While the suggestions for f/2.8 zooms are good, you'll soon find out that those lenses are rather expensive, as well as fairly large and heavy.
You mention specifically shooting cheerleading and that might be possible with prime lenses instead of zooms. Lenses like the EF 35mm f/2 IS USM, 50mm f/1.4 USM, 85mm f/1.8 USM and 135mm f/2L USM are not only smaller, lighter, and generally more affordable... these lenses also are one to two stops brighter, so will be even better in low light shooting conditions when you can't use flash. Of course they don't have the versatility of a zoom lens. But they might be worth trying.
In case you are unfamiliar with them, "full" lens f-stops from large to small are: f/1.0, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22 (etc.) Each stop smaller reduces light by 1/2... or each stop larger doubles it. So an f/2 lens is twice as bright as an f/2.8 lens. Or an f/1.4 lens is 4X brighter than an f/2.8 lens. (Note: Those are all "full" f-stops. Cameras and lenses also operate in 1/2 stop and even 1/3 stop increments. A lens like the EF 85mm f/1.8 USM is 1/3 stop brighter than f/2, for example. Your EF-S 18-200mm at 18mm is f/3.5, which is 1/3 stop brighter than f/4. I kept to full stops above, just for sake of simplicity. You will find the other exposure factors... shutter speed and ISO... also work in full stops, along with either 1/2 or 1/3 stop increments.)
The lens you have now has a variable aperture that's f/3.5 at 18mm but closes down to f/4 at 24mm and another full stop to f/5.6 when zoomed to 90mm or longer focal length. The recommended f/2.8 zoom lenses are 2X brighter than your lens at 24mm and 4X brighter than it at 90mm and longer. That would help a lot. BUT, a 35mm f/2 or 135mm f/2 would be 8X brighter, while a 50mm f/1.4 is 16X brighter!
To decide which of the various focal length prime lenses might work best for you, look at the photos you have been taking with the zoom you have now. What focal length did you use for them? (This info is recorded in the image file EXIF data, which can be accessed with various software.) You will probably find that many of your shots are done close to one or two focal lengths. Of course, with prime lenses like these you might also be able to "zoom with your feet"... simply get closer or move a little farther away to adjust your compositions.
You might get a copy of Bryan Peterson's book "Understanding Exposure". It's a very good explanation of how all cameras work and can help you get away from relying upon "auto" for everything (which limits you in many ways, not just exposure control).
Finally, you mention using 7D, which is a quite good sports camera. However, something you will probably see happen is difficulty getting a good exposure under typical gym/arena lighting. The types of lighting used in sports venue often cycle on and off rapidly, 60 times per second. It's so fast our eyes don't notice, but our cameras sure do! This is a problem when shooting any sort of sports, where you need to use a fairly fast shutter speed to freeze subject movement. Some shots will be badly under exposed, when the shutter happens to fire when the lighting is in the "off" part of its cycle.
With the camera that replaced the 7D... the 7D Mark II... Canon introduced a new feature called "Anti Flicker". When that's enabled the camera detects the cycle of the lighting and times the release of the shutter to match the peak output of the lighting. I can tell you from experience this works very well. It solves a problem many of us sports shooters have had for a long, long time. Most of the Canon interchangeable lens cameras introduced since the 7D Mark II have had this feature. A few other camera makers have adopted similar in some of their cameras, too.
There is a more thorough explanation of this problem and solution(s) here: The Digital Picture... Canon Anti-Flicker
The original 7D doesn't have that feature. Short of replacing your camera with a newer model that has Anti-Flicker, other methods of dealing with the problem are:
- Upgraded lighting... obviously not something the photographer can do.
- Global strobe lighting... is found in many pro-level stadiums. Photographers are given access to it via wireless controllers. Most amateur arenas don't have this option.
- Portable flash.... which is prohibited at most sporting events.
- Use a slow shutter speed... 1/30 or below. Not practical for sports photography.
- Take lots of extra shots because it's likely many will be poorly exposed and unusable.
- Shoot RAW files (instead of JPEGs), in order to have more adjustability in post-processing.
. I hope this helps!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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