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I've now got to a point where I get a reasonable percentage of successes, although some flowers make life difficult because of the amount they move during the process: some move in their entirety (wilting, esp. under the bombardment from flashguns), and some just waggle their stamens about. Dandelions are particularly irritating in this respect. This movement is a problem because it can easily take 30-45 minutes to complete one stereo shot. This is because I use focus stacking to get the image quality and depth of field, and that can mean 100 shots for each of the stereo pair of images.
The traditional way to make stereo pairs is to move the camera sideways between the two images. For image distances of 1-10 metres, the sideways separation would be the inter-ocular distance of 6 or 7 cms; for greater image distances you would use greater separations (I have used 100 metres for a subject 12 miles away), and for shorter distances a smaller separation. However, for macro this does not work - with even a small separation the image disappears from the field of view. So you need to use a toe-in approach - swing the camera through about 5 degrees between the two stereo images, and then move it sideways until the image comes back into the field of view. There is nothing magical about 5 degrees - it is the angle between the line of sight of the 2 eyes for a subject at 0.5 metres. Other people use 3.7 degrees, or some other number. If you read materials about stereo photography, they often say that toe-in is a definite non-no, but modern 3D software can handle it perfectly. (I use the excellent and free Stereo Photo Maker to create the stereo image from my stereo pairs.)
One of the difficulties with any kind of macro work is the shallow depth of field that you experience. To overcome this I use focus stacking - taking a number of mages focused on different planes in the subject, and combining them in software to get a single sharp image. I use Zerene software for this. This also overcomes the problem of how to focus accurately in UV, because all you need to find out is where the image starts to come into focus and where it starts to go out of focus.
Another difficulty with UV+macro is getting enough light on the subject. I use 3 cheap-from-China but powerful WS-560 flashguns (with UV-absorbing "lens" removed) a few centimetres away from the subject. The repeated shooting for focus-stacking overheats the flashguns, and already three have failed for this reason. But they're so cheap (I just bought a couple new for $20 each) that they're effectively a consumable rather than a capital purchase.
Let's look at some examples. They're all taken on a full-spectrum Canon EOS M, U340+S8612 filters, flash, white-balanced on PTFE. Lenses were either a Steinheil Cassar S 2.8/50mm and El-Nikkor 5.6/105mm, always stopped down to f/8.
First, one that didn't work so well. This is a type of Geranium AFAIK. The body of the flower is OK, but the central area is not so good to look at. This is because of stamen movement.
I mentioned above that Dandelions cause movement problems. This shot isn't too bad, but I had to crop it a lot to get rid of moving petals.
Fruit blossom seems to work well - here is Quince, Pear, Alpine Strawberry.
On the strawberry, you'll see a couple of tiny spiders in cyan. This is an irritant that comes from focus stacking - insects that wander around the flower while you are taking the images. In fact on this shot there were about a dozen out-of-focus spiders in cyan (i.e. on the right image) and a few in red (i.e. on the left image) which I had to post-process out of the image.
Now we have a Daffodil. This works really well in a full-resolution image, with the a great wander-about capability.
Here are a few shots of an Orchid - full flower and then a macro shot of the interior. I have provided a visible light shot (taken on a Canon EOS 6D Mk 2, Sigma 105mm macro lens, ring flash) of the interior for comparison. The UV interior shot is another great one to wander around.
Now a Bluebell:
A chrysanthemum:
A daisy:
A Grape Hyacinth:
An "ordinary" Hyacinth:
Magnolia (this is another flower that can move significantly when young - I could actually observe it twitching):
Snowdrop (also good for wandering around inside):
Forsythia:
And finally a Sunflower:
Edited by Bernard Foot, 29 April 2019 - 13:58.
