Hi Tim,
This is exactly what I'm experiencing, I was hoping it's not the camera just with all the focus issue flying around it was making me think it could be the cause. I must admit I've not had the issue with the 24-105 but again was making me think am is seeing focus issue with this as well. Would you recommend the Focus chart as a good test ? (Spending this much on gear I need to ease my peace of mind)
I'm on the fence about that focus chart, but if you forced me to choose I'd give it a miss. My suggested testing approach is to aim at a focus target which is exactly square on to the camera, not angled at all, and at least large enough to fully cover
all AF points, even though you only use the centre point for calibration purposes. The distance to the target is important too. Ideally the target should be at a distance between 25X focal length and 50X focal length as a general guideline, although if you regularly shoot at some other distance outside that range you might as well calibrate at that distance. For a 50mm lens the suggested distance for calibration testing would be between 1.25m and 2.5m. The focus target should be well lit and contrasty. You are trying to test focus calibration accuracy, not focus performance in difficult conditions.
If all you want is a flat target then IMHO a brick wall makes an excellent choice. The edge between brick and mortar makes a great focus target and the texture of the brick should allow you to judge how sharp or soft the image is. Example viewed at 100%....
If you prefer you can add an angled scale to the subject, from which you can judge the extent and position of the DOF. This will make it easier to see just how far off you are, in what direction, and whether the error is constant or variable. You do not focus on the angled scale. You still use a large, flat target to focus on, with the scale to one side....
It's worth mentioning that you will probably not get absolute mm perfect performance every single time you hit the AF button. Also, in the real world, with a live/moving subject and a hand held camera it might be of limited use to have the AF accurate to within the mm. Sure you want it as close as you can get, but there will be some wiggle room in the results. Pixel peeping can be a dangerous game that ends in frustration. The real question is whether the shots you get are acceptably sharp when viewed at "normal" size or are they unacceptably soft. The 50/1.8 has more wiggle room than most.
so excited, will go test it with my nifty fifty over the weekend!
