What Is a Focus Limiter And WHY IS IT SO IMPORANT a Prime Lens like a 600 f4? An AH-HA Moment
I just returned from a trip to Costa Rica and one of the most important lessons for me was learning about why the Focus Limiter is so important on a Super Telephoto like a 400 f2.8 or 600f4. Of course, I knew that my others lens have a focus limiter but it never seemed that important with a 70-200mm or 100-500 mm lens. However, on a Super Telephoto the focus limiter is very very important.
On this trip, I rented a 600 f4 lens from LensProToGo. It was the first time I had ever used a Super Telephoto Prime Lens. On our first morning of shooting, we were taking photos of Hummingbirds. The feeder was extremely close to our position and I was having a really hard time getting anything in focus. There was a fence behind us so I could not back up further. So the workshop instructor, Colby Brown, asked me if I know the minimum focus distance of this lens and have I adjusted the focus limiter? I should have known the answer to both questions but I did not.
A quick internet search revealed that the Canon RF 600 f4 lens has a minimum focus distance of 4.2m ( or 13.8 ft). This means that I have to be at least 13.8 feet from the Hummingbird feeder so that my camera could focus on the hummingbirds. So moving back further helped, but I was still struggling with focus.
There is 1 more step to getting the focusing system to work properly!! I had to change the focus limiter setting as well! On this lens there are three focus limit modes available: Full, 4.2m-16m (13.8 Feet to 52.5 Feet) and 16m (52.5 feet) to infinity. I usually kept the lens on FULL or which uses the full focusing range of the lens, from close (4.2 m or 13.8 feet) to infinity.
What Is a Focus Limiter?
A focus limiter will restrict the range of distances the camera will focus or “hunt” on. Choosing the wrong mode will cause the focusing problem I encountered in Costa Rica. In addition, a focus limiter helps improve both the speed of focus and accuracy, especially if you are aiming at subjects that are very close or far away from you.
So when I switched the limiter to the middle position (4.2m to 16m) the limiter instructed the lens to focus on the short-end of the range ignoring subjects more than 16 meters away. Since the camera’s focusing system is searching a smaller area the focus speed becomes much faster. Once I switched the focusing mode, my camera began to instantly focus on the hummingbirds. It truly was like magic. It was a night and day difference.
The Focus Limiter Button
The Difference was a Game Changer
All of a sudden was able to focus on Hummingbirds which are extremely hard to photograph. They are tiny and you need to shoot them at 1/4000th of a second. Take a look at the result below—
and here is another one
Conclusion
There are several lessons I learned from this situation. First, it is important to understand your camera equipment before going on a trip especially if you are renting new gear. I should have known the minimum focusing distance. Sometimes, you get so excited that you just want to start taking photos. But in the end we want great photos that are tack sharp. Second, if I ever buy or rent Super Telephoto Lens again I will keep an eye on the focus limiter because on these big lens it can make a huge difference.
I hope you found this information useful. What is your experience with Super Telephotos? Have you tried the different focusing ranges?