The Canon EOS and Photography Forums

I’ve been using long lenses (600mm +) for more than 25 years, with a few hiatuses due to the expense of keeping up. Lately I’ve concentrated on birds, rather than them being occasional subjects, and that has led me into the upper realms of long lenses – 1920mm maximum effective focal length.

Of course my starting point was a full frame 35mm (film) camera with a 600mm lens, BUT, lots of birds don’t want to be close enough to be reasonably large in the frame for a good image. And, since all I do are birds now, I’ve been stretching for longer lenses to be able to make decent images from distant subjects.

My present system is a Canon 7dii, with an EF600/4LIS (effective focal length = 960mm), plus 1.4x converter (effective focal length = 1344mm), or with a 2x converter (effective focal length = 1920mm). One or another combination of these elements will pretty well cover most jumpy/shy bird situations.

There are times and conditions when I can photograph a large bird, like a Great Blue Heron, at 250 feet with success, but there are other times when working at even 60 or 70 feet yields nothing but blurs. The summer before last I was at wit’s end trying to find out why all my images, except the closest ones, were unusable and I simply didn’t make the connection with atmospheric disturbance – I had never heard or read that heat waves would be a serious problem with the high magnification of a long lens on just about any sunny day.

You, too, must have read a lot of those Africa phototour reports, if you’re interested in long lenses and are reading this: do you remember anyone saying that 600mm and longer lenses are useless in the heat of Africa? A lot of those reports do say they prefer to use shorter focal lengths, but usually they say it’s because you can get close to good subjects with them on safari and/or that the big lenses are very cumbersome in the tour vans and on planes.

Even Canon technicians don’t know enough to suggest that repeated problems are likely due to atmospheric distortions. It took a lot of searching and finally getting Roger N. Clark (ClarkVision.com) in on the problems to finally have someone tell me what was causing my them.

Now that I know to look for it, I can see distortion affecting my images almost every day, certainly every warm and sunny day. There are, however some circumstances when heat waves are minimal and I can expect to get a decent percentage of sharp photos at normal working distances: cold and cloudy days (it’s great to be in Oregon!), early in the morning before the sun has much time to heat things up and, possibly, over water, which may not heat up as much as the land surface and thus subdue the airborne gyrations.

Finally, I have one trick that helps when things aren’t too bad and the subject is still: use LiveView at higher magnification and watch the distortion affect the subject then try to make your exposure(s) at the best instant(s). If I do 10 or 20 frames this way, I might get a couple of good ones even at 250 feet and at 1920mm effective focal length (almost 40x magnification compared to an image at 50mm effective  focal length).