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75-300mm lens not working on Canon m50


I use a canon eos m50, with a 75-300mm lens, and a commlite adapter for the camera. I’ve used the auto focus many many times before. But recently when I go to use the auto focus, it won’t even attempt to focus, and gives an MF (manual focus) sign on the upper left of the screen. And then when I switch it into manual focus, and manually get the image into focus, there are red lines outlining everything in the image. And no matter what, the images aren’t captured even when I click the button. If someone would be able to help that would be great, I take pictures for my high schools baseball team and they have an upcoming playoff game on Friday.



Hi and welcome to the forum:
There are a couple of potential issues here:
1. Using a third-party adapter adds a level of unknown, (i.e. risk) compared to using a native Canon unit and will make it hard for Canon to provide service solutions for anything attached via that device.
2. The EF 75-300 series are, IMHO, Canon's worst optic: it is unstabilized, fragile and has mediocre optics.  If you have been using this lens a lot, it is not impossible that it is wearing out, or been inadvertently damaged, but with the complication of the adapter, it is hard to be definitive.  I wonder if you have a DSLR body you can try the lens with to see how it behaves?

I realize this is not an immediate solution by Friday, but if you decide to eventually replace the lens, there is a far, far better alternative in the EF 70-300, of which there are several versions, and all have a better build, solid construction and stabilization, and above all - way better optics.   I did a review of the 70-300 range some years ago in the following article: 70-300 Canon Lenses In-Depth Analysis - Canon Community.

As to the red lines that appear around objects while in manual focus mode, that is likely the  MF Focus Peaking feature that will outline what is precisely in focus in the colour of your choice.  I refer to the User Manual:
User Manual ( 



cheers, TREVOR

"The Amount of Misery expands to fill the space available"
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris


First completely reset the M50. Check your manual. That is always the best advice to do when things go wrong. Now first off, the M50 works as it is supposed to with other lenses? Can you try the offending lens on another camera. These two things will tell you where the problem lies. Of course we hope the full reset clears it up first off.

I agree with the thought above, your lens is not designed for heavy duty use and it is possible it is simply worn out. But again that is a possible but not probable thing. You would have to use it daily and a lot of the time each day.

An immediate fix is most likely a different lens. Our school use this lens and for the most part they are all fine and do receive a lot of use by the students. But you know anything made by the hand of man can and will eventually fail.

EOS 1DX and 1D Mk IV and less lenses then before!