Keeping sharp – Part 2

Shoot at the right time

We ask a lot of our tele’s. We pull them out the bag and aim them at tiny distant objects expecting the reach, the image stabilisation, and the autofocus will produce a crisp image. So often this isn’t the case. Quite often the longer the telephoto lens, the worse it gets… So what’s wrong?

A lot of the time it is because we aren’t shooting at the right time of day. In the mornings and evening, it is cooler and often less windy. The heat in the atmosphere is going, the dust is settling down, the shadows are no longer a hard blue.  All this means that your image will be sharper because there is less going on between you and the subject.

Sometimes it is going to be the case that you should leave your camera in the bag and enjoy the moment because no matter what you do the image will be a poor one due to hot shimmery conditions and harsh shadows.

Expose correctly

We don’t talk about exposure much when it comes to image quality. It is a huge issue because we rely on our cameras to expose correctly and a lot of the time they just don’t! I reviewed a pair of images recently of the same birdshot by different photographers at the same time. The argument was that one camera make was clearly much better than the other due to the relative quality of the images.

The photographer couldn’t understand why, with the more expensive equipment, his image was so poor in comparison. The answer turned out to be exposure. The photographer had photographed a bird against the sky and allowed the camera to make its own decision on exposure (typical of using a mode like Aperture Priority or Shutter Priority without engaging exposure compensation). He then relieved the shadows in Adobe Lightroom and watched the shadow quality and feather detail become a mess of indistinct noise.

The other photographer had exposed correctly and his image, 1.5 stops brighter, looked much better after processing.

Set for success

Settings can also influence image quality.

Aperture

Too shallow a depth-of-field (DoF) and you may miss focus or miss a crucial detail. If your aperture is wide open at your maximum focal length and your subject is 5 to 10 metres away you will be dealing with a DoF of mere centimetres. Check out the table below for some common lens focal lengths:

Another aspect of Aperture is directly related to sharpness, wide-open, your tele lens will not be as sharp as when stopped down a little. The same is true when you stop down too far as diffraction comes into play. Your lens will have a ‘sweet spot’ that you will find varies for subject and distance. You must find it through trial and error.

Shutter speed

Shutter speed is a setting that is crucial for achieving a sharp image. A high shutter speed will freeze any movements your subject makes as well as movements you make while holding the lens and camera. Personally, I find I make a rotational movement when pressing the shutter release too. It’s important to get to know the kinetics involved in your own personal stance and adjust or practice accordingly.

So what speed do we need? Well, some people reckon 1 over the focal length of the lens on a full frame camera is a good place to aim. So a 400mm lens would require 1/400’th of a second.

When using a crop sensor you can multiply this by the crop. So for a Canon 1.6 Crop like the 7D the minimum shutter speed would be 1 / (400 x 1.6) or 1/640’th of a second.

All this is great for starting out and reducing camera shake, but with the higher pixel pitch bodies now available I think this is too slow for safety. For bird photography, I like to shoot at 1/2500th of a second. I know that at this speed I will capture a good deal (but not all) of the birds’ movement and limit the risk of shake from my own.

Of course, it is not always possible to shoot at 1/2500th of a second. Often the light isn’t good enough so I might drop it to 1/1000 if I’m really desperate and down to 1/250 if I am photographing a stationary subject and take special care.

Just a note, If I am achieving high shutter speeds of 1/2500 I will often switch off the IS. I find this helps with image quality on my own set of lenses.

This Black Shouldered Kite was photographed with a Sigma 300-800mm lens and Canon 7 D Mark II. Shutter speed is 1/320 and the focal length is 730mm, ISO is 320, the final image has been cropped too. Not the sharpest pic in the world but it was far away!

This is extreme for this focal length (with the crop sensor it is 1168mm) and great care needed to be taken. I also used a polarising filter. This had the negative of darkening the image but the positive of reducing glare, shimmer and haze and adding some contrast on the distant bird. Polarisers are very seldom used on long lenses but they can really make a distant shot work.

ISO sensitivity

The final setting is the gain or sensitivity of the sensor. Think of it like the volume on an old stereo. If you have a low volume you may find it difficult to hear but you will have relatively little distortion from the old speakers on the stereo. The sound will be low but faithful to the original.

Turn the volume up and you will start to hear the sound better but also hear more distortion and crackle. Turn it up really loud and you will start to lose the faithfulness and quality and hear lots of distortion, crackle and bass but you will definitely still hear the music as well.

The ISO works in the same way, just with a picture. Too low and you will have a dim but faithful record. Too high and you will have a bright but distorted picture. You have to find the right spot for every image you take.

ISO helps you because turning it up high allows you to adjust the other settings, aperture and shutter speed, down and up respectively. The higher the ISO for a given exposure the less light you have to let in, so the faster the shutter can go or the narrower the aperture can be.

Long lens technique

If you still aren’t getting sharp images at this point, you need to start considering your long-lens-technique (LLT).

LLT involves minimising shake from body movements and slap from the camera shutter. To minimise shake, you will mount the lens and camera on good support and while resting a hand on the forward part of the lens and pushing firmly down against the support you will force your eye and forehead into the viewfinder and the back of the lens.

You will breathe carefully around the shots, take a half breath and hold it, then carefully hit the shutter release.

You can go further than this and use a remote shutter release while standing clear of the lens.

Slap is the movement that occurs due to vibration of the shutter during an exposure. Some camera bodies manage it much better than others. To minimise slap rest a beanbag on top of the lens close to the body or shoot in live view mode. When using live view I’d advise an inexpensive remote shutter release.

Flash

Using a flash is an important method to add a little contrast sharpening and detail to a shot and it should not be thought of as just a tool for night-time. Flash also fills in unsightly shadows. In the harsh light conditions I shoot in, it can be really important for allowing me to take shots further into a bright day.

Too often the conditions in summer will preclude photography after 8am. If you have travelled a long way to a site this is a real pain in the butt. I use flash to get around this problem because it can very successfully relieve dark areas.

This Little Grebe was photographed at midday with the sun overhead. Shots without the flash would have had a deep shadow on the chest and face. The flash has relieved these really well and made a usable picture from an unpromising opportunity.

Tip – I am always careful to remove the second point of light created by a flash in a subjects eye. Usually, both the sun and the flash can be seen reflecting in the eye and it is a dead give-away that flash was used.

There is another aspect to flash work. You can use the pulse of light to freeze a moment more reliably than the camera shutter in the dark. The Bat shot in the title image relies on this technique. Shot at a slow shutter speed of 1/200 second (the flash sync speed of the Canon 5D mark iii) the animal is still relatively sharp and frozen. This is because the pulse of the flash was so bright compared to the general conditions that the sensor recorded only this moment during the long exposure.

Calibrate your gear

If you have stuck with me up until now and you still have issues then the likelihood is that your focus, body or lens elements are out of whack.

Ensure your viewfinder dioptre is set correctly for your eyes. Compare the images taken in tests with the viewfinder and with live view. If Live view is better, you may need to calibrate your gear. Some bodies allow you to calibrate using the operating software. Sigma produces a dock that calibrates its lenses. Other cameras require you to get a technician involved.

If your camera does support internal calibration (Canon call it Micro-Focus Adjust MFA) do it. It’s easy and there are plenty of guides on the internet. Some Canon bodies also allow MFA at both ends of the zoom range. This can be very useful!

I hope this guide helps! But remember, sharpness isn’t everything. Sometimes you want to go the other way for creative effect. Photography is about communicating a message and it can take many forms.