Hi, my name is ***** ***** it would my my pleasure to help with your issue today. Can you give me the full model of the lens that you are trying to use with a tele.
These teleconverters are not compatible with the 70-300mm that you have. There are third party teleconverters that will work, but the Canon 1.4 will not. This one works in a limited fashion (only F/8). Click Here Hope this helps. Let me know if you have any further questions.
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