ItsMeSri wrote in post #15008420
Thanks guys.. I took couple of pics from the event. I don't understand how those pics came like this. I focused on object, but object is blurred and background are clear. I want other way round. I want object should be clear and background is blurred.
check these pics...
Updated: I used Tamron lense EF-S 18-55mm I'm not familiar with the Xsi, but on the Canon bodies I know you can ask it to show you the focus point(s) that were used when you took the photo (take a look through the menu options for image playback).
For the second and third shots it's possible the focus point wasn't on your intended subject.
For the first image, it may be, as has been pointed out, that the subject was simply too close for the lens to focus. I know kids can often move quickly and go out of your focus distance, but with that first shot, the focus was clearly further on the background.
Come to think of it - I wouldn't usually expect the camera to take the picture unless you'd got focus (though you can turn that off in some bodies), plus the focus seems to be a fair distance from you in all three shots... so... are you sure you didn't have the lens set to manual focus (MF) with the focus ring set to somewhere in the distance? That would've happily allowed you to fire the shutter even though you'd not actually focussed on anything specific. On a 7D, selecting to display the focus points on playback shows no points if the lens was set to MF, so if the Xsi does the same that'll give you your answer (i.e. you'll see no focus points on those images).
Your shutter speeds were high enough to avoid camera shake given the focal lengths, though I don't understand why the first shot was 1/2000 at ISO400 (1/500 at ISO100 would've been fine).
A very rough rule of thumb for 35mm film cameras was at least 1/focal length in terms of shutter speed; i.e. the 50mm (non-stabilised) lens would need 1/50s or faster for a sharp shot. As the Xsi is a 1.6x crop, you get a shot as if you'd taken the image with a 50x1.6=80mm lens, hence the suggestion to keep the shutter speed faster than 1/80s. A stabilised lens (IS) will allow at least a couple of stops slower - e.g. a 50mm (effective 80mm) IS lens should be OK at 1/80 x2 x2 = 1/20s (maybe even slower). Remember that only freezes your movement, not the subject!
The 50mm f1.8 II is pretty soft up until f2.8 (and the depth of field (DOF) will be so shallow it may be difficult to keep things in focus anyway). Best thing to do would be to put the camera on a table (or tripod) with a few objects on the table. Focus on an object in the middle distance, and take a set of shots at f2, f2.8, f4, f5.6 etc. to see the difference. An effect called diffraction will cause your whole image to start to become soft as you go much beyond f8, so despite getting more DOF, by f13 you should see a noticeable softening of the whole image.