canon rebel XT - sharpness issue ?

Now that I have browsed the lens forums extensively, I am almost positive my camera is not focussing well.

I have the nifty fifty and I have seen some really great results in this fourm.

Here are a 2 test pics 100% crop taken with the nifty fifty.

first pic 1/320 f 5.0 - 100% crop

I can only see the building shot, but need to tell you that it's much bigger than the POTN image-posting guidelines (here https://photography-on-the.net/forum/showthre​ad.php?t=51022) allow. As to sharpness, it looks pretty sharp/in-focus from here. You need to post some 100% crops of images with fine detail for us to be able to give you a better read on focusing and sharpness.

well I have been comparing these images and all others I have taken with this lens to the lens sample photo archive, and I do see a very big difference.

I will crop these, done

AMG wrote in post #10631521
well I have been comparing these images and all others I have taken with this lens to the lens sample photo archive, and I do see a very big difference.

I will resize these, I did not have a photo editing software

I think your buildings shot will look very sharp re-sized, because it looks sharp full size. I can't see your other shot - our firewall is probably blocking it for some unknown reason.

I can't quite see what you mean from the sample images...

The sharpest point in your image won't necessarily fall at the exact point you focused on. One thing about the XT is that it doesn't have a center f2.8 high-precision autofocus point like the XTi, Xsi and higher models. This means that with a wide aperture lens, according to what Canon has said, the point you focused on is only guarenteed to fall somewhere within the DOF.

From my own tests with the XT (I had also had autofocus issues with the XT) and a wide aperture lens, the center of the DOF can vary quite randomly and the focus point can even fall at the very edges of the DOF. I found this to be worse under lower available light levels.

Try this focusing chart. Be sure to read the discussion of autofocus and then follow the directions closely. Note that the center of the chart will not neccessarily fall at the center of the DOF but should be within the DOF.
http://www.focustestch​art.com/chart.html

I think your problem is that you're using 100% crops. If the full image is sharp enough, the hell does it matter what the crop looks like?

Secondly, you chose two very bad examples. If you shoot far distances the haze will detract from the image quality. If you shoot very close distances, the depth of field is too small to tell anything concrete.

If your convinced you have a focusing problem the only real way to rectify it on a rebel XT is to send both the body and lens back to Canon for calibration.

thx, there was a lot of helpful information in this thread. I admit I have some sharp results as well, if I had no images at all that came out sharp, then I guess this would be evidence of a real defect. In my case, there are some shots in lower light that didnt come out sharp. But there are a few in daylight that came out a bit soft that I havent been able to troubleshoot. shutter speed was fast enough technically, it seems the focus point was correct, and the subject wasn't moving, I realize some open wide f stops can get soft on most lenses, but I thought what I was seeing was going beyond softness, and rather a light out of focus image. I am going to do focus test, and also do some field tests to try and recreate the images I didnt like.
Some of the worst shots I have are definetely from the 28-105. here are a few with 18-200.

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also you might consider that images in the lens samples are probably best case. Don't compare your average-bad shots with images that people have uploaded for bragging rights

On your three latest examples:
First one looks fine to my eye - what were you focusing on?
Second one may have a tiny bit of back focus, but that's uncertain.
Third is from hand shake - too slow of a shutter speed for the focal length (1/40th for 190mm). And it's overexposed.

1/40th with IS is not sufficient ? if not, what is a good guideline for accceptable shutter speed with IS as the focal length increases ?

the first one i believe I was focusing on the closest corner, maybe near the sonata part.

AMG wrote in post #10650228
1/40th with IS is not sufficient ? if not, what is a good guideline for accceptable shutter speed with IS as the focal length increases ?

Depends how much you were shaking.

Don't rely on IS. You can use IS as a crutch, but think of it more as a helping hand than something that you absolutely need in order to get the shot. So if you shoot at a longer focal length (i.e. 190mm) with a slow shutter speed, don't expect sharp results all of the time. With your XT you should have been at closer to 1/250th of a second without IS at that focal length. At 1/40th you're very close to the limit of the IS, even in optimal conditions.

At that size the tire looks to be what's most in focus, so if you did indeed focus on the "Sonata" type there is a little backfocus in that shot.

I'd shoot some test charts first. If you get same results with multiple lenses (i.e. the in-focus area is off the zero point you were focusing at with more than one lens) then it's likely your camera needs to be recalibrated. Happened to me on my old XTi. Otherwise it may be the tehcnique, a particular lens, or unrealistic expectations.