Can a busy background screw up IS.

Though I love my 100-400 it is still a very problematic lens. The 50D has solved the focus issues and it is now focusing spot on but occasionally I still get very strange pics. Below are two pics that show the problem clearly. Both are almost identically shot, subject, lighting almost identical, both hand held, and both focused spot on. I have only included the heads because it shows the problem better, but if I look at the feet and the corn stalks I can clearly see that there is no front or back focusing going on.

THe second pic is what I expect from the 100-400 but the first one has a very odd bokah and is very soft. In the first pic if you look at the background it looks as if something was vibrating very quickly causing the corn in the background to sort of make groups of four lines. But if you look closely at the lines there is no perceviable pattern. Some lines run horizontally and others vertically. It's almost like there is some type of interferance. The second pic is what I expected to get.

The only thing I can surmise is that in the first pic the background is very busy and causing some type of interferance or ossilation with eiother the IS or with the image processing. One shot would not cause me concern but i have dozzens like this and the only thing I can see that is in common is that if the background is farther away and more OOF, the subject focuses great. If the background is busy with lots of details, the pic is like the first.

Anyone have a clue whats going on?
Anyone seen something like this?
I'm going to run some experiments with IS on and off but I wont get to them for a few days.

Any input would be appreciated. BTW, I have quite a few shots of these birds in flight and all are focused sharp. THe pics below are screenshots of unprocessed raw files as they camer from the camera.

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IS uses gyroscopes so I don't see any way that the image itself could have an impact.

It looks to me like you're simply moving the camera more than the IS can handle. Could it be that you're not giving the IS a moment to "start up" before taking hte shot?

IS relies on data from gyroscopes to move a lens element with electromagnets. All it knows is what the gyroscopes are telling it, so the image has no impact on it. Maybe you did not allow enough time for the IS to warm up before taking the shot, usually about a second with my lens....
Maybe also the in camera sharpening or whatever is doing weird thing to the first shot, but I don't think so...

I've seen bokeh issues like that from UV filters...did you have a filter on by any chance?

Lens hood on, or off?

krb wrote in post #6789200
IS uses gyroscopes so I don't see any way that the image itself could have an impact.

It looks to me like you're simply moving the camera more than the IS can handle. Could it be that you're not giving the IS a moment to "start up" before taking hte shot?

I tend to not be a rapid fire shooter and use the double tap method to focus so the shots probably have multiple seconds to stabilize.

pendulum15 wrote in post #6789770
..Maybe also the in camera sharpening or whatever is doing weird thing to the first shot, but I don't think so...

These are screen shots of the raw file with picture type standard. It's the same picture type for both shots so I would expect the DPP processing to be the same.

Jman13 wrote in post #6790050
I've seen bokeh issues like that from UV filters...did you have a filter on by any chance?

I'm running filterless. Actually this lens hates filters. If i put on a polerizor the IQ goes to he!!.

S.Horton wrote in post #6790069
Lens hood on, or off?

Lens hood on.

The thing that really has me stumped is that this is not the only pic like the first. About 1/2 of the pictures I took in the fields have the weird background and the softness of subjectt. Of all that are messed up, there is a busy background. The same type of pics taken at a lower angle where the backgrounds was farther away come out sharp. All of the pics I took with the birds in the air are sharp. It's almost as if this lens does not like corn stalks.

IS is a manual adjustment of lens elements that is a response to small amplitude high frequency movement typical in hand holding. It does not respond to optical characteristics of the subject.

In the first one, were you panning to follow the birds? In many lenses, you need to disable IS if you're panning because it will try to stop the camera movement in the panning, but be overwhelmed by the large amplitude. Some of the L series lenses can sense panning and shut off the IS on their own. Others can be switched to stabilize only one axis, specifically when you're panning in the other. Check your lens manual.

I think there's a lot of misinformation out there about IS. Sadly, the lens manufacturers haven't gone overboard in straightening it out by posting performance data under various conditions of movement. For example, I have had difficulties with IS when shooting from a pitching/rolling/yawin​g sailboat. IS can't handle the magnitude of the movement. I usually shut it off.

I hope these images are not the best examples of the 50D with focus corrected. If they are, I'm keeping my 20D and 40D. They are both badly out of focus or have a severe case of camera or subject movement. The second one is almost back lit, which is not kind to your subjects.

The problem could be simply that the autofocus system is seeing high contrast elements other than the birds.

