Strange focus failures and purple fringe with 760D and 50 f1.8 stm

Hi,

I recently bought an EOS 760D, stepping up from an old 350D. Yesterday I tested it out (with a 50mm f/1.8 stm), and I encountered some strange things.

first, I got a lot of blurry, wrong focused pics. Since I'm not used to automatic focus point selection (thanks to that old 350D) I set the 760D to manual selection.

It might look OK but if I crop it...

...the Ferrari logo is extremely unsharp

Did this happen maybe because the middle focus point (which was selected when I took the photo) is covering a much smaller area than on the 350D?

Next: I got some strange purple fringe at f/1.8:

This is a cropped image, from the middle. Check out the purple fringe around the edges

I've never seen something like that. It's awful at the edges

Are these just "bad luck", and bad shots, or some camera/lens issue?

Thanks,

Tamas

Some chromatic aberration (purple fringing) is to be expected with this lens at f/1.8. It should mostly go away by f/2.8. It can also be neutralized pretty well in Lightroom or equivalent. However, the amount in the last photo, even if cropped to 1:1, seems pretty excessive and might indicate a defective lens.

In the Ferrari pic nothing seems to be in focus. It might be that the focus plane is way in front of where it should be - you should do some experiments in a controlled environment to see where exactly the lens focuses. It might front-focus badly, or even have a lens alignment issue such that nothing is sharp.

macfly66 wrote:

It might look OK but if I crop it...

Did this happen maybe because the middle focus point (which was selected when I took the photo) is covering a much smaller area than on the 350D?

Yeah, nothing is in focus, but the foreground is closest (to being in focus), so I'd say your focus was way short of the car.

Did you focus and recompose, or focus with that framing?

If the second case, it looks like the AF point was over the centre of the bonnet, which is featureless, providing nothing for the system to lock onto. You need to give the AF sensors some detail they can "see" and work with. I would have put the badge under the centre point, locked focus, and recomposed, or used one of the lower AF points if that required less of a recomposition movement.

I know what someone will reply with, so before they do... no! Focus and recompose would not have taken the whole car and foreground out of focus with such a small movement at that subject distance, so that's not the culprit. And if you're worried about that, recompose by moving the camera in the plane of the sensor, rather than pivoting. You'll be amazed how little you need to move to get quite a big recomposition.

Regarding the first shot, I don't think that the all car will fit in the depth of field at f/1.6, something will be out of focus and if you try to get the windshield, the logo will be blurred,

Then look at the bus lights, it seems that you moved during the shot, there is more effect to the background than foreground, probably a small rotation of the camera under shutter release, at 1/800 it is weird but possible if your not completely used to the new camera, and had to bend down to be the correct height. and didn't want to stay for long in the street.

Doesn't mean that there is not issue with the lens, is it a new acquisition or did you used it successfully with your previous camera?

Regarding the purple fringes, I've never seen so much of them with my own 50 f/1.8, again, have you used this lens successfully with your previous camera or is it a new acquisition?

Jpeg or raw?

CQui wrote:

Then look at the bus lights, it seems that you moved during the shot,

It's a motor vehicle on a street... more likely it moved.

I can't see any motion blur in the subject.