Let's help you solve some problems
Hello everybody it's Chris here looking to help you out with your cameras autofocus system. Over the past years I have spent countless hours photographing birds. In the beginning I would come home with more out of focus pictures then in focus. Going back out everyday trying to get those flight shots of raptors and perching birds. I could not understand why I was not achieving the picture I desired? My shutter speed was up over 1/2000th of a second my aperture was at F8 for a good depth of field but still more garbage shots than keepers? Let me tell you some secrets about autofocus and how it really works.
Cameras have many different focus modes so that it can react properly to stationary or moving subjects. To start off you need to switch your camera to AF-C for Nikon or Continuous mode and for Canon AI servo. These modes will allow your camera to continuously focus on a moving subject. Next we need to help you select the proper focus button, most new photographers use the top button or index finger button to achieve focus on subjects. While it is possible to track and get some pictures by half pressing the button to keep the focus its not the most efficient way. The optimal way is to set up your camera to focus using back button focus only. This way you keep your thumb locked on the back button while tracking the bird and using your index finger to press your shutter button. This may take some practice getting use to but in the end it will pay off big time!
Next we need to select our focus points or AF area. My go to is one focus point set to the center point, sometimes I may adjust it to the top or side to help for composition. Remember to set your camera to have the lowest number of focus point selection. This allows you to move this point fast and on the fly while tracking a bird in flight. Some of the new cameras or mirrorless cameras have predictive or tracking focus. These modes can be great in certain situations but in others they can suffer in poor contrast. Poor contrast is when your subject (the bird) blends into the background being close to the same color or dark on dark or white on white. You will start to notice in all af modes that this is the most difficult situation. So what do we do now just suffer with the loss of pictures?
No way, we have something that will help cure that too. In your camera menu you will have settings for your AF sensitivity. These are modes that I adjust daily or many times per day depending on the type of subject I'm shooting. The reason for these sensitivity modes is to help your camera lock onto a subject. Let me give you some examples of why or how I adjust these sensitivity settings. In my top picture with the Golden Eagle flying in tall colorful weeds my cameras autofocus was picking up the weeds as I was panning with the Eagle. So I went into my Nikon menu and slowed down my AF to Long. This meant when holding my back button focus constantly when a weed popped into my focus point my AF would not pick it up as I slowed down the sensitivity. Another time I like to slow down my sensitivity is when I'm trying to photograph a Snowy Owl on a grey day or a day that's snowing. The AF has a hard time picking out the subject in the white on white scene. Or if its a big fluffy snow flake day it will possibly pick up the odd flake.
If you find that you are shooting in a clean no contrast area with no distractions from backgrounds or foreground you can pump up that cameras sensitivity to fast or short in the Nikon menu. While prime lenses can have a very fast AF some zoom lenses tend to be a bit slower. If you have never adjusted this function your factory default settings are likely set in the middle. So I would try adjusting this if you find the AF to be slow with your lens.
Remember to keep those shutter speeds up so you don't get motion blur in the wings if your looking for that tack sharp image. Most of the time when I'm photographing birds I keep my shutter speed at a minimum of 1/2000th of a second. Another factor you want to take into concern is your aperture, every lens reacts differently to the distance to the subject creating a challenge with your depth of field. This is something you need to practice before hand to see how much depth of field you have at different focal distances. If you want a tool to help figure out your dof at different distances check out this linkhttp://michaeltapesdesign.com/lensalign.html
I hope you found this blog helpful, now get out there and start shooting!
To view Chris' workshops please visit the link below