Thanks useful information: 
Introduction
As requested by sans2012 and others, I am posting the details of the lens reversal macro setup I improvised, first mentioned in the threads in the Macro forum:
http://www.ausphotography.net.au/for...ead.php?t=2900
http://www.ausphotography.net.au/for...ead.php?t=2926
http://www.ausphotography.net.au/for...ead.php?t=3135
Lens reversal as a macro technique is well-known as testified by much literature on the Web. The ones I've perused and found particularly relevant include:
http://www.cs.mtu.edu/~shene/DigiCam.../Reversal.html
http://www.flickr.com/groups/techniq...as%20Macro.htm
It is a cheap method compared to macro lenses, bellows, teleconverters, and even extension tubes, especially like me you already own a lens from your manual SLR days. And the real plus is that they can be from other camera makes and mounts!
The most common and accepted way to implement a lens reversal macro system is just to buy a reversing ring which is just a metal ring with a bayonet connector at one end (for connecting to the the SLR body) and a threaded ring on the other end which is compatible with the filter size that the lens takes. In Oz this is rather a rare shop item and the only place I've seen it advertised is on eBay (sellers from Hong Kong and the USA) for around $15 + freight.
There is however a small but active DIY photo community on the Web. san2012 has listed one such site (to which I've added another): http://www.ausphotography.net.au/for...ead.php?t=2729
and the next implemention is a DIY reversing ring based on an SLR body cap glued to a lens compatible filter such as the ubiquitous and cheap UV filter. The process involves the hollowing out of the body cap, the removal of the UV glass/plastic from UV filter and gluing the two together so that one end can be bayonet-connected to the body (like a normal lens would) and the other ring end such that the connecting thread is to the outside for securing to the front of the chosen lens.
This was my DIY project but age has weakened the muscles somewhat and I'm finding the cutting out of the body cap a tougher chore than the literature would indicate. So I'm recruiting my adult son to the task and until he's done that I improvised a crude way to start experimenting with lens reversal macro.
The Improvised Rudimentary Setup
Here is an illustrated summary of what I did. As mentioned earlier I had a few lenses lying around unused from my manual film SLR days based on the Minolta XG1. I found that the Tokina RMC 28mm f/2.8 prime was an ideal candidate because its front diameter was just smaller than the opening of the Canon EOS body, so that it fitted snugly inside it and made the job of securing it there with crude means quite feasible and secure (see #2 with the label indicating the inner rim of the lens front which fits inside the body opening).
Note:
For the illustration I've substituted my old EOS 650 body as I needed the 400D for photographing this.
The first three pics illustrate this point.
The rubber-bands were added later for extra security just in case the bluetack was unequal to the task. But in mild and warm weather, this is unlikely. The other plus of the Tokina lens is its light weight - making it easy to secure.
#4 shows the improvised setup for macro work with flat and inanimate objects like the coins I posted in the Macro thread. The old laboratory retort stand made a suitable and stable holder. The lens to object distance is only for illustration - it is longer than the 60 mm required for this particular lens+camera system.
Here I've substituted an old minipod (1980s vintage) I bought in Germany for clamping the camera+reversed lens to the stand. The retort clamp at the back would have been actually used, the claws ideally sized to grasp the tripod quick release base screwed onto the camera.
That's basically it. For horizontal shots the camera+reversed lens is secured on the tripod in the normal way.
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Image 1: The Tokina prime lens
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Image 2: The lens shown reversed next to the EOS SLR with body cavity open
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Image 3: The lens reversed sits snugly on the SLR body
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Image 4: Bluetack added around the joining interface - hitech stuff.
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Image 5: Setup on the Improvised Macro Stand
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Points to Note
1. The DoF is very narrow - only a couple mm or so. Ideal for flat objects but requires some thought for other configurations e.g. which part to emphasize. Scope for creative artisitic effects though. The DoF can be maximised by using a low aperture value but the tradeoff is the darkened view through the eyepiece which makes focussing somewhat trying.
2. The practical way to focus (it's all manual) is to move the camera towards or away from the subject. With some practice this can be become quite accurate and not too time consuming.
3. A manual lens is ideal because you can set the focus distance and aperture yourself.
TIP: With AF lenses the trick for cameras with a depth of field preview is to set the aperture (on AV priority) then use the DoF button which adjusts the aperture to the set value. Then quickly remove the lens and you have the aperture set at the value you want. Otherwise when you remove such a lens it is always at the maximum aperture.
4. There is some sort of inverse relationship between focal length of the lens and its magnification with lens reversal. The three experiments with the 28mm Tokina show the high magnification that can be achieved. A preliminary trial with a 50 mm prime showed a magnification reduced more than twofold and the required lens to object distance roughly doubled. More quantitative data to come later.
5. The images were taken in my improvised "studio", the old playroom with side-length windows on the East and West, so natural light was fine during the early morning and late afternoon. In the rush to get this write-up finished I did the takes at the least optimum time with the sun overhead and hence the less than optimum pics.
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And finally the usual disclaimer:
The method described is the one I actually use without any negative impact on my system but I take no responsibility for any negative effects that may befall anyone trying this out. In other words, do this at your own risk.
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