"Movies can also be shot at two different crops from the sensor, FX and DX. This makes it easy to vary the field-of-view for grabbing footage, even if you’ve got a prime lens mounted. However, the ‘FX’ size is a significantly cropped version of the full sensor (it’s 91% of the sensor’s width), so the field-of-view will be a little narrower than you’d expect for any given focal length."
interesting. I will be testing it now that I got a hold of a D800. but every 5DIII vs D800 comparison looked identical. the live view does look cropped.
so I did some testing and found that yes there is indeed a slight crop. I'm unfamiliar with the camera, but I found it on the manual(so Nikon does disclose it using a diagram). The actual factor I roughly calculated is about 1.095X from a quick snap vs video. So yes, technically you'll gain some focal length (or lose wideness if you prefer). So I guess I owe Ken an apology...this ONE time.
Reading the manual, I found that the HDMI out has two modes. 95% crop or 100%. I don't know if the HDMI set to 100% does this out does this as I have not yet used a external recorder (but definitively plan to since one reason I'm switching to the D800 is the 4:2:2 8bit for external recording).
Once I find out, I'll report back here for whoever would like to know.
The question is it noticeable? I think the answer is it depends. If you are shooting very wide AND look for it (and I'm talking below 24mm before the FOV change may matter in composition) you'll see footage is not as wide as with a 1.0 crop. I just took delivery of the D800 yesterday and had been shooting video quite a bit, and hadn't noticed which tells me I don't shoot that wide that much. For mid lengths to telephoto, the difference is far less noticeable.
For practical purposes, I think the full frame "look" (if there is such a thing since they all crop the tops) of the footage isn't affected by the slight crop (this isn't like a 1.5 crop or anything like that). But if you're shooting sweeping vistas with an ultra wide it is definitively something to keep in mind. Conversely if you shoot telephoto (bids, sports) the slight crop is a plus. Not a big issue IMHO (and actually a plus if you shoot telephoto) but YMMV. As mentioned, I'm ordering an atomos Ninja and will test the 100% HDMI out output setting from the menu to see if that yields the missing 0.095