06-24-2017 07:26 PM
The Sigma 10-20mm f/4-5.6 EX DC HSM Lens for Canon EF has been discontinued. It has been replaced by the very good Sigma 10-20mm f/3.5 EX DC HSM Autofocus Zoom Lens. No lens in this range will be any better. I would look to other focal lengths that you might like and not duplicate this one.
Do look at the different 50mil offferings. BTW, there is no 'e' at the end of the word lens.
06-24-2017 10:10 PM - edited 06-24-2017 10:28 PM
If you have never done so, I recommend watching 2 or 3 free tutorials on YouTube or google videos, etc, on the "exposure triangle". It gives you the central idea in photography, that there are 3 variables you can manipulate in order to get the right amount of light into your camera.
These 3 variables are 1) the size of the opening in the lens, or "aperture", and 2.) the amount of time the camera opens up to let light in, or "shutter speed", and finally, 3.) the sensitivity of the image sensor , or "ISO").
In addition to controlling the amount of light getting in, the variables have side effects that affect your images. The side effect of aperture is the thickness of the in-focus portion of your photo. Sometimes you want everything in the shot to be in focus, from the flowers in the foreground to the mountains in the background. Other times, though, you only want your subject in focus and you want everything else to be gently blurred so they do not distract the viewer's eye from your subject. It is a large aperture that gives you a shallow depth of field in focus. Kit lenses don't have large apertures. Lenses that do have large apertures tend to cost more. As mentioned earlier, though, if you don't get a zoom lens, and you instead get a fixed focal length "prime" lens, like a 50mm or a 40mm or an 85mm, etc, they almost always come with large apertures, they tend to be lighter and sharper than zoom lenses of equal price, and primes generally cost less than zooms with equal image quality.
This can give your your photos a look they do not already have.
The obvious other advantage is that the large aperture lets more light in. A lot more. In some cases 8x more light than kit zooms. With 8x more lights you can keep a fast enough shutter speed without having to raise ISO. Your T2i will show image degradation by ISO 400 and bu ISO 800 it is looking pretty bad due to grainy static and loss of detail. The larger aperture lets you stay at ISO 200 when a kit lens would have forced you up to ISO 800 or even ISO 1600, probably ruining your image.