Canon 70-200 - focal plane loss

[JazzJ]

Hi all,

Hoping someone can give me some advice. I am shooting on a Canon M50 with a Canon 70-200mm f2.8 IS USM II. Recently, I have been noticing a loss of focus/ some soft areas in my images. I can't decide whether it occurs at a certain aperture or focal length, or if it's just something very weird. See below the images as an example.

You can see the surfer taking off on the wave is sharp, but the surfer on the right hand side is soft. Basically, from that position in the frame, it's all soft. Almost 1/4 of my frame. It doesn't bother me too much, but it's something that I just can't wrap my head around.

Any advice welcome.

TIA

[JazzJ]

The sharper one was taken first, but no water got on the lens. And inbetween there are sharp images and some with the same focal/ softness. I actually first noticed the softness last June on another surf trip. 

Could it be to do with maybe the camera's AF settings? Just thinking out loud. 

[ebiggs1]

"Did maybe some water splash on the lens?"

You may have something there. I loaded the Raw file into PS and enlarged it drastically. None of the image is really sharp.  It is as if the SS was very slow.  Star trails kinda stuff although exif says 1/4000. I don't think there is anything wrong with the lens. Something outside happened. I know it might be unlikely but camera motion? 

[JazzJ]

Maybe my IS is playing up and messing me around? 

[kvbarkley]

Time for the newspaper test

http://www.bobatkins.com/photography/technical/lens_misalignment.html

[JazzJ]

Hi all,

Managed to do more research and finally tested with decent light and in a controlled environment. I suspect a decentered element.

Anyway, below are some images cropped to the bottom right where the issues/ softness occurs, at different focal lengths and apertures.

Noticeable clarity is lost af2.8 on edge of the frame, after f8 it seems to negligeable. I have contacted an authorised canon centre here now too, but with Covid restrictions, I'm not sure it will be repaired anytime soon. But atleast I may have found a work around for the time being.

Thank you to you all for your input and time. Feel free to offer any further suggestions if you have. 

[Waddizzle]

I think your samples just above are more normal than Abby Normal.  Despite opinions ot the contrary, I still think you are looking at a DoF issue in the original "bad" shot.  There is a lot of horizontal distance between the two surfers, so it is entirely possible that the one on right outside of the DoF, even if just barely.

As for your above sample shots, you are using an M Sries body with an EF/EF-M adapter.  You are likely looking at a DoF issue again.  How far away was the target from the camera?  How large was your target?

I look at DoF tables differently. DoF tables do not really tell me what range of distances should "in focus".  I regard the numbers as the range of where the plane of perfect focus should be.  

Having used this online caculator app for years, I have come to treat the results as being a bit generous, at least according to my eyes.  I use half the estimated range as the actual effective range.  At a target distance of 10 feet, your DoF is quite narrow.

And then, there is the mount adapter, which may not always perfectly align the lens..

[EDIT] In other words, your "decentered " lens could be a symptom of using the adapter with such a large lens.  I feel the adapters are not intended to use any EF mount lens for handheld shooting.  

BTW, I assume your test shots were captured using a tripod, and that the "focus target" was parallel to what should have been the plane of focus.  You do not want to shoot the target at any sort of angle.

[JazzJ]

That's very interesting. My 'test' shoot was on a tripod and perfectly straight on to the wall. So perhaps you're on to something thare with regards to the adapter. I'll get a DSLR and test without the adapter and see if I notice anything. Thank you!

[Waddizzle]

According to the screen shots you are using One Shot AF.

[ebiggs1]

John I agree. But a reduced jpg quality doesn't help.

I do think the lens needs to be looked at. Can't hurt and might just help!

[rs-eos]

In looking at the first image, it appears soft all around and only sharp in the center.

e.g. if looking at the upper-most wave in the image (with the surfers) from left to right... it starts off soft, then the mist, water and middle surfer are sharp, but then softens as you move to the right.

Same for the breaking wave about 1/3 from the bottom.  Starts soft, then gets sharp near the middle, then soft again.

Since there's a decent distance from this breaking wave to the middle surfer, and the mist behind the middle surfer also being quite crisp, the DOF would have been large enough for the other surfer and other parts of those waves.

As mentioned earlier, try taking an image of a brick wall or some vertical surface with enough detail.  Have the lens be as perpendicular to the vertical surface as possible.   Try different apertures;  When wide open, lenses can exhibit softness near corners/edges, though I wouldn't think it would be this extreme on such a lens as yours.