I kept playing with the reversed lens setup and I have found some interesting stuff that help getting more interesting images, but then you have to trade the image quality for the amount of light going through the lens.
What I am trying to say is that the way to gain a better deep of field when using this setup is not by stopping down the aperture in the lens mounted in camera, as all it does is creating more vigneting and giving you less of a photographic area, the solution is to stop down the reversed mounted lens. It is not as if you are going to gain an infinite deep of field, but what was only 1mm or less of area in focus becomes two or three times as wide, letting you have more of the subject matter in focus.
Now the challenge is that by stopping down the reversed lens the light going through the lens starts falling rapidly and by the time you get to f/16 in the reversed lens it is almost pitch dark and it becomes very very hard to try to focus. It also makes you require extra lighting, at least a flashgun, to light the subject matter.
The light fall is not an isolated phenomenon of this lens configuration, all those people that have worked with a view camera have witnessed how their scene becomes darker and darker when they stop down the lens. In the modern DSLRs it is not noticeable because of their design. In your DSLR the aperture stays wide open to help you focus quicker and the lens only stops down when you click on the shutter release button and before the shutter actually runs from one side of your camera to the other.
We are really fortunate in that with digital cameras we are able to see instantly if we were able to capture the image or not. With film cameras you have to actually calculate your exposure before you capture and it is not as easy as it sounds, because with two lenses you have to apply belows exposure compensation to your raw exposure and f/16 in the reversed lens is not exactly that when two lenses are stacked together.
The other challenge then is with the flash gun. You need to be able to have it in front of the lens, but then remember that your lens is just centimetres or millimetres away from your subject. Also it is important to avoid the light to go into the lens causing flare and loss of contrast. Today I was holding the camera with that heavy lens setup in one hand and using my other hand to rest the front barrel of the lens and hold the flash close to the end of the lens. I can tell you that it gets really tiring after a short while. I will have to look into one of those DIY solutions to hold the flashgun and maybe add a little reflector or another flashgun.
Depending on what you are shooting it may be a good addition a micro-metric focusing rail, like the ones in the view camera standards. That would allow you to prefocus with the reversed lens wide open and then stop down, just as you do with the view cameras, but it depends on your subject matter, insects are not known for taking modelling instructions very well, they just walk or fly out of the frame without caring, just as some spoilt famous models.
Enjoy the photos and please don’t be shy, let us know your thoughts and your experience with this technique.