70-200 mm f/4 L IS - Very shallow DoF

I picked up at 70-200mm f/4 L IS recently used. The guy (allegedly) has only used it few times over various trips and found he doesn't use it anymore so I picked it up to replace my lack of a proper long range lens.

My comparison is against the 55-250 kit lens that Canon has. Its been the worst lens in my bag so figured it was time to upgrade it. Now my problem with the 70-200 is the DoF seems to be insanely shallow. At f/4 I can basically get a letter on a piece of paper in focus but basically almost nothing in the real world. Where as on the kit lens f/4 acted shallow but usable for people or other simple items on open backgrounds.

Is the 70-200 a lot to get used to? I seem to have to crank up the aperture to 9+ to get something in any form of sharpness.

I've looked at a few focus charts online but they seem to be for the auto focus testing. Through the view finder, the 70-200mm does very well until the image gets spit out.

Any suggestions on how to confirm or test this?

Sounds like it's most likely either front-focusing or back-focusing, although there could also be something wrong with the lens

Try putting the camera on a tripod and taking a picture of something using autofocus, then go into live view, manually focus the lens, and take another picture. If there is a significant sharpness difference then the AF is off. If you can't get a sharp picture even manually focusing then there is something wrong with the lens. The 70-200 f/4 L IS should be a very sharp lens, even at f/4

What camera are you using? If you have MFA then you might be able to fix a front- or back-focus problem

I used to have one of these,it was tack sharp to the point that I rarely needed to stop it down.
Like yellowt2 says something seems not right

yellowt2 wrote in post #18004867
Sounds like it's most likely either front-focusing or back-focusing, although there could also be something wrong with the lens

Try putting the camera on a tripod and taking a picture of something using autofocus, then go into live view, manually focus the lens, and take another picture. If there is a significant sharpness difference then the AF is off. If you can't get a sharp picture even manually focusing then there is something wrong with the lens. The 70-200 f/4 L IS should be a very sharp lens, even at f/4

What camera are you using? If you have MFA then you might be able to fix a front- or back-focus problem

I will give it a shot and post the results. I tried manually focusing and hand holding it previously and it was a similar result. I suppose photos would help convey it a lot better.

I still have the 7D which thankfully supports MFA.

troutfisher wrote in post #18004889
I used to have one of these,it was tack sharp to the point that I rarely needed to stop it down.
Like yellowt2 says something seems not right

Hopefully this is fixable with the MFA in that case since it feels like a great lens otherwise.

How close are you to the subject?

A reasonable distance. Maybe 15-40' with my various fooling around with it.

I found one from last weekend where I took a few shots of a tire to test the depth.

This is a 100% crop with the focus hitting the center of the tread portion of the tire. No sharpening or resizing done.
http://i.imgur.com/o8F​YS7G.jpg

Vladimer wrote in post #18004957
A reasonable distance. Maybe 15-40' with my various fooling around with it.

I found one from last weekend where I took a few shots of a tire to test the depth.

This is a 100% crop with the focus hitting the center of the tread portion of the tire. No sharpening or resizing done.
http://i.imgur.com/o8F​YS7G.jpg

That's at 70mm, f4 and 15'? If so, DOF seems correct to me.

FarmerTed1971 wrote in post #18004962
That's at 70mm, f4 and 15'? If so, DOF seems correct to me.

Its at 151mm. The DOF is correct when you look at the image as a whole. I mean when you click on it and view it at 100%. The focus spot was on the center of the tire tread yet I can't find a single lug on the tire that is actually sharp.

SS was 1/1250 and 100iso so its not due to hand holding or shake

Edit: DOF is probably not the term I should be using since as a whole on the image, the DOF looks right. Its the lack of being sharp at 100% that seems to be out to lunch.

Something weird is going on, I'm kind of thinking that the lens has a tilted or decentered element.

Looking at the photo, the lugs in the very center of the photo are not quite sharp, and then the whole image gets progressively less sharp headed towards the tire in the background. So based on that, my quick answer would be that the lens is probably front-focusing a bit and so everything visible is a bit behind the plane of focus.

But then I look at the lugs on the far left side of the picture. They are sharper (but not perfectly sharp) than the lugs in the middle of the frame, despite being a bit further away from the camera. That doesn't seem plausible with a correct lens.

Before accepting this quick assessment, try some additional targets. Especially look to shoot some targets where you can see a full sweep of ground before and behind the target so you can tell if the lens does indeed have an issue or if this tire shot just has an illusion as to what is and is not closest.

There is simply no better way to diagnose these problems than for you to post actual pictures with exif intact.

You bet guys. I'll print off some of the charts and get a bunch of shots this Sunday. I'll post them with the exif

either a lens or photographer problem but there's no way of knowing

Here we go

This one is with auto focus

And evidently you can't view it at 100% when uploaded to the forum. Let me see if I can find something else to upload to

Assuming you have both the 55-250 and the 70-210, if you put your 55-250 to its widest aperture and 210mm setting, and you do the same to your 70-210mm, at about f/5 (my guess, about the largest aperture size at 210mm) the DOF should be a bit deeper with the 55-250 than the 70-210 when both are set to same FL. Do directly comparative testing...

• 210mm focused at 100' distant target is DOF zone of 3.66' at f/4 (assuming 20/20 vision of the observer)
  
• 210mm focused at 100' distant target is DOF zone of 5.12.' at f/5.6 (assuming 20/20 vision of the observer)
  
• 210mm focused at 20' distant target is DOF zone of 0.14' at f/4 (assuming 20/20 vision of the observer)
  
• 210mm focused at 20' distant target is DOF zone of 0.2.' at f/5.6 (assuming 20/20 vision of the observer)