lens - How can one use a reversing ring with Nikon G lenses?

So, this blog (credit to mattdm for pointing it out) says:

Firstly, when you turn the lens around you obviously lose the CPU connection between the lens and the camera, so say goodbye to autofocus, metering (in most cases) and aperture control (though I’ll come back to that)

Then:

The advantage of this old lens is that it has a manual aperture ring, which neatly neutralises the loss of automatic control mentioned above.

So, since G lenses don't have an aperture ring, aperture can't be controlled anyhow if we reverse the lens?

Secondly, is it practical that we set the metering and the aperture (manually) before taking the lens out and reversing it?

Is there any other way to get around this problem in G lenses (assuming that the camera bodies have the manual focus, aperture, metering controls)?

Answer

With some non-G lenses, there is a switch on the lens that will release the aperture ring so that you can manually control it, even off camera or reversed, to set the aperture to whatever value you want (but as you close down the aperture, the viewfinder will get dimmer).

With G lenses, there is no aperture ring. There is a mechanical lever though, which closes down the aperture. You can slide that lever and the aperture will close. As the blog points out, you can fix that lever in place with tape or poster tack.

When you reverse the lens, the aperture will close to its smallest opening (f/22 or whatever). Moving that lever can open it back up to the widest aperture, or somewhere inbetween (although very hard to control exactly)

The camera body will not know what aperture is set since it will not have any electrical contact (and will wonder where that lever went!). So best to set exposure to manual and set an appropriate shutter speed. You won't need to set an aperture since the camera can't control it anyway.

There isn't really any point in setting the metering before reversing for a number of reasons:

• 
  

  metering will assume an aperture, but once reversed you will be setting (potentially) a different aperture using that lever

  
  


• 
  

  you are unlikely to get the same amount of light through the lens when reversed, depending on the size of the two ends of the lens - most surely there will be less light transmitted when reversed.