I have been using the Canon EOS 2000D and Sigma 150-600mm lense for about a year with no problem. Today when out taking photos the lense just stopped focusing on subjects (birds etc). It only continued to focus on far away objects. I feel like I may have knocked something, but can't see what, unless it's possible for it just to stop focusing on a subject between two shots. It still focuses on further away objects, such as rocks in the sea ~20+ meters away, but when my subjects are all closer, that's of no use.
My subjects at the time of it stopping focusing were chicks that i have photographed multiple times with the same set up, and from the same distance I was at.
When I hold the shutter button half down, it doesn't even attempt to focus on things close up. Through the view finder it is just a blur.
Any help would be greatly appreciated.
This lens has a MFD, minimum focus distance, of around 3 meters, or 10 feet. Typically, this specification applies at the shortest range of a zoom lens. As you increase the focal length, the MFD for most lenses will also increase.
There is also a focus limiter switch on the lens body. This setting can also affect the range of focusing distances the lens can capture.
I agree with Waddizzle - and the likely cause is that you have brushed and moved the focus limiting switch. Look on the side of the lens barrel and check the position of the switch. If you want to focus on objects close by it should be set to FULL, as opposed to 10m- (infinity), set to or 2.8-10m to limit the focus to close up. These settings help the lens focus more quickly vs the widest possible distance range.