Any insight on a focus issue, maybe camera shake?

[Redcrown]

I did a brief practice session to see what I could get away with for hand-held shutter speeds, using a monopod for the first time. A Canon 70-200 lens plus 2X teleconverter on a Canon 5D4 body. On the monopod using the lens ring mount, f/8 at 400mm, auto ISO.

Things went well, better than I expected. I got 99% good focus at 1/400. I got about 80% success at 1/250 with image stabilization. Shots at 1/400 or greater with IS on were OK too. The IS did not misbehave.

But I had this one shot that confuses me. The shutter was 1/400, and it looks like some camera shake on the left side of the image only. There is a faint double image of the white lettering. The center and right look OK. On another shot of the same car at 1/800 everything is in focus. Other shots show no edge or corner softness at 400mm.

Can camera shake affect only part of an image? Or is something else going on?

[Ghibby]

I don't think this is camera shake, looks more like it is slightly out of focus on the left. I would imagine this is more likely to be a very slight optical decentering in the lens. Perhaps masked by depth of field and precise focus placement in the other shots. After all the AF is going result in a slightly different focus point for every shot. What aperture were you shooting at?

Have you set the camera / raw processor to remove CA or defringe the images? If you switch this off and look for the natural rendering of the lens you may see slight magenta / green edging that would confirm a slight focus error, especially if you were shooting wide open. I'm sure the canon 70-200 exhibits this behaviour as it is not a fully corrected apochromatic lens.

Ben

[rdonson]

Is back/front focusing a possibility?  That's something that drove me crazy with several Canon lenses.

[Redcrown]

Thanks for the comments.

If I turn off CA I do see a slight magenta cast where the faint double images are. Focus point was dead center in the frame, and I was not perfectly perpendicular to the car. So maybe this is just a case of the left side being outside the depth-of-field.

It's just that I'm used to seeing out-of-focus as a uniform blur, not a double image. I associate double images with camera shake or mirror slap vibration. Plus, here is another shot of the car taken at the same settings (f/8 and 1/400). It shows good focus and equal focus across the whole frame. The only difference is that it was taken about 2 minutes later and 10 feet closer. Being closer, I should have had an even shallower DOF.



Full size here:
https://photos.smugmug.com/Other/Temp-Upload/n-5RJTN/i-tpGPLqp/0/O/i-tpGPLqp.jpg

[ppmax2]

Looks like "smear" from IS. We're you panning at all on the monopod?