Half-sharp
QThe images from my 300mm lens don’t look sharp enough. Do I need a more expensive one? Pete Smith
Andrew says There are only two factors that can account for this: either the lens itself isn’t particularly good, or your technique is letting you down. The most consistent error with long lenses is not using a fast enough shutter speed. You can’t hand-hold a 300mm lens, even with Image Stabilisation switched on, and expect to take a sharp shot when your shutter speed is hovering around 1/200 sec. With your 300mm, I’d want to have it at no more than 1/400 sec, but preferably 1/500 sec or faster.
The other thing you need to look at is your focusing. If you are not specifically selecting a single AF point to make sure you are pinpointing where the main area of focus should be, you need to start doing that.
Also, is the lack of sharpness more obvious at any particular apertures? While a large aperture will naturally limit sharpness, a smaller aperture may also show a lack of sharpness around the edges of the frame. Typically, the ‘sweet spot’ of a lens will be about 2-3 stops from its maximum aperture. So, if your lens has a maximum aperture of f/4, the sharpest will be f/8 or f/11. Take a look at the images you think aren’t sharp enough, and be critical with them. Look at the Exif data for the shutter speed and aperture, then try to work out where your point of focus is and if that’s where you meant it to be. If all these are fine, then and only then should you consider upgrading your lens.