The camera and its autofocus system have no clue as to what your idea primary point of focus should be unless you do something to isolate a contrasty edge that IS your intentional point of focus. That's why I often resort to manual focus for tricky situations.

John,
Which focus point was it on ? I see you were in one shot, so it should have locked focus before releasing the shutter, but I'm wondering if the focus motor was actually moving when the shutter tripped ? I don't see how it could have happened....but

george w

joedlh wrote in post #6790726
IS is a manual adjustment of lens elements that is a response to small amplitude high frequency movement typical in hand holding. It does not respond to optical characteristics of the subject.

That is my understanding as well.

joedlh wrote in post #6790726
In the first one, were you panning to follow the birds? .

No panning, birds were moving very slowly or stationary.

joedlh wrote in post #6790726
I hope these images are not the best examples of the 50D with focus corrected. If they are, I'm keeping my 20D and 40D. They are both badly out of focus or have a severe case of camera or subject movement. The second one is almost back lit, which is not kind to your subjects.

The birds were in a horrible location just before sunset. Both are taken with the birds quite a distance away, maybe 30~40 yards or so. The pics are 100% center crops, unprocessed, unsharpened and not the best shots of the day. They were choosen because it clearly shows the issue and both shots are nearly identical in settings and composure.

SkipD wrote in post #6790740
The problem could be simply that the autofocus system is seeing high contrast elements other than the birds.

The camera and its autofocus system have no clue as to what your idea primary point of focus should be unless you do something to isolate a contrasty edge that IS your intentional point of focus. That's why I often resort to manual focus for tricky situations.

That was my thought. The busy background is causing the lens to ossilate somehow.

george m w wrote in post #6790757
John,
Which focus point was it on ? I see you were in one shot, so it should have locked focus before releasing the shutter, but I'm wondering if the focus motor was actually moving when the shutter tripped ? I don't see how it could have happened....but

george w

Center point only and if I look at the first pic, I can clearly see the the DOF band is centered on the subject. That's as focused as that pic will get.

You "double-tap"? Try partially depressing and holding before release. IS takes a second or two to come up to speed and it'll shut down again in a few more seconds if you back off the shutter release or AF-ON button.

Have you tried switching off IS and use some kind of physical support to rule out IS as the cause of the problem?

Jon wrote in post #6791155
You "double-tap"? Try partially depressing and holding before release. IS takes a second or two to come up to speed and it'll shut down again in a few more seconds if you back off the shutter release or AF-ON button.

Yes, thats what i meant by double tap. I shoot slow, hold over from film is guess, so I will press once for a few seconds, press again, maybe even a thord time until I'm happy with the focus. But it's worth experimenting a bit to see if my technique is causing the issue.

One other piece of info. This is not the only pic I got like this. Out of the 100 or so I took that day about 25~30 are like this. The one thing that they all have in common is that they are all corn field shots. The ones in bean fields, grass or sky do not do this.

I will pay close attention to how I am composing though.. I'm wondering if the lens is having a harder time focusing in the corn field which is causing me to re-focus more often. It's something to look at, thanx.

hennie wrote in post #6791196
Have you tried switching off IS and use some kind of physical support to rule out IS as the cause of the problem?

No, that is definitly something I want to try.

Firstly - don't touch the camera.
A tripod like a classic Manfrotto will still result in noticeable blur when you press the shutter button. Even if you try and be gentle you can still see it in the images.
Either use the self-timer or a cable release.

Secondly - It may be the mirror moving up out the way.
That audible CLACK can really vibrate long lenses. My old 5D film camera used to never get sharp piccies at 1/125s and 300mm with the 75-300mm lens.
The solution I found - and what I recommend to you now is to use mirror lock up.

In practice, to get a critically sharp image with a long lens you need 1) no wind or a very good tripod. 2) A cable release. 3) Use mirror lock-up.

With regards to IS causing the problem...
I've heard of IS fighting resonances caused by the tripod which makes the overall image quality worse.
It's a problem caused by the whole lens, body, tripod combination AND a source of vibration.
I think this is because the IS is designed for hand-holding which is a relatively low-frequency problem. When the camera is strapped to a tripod the vibrations are much higher in frequency and hence outside the IS design parameters and depending on the lens may or may not be affected.

My money would be on your 'double tap' method being the cause.
Get a cable release, try mirror lock-up and report back.