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.