Thanks for posting the samples. The photo of the child is a very appealing shot, but there is clearly some camera motion blur in this one. It
also does not appear that the camera autofocused on the subject. According to the EXIF data it was shot at 1/90 second and f/5.6 at ISO
200, so there shouldn't have been any autofocus problem on that account and with some care you should be able to hand hold the camera
for a shot like this at 1/90. In other words, slow shutter speed caused by not having a large aperture available played no part in the
sharpness problem in this one.
A couple thoughts on this one. Since you have the XSi, I presume that you use the EFS 18-55mm image-stabilized lens. You may already
know this, but if not... image-stabilization does not engage instantaneously. It takes a fraction of a second for the mechanism to spin up.
The usual approach is to half-depress the shutter button and pause perhaps at least a half second or even a bit more to allow IS to fully
engage. This also activates AF so look to see if an AF point lights up on the right part of the subject - important since it doesn't look like
your camera AF'ed anywhere on the subject.
Bottom line on this shot: I am pretty sure that the camera and/or the subject were in motion and causing some blur, and it does not appear
that the camera autofocused on your subject - and the settings you used are well within the range of what your current lens can do. (Look at
the red toy in the child's hand to see a good example of motion blur in this image.)
The other shot was at 27mm and f/11 and 1/250 at ISO 200. It is also almost a full stop underexposed, though the dynamic range of the
scene is not very wide and even the dark tones fall within the histogram. Why does it not look sharply focused? There are several issues in
this photo that may play a part. The underexposure means that you have a bit more noise and reduced detail in the dark areas beneath the
fog bank. I think that your meter may have been "fooled" by the bright fog. Always look at your histogram after exposing if you can - in
general, though there are exceptions, the histogram curve should be closer to the right side of the display. (But always try to avoid going
past that - this will be indicated by the blinking black areas in your display.) There is not reason for this scene to be photographed at f/11.
The optimal apertures for sharpness on this lens/camera are likely to be around f/8. Although the effect is probably not great in this shot at
f/11, diffraction blur can begin to be noticeable if you stop down past about f/8 on a 1.6x cropped sensor camera. I don't have any way of
checking, but I wonder what you camera picked for its AF point in this scene. There is a possibility that it couldn't lock on anything give the
low contrast and the fog, especially if you didn't have all the AF points active. (I think you can determine what AF points activated by using
DPP software that came with your camera.)
In the fog image, even it it were sharp, you still would see an image that "pop" because of the very low contrast levels and generally dark
image. Some post processing could help here. I'll attach an quickie example, though I can't do a whole lot with this jpg.
Do you ever get a sharp photo? If not, are you seeing AF lights come on in the viewfinder when you shoot? If so, it might be worth doing a
simple test to rule out a misadjusted camera and/or lens.
If you have a tripod, put the camera on it. If not, place the camera on a solid surface like perhaps the edge of a table top, etc. If you have a
remote release, use it - if not, use the self-timer so that you don't have to be touching the camera when the shot is made. If you do have the
remote release, also enable mirror lockup. (I'm not sure you can do that with the self-timer, but if you can use it there, too.)
Point the camera at a subject that is easy to focus on - good contrast/texture and mostly in a plane more or less parallel to the sensor in
your camera. Using aV mode (where you can manually change the aperture), start at your widest angle setting and your largest aperture - I
think that is f/3.5 on your lens - and make an exposure. Then manually change the aperture to f/4 and repeat. Then to f/5.6 and repeat. Then
to f/8 and repeat. This should be far enough on the crop sensor body.
Now repeat the process at two or three different focal lengths, ending at the most telephoto setting - each time taking the series of
exposures.
Now look at the images closely. They may not be perfectly "tack sharp," but they should look pretty decent, especially in the shots done at
around f/8. If you look at them at 25% magnification they should look darn good. At 50% they should still look pretty good, though they may
show a bit of softness. You could inspect 100% magnification, but unless you know what to look for you could be fooled by what you see
here.
If your 25% magnification inspections do not look fairly sharp on screen it is possible that you have a camera/lens that is/are out of
adjustment. (It is also possible that some other settings are not correct on your camera, but I'm afraid I can't go through all of those
possibilities.) Take it to a shop or send it to Canon for further analysis.
If these shots do look pretty good at 25% your problems are almost certainly not due to lens problems, and could be along the lines I
mentioned above.
Dan
, Aug 29, 2008; 02:04 a.m.
