The Canon 800mm f/5.6L IS is capable of very sharp results, but there are a host of gremlins that will degrade the potential quality— don’t expect to start using this lens and instantly get great results (unless you already know how to operate a super telephoto).
The factors that will affect results include at least the following:
- Shutter speed— A handheld speed of 1/2000 second should be considered the minimum speed to reliably produce sharp images in a handheld or similar situation. Dropping to 1/1000 second or lower drops those odds. Part of the issue is that it’s not easy to support the lens without a tripod, due to its bulk and weight.
- Focus — Extremely shallow depth of field makes focus a serious challenge. Trying to focus on an eye for wildlife is pretty tough when the subject doesn’t stay still for more than a moment. The camera must not have any error whatsoever, because even at 100 feet (33 meters), there are only inches of sharpness.
- Tripod and head— plan on getting a gimbal-type head for any lens 400mm or longer especially this 800mm; it should be considered a mandatory accessory. Other solutions are possible, but they are awkward. Whenever possible, use
- Image stabilization — definitely a win in some circumstances, but it can produce blur on a tripod, and possibly in other situations. It can also drive you nuts in a handheld situation, as it “jumps”, which throws off the focus point.
- Technique — it’s best not to assume anything; test your own technique with your own equipment and see what actually works best.
- Wind — wind vibrates a tripod and the lens like crazy. A little wind = blurred images. Get the lens low fully supported front to back (eg a big beanbag). To see this, just put the camera into Live View mode, magnify, then gape at just how much things jiggle.
- Atmosphere — haze can lower contrast by a huge amount, and disturbed air can produce alternating blur and sharpness for very strange-looking effects.
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