Why are my distant bird photos less sharp with a Canon 1200D and 55-250mm lens?

Question

I use a Canon 1200D with the 55-250mm kit lens for bird photography. I’ve noticed that birds closer to the camera look much sharper, but birds farther away often look soft, even when focus seems correct.

Example 1: Laughing Dove — 250mm, ISO 400, 1/100s, cropped heavily, shot late in the day under overcast light, then brightened in post.
Example 2: Indian White-eye — 250mm, ISO 100, 1/400s, cropped less, shot in better mid-afternoon light.

I shoot RAW, use both autofocus and manual focus, and edit on iPhone Lightroom plus the built-in editor. Is there a way to improve sharpness for distant birds at longer focal lengths?

user75947 · Answer

Several possibilities:

In the examples shown, it could be a problem with the subject. The center of the picture is a rather fuzzy plumage for the dove and sharp lines for the white-eye.
Your 55-250mm is not so sharp at the long end. Decent lens, but not built/checked to stringent specs like a L series. Only way to tell is to try another lens.
Your camera's AF is struggling. The AF works better when the lens has a wide max aperture. At the long end your lens max aperture is f/5.6, pretty close to the AF working limit (officially f/5.6, in practice f/6.3 with good light). Your 9-point AF is a fairly old tech, I had the same in a 450D (ten years ago). I improved all my lenses by moving to a more recent body with a much better AF.
The lens IS isn't doing miracles. At the long end very small residual moves can induce some blur.

To remove as many variables as possible from the equation, you can do a rough test of your gear:

Tape a newspaper on a wall, under good lighting
Put your camera+lens on a tripod if you have one, or on a table, sufficiently far from the wall (at bird shooting distance...) and aim the camera at the newspaper
Use a remote trigger or use the 2-seconds timer on the shutter, so that you aren't touching the camera when it takes the picture.
Do one image (or a series of shots) with AF.
In the same test conditions do another image using manual AF. For this use LiveView and zoom in. This can be a bit fiddly because the focus ring on the 55-250 is a bit coarse.

If the image with manual focus is sharp, your lens is OK

If the above and your AF image is also sharp then your AF is OK. Otherwise by giving some forward slant to the newspaper you can evaluate the amount of front-focus/back-focus (see which part of the page is really in focus) and take this in account when shooting the birds (pre-focus on some foliage before/beyond the bird).

Why are my distant bird photos less sharp with a Canon 1200D and 55-250mm lens?

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