It turned out that it seems to be a quite useful lens for VIS and also for UV and IR on my UV camera(s), although it has quite some focus shift in UV and IR (as expected from that simple design). The focal length has been confirmed by further measurements to be around 25 - 26mm, so let's stay with 26mm.
Here (again) that technical article of my friend Marco Cavina, that covers such ultra wide angles nicely with lots of images and diagrams as well as showing never finished prototypes.
Now a photographic result of a spring crocus taken a few days ago ... [click on image to see a larger one]
This lens works very well for 3D stereo images, as it is sharp all over. I will certainly also this year do some UV work using this lens....
Just in case you are not able to see that crosseye 3S stereo image, here some instructions which may help:
1) look at the image, center on the middle gap between them (with your glasses on that you need for reading this test sharp = in focus)
2) place the pointer finger at your nose tip without changing your viewing
3) now still looking straigt to the image, try to focus on your finger
4) move the finger towards the gap between the images
5) follow the finger while keeping focused on it
6) at a certain moment an image "between the images" will appear (looking three dimensional); your finger will be approx. 20cm = 8 inches away from your nose (depending on viewing distance from screen)
7) move your concentration towards that "image between the images" and leave it there (and remove your finger then...)
8) that's it...
Stay tuned, more will follow on that fascinating subject...
More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos
