For shooting frogs in ponds the best focal length would be a telephoto macro lens in the 180mm range or a zoom lens that will reach out to the 270mm or 300mm range.. The images you see here would have been impossible to capture with a short focal length macro lens. To fill the frame with the frog you would have to be right in the frogs face if using a short focal length macro lens, which would be hard to accomplish in these wet muddy conditions and to close for comfort for the frog.
I’ve got a frog in my viewfinder.
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Couldn’t have shot these with my 90mm or 60mm macro lenses.
Mike Moats 
Thanks for the tip, Mike. Always love to read your tips.
Love the frog photos!
300mm, didn’t think of that for frogs.
300 is good to if you don’t mind carry that be heavy thing.