Bizarre focusing issue with Nikon D750

[dtcls100]

This is a problem that doesn't have any practical photo implications, because you can't use a Nikon D750 (or any digital camera) without batteries. But I am curious about this problem and would appreciate it if any of you can explain how and why this happens.

I was charging up the batteries in my Nikon D750 and MB-D16 battery pack today, given my role as official photographer at my daughter's 13th birthday party and a community holiday event tomorrow evening, as I expect to take about 1500-2000 photos. After removing the batteries, I happened to look through the D750's viewfinder and saw everything was somewhat dark and blurry, which didn't change when I tried to focus the mounted manual Nikon 28 f2.8 AiS lens. I thought the diopter adjustment had slipped, but that was not the case. When I put the batteries back into the camera (even without turning it on), the viewfinder appeared normal. Took the batteries out again, the viewfinder was again dark and blurry.
Put them back in, the viewfinder returned to normal.

I wonder why this is. Nikon lenses (whether AF or non-AF) are not focus by wire lenses, as they focus perfectly well on my non-AF bodies -- FM3a and FE2 -- as well as my Nikon F6, even without batteries. The viewfinder of the D750 is an optical viewfinder whose view should not be affected when the batteries are removed. Obviously, I am missing something here. Anybody know something about this?

 

[Fraser]

D700 was the same I think it's to do with the focus point illumination things etc being projected onto the fresnel screen.

 

[Highway 61]

The viewfinder of the D750 is an optical viewfinder whose view should not be affected when the batteries are removed. Obviously, I am missing something here. Anybody know something about this?

The same with all Nikon DSLRs. There is an electronic grid between the focusing screen and the prism which is used for displaying all sort of things in the viewfinder including an optional composing array and the AF collimators. No battery = dark and blurry image. Nothing abnormal. IIRC this is correctly explained in the user's manual.

 

[Timmyjoe]

Yep, my D4 and D700 do the same thing. The first time you notice it can be disconcerting, but rest assured, it's normal.

Best,
-Tim

 

[dtcls100]

Since the viewfinder looks fine with the camera in the off power position (with batteries installed), there must be some battery drain at all times, correct?

 

[ColSebastianMoran]

Yes, I've seen this on other Nikon DSLRs. In particular, on a broken D600 where nothing would make the grayness go away.

Battery drain? Haven't see it. It may take a jolt of battery energy to clear the electronic grid and then little or no energy to hold it in that state.