The best AFAIK is this little beastie
http://www.dailymail.co.uk/sciencete...le-itself.html
The next-best is
http://www.mir.com.my/rb/photography...yes/8mmf28.htm
Now... go take a look at the prices for one of those lenses... mind boggling.
You can use lenses - but there is a catadioptic solution if you want a fisheye view of the whole sky recorded in a circular image... this is especially suitable if you want a really fast lens - and I am sure most of you could make one of these.
Find a large convex lens - for a full-frame camera you will need one approximately 150mm diameter, the radius isn't important as long as it is really strongly curved like the meniscus of a Maksutov - and have the convex surface aluminised. This will give you a very good convex mirror. In my case I used a condenser lens from an old overhead projector.
Find a piece of board to use as a base (MDF will do) larger than the lens, paint this black and glue the lens on it, convex side up.
For the camera, if you're using a full frame camera (in my case a 35mm film SLR) the ideal lens is a 135mm telephoto able to focus at about 1 metre, the faster the better. For an APS-C camera, about 100mm, or 75mm for m4/3 body.
Make a tripod using 6mm clear perspex strips for the legs such that the camera is suspended over the convex mirror, pointing down at the mirror. The reflection in the mirror is a very nice fisheye view. In my case the condenser lens gave a 200 degree field of view - the whole sky, plus a bit of the ground too right up to the mirror. The reason to use the perspex is that it is sufficiently transparent that the legs will not be seen in the shot. With a bit of creativity I'm sure you could bend a thin strip of perspex into an arc to support the camera well enough.
If you are using a compact camera with a good macro capability you could scale the whole thing down quite nicely - a 60mm condenser lens should do nicely.
Even though the plane of the virtual image in the mirror is curved (at half the radius of the mirror) the lens combinations that I tried this with will have enough depth of field to give quite a good image.
The effective focal ratio of this setup is determined by the f/ratio of the camera lens. In my case, I was using Pentax Takumar 135mm f/2.8 and the image was beautifully sharp, and the image was equivalent to an 8mm.
Other aspects:
- the only downside is that the camera body will appear in the shot.
- you need to use the self-timer to trigger the camera, and run away to get out of the frame before the shutter opens !
- while it is important to keep the mirror clean, the focal plane of the virtual image seen in the mirror is located at R/2 behind the mirror. With a fast camera lens, minor dust on the mirror won't be in focus and should be so blurred that you won't see it in the image.
- with an effective focal length about 8mm the depth of field is huge - everything beyond the perimeter of the mirror will be in focus.
- dew may be an issue on the mirror, but since it is a thick piece of glass, the simplest solution is to warm it up a bit before taking a shot.
Even better - if you have a short telephoto lens that is even faster, say f/2 or even f/1.4, this will work too.
NOBODY makes an f/1.4 8mm fisheye... such a thing does not exist, unless you make one as per the above.
Here's an unboxing video and a demo of it attached to a D800:
