Manual Focus Issues
I am practicing focusing using manual focus and I seem to be having trouble getting sharp close ups. I'm not sure if it has to do with my newer lens (switched from using the lens that came with my old film rebel to a digital lens with stabilizer). It seems I can only focus when further out from the subject. As you can see a very small part of this baby's face is in focus. I've read up on F-stops but still seem to be hit or miss when it comes to picking the right setting to get that clean shot. Any advice? Thank you--Shannon
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And in the case that I'm totally misinterpreting your question, the other possible answer is that when you shoot with a low f-stop, like f/2.8, it'll blur anything that isn't on the same vertical plane (blurring more with the more distance from subject), so try bumping up to like f/8(?)
Unfortunately, if that *is* the problem, a quick googling indicates that the Canon Rebel XTi doesn't allow you to micro-adjust the focus, which would help mitigate that issue.
Still, it may be worthwhile to test your camera & lens by shooting a ruler. Focus on a given line on the ruler, with the ruler slanted away from the camera, then you can see if the focus plane seems to be in front of or behind that line. Be sure not to use focus-recompose for this; use a tripod.
Other than that... yeah, keep in mind that the closer you are to your subject, the shallower the depth of field. For this shot, you had the focal length at 36mm and aperture at f/5. At 10 inches from your subject (which is close to the minimum focus distance of your lens), your depth of field is only 0.32 inches (used dofmaster.com for calculations). At f/8, you would get about half an inch, and at f/11 0.72 inches. So basically, when you're that close, only a very thin plane will be in focus, but the more you stop down, the more depth of field you'll have.
The flickering flash is a set of flashes designed to brighten the scene to allow the autofocus to work. I switched mine off...you may need to check if it's a normal or a custom setting on the XSi. On the XTi it's a custom function, number 5, in the menu. It is useful in low light, however.
So, with my XTi (400d) I acquire focus with a half press then as soon as I get the beep, or the little LED in the viewfinder, I complete the shot by fully pressing. If the subject is not ready, you can wait before fully pressing, but the camera is locked on to a focus point...if the final position of the subject is not ON that focus point, then it will be out of focus.
The other "issue" I see is the use of Tv. This is fine, but you must understand that when in low light, this will give a low aperture number, i.e. a WIDE aperture. This makes the Depth of Field very small, so the distance between what is in focus (say a kids eye) and what is not in focus is very small.
Wide aperture (low f number) means the eye may be in focus, the ears may not.
Narrow aperture (higher f number) means that both the eyes and the ears, and probably the back of the head and so on will be in focus.
But it's a trade off...If you use Av (which I do quite a bit) you control how much is in focus, but in low light, the camera has to slow the shutter down, and you can get camera shake blurring. In bright light, the shutter will speed up, but if it's too bright than it might not be fast enough for your chosen aperture and you overexpose the shot.
Hope that helps a little.
Take the usual lens, probably an 18-55mm, position yourself close to the subject and zoom to the appropriateplace to get the shot. If you can't get focus, it could be that you are too close...move back. If you can't get the close image you want then, you could crop the image in your editing program to the size you want.
The issue is with the flash...position the subject near the window, perhaps, set the Aperture, in Av to something like f5.6, or f7.1, and see what you get without flash. The shutter speed MAY be slow, but anything from 1/100s will be ok to avoid too much shake...take the picture steady! Remember, if you can't get a decent speed from the shutter with the aperture at f5.6 or 7.1 then you could widen the aperture (lower f number) but you risk parts of the subject being unfocussed. This is ok, even desireable in some images, but in 99% of cases you need the focus on the eyes. You could also raise the ISO a little to get a better amount of light, raising the shutter speed for you. My 400d (XTi) is fine at ISO 100, and 200. Quite useable at 400, but not so good from 800 up...it gets "noisy", that is, the images have noise in them. I don't kow if the XSi is better with higher ISO than the 400d...possibly. It's a revised version, rather than much of an upgrade, I think.
Hope that helps some more.
That's why I recommended testing your manual focus up close on an object that doesn't move, with a tripod, so that you can be certain that there wasn't any motion between focusing and shutter release that was causing it. As is, it could very well just be a shallow depth of field (not much more than a quarter of an inch!) combined with slight motion.
I knew what camera, lens, focal length, and f-stop you used because all of that data is stored in the image as part of its EXIF data.
As Bend the Light mentioned, in dim situations cameras will use a flash or light to brighten the scene a bit to make it easier to autofocus. On my camera it's called an AF Assist Lamp, and it can be turned off, but I'm not sure what it would be called on yours.
I've never used one of Canon's SLRs, so pay attention to Bend the Light's advice on those specifics