So, I want to make decision about buying a telephoto lens, the Canon EF-S 55-250mm f/4-5.6 IS STM and Canon EF 75-300mm f/4-5.6 III USM. Which annoys me is the IS function, my friends asked me "what are you photographing?" then I said, I would like to use the tele for outdoors and sport (with high-shutter speed of course), but within the shutter 1/200, my hands still shaky or something.
How much benefit will using IS give over not using it at all, in general?
Image Stabilization (IS). The EF 55-250mm f/4-5.6 IS has it, the EF 75-300mm f/4-5.6 doesn't.
IS lets you shoot at a slower shutter speed before camera shake becomes an issue. If you are shooting at shutter speeds fast enough that camera movement is not an issue for you, then IS has very little to no effect on your image. Also, IS will not help you if your subject is blurry because the subject is moving too fast.
The IS on the 55-250 is good for about 3 stops of shutter speed (Tv). This means at 250mm instead of needing to use a Tv of 1/400 sec or faster, you can use 1/50 sec and expect to avoid blurring due to camera shake if you are practicing good camera stability techniques when shooting.
For a more complete comparison of these two lenses, please see this answer to Canon 75-300mm f4-5.6 USM or 55-250mm f4-5.6 IS lens?. When comparing these two lenses, optical image quality is probably just as important a consideration as Image Stabilization is.
This addresses speed / focal length aspects only and does not address issues wrt specific lenses.
Overlaps with what others have said.
As others have noted - antishake / stabilisation only helps to compensate for camera motion - not subject motion.
Traditional rule of thumb is minimum shutter speed is
1/s = mm
ie 1/50s at 50mm, 1/250s at 250mm etc
This is modified in the real world by various factors - here shown as K_xxx
CF = crop factor makes things worse as lense is effecively "longer" by a factor of CF.
Other factors MAY make things better (ie longer allowed shutter speeds).
In "the real world" an experienced photographer with an unstabilised system and no external bracing can usually better the rule of thumb by a factor of 2, getting marginal at a factor of 4, lower happens - see Kyou below.
Any sort of bracing against an external solid support helps.
(Monopods are said to help but don't seem to help me overly much unless used as part of a body triangle.)
CF = crop factor (about 1.5 for most APSC systems)
Converts focal length to "35mm equivalent".
If focal length is expressed in 35mm equivalent (as on some point & shoot cameras) then this factor has already been allowed for.
K_is is anti-shake / image-stabilisation system gain.
4+ usually (2 stops)
8 if lucky (3 stops)
16 if you believe the marketing department's blurb.
K_you is based on your experience, skill and Ninja breathing abilities.
1 is safe,
0.25 can happen,
2 is not unusual,
4 is grand master if consistent.
Larger has been known to happen.
Helps to wedge camera against a post, brace 2 legs and body against something solid etc.
Holding breath around moment of shutter release helps - many recommend exhaling. I find inhale and hold better for long delays (when will it fly ...?) as Oxygen in lungs can prove useful.
I'm told that slowing your heartbeat rate helps, but it's not something I've mastered :-).
K_luck is a happenstance factor and can be amazingly large - and may not be.
I sometimes find that photos taken in the 0.1s - 1s shutter speed range, while not actually "sharp" are acceptably usable, when this is not really expected. Other times they are a blurred mess. It's hard to be sure what factors apply here but lack of subject movement and the ability to keep what movements do happen inside a small range no doubt help. An IS mechanism can help over long periods exceeding the normal claims if the total motion range is inside its mechanical motion limits.
Moving objects make this worse quite apart from the direct effect of their motion.
Panning can help and may not.
There is one rule about the speed and focal length. To avoid camera shake i.e. blurry photos you should use shutter speed = 1/focal length. Let suppose you use 300 mm so your speed should be at least 1/(300*1.6) = 1/480s. For crop cameras you should take in consideration crop factor too (which is 1.6 for Canon crop cameras)
With image stabilization you get possibility to shoot with slower speed. For example if your lens have 3 stops stabilization you can shoot (from example above) with 1/(300*1.6)=1/480. 1/480/2/2/2=1/60s (the speeds are just example)
P.S. Of course the above rule depend of how stable you can handle your camera. I personaly have some photos, created at 1/8s (w/o IS) which are in focus, w/o any blur. From other side have other photos at 1/100s (with IS) which have motion blur :)
Generally, image stabilization is specified as giving a number of "stops" — see What does "N stops" mean when describing an image stabilizer?. For your lens, Canon claims a 4-stop improvement. This means the system can cope with a shutter speed about 2⁴× (that is, 16×) slower.
So, if we follow the one over shutter-speed rule, adjusted for sensor size that means at 200mm, the nominal shutter speed to cancel out camera shake would be ¹⁄₃₀₀th of a second — but with 4 stops of IS, you could get sharp images all the way down to about ¹⁄₂₀th of a second.
Of course, that doesn't help with subject movement. And the shutter-speed rule of thumb might not be sufficient for today's pixel-peeping pickiness. But still, you should be able to get noticeably better results at ¹⁄₁₀₀th or so, and yes, probably also at ¹⁄₂₀₀th (although the relative effectiveness does go down as shutter speed goes up).
