I have a problem with blurry photos, and I’ve been searching around the net doing research on why. Having spent a good four to six months evaluating different reasons and doing a bit of experimentation, I’d like to share a bit of what I learned.
Sharpness is one of the big key points most photographers look at when evaluating quality. If you shoot digital, as I do, there are a number of different reasons why you could be having issues with blurry or soft images. Those issues fall into three basic categories, User Error, Equipment Quality, and Rounding Errors in Digital Processing.
The most common problem is user error. Motion blur is hard to eradicate, especially when most people are shooting in less than optimal conditions the majority of the time. You can help this problem by buying fast lenses (i.e. lenses with wide maximum aperatures) and lenses with Image Stabalization. You can also use a tripod, and if sharpness is an extremely important factor, use a timer (to prevent your hand from causing camera shake when you press the button) and mirror lockup (to prevent shake from the mirror when it slaps up to allow the photo to be taken).
Equipment Quality and Limitations
The second most common issue is equipment quality, which often plays into the hands of user error. Lens manufacture varies from lens to lens and from brand to brand. You should make the mistake of thinking that since Canon glass is usually better than Sigma, that all Canon lenses will outperfom all Sigma lenses. To give an example, the Sigma F/1.8 20mm prime is equal to if not better than the Canon F/2.8 20mm prime. Before buying a lens, try to find a review that details how a lens performs at each f/stop and if its a zoom, at various focal lengths.
You see, most lenses perform poorly when wide open, i.e. stopped completely down. Also, most zoom lenses suffer some degradation in sharpness and rarely compete well with a prime (i.e. a fixed focal length lens). In fact, the longer the focal range on a zoom lens, the more likely the upper end of the range will be soft. Its difficult to maintain a sharp focus throughout the zoom range, so usually one end of the range will suffer, and if the lens is cheap or poorly constructed, both ends will suffer. Most lenses perfom best when the aperature is in the middle, and if its a zoom, the focal lenth is somewhere in the middle also.
In general, the faster a lens is the sharper it will be, because you will have more light to shoot with and will have less motion blur. Also, with faster lenses, you can afford to stop up the aperature and shoot comfortably, thus coming closer to the sweet spot (the sharpest point in your lenses configuration).
Rounding Errors and Digital Image Processing
Lastly, if you are shooting digital, you have one more issue to deal with, and that is the effect rounding errors have on digital image processing. Digital photographs convey sharpness by what they call acutance, which is the level of contrast between two pixels. The more contrast between two pixels the sharper it will appear. The problem with digital is that when the image gets tranlated from analog to bits, light values are rounded off causing a subtle softening of contrast between the individual pixels. All digital images should be sharpened in post production. In fact, most cameras apply sharpening to images right after they are taken, but often the amount of sharpening isn’t enough. If you shoot RAW, then no sharpening is applied in camera and you must do so in post production.
My problem is I have a Sigma 28-300mm F/3.5-5.6 zoom lens. Its a nice lens for hobby type work, but produces soft images from about 200-300, regardless of how still my camera is and how much light I have. Because its relatively slow, I am often forced to shoot with the lens wide open, making my shots even worse.
What’s my solution? Well, my Sigma 28-300 cost me about $300 dollars. I’m going to eventually replace it with three lenses. A Sigma 20mm f/1.8 prime, a Canon 24-70mm f/2.8 zoom, and a Canon 70-200mm 2.8 IS zoom. That will cost me roughly $3000.00. *grin* hoy… I should have picked up a cheaper hobby…