Among aerospace photography subjects, helicopters are more of a challenge than many. Except for images made with intentional blurring, "quality" photography requires (among many factors) sharpness. Rockets, jets, piston-powered-props, helicopters, and more — any vehicles that are on the move — require specific techniques to capture the image with crisply rendered details, what can be termed "rivet sharp." What makes helicopters special is you also need their various blades to appear in motion.
For sharp images of moving subjects, a common technique is to use fast shutter speeds. For instance, if you're shooting a U.S. Navy Blue Angels F/A-18, crank the shutter speed to 1/2000 second and the aircraft will appear fairly sharply rendered, even as it slices by in the sky.
But photographing helicopters, especially air-to-air, with sharp details is a balancing act because using a short shutter speed visually stops not just the motion of the vehicle, but the motion of the rotor blades, too! So, slow down the shutter speed, right? Instead of 1/2000 of a second, go to 1/1000? Nope — still much too fast. 1/500? Better, but not good enough. 1/250? Try again. Okay, 1/125? Yes — that's a pretty good speed to show enough blade blur. Even a smidgen faster works, like 1/160. These speeds will allow the blades to appear pleasantly blurred.
The challenge with these shutter speeds is holding the camera steady.
What? It's easy to hold a camera steady for 1/125 of a second, isn't it? That's less than a tenth of a tenth of a second!
When you’re photographing on the ground, 1/125 of a second is typically easy. But in air-to-air photography, the aircraft holding you (the photographer) is often cramped, bumpy, and vibrating, while the aircraft you are trying to capture is usually moving relative to you, sometimes on purpose, or because of turbulence, mismatches in speed, or pilot comfort levels. Keep in mind, too, that you're usually using a longer lens when photographing helicopters air-to-air, and a longer lens is harder to keep steady.
So, you have to shoot slow (longer shutter speeds) with a lens that amplifies any unintended motion, from a platform that is jiggling and buzzing. Plus, the air is rushing by and, if it strikes any part of you or your equipment, it adds even more uncertainty and motion. What to do?
Here are some quick tips for capturing great shots in these challenging conditions.
Starting with a "don't" — you don’t want to lean against the door frame or seat or anything, really, because those structures are being vibrated by the engine and rotors and air flow around the aircraft. Touch the aircraft as little as possible — let your body absorb the vibration and jiggles.
Speaking of air flow, unless your airspeed is extremely low (which is possible in a helo), keep your lens out of the slipstream just outside the door or window. Even if you can’t see the vibration through your viewfinder, your lens will flutter out there. This applies to lens hoods, too. Keep them out of the wind, or take them off (and stow them securely).
Next, if you have stabilization features in your camera or lens, try using them; they should help. But review some shots carefully to be sure the features aren’t making things worse. Sometimes the system will move the sensor or lens elements or whatever, during the time the shutter is open, and the result is more blurring. A gyroscopic stabilizer can be a big help, not only by functioning as intended — countering unwanted motion in the camera with opposing motion induced by the gyro — but by merely being heavy they also tend to dampen smaller motions caused by vibrations. These systems add complexity, with batteries and cables extra bulk, and that extra weight can be awkward and compounded by G-forces during maneuvers, but they can greatly increase your percentage of good shots.
Finally, shoot a lot — digits are cheap, while aircraft operations are not — and check your results closely when you have a lull in the action, such as when the subject aircraft is maneuvering away from you. Zoom in on the display on the back of the camera to make sure your settings and technique are achieving the desired effects. And if you are not getting sharp details in the subject aircraft with suitably blurred blades, improve your technique or go ahead and increase your shutter speed. Coming back with usable, if not ideal, imagery is better than coming back with nothing but blurry ones. Oh, and fly safe. Listen to your pilots, ask them for what you’d like, but accept what they’re willing to do. No image is worth injury or death.
For extra credit, you can attempt what many fixed-wing photographers aim for — a full rotor disk. That is the effect whereby the blades blur in a sufficiently wide arc as to overlap the next blade's blur. The result, when accomplished, is a solid disk, a platter of color and blur. The shutter speed required to achieve that varies, depending on the number of rotor blades, but it's usually something in the realm of 1/10 of a second. Maybe 1/15. The fixed-wing guys have it a lot easier, as an airplane's propeller spins 7 to 8 times faster than a helicopter's main rotor (so, 1/100 of a second might just do the trick; maybe 1/80). Give it a try, but be sure to take the advice in the previous paragraph and shoot a lot.
So, shoot slow, don't let the aircraft or the wind shake you or your camera, use built-in vibration reduction or a gyro, and take a take a lot of pictures. Of course, get your exposure correct, focus carefully and accurately, get your and the other aircraft in positions that allow interesting compositions, and close enough to allow a range of compositions to be useful in a multitude of media, make sure the background is appropriate and appropriately exposed, too. But those are topics that need to be explored at another time.
Fly safe, and good shooting.