I am currently in the process of upgrading my equipment on a budget, so I am trying to figure out where my limitations are. I have been getting inconsistent results from my photos, some soft, some sharp, so I wanted to pinpoint the cause.


I decided to run a little test. I mounted my Rebel XT onto a tripod and aimed it directly at a piece of sheet music, testing both my lenses (Sigma 28-70 f/2.8 and Canon 50mm f/1.8). With the Sigma, I got various results over the range of the barrel, which is what I expected. Most focal lengths at anything less that f/5.8 were terribly soft.


I noticed that I wasn't getting consistent sharpness across pictures at the same settings, so I threw my Canon 50mm on there to see if it was just the crappy Sigma giving me trouble.


At f/1.8 the shots were soft, but to varying degrees. I was able to get a few sharp shots at f/2.8 and f/4, but not consistently.


Here are the results from the Canon 50mm f/1.8. Taken from a tripod, one after the other. 100% crops of the center of the frame (lets not even talk about the edges):


f/2.8:





f/4:





Is this much variation in sharpness normal?


If not, would you say it is my camera (the variations happens with both my Sigma and Canon lens), or my lenses (both are cheap, could just be a problem with their AF)?


I want the get the best bang for my buck on upgrading, but I don't want to buy a $1k lens if it is going to give me inconsistent results because something is wrong with my body, and vice versa.





UPDATE: I just tried the exact same setup with my wife's Nikon D40 and her kit 18-55mm at 55mm. 6 shots, all sharp, hardly anyperceivabledifference between them. Now I know something is up!