Veteran Member Join Date: Dec 2006 Location: Dallas, Texas |
Derek,
Auto-ISO can be useful in a number of situations, but if you're trying to figure the camera out, I recommend that you take charge and tell the ISO to sit and stay! Set it on 200 or 400 and leave it there for a few days or a week and get familiar with the two primary controls -- aperture and shutter speed.
Neither aperture nor ISO has anything to do with sharpness. Aperture has a lot to do with depth of field, as you know. But if you shake the camera while you're shooting, well, aperture ain't going to help you out. You're still going to get a blurry picture. And using a faster or slower ISO doesn't make a photo sharp. Using a higher ISO may result in a noisy image, and noise can have the effect of making a photo seem less sharp. Actually, I would even say that the shutter speed in itself doesn't determine whether an image is sharp. You can shoot at 1/1000sec and get a picture that's not as sharp as it should be. Sharpness is largely controlled by four things: stabilizing the shot, focus, lens quality, and post-processing. First, you have to stabilize the shot.
I started to say "freeze the action," but that's not really the right way to put it. You need to freeze the relationship between the camera and the subject during the time of exposure. If you're shooting sports and the subject is, say, doing a somersault, then that means a fast shutter speed. But if you're shooting a mountain landscape at sunset, obviously the mountain isn't moving around, but you may need a slow shutter speed here to be able to take the picture without undue noise, and so you probably need to use a tripod.
How fast a shutter do you need to freeze the action for a moving subject or when you're holding the camera in your hands? It depends, but there is a fairly straightforward rule about this: Keep the shutter speed at least as fast as the reciprocal of the focal length. In other words, if the focal length is 200mm, then you would do well to set your shutter no slower than 1/200second. Second, focus!
This is a negative factor, rather than a postive one. Focus is not the same thing as sharpness, but an out of focus shot can never be sharp. If you shoot a building at 1/1000s, you've got a nice stable relationship of camera to subject, but it's still not going to be a sharp photo if the camera isn't well focused. Depth of field can help here, but you have to get some crucial part of the photo into clear focus. Keep in mind that you should not usually be worrying about your images being grossly out of focus; you should be worrying about getting them as precisely focused as possible. In other words, a photo that's just slightly out of focus might look like it's not sharp -- but the problem isn't sharpness per se, it's that the subject was just a teeny tiny bit out of focus.
I find auto-focus pretty effective, at least for normal shooting, where there's enough light and a reasonable amount of contrast in the subject. I'm not one of those who thinks that auto-focus is for wimps. But there's no denying that in some situations -- say, when you're shooting macro -- manual focus often produces better results.
There's a lot more to say about this topic but I'll leave it at that for now. Third, good lenses produce better results than bad ones -- and most lenses have a sweet spot.
There ain't much you can do about the quality of your lenses without spending money, but it's worth keeping in mind that some lenses are simply better than others. The acuity of the lens isn't the only thing that matters. Price matters to me! So does versatility, by which I mean that a 28-75 f/2.8 Tamron lens is worth more to me for the kinds of photography that I do than, say, a Pentax mid-range prime lens that might have better lens acuity. But the fact remains, lens A may simply be a better optical instrument at its best than lens B at its best.
It's also true that zoom lenses often have "sweet spots." The sweet spot is usually NOT at the extremes of the zoom. SO if you're shooting with the Pentax 18-55 kit lens, you might find that you get somewhat better (sharper) results -- other things being equal -- if you shoot around 35 or 40mm. Fourth, post-processing makes a difference, too! Finally, it should be noted that the data that the camera stores on your SD card may benefit from a little sharpening in your post-processing software. A little of this goes a long way, so be careful. One of our colleagues has a wonderful line in his sig: "We live in the age of over-sharpened images". I like Picasa (Google's free photo editor) but it doesn't allow me to control the degree of sharpening, and it invariably OVERsharpens the images. You should be aware that there is a significant difference between the way things look to you on your computer screen and the way that they look, say, in print. An image that looks a bit soft on screen will often print out looking really good -- and images that look tack sharp on the computer may be too sharp when printed.
So, to maximize your chance of getting a sharp image, make sure you have plenty of light, keep the shutter speed reasonably high and the ISO low, get the focus right, use your best lens in its sweet spot, tell the subject to hold still, use good technique when depressing the shutter (so you don't move the camera), and expect to add a little sharpening in post-processing. If you wonder whether your camera and/or your lens is capable of achieving sharpness, do some tests with a tripod and remember to turn SR off while testing.
__________
I'm ultimately more interested in taking interesting shots, with nice compositional qualities, good tonal range, well exposed shots, well focused shots, than I am with worrying about getting things tack sharp. For fashion photographers and commercial product photographers, anything less than tack sharp may simply not be acceptable. But for most of us, even those of us who are really serious about what we're doing when we have a camera in our hands, sharpness is just one of the components of an image, and it's usually not the most important one.
Hope this helps.
Will
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