How can I take a picture of water rockets as they fly through the air? What settings would be best under normal daylight conditions? What is the slowest shutter speed I can use that the lighting will still look natural, but it will also capture the water trail and droplets? And what would be the best aperture so that the background is not in focus, and the main thing in focus is the rocket?
"Real" water rockets accelerate EXTREMELY fast. While some with restricted orifices may stagger off the launcher, anything that aims at performance accelerates faster than almost anything else you are likely to photograph. A top rocket 9by calculation and experience) accelerates at up to about 100 g !!!.
There are various shots you can take. Looking up at the rocket well above you is a fairly general shot and panning can work. Exposures and shutter speeds can easily enough be arrived at by experiment.
Getting a good shot as the rocket leaves the launcher up to say 10 to 15 feet in the air, takes care, planning and luck. Smaller aperture for better depth of field helps. Fast shutter speed can help BUT there is another way. Set camera to manual, adjust for a relatively low shutter speed - below max flash sync speed, and then add flash. Rear curtain flash is even better if you have it. Adjust flash to ambient lighting so rocket stands out when the flash operates. Good shots may be had by framing from launcher to about 15 feet pointing upwardsish from near the ground so the rear curtain flash catches the rocket sharply. You get a water trail with some blur (depending on shutter speed) and a sharp rocket IF you are lucky. Just using flash plus ambient can also be good.
An interesting point to take photographic advantage of is that a rocket which has the majority of its mass as propellant and which is not very restricted in its jet will accelerate to faster than its own exit velocity. (The rocket equation makes this clear when you look at it and plug in high Full/empty mass ratios). Using an eg 1.5 litre bottle with about 100 to 120 psi and bottle mouth as orifice and 1/3 fill (about optimum) the water will be all exhausted by about 15 feet after takeoff BUT the rocket will exceed its exhaust velocity after about 5 to 10 feet from the ground. This means that water below this point is being ejected with a downwards velocity BUT above this point the ejected water actually has a net upwards velocity. The end result is that the water plume in the air changes shape as the water exiting slows and then reverses. Above the reversal point it starts to fan into a cloud with increasing spread as the upwards velocity of the water increases with height and is spread more by th air as it hits it faster. When I first saw my photos of this I did not understand what I was seeing but it makes sense once you realise. The effect is amazing - quite unlike what you expect to see and fast enough that you don't really notice with the eye alone unless you are looking for it. So the photos are especially surprising.
I can find some photos of this effect if of interest. Quite some years ago now :-)
Also fun is a two or more photo sequence of the ascent with the photos manually stuck together. That they don't quite match due to change in perspective and angle doesn't matter. People see immediately what you've done and appreciate it for the fun effect. (I have one such pair where the rocket went to about 6,200 feet ASL - BUT it was launched from 6,000 feet ASL ;-) - highest altitude water rocket shot in NZ (I think). Have the photographer stand back some way to do this. First shot shows water plume standing maybe 20 feet in air plus some sky above and second shot overlaps and has lots of sky and cloud and rocket high above. Chances of getting rocket in the first shot is about zero but water plume is easier. Rocket in second shot is at apogee so easy.
NB - be prepared to get you and your camera deluged.
You could try "cheating a little" :-):
As an alternative to dpollitt's answer, you could also try panning the shot.
A fast shutter speed, as he suggested is the best way to get a sharp image. But if you also want to throw the background out of focus by using a a long focal length and getting close to the subject, as drewbenn suggested, then the problem is going to be getting the thing in frame. It will be moving fast and it may be hard to get the timing right.
Also, freezing the motion at 1/2000 or 1/4000, you should be able to get everything sharp, but you may lose the feeling of motion. This happens in motorsport photography, where you see a car that's doing 150mph look like it could be parked for all you can tell from the photo.
So I'd try panning the shot. That should make it easier to keep in the frame, the background will blur completely. Depending on the speed of the rockets, you might try between 1/15 and 1/60th. Using a slower shutter speed also means you can use a smaller aperture, so you'll get more depth of field on the subject, so should make focusing easier. Panning won't be easy: you'll get a lot of dud shots, but you will hopefully get a few really spectacular ones. Assuming you can make a lot of attempts, I'd first use dpollitt's advice with a fast shutter and wide aperture, then try some panning shots.
Well without knowing anything about the equipment you are using. Very generally speaking you want to use a fast shutter speed, something like 1/2000th of a second or so since this will be a very fast moving subject. I would put the camera into a sports mode if possible, that is probably the easiest way to achieve this if you are not familiar with manual settings.
If you want a shallow depth of field, with the subject in focus and the background blurred, you would want a wide aperture such as f/4 or larger(f/2.8 etc). If you are constrained by your aperture and shutter speed, you will probably get stuck with whatever ISO your camera ends up selecting to still get the exposure correct. You could use neutral density filters to darken the image and allow larger apertures if it is necessary during bright daylight as well.
Focus is another component here. If you are shooting fast moving subjects, I would use a mode similar to Al-Servo mode, where it continuously adapts the focus for a moving subject. You can play around with what focus points to select, and if panning works well or not for your artistic vision.
Another note, no shutter speed is going to make the lighting look "unnatural" in a properly exposed image. If you add in additional lighting with a flash or similar device, then of course you could achieve a more unnatural lighting effect. I don't think this would be a major concern for most users. If you are speaking of "unnatural" in the sense that a slow shutter speed will make the rocket blurred from movement, that is what you would want a fast shutter speed for - to freeze the subject and the water droplets.
Have you tried any shots? The real answer depends on how fast the rockets are and what image you want. I usually don't like the results of very high shutter speed, because it freezes everything, and loses all sense of motion.
Panning is usually the answer. How much to pan and what shutter speed to use can only be found by experimenting.
Go shoot some tests.