not sharp when using AF or confirmation?

[mxracer32]

here lately ive been struggling with my sigma 24-70 2.8 to get sharp photos. it seems as though the af hunts a lot and will go from one end of the focus spectrum, to the other, twice before deciding what to focus on, and then when it does and i snap a pic, its not sharp. while using manual focus and i get the focus confirmation and get the same results, but ive noticed if i get that confirmation, and back off the focus ring a tad, snap a pic and check it on the pc its more sharp then where the AC is set. have i changed some setting accidentally? it wasnt like this when i bought it, i checked my 70-300 f4 lense and it looked more sharp then my fast lense so i thought maybe it was the lense and not the camera, but now im just looking for any info or advice then can help me remedy the problem, im shooting on a 20d canon. i consider myself a newb so if there is something super simple that i might of done, dont hesistate to call me out on it.

 

[Sherman Banks]

You should post up some examples. Comparison shots between both lenses would help too.

 

[rlcphotos]

good post,,I have the same problem with my Sigma 24/70mm 2.8.. if I switch it to manual on the lens then Im fairly good..old eyes and all, but on the AF its not always on target....

 

[mxracer32]

i'll get some shots up but it will have to wait until later tonight. thanks.

 

[mxracer32]

autofocus

manual, but backed off slightly from where the auto confirmation said it was 'clear'

 

[Muay_Thai_Dan]

your lens is back/front focusing. you gotta get it calibrated at a service center.

 

[mxracer32]

your lens is back/front focusing. you gotta get it calibrated at a service center.

im did not know of that, do you happen to know ballpark on what that costs and where i can take it? im leaving for a caribbean vacation in june...id like to get it taken care of asap if at all possible.

 

[Muay_Thai_Dan]

search up your local camera shop, or camera service center.

a camera shop will also be bale to direct u in the right direction.

unfortunately, i have no idea how much that costs. i just know that this is what you gotta do.

but u should know, to calibrate it, they need to open your lens. will it get fixed? probably. but ive heard many horror stories. id recommend trying to return it or selling it, and getting another one that has no focusing issues...

 

[mxracer32]

frusturated with my findings, i decided to go out and shoot again. i noticed that the pics i took were in low-light situation so i bumped up my iso to 800 and went to shoot in the sun with my aperture at 5.6 with both my 24-70 2.8 and my 70-300 f4 to compare. in the sun, with my eyes it seems to be more crisp (faster shutter speed helps im sure) my file names give the info. the first pic, in example is file 247070mm1250f56iso800, lens is 24-70, focal distance is 70mm, shot at 1/1250 shutter, with 5.6 aperture at an iso of 800. simple enough..im sure most of you have the software to just right click and see the picture data anyways.

calibration should be something that would affect the camera in ALL lighting, no? maybe i have a setting off in low-light situations that is causing the lens to hunt/focus?


shot with the 24-70 (lens ive been having problems with)

70-300

some other random shots with the 24-70 to check the sharpness, seems fine in lots of light/faster shutter speeds

then one more in low-light. this was shot with the 24-70, at 70mm, aperture of 6.3, iso 800 shot at 1/4 sec. (on tripod)