A Primer for Achieving Sharp Focus on Super-Telephoto Lenses

By: Gary Gray

(December 7, 2015)

Sharp focus techniques  by Gary Gray

Mule Deer Buck.   Canon EOS 6D, Tamron 150-600mm f/5.6-6.3, Di VC USD, f/8, 1/800sec, ISO-2000, 483mm


 
A few tips for beginners and folks learning how to use a super-telephoto lens like the Tamron 150-600mm.
 
In my workshops, the biggest problem I see students have with long super-telephoto shots is getting sharp images. It's normally a question of technique and knowledge of how to use the lens.
 
First rule to learn is the reciprocal rule. The minimum shutter speed should be the reciprocal of the focal length. If you're shooting it at 600mm on a full frame body, you don't want to use a shutter speed slower than 1/600th second. If you have a crop sensor camera, multiply your focal length by the crop factor.
 
I seldom shoot wildlife or any telephoto subject at less than 1/1000th a second, and faster is better if you have the light for it.
 
Don't try panning shots at less than 1/1000th a second as your hit rate will be low. At least until you learn to do it perfectly.
 
I try to at least use a mono-pod when possible even though you may have a fairly usable lens hand held. A tripod is best though if you can use one.
 
Turn off Image Stabilization when using a tripod, it will not help you and may ruin images by correcting while stable.
 
On a tripod shooting a fixed subject, use your mirror lockup function. It can take 10 seconds for the lens to steady up after barely touching the camera.
 
Use a tripod rated for the weight of the entire setup and use a high quality head for stability.
 
If you know how to do it, adjust the lens micro-focus. My super telephoto lens is the Tamron 150-600 and is very close to perfect but did have a tweak of 2-3 clicks on both my main bodies. I've seen Canon L lenses be as far off as 16 clicks, so don't let major adjustments freak you out. Every lens is different. Micro-focus calibration does help a great deal sometimes.
 
I usually fire shots in 3-4 frame bursts, not for spray and pray, but for sharpness. When you push the shutter button, you'll flinch and move the camera. A burst will allow the flinch movement to dampen out and one of the shots will almost always be sharper than the others in the burst.

When working from a vehicle, here are a few tips to keep your images looking good.
 
When you stop the car, turn the engine off and allow the vehicle exhaust to dissipate. This is especially important in cold weather. Automobile exhaust can waft into the field of view creating distortions and even visible exhaust vapor in the image. In addition to the vapor issue, a running automobile is vibrating. Motor vibrations will transfer to the lens and will result in a loss of sharpness. If others are in the vehicle, ask them to remain still. There's nothing worse than trying to hold a subject steady in the viewfinder at 600mm with someone doing the wiggle dance elsewhere in the vehicle.

Another consideration is the temperature differential between the inside of the vehicle and the outside environment. When searching for wildlife that I'll be photographing through a window, I try to keep the inside vehicle temperature as close to the outside temperature. Rolling down a window in very cold weather with the inside of the vehicle being toasty warm can result in additional vapor distortions from the warm air hitting the cold air, at the point of interface, your window. A stable temperature will prevent the lens from clouding and will lower distortions.
 
There are beanbags made specifically to drape over a partially raised window for resting your camera on. With the engine off, using a beanbag will help you steady the shot in a manner similar to using a mono-pod. It doesn't have to be expensive to be effective. Even a small amount of cushioning between the lens and window will help.
 
Camera body settings.
 
Most brands of cameras have similar functionality; however, the names the mfg uses for these functions may be different. Some of the settings I use are as follows.
Auto-focus is always set to AI Servo mode. I want the camera auto-focus to continuously track the subject. Why? Everything is always moving. You move, the subject moves. A single focus lock is insufficient to insure good focus on any moving subject, at any speed, at any distance. You see an animal, you push the focus button, the camera focuses, by the time you fire the shutter the subject and you have moved. Continuous focus tracking will give you a much higher likelihood of getting an in focus image.

Back button focus. If your camera allows you to use your thumb to press a button on the back of the camera to turn start the camera focusing, use it. I always use back button focusing and shutter button for exposure and shutter firing. Thumb and index finger coordination is pretty simple unless you have a deformed hand. This technique also allows you to focus and recompose.

Use the center focus point. The more focus points you use to auto-focus, the more likely the camera will get it wrong. The camera doesn't know where a deer's eye is. Spot focus on the eye, recompose and fire the shot. The internal processor will also have less work to do calculating a correct focus and it will speed up the focusing action.
 
Correct diopter setting is a must for monitoring focus accuracy. The diopter adjustment is found along side the view finder. Your first line of defense against an out of focus image is your eye. If the diopter is not correctly set, you'll never know if the image is in focus until you look at the image on your computer. Change your lens, change the diopter. Change your eye glasses, change the diopter. When you are firing off shots, be aware of the focus quality you see in the viewfinder.

Some DSLR's will allow you to configure the shutter to not fire if the lens isn't reporting a focus. You'll have a choice of setting the shutter fire priority to either focus tracking or shutter priority, meaning if you set your camera to fire shots even if the lens isn't reporting a focus, you'll probably end up with a lot of out of focus shots. This may work for spray and pray, but an astute photograph doesn't waste time and chip on getting bad results. The drawback to using focus priority is that the camera may not fire when you think it should because it's not in focus. You'll have to make the call on how to configure it, but at least be aware of the techniques and configuration possibilities.

Depending on the brand of lens you are using, the manual focus ring may be able to cause problems if you have your hand cupped around the lens over the focus ring. Some lenses allow manual focus while auto-focus is enabled. If you have a grip on the focus ring, simple hand movement can defocus the camera. Watch where you place your hand when shooting. I try to keep my hand as far out towards the end of the lens as possible, away from the focus ring and only touching the zoom ring. Same thing when resting the lens on something. Don't rest the lens on the focus ring.
 
Lastly, Get out and and shoot it often, review your results and correct your mistakes.
 
Practice makes perfect. Perfect is an acceptable result.