I want to buy a lens for my new camera and everyone says that STM or USM Lenses are the best choices but also they said STM and USM lenses will not work for Canon Rebel T7/ 2000D !
is this correct?
No, it's not true.
I have the Canon EOS 2000D.
I also have a 50mm f/1.8 STM and great many other STM lenses. All of them work just fine.
I also happen to have one USM lens: 85mm f/1.8 USM. It works fine, too.
I agree that STM and USM lenses are the best, so you should consider only those. About the only non-STM non-USM lens today offered as new is the cheap kit lens.
There may be difference in focus speeds, but the main differences are the two main features of STM and USM lenses:
- STM and USM lenses allow instant manual focus override
- STM and USM lenses are much more quiet, being far more useful for video with autofocus
STM is manual focus by wire, USM allows direct manual focus which some people prefer. I found STM to be good enough for my uses (focusing to distant stars in astrophotography).
Usually (always?) STM and USM lenses have a non-rotating front element, meaning focusing doesn't mess up the orientation of your polarizing or graduated neutral density filter, should you use one. At least my non-STM non-USM cheap kit lens has a rotating front element.
Also, if you want quick autofocus on your 2000D, you should prefer these modes in this order:
- Shoot through the viewfinder.
- Shoot using live view mode, but use quick mode autofocus. Note there's a slight interruption in the image as the mirror flips to use the phase detect autofocus sensor.
- (least preferred): Shoot using live view mode, using non quick mode autofocus. Now there's no interruption in the image, but the autofocus is slow.
So, autofocusing speed is mainly dependent on how you use your camera.
As far as still imaging goes, all STM lenses should work on your Canon Rebel T7/2000D.
In terms of using continuous AF while shooting video, the Rebel T7/2000D lacks Dual Pixel CMOS AF that many higher Canon EOS models, including the Rebel T4i/650D and later models in that series, feature. It probably also lacks the capability to continuously focus with STM (or USM or non-USM/STM) lenses while shooting in video mode. That's where you may have gotten the idea that STM lenses don't work with the Rebel T7/2000D.