Very strange aperture behaviour XT3

[Pedro Zajden]

Hello!

So, I'm trying to understand if this strange behaviour of the XT3 is a bug or if this is intentional and has actually some reason behind it. It's a little hard to explain, so bear with me here!

For some reason, the only time this happens is when the SHUTTER SPEED is set to AUTO. If I set the shutter to any number, let's say 1/60, then the aperture stays still.

So, I'm setting the aperture to a fixed number, like f2. But when I move my câmera, depending on what amount of light it's receiving, the aperture starts opening and closing by itself. Note: I'm not touching anything, not pressing ANY button, just moving the camera around. So as the example, let's say I set the lens to f2. Sure, when I half press the shutter, the lens goes straight to f2 and my picture is fine. But before I press anything, the aperture keeps changing, f2, f8, f11, f2.8, f4....It's like it's changing to keep a good preview of the image? But this sucks, because while I'm framing (not pressing any button), the deph of field keeps changing and changing, until I half press the shutter and it stops where it should.

Also another problem with this: let's say I'm just walking around with the camera turned on, strapped around my neck. It will keep changing the aperture, draining battery, and wearing out the lens while I'm not even looking at the screen!!

I know this is very hard to understand, so I recorded a video to demonstrate. The first video is the crazy aperture moving by itself. (Again, I'm not pressing ANYTHING, just moving the camera. The lens is set to wide open f2)
https://drive.google.com/open?id=1-wo72nNMlACZXscDANDvRm34LIZfSga1

And the second video is just to show what the camera is seeing from behind.
https://drive.google.com/open?id=1-6yM0_7B5yBcrr4lt7Df7Bf7hEyZvdX1

Does anyone has a clue about it? A common behaviour? A bug?

Thanks

[Doug Pardee]

2 hours ago, Pedro Zajden said:

It's like it's changing to keep a good preview of the image?

Exactly. The viewfinder is trying to display 100 frames per second. That requires the camera to play with aperture if there's too much light, and ISO if there's too little light.

[Pedro Zajden]

I see. So guess I'll just live with it!
It's an amazing camera, I think we get too picky with the tiny little problems nowadays, with all the technology that works like magic