This fresnel lens solar cooker was made by Bruce Joseph () in Tucson, Arizona. Bruce has done a few versions and is constantly working on improvements, as you can tell from the sequence of photos below. My own use of a tripod came from looking at his photos. Thank you to Bruce for sharing this for all to benefit.
A bit about Bruce's work in solar (as of June 2011): I just was appointed the Chair of Citizens For Solar, a Tucson non-profit which has held a large, open-to-the-public Solar Potluck for the last 29 years. (I've only participated for the last three.) I also run Tucson's "Solar Society" Meetup group. I'm also a "Tucson Green Technology" writer for Examiner.com.
If you're unfamiliar with fresnel lenses see this page all about fresnel lenses.
I use a table setup rather than a stand and a tripod for my Fresnel lens grill. [Bruce used to use a tripod. See first photo below.] I've cooked burgers, steak, chicken breasts and grilled cheese sandwiches on it. Because the Fresnel cooks from the top, I heat my skillet first, put my food on it, then cover the food with a flat lid that rests on the food. This helps heat the food evenly, and keeps me from having to constantly stir it. I found that the table is much easier, and safer to use than the tripod setup, and it was very easy to build. I also have a SHE Hot Pot that I've used to cook chicken, pork, ribs and paella.
[The remaining photo's are of a newer version. Notice how the food is always at the focal point of the fresnel lens. This is done by having the pivot point for the lens' "legs" lined up with the grill table no matter what angle the lens is at. The animation beside the photo below illustrates this.]
I usually use the grill "full out", so the window blind is for "emergency shutdown". In reality, I don't use it very often. It's just as easy to pivot the lens out of alignment with the sun if necessary.
Notice that in the above two photos the wheels are on different legs. Moving the wheels had to do with transport. When not in use, the lens arms are bolted to the frame, and extend beyond it. Putting the wheels at the opposite end let me use them as handles, and roll the grill like a wheelbarrow. When cooking, it would be better to have the wheels at the front, so that you could pick up the back end, pivot the grill, and set it back down. The next version may have 4 lockable wheels. (I think that slightly larger wheels would work much better.)