Telephoto lenses are perhaps one of the first people buy to add to their kit, as they are useful in many genres of photography. The reach that a telephoto lens can offer is crucial for a lot of sports, wildlife or other ‘action’ photography. However, it is that same reach that can introduce the problems that prevent people getting sharp results. Here are six tips to help you perfect the technique of maximizing sharpness with a telephoto lens.
1. Shutter Speed Selection
One of the biggest hurdles to overcome when shooting with a telephoto lens is camera shake – softness introduced by not being able to hold the camera steady for the duration of the exposure. One of the easiest ways to overcome this is to make sure that the shutter speed you select is faster than the reciprocal of the focal length. For example, in order to minimize the effect of camera shake with a 300 mm lens, a shutter speed faster than 1/300th second is recommended.
To take this one step further, it is best to consider the “effective focal length” (EFL) of the lens by taking the crop factor of your sensor into account. If you are not shooting with a full frame camera, you are most likely shooting with a crop sensor (or APS-C) camera. The sensors within these cameras are smaller than full frame sensors and, as such, give the result of multiplying the focal length of any lens put on the camera (see Crop Factor Explained for further explanation). The result is, when you are using a 300 mm lens, on a camera with a 1.5x crop factor, the effective focal length is 450 mm. Thus meaning you need to be looking to use a shutter speed quicker than 1/450th second.
So just make sure you are aware of the crop factor of your camera, so that you can quickly approximate the required shutter speed, if shooting handheld.
2. Use a Tripod
Another very simple way to overcome image softness due to camera shake is to use a tripod. Not everyone enjoys carrying or using a tripod at all times. However, it is a really quick and simple way to help minimize camera shake and to give you more flexibility in using slower shutter speeds, compared to shooting handheld (i.e. not a necessity to stay at “1/EFL”, though still recommended where possible).
There a numerous tripod heads available that have the freedom of movement that is often needed when shooting sports or wildlife. You can also be safe in the knowledge that even at the end of a long day of shooting, when your arms would usually be tired, the tripod will continue to hold the camera steady.
A lot of larger lenses come with a tripod collar which mounts the lens to the tripod, rather than the camera. Most of the smaller, lower budget (but still very long, in terms of focal length) telephoto zoom lenses do not have one, meaning that the camera is mounted to the tripod and the lenses are left dangling off of the camera, susceptible for small vibrations. Some tripod manufacturers make special brackets to overcome such situations, allowing smaller telephoto zoom lenses to be tripod mounted and become more stable (see image below).
3. Image Stabilization
Obviously if shooting handheld, image stabilization (IS or VR) can again help overcome camera shake. Though you will want to avoid this if you are opting to shoot on a tripod, as image stabilization will actually introduce movement in that situation.
4. Aperture Selection
Shutter speed selection, as mentioned above, was all about considering shutter speed in relation to freezing motion. Aperture selection, however, is two-fold:
a) Diffraction – this is generally a rule for all, but the top of the range telephoto lenses, but shooting at the widest aperture (smallest f/ number) your lens allows will often result in image softness due to diffraction. This is where light entering the camera is diffracted before hitting the sensor, resulting in the appearance of soft focus throughout the frame (though generally far more noticeable in the corners). Therefore, if you choose a slightly smaller aperture, e.g. from f/5.6 to 6.3 or 7.1 (known as stopping down) you will minimize the diffraction and see an increase in the sharpness of the resulting images.
b) Ensuring you have enough depth of field - a key component of wildlife and action photography is depth of field. Often, you shoot as wide an aperture (small f/ number) as possible, to try and isolate the subject and give a soft diffuse background. However, at long focal lengths, with a close subject, the depth of field (i.e. the region of the image which will be captured in sharp focus) can be as small as a few millimetres, meaning that tiny errors in focusing accuracy will mean that the crucial part of your wildlife shot that needed to be in focus, will be soft. There are plenty of mobile apps or websites that help you calculate the depth of field for your given camera, aperture and focal length, so make sure you have an awareness how small an aperture you actually need in order have enough depth of field.
5. Bump the ISO
Don’t be afraid to boost the ISO on your camera. Wildlife and sports photography is a constant compromise between shutter speed and aperture to ensure that you are using a quick enough shutter speed to freeze motion and overcome camera shake, and a suitable aperture to give you enough depth of field and avoid diffraction. To alleviate this, you can increase the sensitivity of your sensor by increasing the ISO. This will let you use quicker shutter speeds for the same given aperture and exposure. Increasing the ISO will introduce more noise into the final image, but it’s better to have a sharp, yet noisy photo, than to have missed whatever fleeting moment you were trying to capture by not being able to use a fast enough shutter speed.
Often available in 1.4x or 2x magnifications, teleconverters are great for extending the focal length of your lenses on a budget. The increase in focal length does come at a cost however, as they increase the maximum aperture of your lens by one or two stops respectively. Most consumer DSLRs do not allow autofocus with lenses with a smaller aperture than f/8.0 (i.e. f/5.6 + one stop) so you are limited in what teleconverter/lens combinations you can use. You need a fairly fast lens to begin with, i.e. a wide maximum aperture of f/2.8 or f/4.0, to make the most of a teleconverter. Once the teleconverter is attached, autofocus will generally be slower (less light to play with) and any flaws of your current lens will be magnified – so stopping down, as per in point #4 above, becomes even more important.
Overall, the above tips are just a few considerations for maximizing performance of your telephoto lenses. It’s easy to get carried away thinking that you need more focal length, just to get that little bit closer to your subject. However, it is important to understand the complications of working with such lenses and learn the techniques you can use to overcome the difficulties introduced by such long focal lengths.
[post syndicated from Digital Photography School]