Teleconverters yes or no? This is always a hot topic in photography forums—hot meaning controversial and often heated. The one genre of photography where teleconverters become relevant is wildlife photography. Teleconverters basically increase your Effective Focal Length but not your actual Focal Length.
What many photographers don’t realize is they also change your Effective Aperture (f-stop) but not your Actual Aperture (although your Depth of Field will change). This can be a challenging and elusive concept for new photographers to grasp and may not even concern you if you don’t shoot wildlife with telephoto and super-telephoto lenses (200mm and up).
Moose Peterson is a world-famous wildlife photographer. In this video he provides one of the best explanations I’ve heard regarding teleconverters and their use. He is very much in favor of them and considers them to be invaluable tools of the trade. I have used a 1.4x TC on occasion (when the situation warrants it) but I tend to shy away from them at other times. However, Moose is an acknowledged expert in the field and I would never question his advice. If you shoot wildlife, or would like to, I would invite you to watch this video and pay close attention.