Mon 07-Feb-11 09:41 PM | edited Tue 08-Feb-11 07:26 AM by Len Shepherd
>Below is an image where the EXIF indicates the focus is infinity, The distance the lens focused at is about 250 feet - so the EXIF is likely showing anything further than 250 feet as infinity. How do I know the focus distance is about 250 feet? An "old trick" is a 50mm lens on FX covers a 10 foot wide subject at 5 yards focus distance, a 200mm lens does this at 20 yards and so on. Based on the size of the horse the picture area is about 40 feet wide, indicating a focus distance of 20 yards (for 200mm) times 4 (for 40 feet wide subject) - or 80 yards - about 250 feet. Back to the original pictures, as EXIF shows infinity at around 250 feet in this latest picture, the lens could focus at 250 feet and indicate infinity with the mountains 7 miles distant. As the background is already out of focus at 250 feet it could also easily be as soft as in the first 3 images if the AF was fooled into focusing at the wrong distance by the low contrast and lack of distinct detail in the distant hills. When you get a clear day using manual focus you could do some test shots around infinity on the focus ring (which should be decently sharp) and also progressively closer to learn how close you have to focus to get the EXIF to record closer than infinity with this lens.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.