One of the biggest challenges to aviation photographers is to manage to capture the ever-elusive “Full Disk” of propeller driven aircraft. When shooting jets, it’s not a big deal to get crisp images. Just use the sharpness rule of thumb and crank up the shutter speed to twice your focal length and you’re usually good to go.
But prop driven aircraft are a whole different world from a technical sense. If you tried that sharpness rule of thumb, you’d end up with what we call “Popsicle Sticks”.
Essentially your shutter speed is so fast, that it will stop the propeller motion, which makes the plane look as if its engine is stopped. By the way, setting the shutter speed too fast is a very common thing for most people and reasonably understandable. General logic would seem to dictate that air shows tend to have fast aircraft. Perhaps a fast shutter speed would be best? After all, you typically would use fast shutter speed when capturing the action of sports, right?
In the aviation photography world however, this is a bad thing. We want prop blur to convey to the viewer a sense of motion, which then gives the picture the proper context of the aircraft is flying and not just sitting up in the sky.
So how do we fix this? Well in general, you will want your shutter speed to be no faster than 1/160 of a second to capture prop blur. The slower the shutter speed, the more you get away from the dreaded “Popsicle Sticks.” Ideally, you are going to want the shutter speed to be less than 1/125 of a second. How close you come to “Full Disk” (where the prop blur looks like an uninterrupted circle) is going to depend on the engine type (inline vs. radial), the current RPM of the engine and your shutter speed. So you will have a better chance at getting full disk on take-off or a high speed pass, where the RPM is at its highest. And typically, inline engines (like the Rolls Royce engines on P-51 Mustangs) usually run at a higher RPM in general compared to radial engines (like on F4U Corsairs). Faster RPMs mean you don’t have to set the shutter speed as slow to achieve the same amount of prop blur.
So this should be easy, right? Well here’s the catch. Go back to the rule of sharpness we talked about earlier; double the focal length and set your shutter speed to that. Most often, when shooting ground to air shots, you are using a super-telephoto lens, where you are well beyond 200mm. Apply the rule at 200mm and you should be shooting at least 1/400 second. That’s a pretty big difference in shutter speed to the desired 1/125 sec or less (and even greater when you use longer focal lengths, like 400mm or 600mm). So chances are you’re going to be having a difficult time to get the plane in focus and show prop blur at the same time.
This is where panning comes into play. In simple terms, this is where you do a torso twist to follow the path of the aircraft. Seems simple, right? Nope. The catch to this is that there’s what I refer to as a visual Doppler effect. Much like how sound changes as it a vehicle approaches and passes you, the rate of travel of the aircraft will also change visually and exponentially as it approaches and passes by; slow on approach, speeding up until it’s the fastest when it’s right by you, to slowing down as it travels further away. It is not a constant rate of torso turning. So your panning speed needs to match the aircraft approach speed change as closely as possible to give you the best chance of getting the aircraft as sharp as possible and capturing the prop blur. Trust me in that this takes a TON of practice to get right. Full disk shots typically happen at shutter speeds slower than 1/80 sec. WHEW! Got all that? 😯
In the aviation photography community, when a group of us get together at airshows, we sometimes like to have fun with it and set up a challenge to only shoot at a certain shutter speed or slower. Typically, this starts out at 1/80 sec. Because who doesn’t like to make things as challenging as possible?
So the next time you see a tack sharp image of a vintage aircraft in flight with a good amount of prop blur, keep all this in mind. I have a bunch of respect now for those aviation photographers! I hope this sheds some light on the challenges of aviation photography. Thanks for reading!