I was curious to learn whether the 105/1.4E could operate with extension. Of course it does, just don't fall for the myth that 'extension doesn't impact quality because there is no glass inside'.
The inescapable fact is that any extension added to a lens not designed for this will adversely impact quality. The 105/1.4E isn't designed for extension and its quality certainly suffer. Now, the more interesting points are how much quality is lost, and how can one control the aperture of the 'E' lens?
Extension adds the expected spherical aberration causing some veiling and lowering of contrast, but changes in field curvature were not dramatic. These are good news as the veiling can be used to create dream-like images, and contrast can be boosted to some extent later. Being able to stop down would also improve contrast and cut back on the spherical aberration. To this end, one either needs an extension tube with pass-through contacts (Kenko or similar; alternatively, butcher an 'E'-type TC and remove the glass inside), or utilising the dirty trick described in the next paragraph.
The cheap approach is using any F-mount extension, for example, an M- or E-ring as they have a maximum clear opening inside. Before adding the extension, conduct the following steps with the lens on camera: To put the aperture at the wanted setting, dial the number in from the camera, press the depth-of-field preview and at the same time, push the unlock button to detach the lens. The aperture will now be 'frozen' at the specified f-number. Add extension to the lens and put it back on the same or another camera. Fire away.
