02-20-2014 09:48 PM
I have recently upgraded my old kit lens (18-55) for my RebelXS with a refurbshed EFS 17-55 2.8 USM and have been a little disappointed that my nature photos have not been that much sharper. Any ideas or advice out there? Is there an apeture setting that is best for sharpness with this lens?
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02-21-2014 05:46 AM
02-21-2014 02:55 PM - edited 02-21-2014 03:13 PM
Have you fitted your new lens with a "protection" filter? If so, remove it. I've seen filters mess with focus and sharpness.
Do you have the lens hood? If not get it and use it instead of the filter. It offers good protection for the lens and might even help with focus by keeping some oblique light off the lens.
Most lenses benefit from stopping down slightly. Optimally, an f2.8 lens may be best at f4, even though it's likely still quite "usable" wide open. Even stopped down to f4 at all it's focal lengths is still quite a bit better than your old kit lens, where closing down one stop would put you at f5 at one end of the zoom range and f8 at the other.
I agree with the previous response, too... you have to be careful not to use too small an aperture. Beyond about f8 diffraction will start to rob the image of fine detail. At f11 it's probably so little as to not be a problem, but I'd make that about my limit on a crop sensor camera such as yours. Avoid f16 and f22.
The 17-55 also has IS, which your 18-55 may or may not have had. IS can help a lot with sharpness, especially at slower shutter speeds. I'd use it all the time when shooting handheld or on a monopod... even on a "loose" tripod. However, if locked down solidly on a tripod, it might be necessary to turn off IS manually at the switch. I am not certain about the 17-55, but on some lenses with stabilization, when there is absolutely no movement the IS can go into sort of a feedback loop that actually causes movement! That can look like poor sharpness. So if you are using the lens tightly locked down on a tripod, try turning off the IS.
Another benefit of the upgrade, the 17-55mm has USM focus, which is considerably better than the micro motor in your kit lens. It might not be too noticeable in good light, but in more challenging situations I bet you'll find the lens faster focusing, as well as more consisten and accurate... quieter, too.
There is a chance the lens you bought isn't up to spec for some reason, it might even have gotten damaged in shipping... I'd suggest you go shoot a lot with it and see if you can't get some good results. You might want to do some carefully controlled tests with the camera and lens on a tripod and shooting a detailed subject such as a brick wall or a weathered fence. If after some additional testing and shooting you still think the lens might be faulty, talk to Canon about having them check it or do an exchange for you.
02-21-2014 06:11 PM
Thank you for your quick reply. I will try to use apertures around f8 and see if this makes some difference. In all this snow here in Maine I have been using smaller ones. I will consider a lens hood as well.
02-21-2014 06:24 PM
I bought the lens from the Cannon store, so I'm hoping that the lens is performing up to the specs that they claim for their refurbished lenses. I did buy their ninety dollar "protection filter", so I will try some photos without it as you suggest. I did not get a lens hood so that is something I will get soon.
Your comments and suggestions about not going beyond f11, I will pay attention to as well. Also the IS issue could be a problem since I use a tripod quite a bit. I like your idea about doing some testing on a brick wall and I will do some shooting at f4.
I really do appreciate your taking time to give me these helpful ideas!