Changing lenses with the power on is a great way of attracting the dust fairy too....and as yet there isn't a dust removal in camera that truly works....

It's a semi soft operation. The sensor powers down fully when the camera is off, vs in standby. Yes some of the boards retain power, via the internal clock battery, but critical systems power down. I highly doubt the engineers told the manual writers to have users turn off the camera because it might send confusing information to the lens. Unless the camera is focusing it shouldn't be sending any information at all.

Powering off and on again is really a "soft" operation. (think about what is still "on" when the camera is "off"). The on/off switch is really just a signal to the computer to change states. While the chance exists that changing a lens, memory card, or plugging in a HDMI cable with the camera on could cause a fatal short, I would argue that the chance exists when doing it powered off or even with the battery pulled. When the camera is on it is actively reading from and writing to various inputs including the lens electronics (including the aperture control, which is electronic) If you change lenses in this state, the camera CPU will undoubtedly receive a bunch of garbage when this happens, as will the lens electronics. Usually the camera sorts this out, but depending on the garbage, a weird state could occur. When you turn your camera off it effectively tells the software to ignore the lens (and other) inputs. It also undoubtedly goes through some sort of initialization or reset when turned on. However, if the lens or camera is in a weird enough state from a previous "hot" lens change an off/on cycle may not be enough to cure it. The next step would be to pull the battery.

Then again you could be having a hardware problem. Such as a flaky aperture control system, or the contacts on the camera or lens may be dirty or stuck

Actualy, I turned the camera off and on again when the problem first rised and the problem was still there.
I won't have time until this week-end to make more tests. I'll let you know.

Many thanks for your advices.

lol i should keep this in mind, i always forget to power down the camera while changing lenses.

It's not that it would "confuse the computer", by not turning off the camera you can short out the circuit boards. Then you'd have a $2999 paperweight. Just because it hasn't caused a problem before doesn't mean it cannot.

"Be sure the camera is off before removing or exchanging lenses"
Page 25 in the D800 users manual.

Been true for every DSLR ever made. You don't want to confuse the computer. This isn't your fathers Nikkormat :-)

It may be the new bodies have electronics that when connected hot, create problems in how the body sees the lens. Remember the contacts roll over a series of balls and aberrant connections are made if power is on during a lens change. Static electricity, a micro spark, anything can contribute to problems. Having said that, my camera is on, sometimes for days at a time. Except, when removing memory cards and changing lenses. I would suggest power down the camera before changing lenses and see if this corrects the problem or in any way makes a difference.

Understand, this is only my opinion, not worth anything more.

I don't know if it is an aperture or shutter problem... I was in a safari when the problem occured really often and wasn't in a mood to diag while losing interresting pictures of animals :)

As I said I'll have to go deeper in this issue. You may be right it sounds more like a shutter problem than aperture...

AF-M was ON on both lenses (the mode you can re-change the focus on the fly).
Yes, I always change the lense with camera ON. I've been doing this for years without any issue. Camera is OFF only when going into the bag, once outside it remains ON.
Ths blur is not an AF issue. The shutter may have been stuck in the middle of the frame... giving a blured and dark image on the viewfinder...
Yes, the lenses are fully mounted and locked.

Welcome to Nikon Rumors Forum.....

A couple of questions... how could the aperture ring issue create a blurred image? This would seem to be a shutter issue...hanging open. Second, do you ever change lenses with the camera powered on? Is this a problem with AF on or AF off? Which mode are you shooting in? P,A,S, or M? Have you reset the camera to factory defaults?

I do not know if the answer to any of these is relevant, but on my D4, I get into strange things going on and then find I have set something up incorrectly, AF is off, something which is my error. Oh, are the lenses fully locked into the body, I have had one which was I thought fully locked in but actually was not as I had accidentally pushed the lens release button.

Maybe someone else has had a similar issue. Good luck, and show us some photos on PAD.

I had a first issue with my D800 last week.
I was on a trip in Saint-Felicien zoo in Quebec.
In the afternoon, shooting animals with my new (5 months) Nikon 28-300mm lense, the aperture ring did not release correctly, leaving me with a strange dark and blured image.
It may also be a shutter problem or I don't know.

I tried changing the aperture, or going to live view with no effect.
I had to take a picture to have things back to normal. The picture was almost burnt out, almost white.

Next series of pictures were fine.
I first thought that was the lense, which I kind of hate actualy.

The next day, 7:00 AM, no rain, cold temperature but still warmer than 8 degres celcius, same problem with a Nikon 200-400mm f4 I have for a year now. I never had a problem with this lense on my D700 (and still had no problem with it when I used it later the same day). The issue was happening one every 10 or 15 pictures, for the whole safari (from 7 to 10:30)

My conclusion is that it is not a lense problem BUT a D800 problem... As the aperture ring is controled by a motor inside the D800, could this be the problem ?

The D800 was bought in april from B&H with official grip and 2 official Nikon batteries, almost fully charged when the problem arised.

I still have to do more testing at home now I have time to uderstand the problem better but does anybody out there had a similar problem ?