Canon 70-200 F4 Non IS Question

Is this particular lens known to have soft corner issues?

I've been using it quite a bit lately and whether it's due to my technique or the lens itself, I've noticed that the top right and the bottom left of corners of a few images are soft/blurry.

I'm thinking that if I'm the cause of this, then wouldn't all four corners be soft/blurry?

I'm shooting birds that are on the ground and I'm noticing the grass , leaves, etc, are soft/blurry in the top right and bottom left corners while they appear more in focus/sharper in the opposite corners.

I'm above and shooting down on the birds.
Shooting handheld but resting the lens on a window frame.
Normally at 200mm, using evaluative metering, center point focus, AI Servo.
Using Canon 40D.

Cropping the image gets rid of the softness and I'm left with what I want but, just curious as to what's happening at the corners.

The center focus point included the eye, the widest part of the black to the right of the eye and some of the blue below the black.

Pine needles might not be the best thing to go by but, looking at the attached image, I can really notice the softness at the top right corner.
Don't notice it so much at the bottom left in this smaller image but it is soft.

Most probably decentered. I'd send it in to Canon, as that will look even worse on full frame.

oingyboingybob wrote in post #18158261
I can see the softness. What was the aperture?

f/4, as per EXIF data.

oingyboingybob wrote in post #18158261
Was the shot taken directly in a straight line or were you at an angle ie is the top RH corner closer to the lens than the left?

That is not the cause, as the bottom RH corner is certainly closer, but looks sharp.

Just tried the same lens on my Canon 6D... same results.

I've had this lens for a number of years and just noticing this issue now.
If I did notice it before, I probably just put it off as something I was doing wrong.

Shot from same location, same aperture, focal length and ISO as first picture.
Different shutter speed.
Not sure why EXIF information didn't load with this image.
Must be something to do with saving this one for the Web in Photoshop where I didn't have to do that with the first picture.

Wow, visible even in scaled-down images. Looks like the camera is being held level. I've seen a lot of decentered lenses in my time, but I've never seen opposite corners like this (usually it's a single edge) --- looks like you have an element tilted on a diagonal axis.

If you send it in for service, take some test shots and burn them to a CD in the shipment. I usually tape blank-and-white printed targets (they look like crash test dummy calibration marks) to a flat wall in all four corners of the frame, plus one in the centre for focus. Use a tripod with the camera level and perpendicular to the wall. Take shots at multiple apertures, including the widest. Repeat with a 'known-good' lens to validate the test shots.

You upper left and lower right look nice. It's the opposite corners that look bad. I'm guessing that lens needs some adjustment.

canongear wrote in post #18158244
Is this particular lens known to have soft corner issues?

I've been using it quite a bit lately and whether it's due to my technique or the lens itself, I've noticed that the top right and the bottom left of corners of a few images are soft/blurry.

I'm thinking that if I'm the cause of this, then wouldn't all four corners be soft/blurry?

I'm shooting birds that are on the ground and I'm noticing the grass , leaves, etc, are soft/blurry in the top right and bottom left corners while they appear more in focus/sharper in the opposite corners.

I'm above and shooting down on the birds.
Shooting handheld but resting the lens on a window frame.
Normally at 200mm, using evaluative metering, center point focus, AI Servo.
Using Canon 40D.

Cropping the image gets rid of the softness and I'm left with what I want but, just curious as to what's happening at the corners.

The center focus point included the eye, the widest part of the black to the right of the eye and some of the blue below the black.

Pine needles might not be the best thing to go by but, looking at the attached image, I can really notice the softness at the top right corner.
Don't notice it so much at the bottom left in this smaller image but it is soft.

Hosted photo: posted by canongear in
./showthread.php?p=181​58244&i=i30139521
forum: Canon Lenses

It could be a decentering issue, but you can test it yourself. Here's a link from lens rental.com

https://www.lensrental​s.com …echnique-gets-a-makeover/

You can download the Zeiss Siemens Star Chart by selecting and saving the image to your hard drive. You can display the chart on your computer monitor, and following their instructions, which I have pasted below. It should give you a good idea whether or not your lens is decentered.

If you manually defocus the lens just a bit, the star rays and the white and black circles in the center blur, of course. If the lens is in proper alignment and pointed directly (lineup isn’t critical, you can eyeball it) at the star, the white and black circles remain circular as they blur. But if the lens is decentered or significantly tilted the center blur will ‘flare’ out in one direction or another as you defocus.

As indicated, manually defocus a bit on the center of the star chart and take an image. Make sure you don't AF before taking the image. It must be defocused a bit. If there is no decentering the center of the chart should show a round black dot in the middle of a round and evenly shaped white donut. If there is decentering, the black center will be skewed to a position other than the center, and the shape of the donut will no longer be symmetrical.

One of the first things I do when acquiring a new lens is to perform a decentering test. This became habit after my purchase of a new copy of a Sigma 30 mm f/1.4 EX DC HSM several years ago which seemed to focus more towards the upper right of the image. I came across the lensrental.com test and it confirmed significant decentering of that lens to the upper right as I had observed. I was able to exchange the lens for a better copy, and although I have not run across any decentered lenses since then, it taught me a valuable lesson

Thanks for the link and explanation.
I'll give that a try.

Talked to Canon customer service today and if in fact the lens needs adjustment, the repair cost including taxes and shipping would be a minimum of $310.
That's almost half as much of what I paid for the lens brand new.

The Canon rep suggested I do some test shots using single shooting drive mode and one shot auto focus mode after I mentioned that I was using continuous shooting and AI Servo.
He said AI Servo can cause issues at times.

canongear wrote in post #18159686
He said AI Servo can cause issues at times.

Not this kind of issues.
AI Servo issues causes back or front focus, while a tilted element causes what your photos show.

CheshireCat wrote in post #18159774
Not this kind of issues.
AI Servo issues causes back or front focus, while a tilted element causes what your photos show.

Good information to know.
Thanks

mwsilver wrote in post #18159242
It could be a decentering issue, but you can test it yourself. Here's a link from lens rental.com

https://www.lensrental​s.com …echnique-gets-a-makeover/

MWSilver:
If you see this post, could you comment on the results.
I'm pretty sure what I'm going to end up doing regarding the lens but just curious as to what you think about the results as you have experience using this chart test.


I didn't use the computer monitor as you had suggested but, printed off the chart instead and taped it to a wall.
70-200 @ 200mm on the 6D.
Tripod and camera timer used.

canongear wrote in post #18160950
MWSilver:
If you see this post, could you comment on the results.
I'm pretty sure what I'm going to end up doing regarding the lens but just curious as to what you think about the results as you have experience using this chart test.

I didn't use the computer monitor as you had suggested but, printed off the chart instead and taped it to a wall.
70-200 @ 200mm on the 6D.
Tripod and camera timer used.

Hosted photo: posted by canongear in
./showthread.php?p=181​60950&i=i133826960
forum: Canon Lenses

Hosted photo: posted by canongear in
./showthread.php?p=181​60950&i=i132675821
forum: Canon Lenses

I think you should have shot the images in more light and perhaps defocused a bit more. But based on what I saw decentering does not seem to be your issue. It's been a while since I performed the test and I erred when I told you the center dot was black. It is of course, white. Everything looks perfectly symmetrical on your images. Check the lens rental link I gave you. They provide examples of decentering.

My bad, I said "decentered" while technically it is "tilted".

Thanks for all the replies and suggestions.