Thursday, 7 January 2010

Tips for Sharper Shotz (3)

Fast aperture lenses also help sharpness!
Spend your money on a good lens and you’ll see significant improvements in picture sharpness. I’ve used kit lenses for a number of years and was never really 100% pleased with the sharpness. Most are OK, and a few, like those from Sony and Olympus, are actually good considering the price. But if you want the best in terms of build quality, resolving power and photo sharpness, you need to get a pro quality lens produced by a major camera or independent lens manufacturer. Certainly these are considerably more expensive than kit lenses, but the jump in quality is significantly better. I guess it all comes down to how much you value your hobby. Using a fast, expensive lens is not going to make you a better photographer, but it’s going to open up your creative options significantly. And that’s always worth paying for.
Nikon, Canon and the other major lens manufacturers produce pro level optics that usually incorporate special low distortion glass elements, moisture and dirt proofing (using O-rings) and superb build quality. These inevitably come with fast f2.8 (or higher) maximum apertures, so can be used, hand-held, in low light, yet still produce sharp results. Some of those for Canon and Nikon also come with inbuilt image stabilisation. Cameras made by Sony, Olympus and Pentax have image stabilisation built into the camera body thus all their lenses are stabilised.

All-in-one lenses can be tricky...

To add insult to this technical problem, many newcomers get talked into buying the ubiquitous one-lens-does-all zoom. While these certainly are the answer to all our lens-changing fears, there’s always a downside. Because so much subject magnification is packed into the one lens (and cost has to remain affordable) it must have a variable maximum aperture which is never high, especially once zoomed to its maximum magnification. A typical example might be an 18-250mm zoom with a variable maximum aperture of f3.5 (at the 18mm focal length) to f6.3 at its maximum 250mm magnification. In most lighting this means you have to shoot at ISO 800, or higher to get a sharp shot, or use a tripod, which few like to do. Companies like Tamron and Sigma realise that this is an issue (the inability to let enough light into the camera to maintain a safe shutter speed) so are now adding image stabilised versions for its all-in-one lenses. Excellent idea! This technology is brilliant and helps produce a sharper, clearer result. While having image stabilisation is an affordable bonus, having a lens with a fast and continuous maximum aperture is the ideal option. A fast maximum aperture enables the meter to use faster-than-standard shutter speeds (hence the term, ‘fast’). A fast aperture also gives the photographer more creative depth of field options. The chart shows the limited options offered by a typical f3.5-6.3 18-250mm lens when zoomed in to its maximum magnification. Because at this magnification, f6.3 is the widest aperture, in certain average lighting, you only get a couple of options for pin-sharp results (in green). The other exposures still give a bright result, but they won’t be sharp unless a cable release and tripod are used.

By using a slow shutter speed and moving at the same speed as these commuters on an escalator, figures appear a lot clearer than if I’d stood still and snapped as they moved past. This is a type of panning used to create a sense of movement without losing all the subject detail.

Night shooting - you need support, no question

The answer is as old as photography itself. Use a tripod. Of course professionals don’t have a problem using tripods because they understand the need for stability, most enthusiasts don’t or are too lazy. I hear loads of excuses about why they don’t need a tripod. “I have image stabilisation”, “I can hand hold anything”, “...a tripod is too heavy”, that sort of thing. All valid maybe, but it matters not. If the shutter speed is a number that’s smaller than the focal length of your lens, you need to use a tripod. In English, this means that if you are taking snaps in a Moroccan marketplace using a 75-300mm zoom lens (and a shutter speed of 1/60s), your shots will be blurred. If you bump the ISO from 100 to 1600, you will get sharper shots, but you’ll also get increased digital noise. If it’s an image stabilised lens, use it because you’ll get much sharper shots, even at lower ISO sensitivity settings.
Telephoto lenses especially need to be operated with a fast shutter speed because they magnify not only the subject matter, but your camera shake as well. We all know how hard it is to hold powerful binoculars steady, so why is it any different for an eight times magnification tele lens? It’s not, so care has to be taken.
We are now seeing new point-and-shoot models with 10X, 12X, 15X and even 20X zoom lenses. Twenty years ago this would have looked silly. Mums and dads walking round with a lens that weighted more than two kilograms and extended way past their knees. Great to have this packed into a tiny 400g camera, but the shake issues remain. In many ways, the inclusion of 400mm+ telephoto lenses in tiny cameras is driving the development of image stabilisation - And this is a great thing for the industry, and our results. However, it sure helps, it doesn’t remove shake entirely.

The more you zoom, the faster the shutter must be
As old as photography itself, you need to match your lens focal length with the shutter speed used. So, back to my shooting example. Let’s say the light is fading and, at ISO 100, the camera is allowing me to shoot at 1/60s with a wide open aperture of f4. The lens is an all-in-one 18-200mm, so I know that shots taken at the wide angle end of the scale (18-35mm) will more than likely be sharp. But once I zoom in using a focal length that extends beyond the 35mm setting, my safe 1/60s shutter speed is not fast enough to reduce the resulting camera shake. Because the aperture is already opened to the maximum (remember that’s how programmers like to work the metering) my only option is to increase the ISO.
Increasing the ISO is like pretending that there’s actually more light that there really is. It’s a great option but you must be careful here. Some cameras get very noisy when the ISO is pushed over 400, especially point-and-shoot cameras (that have small sensors). The higher the ISO setting, the spottier/noisier the results. This is normally OK if you are only printing small, but can be trying if you plan on adding the results to a full page in a digital book, for example.

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