I dunno if it's "normal" but if the cat was mine I wouldn't worry about it
as long as *both* pupils are contracting in bright light, which from your
description they are....one of the saddest things in my memories of Sylvie,
who went to RB the Sat.before Valentine's Day this year, is the fact that
since she had both retinas detached (vet said) she was completely blind. But
she, like the Deadly Duo, liked to lay in the warm sunlight coming in the
windows here
in MileHigh last winter.....but her pupils were both round and black and
never varied in the brightness streaming in.
She was a plump Hemingway (multiple toes) tuxedo, and
had a long and happy life w/us.

I fostered a kitten with this problem, and the vet said it was a problem
with her brain.  She had other developmental problems as well, and was
euthanized (her stomach was in her rib cage, and she couldn't keep any food
down)   I would be concerned enough to take a trip to the vet for some tests
if it were mine.

but then again, my vet joked that I was a feline hypochondriac once because
I don't take any signs for granted.  Id rather be foolish then miss
something  - which I did once and it wasn't a happy ending.