The big Canon 500mm lens, which requires a tripod and rides around in its own suitcase, is unmatched in image quality under the right circumstances. Generally, no matter which lens you use, you want to almost fill the frame with the subject so there is a minimum of cropping during processing. The problem with the 500mm when shooting hummingbirds is with the 4.5 meter minimum focusing distance, significant cropping is required. I wondered how much bigger the image on the original would be if I used my new 100-400mm lens, which has a minimum focusing distance of 36 inches. I didn't get that close to the feeder because I didn't know if the birds would tolerate it, but from 72 inches away, I guesstimate the image of the bird is about 50% larger than with the 500mm twice as far away. The slight color and contrast differences are due to lighting conditions. I took the 500mm image in bright sunlight yesterday, and the 400mm image today with more filtered light. In my opinion, there is no significant difference in image quality between the two hummingbird images below, so I conclude that the 100-400mm at 400mm does as good a job on hummingbirds as the 500mm. In other circumstances with different subjects, I would still prefer the 500mm, such as if a flicker suddenly appeared in the yard.

I had the 100-400 mounted when this Northern Flicker appeared during my testing today. He hopped up on the rocks, then found the bird bath and got a drink before flying away. The last time I got a good shot of a flicker was last August when a female (no red chin patch) hopped up on my fence. In 2021, three flickers made an appearance at the improvised bird bath on my trailcam. Here are today's flicker images, followed by the hummingbird test images, and finally a grackle and a red-winged blackbird at the platform bird feeder, which is stocked with sunflower seeds. The squawked at each other a little bit, but with abundant seeds for all, they settled down and tolerated each other for the moment. This image also was taken with the 100-400 at 400.

Flicker

Flicker

Hummingbird 500mm

Hummingbird 400mm

Grackle and Blackbird