WHat is causing this with my lense? (1 Viewer)

WHat is causing this with my lens?

Im just an amateur camera guy with basic knowledge. I noticed on my last outting that a lot of my photos were not sharp. I did some testing to see if it was me or the settings. Youll notice in the picture that was wide open that the image is blurry and distorted with what looks like some CA. The other image shot at f-11 looks much better. I took several shots at different settings to make sure it wasnt camera shake and every shot at 5.6 looked like crap while the higher apertures were fine. I know that lense is a slow lense, but in daylight why would this occur?

It would help to know what lens and what camera, and what you were focused on. Metering setting would be helpful as well. The focus point on slow lenses (a lens with a minimum aperture of f5.6 would be considered a slow lens) is extremely shallow. But it would also be helpful to know whether you were in an area which was prone to atmospheric conditions, or you were shooting across a roadway...

That top picture in particular reminds me of the 'streaking' I was getting when I put a filter on my lens not long after I had bought the lens. I thought the filter would protect the lens. It turned out the filter was the cause of the problem. It is now being used as a table coaster. Have you recently added a filter?

I'm guessing your f5.6 400mm lens might be the venerable Canon L model? It should be a fairly sharp lens even when wide open although a friend of mine with that lens sometimes has not quite sharp results when wide open too. Most lenses do not perform at their best when wide open - two or three stops down is usually the "sweet spot". It's also tempting to leave the lens set to the widest aperture so that if you have to bang off a couple of quick shots the lens is "ready to go" under most lighting conditions. Therefore many photos are taking using this less-than-optimum setting.

I've not experienced it myself but some people have said that individual lenses can vary in quality, with a few examples being notably poor. They talk about having a "bad copy" of the lens. Perhaps yours is unfortunately one of these. Is your lens new and/or could it be returned/exchanged?

Good luck with finding the cause.

Have you tried calibrating the lens and camera, you may be experiencing front/back focusing hence when you step the aperture down it gives you a deeper depth of field so the object comes into focus

Are you familiar with back or front focus,sorry this is Nikon based but have a look and see what you think

https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/51633/~/how-to-use-the-af-fine-tune-function

Thanks yall. Its a T2I and a 100-400 lens. I had some trouble with wide open pics and the focus. The camera was locking focus, but the different apertures seemed to yield different results. Ill check out yalls suggestions.