Apple → 5K iMac and some newton rings/banding?

I just picked up a 5K iMac. Screaming fast... When I first pulled it out of the box it has some light leaking from around the edges of the LCD, but those have gone away. Besides some screwy fonts on older problems, it's been working fine.

But I noticed when logging in, this newton ring/banding that is going on. I don't see it anywhere else except when putting in my password and the background is blurred. Is this normal? Or any ideas how to reproduce it someplace else?

Presuming that isn't some kind of thin-film interference caused by an antireflective coating and particular viewing angles, I would say, no it's not normal.

Even if it were TFI, I'd say it's not normal.

Since you just bought it, if it were me, I would take it back and exchange it for another one.

I'd have to call Apple care, this one has the upgraded CPU and video card... ugh hate it when this happens.

It's odd. It only seems to happen with the screen saver running and the login window open...

If I reboot the machine and go to the normal login window, no problems.

Hmm .. might be a Yosemite bug.

Have your mac boot to the login window
Tell it to ask for a password "right away"
Go to displays/screen saver
Turn on hot corners
Turn on the screen saver, wait a minute
When you try to resume, you see the screen saver AND the login window at the same time... it has some banding with it (tried it on my early 2008 Mac pro w/23" cinema display). Do you guys see it?

Since it only happens with the screen saver running, you can do a PRAM reset and an SMC reset and fix permissions. If it still does it after that, maybe just call Apple Care. If they determine that it is not a normal thing for it to do, I would exchange it.

I posted while you were typing. If it's a Yosemite bug, then of course exchanging it will not help.

Pretty sure that's just a side-effect of the gradient + blurring effect applied on the login screen. Even on a static background, I see a bit of it on my MBP's screen. Harder to capture it with the screensaver on, but I think I'm seeing the same thing as you. The more obvious, circular lines are just a byproduct of the LCD, but if you look closely between the colored and gray background, it has a similar banding to what you showed.

Yeah, sure seems like a Yosemite bug to me. I can reproduce it on two macs, but the iMac is shows up the worst. I don't think the screen saver and login window are meant to show up at the same time.... I think I'll call Apple care and see what they think.

It's there on my login prompt with blurred image background. On a retina screen, its seems more obvious like a defect.
FWIW-Newton Rings are typically pressure blobs (light and dark). All I see in your image is a moiré pattern. Change your background to a solid (white, grey, black) and then observe login screen.