New Canon 100D not focusing correctly

Some good advice has already been given, I'd like to add a few points (and recap some others).

• The focal length of the first is 200mm, the second is 300mm. The longer the focal length the faster the shutter speed should be, though you dropped it down to 1/400 instead of using say 1/1250 for 300mm.
• The second car is farther away, this can introduce atmospheric effects, especially over damp or very hot surfaces, or with air with different temperatures mixing which can considerably blur the images, especially at 300mm or higher focal length.
• Don't use filters, they can and will cause focus issues and may also blur the image.
• The 70-300mm IS USM is sharper when stopping down a bit.
• Using image stabilizer incorrectly may cause blurry images. If the IS isn't stable at the time you take the picture, it can blur the image when it engages out of locked position. You can see this as a jerk in the viewfinder. Turning IS off or using only mode 2 (if that's available on your lens) may help.
• A longer lens needs a steadier hand, practice a lot at tracking moving objects, you also may need to prefocus at the distance you want to take pictures so that the AF can lock on quicker. See if you can use a monopod or other stable thing like a wall, chair etc.
• Shooting in M (manual) mode may help a lot, and shoot in AI servo mode. Setup the exposure like this: set shutter speed at at least twice the focal length, that's 1/640 to 1/800 for 300mm. Stop down aperture a stop (f/8) and set iso to get a good exposure, even if that means setting it beyond 800 iso depending on lighting conditions. This ensures that the shutter speed never drops below an unusable point and that the aperture is set at the sharpest the lens can give you.
• Use center AF point. This will take out the guess work of the camera and put it into your hands. Whatever is under the center AF point should be in focus.
• Make sure the center AF point is covered by at least double the height and width of the point you see in the view finder. The AF sensor is larger than is indicated. It may pickup the background, especially if that's more contrast than the subject you wish to be in focus. The bright white fence in the background may cause problems.

Simon57 wrote:

My wife has just replaced her old Canon Eos 1000D (10mp) with a brand new Canon EOS 100D (18MP). The photos from the 100D are not sharp or in focus. Is this a problem/fault with the camera or something we have not set up correctly. I have attached two photos. The red AC Cobra was taken with the 1000D and a sigma 18-200mm lens, RAW 1/800 at F6.3 ISO 250. The blue Rover SD1 was taken with the 100D with a Canon 70-300 IS USM lens, RAW 1/400 F7.1 ISO 100.If you zoom to 100% you can see detail on the red cobra but blurred on the blue Rover. Both photos converted to jpg using Lightroom 6