Nikon D300 seems to change and locked on a f stop!

@samanthas636
It's the aperture lever that has to be replaced and NIKON will do it at no cost to you.I just got mine back from NIKON's Melville Repair Center.They are great because they have backed their product and their service and people who work their are excellent!Kudos to NIKON!!!!

Yes. The D300 has a focus motor built into the body and thus does not need one in the lens. The lens will also meter properly with the D300.

The F/stop isn't supposed to change when you focus. Depending on the camera, you change the f/stop by either turning the aperture ring on the lens or turning a command dial on the camera body.

Wow, that's weird. Does it do it with the auto-focus switch on the body turned to manual? I shoot a D300 and know pretty much everything about it there is to know and the D700 is basically the same camera with a full frame sensor. The only things I know of that drop CH frame rate are shooting in 16-bit raw and it shouldn't kill it like that, using full-auto with tracking will also cause a lag in auto-focus but that still doesn't seem right here. If it only does it with the auto focus on then it may have trash on the AF screen in the camera and needs to be cleaned. Try setting the body switch to manual focus, remove the grip and shoot jpeg and see if it still happens. If it does, reset the menu settings and try again. If it still does it than you probably need to give it a trip to Nikon. If it quits than start putting things back one at a time until you figure out what is doing it.
Somebody told me that Nikon will clean the pro cameras for free once a year while under warranty, I haven't looked into it yet to make sure.

The lock that's around the 4-way button that moves the AF point will stop it from moving. The AF switch (says C,S,M) on the body below the lens release button gets knocked to manual and turns off the AF

Only reason the lens will not auto focus when you depress the shutter half way is due to either lens AF switch is set to Manual OR camera body's focus system is on M. There is 3 way toggle switch below the synch port around the lens mount. It should be set to C or S in order for auto focus to work. If all the settings are correct and even "AF-ON", next to rear dial doesn't activate auto focus then the issue maybe in the setting or the body itself. As for the buffer reading r27, I think mine displays r## regardless of burst/continuous mode.

try shooting in manual or aperture priority mode, make sure that the csm selector knob is set to S

Hi taylorrm, I don't know if you have a solution to this but sometimes the AE-L/AF-L but gets pushed which is the auto focus lock button then the shutter release button cannot be used to focus and yu have to reset by pressing it again.  Even though it's confusing at first it's a feature along with the AE/AF Lock to try out to lock your focal area on a subject prior to shooting.
To sbhoward5, check to make sure the switch on the camera body is switched to AF instead of M mode(looking at the front it's on the lower right hand side below the lens release button), which sometimes happens when changing the lens - so then the mode selected is in P,S,A, or M modes on the mode dial. happy shooting,  
randy320sgi

That's just the quirky autofocus of the d80. Try tilting the camera diagonally to focus and tilting back up to shoot.
Unfortunately, autofocus issues like those are the difference between a d80 and a d200/d300 :/

I had the same problem. My issue was with all my lenses. I solved it by going to the menu and selecting the custom setting menu (pencil icon). Then from the right menu select the AE-L/AF-L and press OK. Then make sure it is set on AE/AF Lock. Presto...all my lenses worked on auto-focus.