 Capt Suresh Sharma |
How to Check Sharpness of a Lens I bought a 180mm L-series Canon macro lens. I was expecting to have super sharp images and now I am shocked that it doesn't get that sharp as I expected it to be more sharp than the 105mm Macro. Please help me know how to check the sharpness.
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Jon Close |
Eliminate all other possible contributors to unsharpness. No UV/protective filter. The longer focal length lens is more susceptible to camera motion than shorter focal length, so mount your camera on a sturdy tripod and release the shutter with a wired/wireless remote. Make sure that you are not misfocused on your subject. Set up with plenty of light on the subject for accurate focusing (auto or manual). Manual focusing is often preferred for macro subjects, but it can be difficult if you have a small and relatively dim viewfinder. If so, a viewfinder magnifier such as the Canon Angle Finder C will be a great help. Use mirror lock-up if shutter speeds are between 1/15 and 2 seconds to avoid camera movement/vibrations from the mirror kicking up.
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Capt Suresh Sharma |
Hi Jon Thanks for the response. I have tried all, I have focused it manually, it looks sharp, but when I do the shots, not very sharp. I will try again with lots of patience, once more. Thanks. www.snakecell.org
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John G. Clifford Jr |
A 180mm macro lens should not be any sharper than a 105mm macro lens. It should, however, give you a larger image with equal sharpness. A good macro lens (of whatever focal length) should easily out-resolve any available dSLR, including the 16 MP Canon MkII. The difference between a 105mm macro and a 180mm macro should be that the latter lets you get 1:1 images while letting you be further away from the subject. Of course, a longer focal length means that you'll have less depth of field at the same aperture, and most dSLR lenses start getting diffraction-limited at f/11 (meaning that increased depth of field comes with decreased resolving capability, i.e., more and more of the image reaches a less and less sharp uniform focus). If I wanted to check the sharpness of a lens, I'd put my camera on a tripod, use the camera's mirror lockup with a remote release (or use the camera's self-timer) and do the following: - Take a photo of a newspaper with the camera in portrait mode (vertical), and pointing at a 45 degree angle to the paper's surface. This lets you see if the lens is focusing correctly. Your band of focus should be across the page and parallel with the horizon. If it's not, you may have a bad lens. - Take a photo of a newspaper with the paper perpendicular to the central axis of the lens (paper flat on wall, lens pointing at the center of the paper directly above the center of the paper). I'd try this at different f-stops, and see where the sharpest image was (probably f/5.6 to f/8). If your lens will not produce a crisp, sharp image under these conditions, then something's wrong with it. Take it back and try another lens of the same model.
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Capt Suresh Sharma |
Thanks for all the info, I will try your advice and get back to you, if need be.
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