@emiway wrote:
I have a canon m50 and a EF to EF-M speedbooster. I was looking at purchasing the EF-S 55-250mm STM but then I realized that EF-S lenses only work correctly on cropped APS-C sensors. How would this lens work on my setup, the m50 has an APS-C sensor but with the speed booster it is effectively "full frame".
I think the result would be the same as using an EF-S lens on a real full frame camera, which results in massive vignetting, but I would greatly appreciate it if someone could double check since I am still somewhat of a beginner.
How would we know? What make and model of accessory are you even talking about? Ask the manufacturer.
However, I suggest returning your “speed booster” for a refund, and getting a conventional EF-M adapter. You have a quality camera, which is capable of capturing high quality images when used with capable lenses.
The Canon EF-S 55-250mm STM lens is an entry level telephoto zoom. It is equivalent to using a 100-400mm on a full frame sensor body camera, which is an excellent range for most sports photography. The focal range is also pretty good for wildlife photography.
But, it is not the fastest focusing lens in the world, and your accessory would only slow it down even further. Typically, an accessory that improves on type of performance specification does so at the expense of another specification. Furthermore, I am sure that your accessory contains a focusing element, which will only detract from the original image quality of your lens.
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