topic Re: Softness issue with Canon 100-400 F/4.5-5.6L IS II USM in EF & RF Lenses

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

Seanac — Sun, 22 Jun 2025 23:05:56 GMT

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

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

jrhoffman75 — Sun, 22 Jun 2025 23:11:08 GMT

@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

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

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

Seanac — Mon, 23 Jun 2025 00:26:27 GMT

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=stiachxq0j4bemhwbhcluhlc8&st=bcv0u3pk&dl=0

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

jrhoffman75 — Mon, 23 Jun 2025 01:48:10 GMT

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?

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

Steve_B — Mon, 23 Jun 2025 02:36:28 GMT

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

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

Steve_B — Mon, 23 Jun 2025 02:54:16 GMT

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.

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

Seanac — Mon, 23 Jun 2025 03:21:56 GMT

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&st=ahubozap&dl=0

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

Seanac — Mon, 23 Jun 2025 03:27:41 GMT

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

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

jrhoffman75 — Mon, 23 Jun 2025 10:35:07 GMT

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

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

p4pictures — Mon, 23 Jun 2025 13:05:47 GMT

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.

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

K_ozdragon — Thu, 14 Aug 2025 10:35:00 GMT

So in one of the photos, you're at 182mm, 100 ISO, & 1/640 shutter speed. This is causing motion blur. I'm assuming you're near the planes landing at that focal distance & subject size in the frame. The plane is moving pretty fast. You would need a minimum of 1\1000 for a sharp photo. Don't be afraid to bump up your ISO. Capturing motion is exactly what the ISO is good for. A tiny amount of grain is better than photos that aren't sharp due to motion blur.

You might be able to capture these at those speeds while panning, but unless you're highly skilled at it, you're going to get blur that looks like sharpness issues. The plane isn't centered in the frame, so if it was a pan shot, your tracking is off. Bump up your shutter speed using a higher ISO. That should fix your problem.

Also, be sure you're on servo mode for continuous focus. If that isn't on, there's no way you're capturing a sharp photo on a moving object. I figure you know this, but it never hurts to be sure.

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

Waddizzle — Thu, 14 Aug 2025 18:12:32 GMT

Are you using a UV filter? That particular lens doesn’t perform well with one on a DSLR.

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

ebiggs1 — Fri, 15 Aug 2025 14:39:14 GMT

Even though this thread is 2 months old I will suggest you are the problem. You are all over the place with your AF.

I can almost guarantee Ai-servo is the culprit, use One shot and preferably the center focus point.

"Are you using a UV filter? That particular lens doesn’t perform well with one on a DSLR. "

Absolutely ditch any filter you attached to the lens. ALways use a lens hood for this type work. This lens is not really great with IQ and is hampered more if you put any filter on it.

" I’m considering selling the lens and going back to my Sigma."

You can certainly do that the Siggy has better IQ. I had two copies of the 100-400mm (1st and 2nd model) and could not like either so I sold them both. If you want Aa 400mm lens check out the ef 400mm f5.6L prime it is a fantastic lens and very sharp.

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

Seanac — Fri, 27 Mar 2026 07:46:12 GMT

Thanks, I would like to ask; how do you know my focus is all over the place? I feel like I throw away most shots, even nearly a year later. Is there a hidden technique I don’t know of that I didn’t need to use with my sigma? Would you recommend getting the 90D and the 100-400L II professionally calibrated? Or is it somehow user error that I’m not aware of? I am not using a UV filter and I do use a lens hood. I have never had to use one shot rather than ai servo, but I can try it out.