Softness issue with Canon 100-400 F/4.5-5.6L IS II USM

[Seanac]

I picked up the Canon 100-400 F/4.5-5.6L IS II USM recently and found that many of my images are now soft.

I use this lens with the canon 90D body; and I upgraded from the sigma 100-400

I shoot aviation, and on many occasions half of the plane is soft and the other half is sharp. For instance, the nose is very sharp but then the tail is soft. I am shooting at roughly 220mm and am 1/4 mile from the airplane, so it’s not like a crazy depth of field issue. 
I’m using AI servo, and have tried many different autofocus point modes. With my old lens I used auto AF points, but due to my issues with the new lens I have tried every AF point mode and they all seem to have the same issue. I’m also shooting F/8, ISO100/200 and with a fast enough shutter that I used to have no issues with (1/800). Some shots are fully sharp, but a GREAT majority are sharp in the nose and soft in the tail. 

Really frustrated because I have missed many shots due to this, and am curious why this may be? I’m considering selling the lens and going back to my Sigma. Would love some input

[jrhoffman75]

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@Seanac wrote:

I picked up the Canon 100-400 F/4.5-5.6L IS II USM recently and found that many of my images are now soft.

I use this lens with the canon 90D body; and I upgraded from the sigma 100-400

I shoot aviation, and on many occasions half of the plane is soft and the other half is sharp. For instance, the nose is very sharp but then the tail is soft. I am shooting at roughly 220mm and am 1/4 mile from the airplane, so it’s not like a crazy depth of field issue. 
I’m using AI servo, and have tried many different autofocus point modes. With my old lens I used auto AF points, but due to my issues with the new lens I have tried every AF point mode and they all seem to have the same issue. I’m also shooting F/8, ISO100/200 and with a fast enough shutter that I used to have no issues with (1/800). Some shots are fully sharp, but a GREAT majority are sharp in the nose and soft in the tail. 

Really frustrated because I have missed many shots due to this, and am curious why this may be? I’m considering selling the lens and going back to my Sigma. Would love some input

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Can you post typical RAW images with the problem to Dropbox or One Drive?

[Seanac]

Hi, yes here are some photos. I believe the delta photo shows the problem the best - the nose is sharp and the tail registration numbers are soft. I didn’t previously have this issue with my other lens, and I’m using the same spot at the same time of day. https://www.dropbox.com/scl/fo/51em12tslii58m5cnnvgv/AN9zizedt_ig0r8wn26Mbm0?rlkey=stiachxq0j4bemhwb...

[jrhoffman75]

If all there was was these three images I'd suspect maybe thermal distortion from engine exhaust, but you say it doesn’t happen with the previous lens. 

Have you tried taping a newspaper to a wall?

Is it a new lens or used?

[Steve_B]

Is the lens new? If not, has it been dropped? Have you tried it on another body with the same results? 

[Steve_B]

I think you're seeing engine eflux. I have the Mk1 100-400 L, it's 25 years old and been used on film and now digital bodies, it's still as sharp and capable as it was when new. What aperture are you using, I ask because the Delta 737 is coming in at about 20 degrees or so relative to your point of view, and you might have the nose in focus but not the tail, although I still think that's eflux. 

[Seanac]

Lens is used, hasn’t been dropped or anything and if I shake it around I don’t hear anything loose. ive gotten some sharp photos from it, but a lot of the shots are thrown away. 
I thought it was engine exhaust as well, but it seemed too consistent.
Heres a much better example photo, you can see the registration N number and tail is super blurry, while the nose is much sharper. Also due to the engine positioning it rules out engine eflux
https://www.dropbox.com/scl/fi/sostlgqrr7zw6ioneizia/IMG_0710.jpeg?rlkey=fj0qfyxfltm8hnnho5pkk82wf&s...

[Seanac]

I just wrote down some words on paper and taped it to my wall, every word was sharp at 100mm and 230mm, couldn’t tell a sharpness difference between the canon and sigma. Next time I’m at the airport I’ll take my old lens and compare in the field

[jrhoffman75]

You can contact Canon service and have the lens checked. It is a very sharp lens when in proper condition. 

[p4pictures]

Do you have micro focus adjustment configured on your camera? If so is it set for individual lenses or all by the same amount.

Check custom functions, C.Fn II AF microadjustment.