#55 250 STM 3.5 STOPS MEANING ISO#
When someone says that IS allows you to use a smaller aperture or lower ISO that is what they mean. If you can keep the shutter open longer, you can either lower the ISO or use a smaller aperture, both of which generally improve image quality.
The IS would allow about 1/40 s (slower still for shorter parts of the zoom range). The common rule for shutter speed is 1 / (crop factor * focal length) in seconds, which for this lens would be 1 / (1.6 * 250) = 1 / 400 s. The IS in this lens is rated for 3.5 stops, which means you can shoot about 2^3.5 = 11 times slower than you would want to before getting motion blur. This, in turn, lowers the shutter speed one would need to use to ensure that there isn’t motion blur when handholding the lens. It simply stabilizes the the lens against vibration.
IS doesn’t affect the aperture or shutter speed. The aperture lowers as a result of zooming due to a design compromise to keep the lens smaller. I do not think the two are related at all. Please explain what you mean by image stabilization lowers the aperture. If you have a Rebel and are thinking about a second, longer lens to go with your kit lens, then this is a great choice. Its weight helps stabilize it, and the big aperture is worth the price (which is now down to about $80 a year). I’ve got a Sigma 70-200 f2.8 I use when I want a zoom, and a Canon 100-200 f4.5-5.6 when I need something longer or lighter and less bulky.īoth those lenses are over 15 years old and neither has image stabilization, so I’ll occasionally use this lens if I’m shooting distant moving wild life or something.įor sports or concerts I’ll still use the fat lens and take my chances. It’s a good deal if you have an APS-C Canon camera and don’t want to spend a ton of cash on a longer lens. On the down side, it feels pretty cheap, and I get chromatic aberration and some softness on the edges when it’s zoomed all the way out. On the plus side, it’s pretty long and is inexpensive. I bought it because there was a $100 rebate when I bought it with my camera.
I’ve had this lens for about three years.