmorgan]

That's good news.

 

I put the 28mm lens on a film body today, and am trying some exposures at the same

distance that give problems with the digital back.

==

I find this all interesting. It an example which shows what an odd hybrid a digital SLR

currently is.

 

The fact that 'AF sensors' need to exist, for example. There's a big 'sensor' (the CCD itself)

and a big honking processor which could do all the autofocusing you'd need -- but, the

CCD is behind the mirror.

 

The whole thing is like a sailing ship with a retrofitted steam boiler.

 

...Tom M

[dw fletcher]

Yep. I wonder why they even have to have shutters. Couldn't the sensor just be turned off and on for varying durations?

[melresnick]

Telemachus, have you had a chance to give your 7D a good workout yet? Did KM fix everything? I can just try to imagine the disappointment you've felt dealing with a defective one.

[dw fletcher]

It has been frustrating, but there was one guy at KM that helped me out a lot. Unfortunately, he was at PMA the first time I sent it in and they didn't fix it right. It's working perfectly now.

[tmorgan]

Here's an update from me on my autofocus issues.

<ul>

<li>I shot a test roll yesterday using the 24mm f2.8 lens that had problems on the 7D,

using a 7 (film) body.

<br>Those images are fine; the spot you tell it to focus on is in focus.

<li>I contacted the KM service center, described my symptoms and was instructed to send

the camera in for service.

</ul>

I'll report back after the service.

<br>

...Tom M

[tmorgan]

I sent the camera out last Monday, and it is back today.

 

The problem is corrected.

 

...Tom M