EF 75-300mm lens won't autofocus

[addisonstomack]

Hello! I was at my high school volleyball game and I normally shoot in manual with my EF 75-300 lens. Any other day my camera worked good, but when I went to take photos for this game, no matter what I did, my lens would just not focus. I had to stay at 100 for it to stay focused and if I moved it up or down then it would not focus again. I checked all my settings and everything was right. My AF was switched on. By the end of the night I ended up having to use MF, so I could get some photos. I do not know if this is my lens or my actual camera that is messing up. I did go and clear my camera settings too, and it is still doing this. Normally no matter how far away or decently close I am, the camera never had an issue. 

[addisonstomack]

I forgot to mention that my camera is a EOS T7 Rebel

[Tronhard]

Hi Addison and welcome to the forum! 🙂

The Canon EF 75-300 lens is very slow, by which I mean it required a lot of light to function well and that impacts on the performance of the focusing system. If the focusing system cannot find enough light to discern edges,  the camera will not focus, and thus not take a photo.

Usually that can be overcome by increasing the ISO and decreasing the shutter speed.  If you were shooting in Manual and you did not compensate enough for this yourself, then you would not get the camera to perform.  Frankly, I would suggest if you have that kind of issue, you set the camera to Av, or P modes and let the camera compensate for itself.  You can help that by setting the ISO to Auto with a range up to ISO 3200 or even 6400.

To test if the camera is working correctly, set it into P mode and, in decent light, focus on a sharply defined shape, like a building or its shadow and see if you gain focus and the camera will take the shot.  If that is so, the camera is functioning correctly and you need to change your technique.

[ebiggs1]

"Any other day my camera worked good, but when I went to take photos for this game, no matter what I did, my lens would just not focus."

You can certainly try what Trevor suggests but before you do does the quote above confirm that at other games in the same venue your camera/lens worked as it should?

"I ended up having to use MF, so I could get some photos."

But you left all other settings as they were? You simply switched off AF?

"You can help that by setting the ISO to Auto with a range up to ISO 3200 or even 6400."

Changing your ISO will not make your lens focus any faster or better it has nothing to do with AF.

However to confirm that the camera/lens combo is working as it is supposed to I will ask you to do a further set up before you try the test Trevor suggests. My prefered way is to do a full reset of the camera which means resetting any custom setting too, you may have done either purposely or accidentally. Now on a nice day set the camera to P mode. Set ISO to 200 and Daylight WB. Make sure the AF switch is set to AF on the lens. Go take a dozen random shots and make sure there are some vertical lines like trees or buildings or houses a fence, etc. Just random stuff. Check your shots and if they are OK nothing is wrong with the camera/lens but if there is still a problem either needs service most likely the lens.

Come back for further advice if you need to.