I just purchased a new D500 along with Nikon 200-500mm lens. From the start I ran into some problems. First off I could not format the card with the camera. Out in the field I set the camera to shutter priority at 1250sec. ISO at 2000. It was a gray day, but not too dark. I was hoping to get some shots of bald eagles. I did several exposures and the preview screen showed them to be very dark. As the birds were perched on a tree limb I cranked down the shutter to 500sec. Images no lighter. I than increased my ISO setting to 5000, image still no brighter. I tried many different combinations like this with the same result. I know this cannot be right. Just 2 weeks ago I was using a D750 with a Sigma 150-600mm lens and I had well exposed images at 2000sec and ISO 1250. Does this sound like a camera problem? Or something else?