I purchased a Novoflex EOS/NIK NT lens adapter in order to be able to use Nikon lenses on my 5D MKIII. I was able to test the adapter with the Nikon 12-24mm f/2.8 as well as the Zeiss Distagon T*25mm f/2.0 ZF.2. Here are a couple of notes:
1. Mount the adapter on the lens FIRST. Make sure it clicks into place and cannot be rotated.
2. Mount the lens/adapter combination on to the camera body (5D MKIII).
3. For the "G" type lens, there is a small slider on the adapter which can be used to adjust aperture. For the Zeiss lens, which has an aperture ring, the slider should be set to the "smallest aperture" position.
4. The exposure bar on the camera LCD display seems to approximately indicate the correct exposure. I tested this against a "native" Canon lens using auto metering, in-camera, for the same scene (bright morning sun). Here are the results:
Zeiss 25mm:
f/2 1/4000
f/2.8 1/4000
f/4 1/2000
f/5.6 1/1000
f/8 1/400
f/11 1/250
f/16 1/200
f/22 1/200
Nikon 12-24mm (@24mm)
Slider:
Max open 1/4000 (approx f/2.8)
Mid open 1/500 (approx f/8)
Small open 1/125 (approx f/16)
Min 1/80
Canon 24-105mm f/4.0
f/4 1/1250
f/5.6 1/640
f/8 1/320
f/11 1/160
f/16 1/80
f/22 1/40
Given the slight differences (~.5 stop) between the adapter exeposures and the native lens, it is best to check the histogram and adjust manual exposure if necessary.
Focussing.
The adapter does not allow for AF so all focussing was manual. This was a chance for me to try out the Hoodloop (w/3X eyepiece) in liveview. This seemed to work very well and resulted in achieving critical focus very easily. The liveview menu was set to show the actual exposure but seemed dark compared to the actual scene (and the resulting image), especially when the lens was stopped down. I don't think you can rely on this feature when using the adapter. Also, further testing confirmed that the liveview histogram does not reflect the actual exposure either. Thus, this should be set to "Expo. simulation - Disable" (Shooting menu 4) when using the adapter. However, the exposure "bar" does reflect (semi) accurate exposure. So, adjust the aperture/shutter speed until the indicator on the exposure bar centers at "0".