# Considering a Death Ray science project - is this video real? **URL:** \ **Category:** Factual Questions\ **Created:** [February 10, 2011, 5:01pm UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910 "2011-02-10T17:01:02Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [February 10, 2011, 9:06pm UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910/21 "2011-02-10T21:06:05Z")
> [@MobiusStripes](#): > > I’d guess if you had pixel-sized mirrors you’d start to run into mechanical issue getting the darn things aligned exactly right on the existing parabolic surface. In my mind there’s gotta be a sweet spot in between “mirror the size of a grain of sand” and “mirror the size of the entire parabola”. There is one. A lens or mirror (that is one continous surface) of a given focal length will form an image of the sun of a certain size. The size of that image is independent of the diameter. It is only a function of the focal length. Twice the focal length/distance., twice the size. A small flat mirror smaller than that size is just wasted effort. A mirror twice to 3 times that size probably isnt tooooo bad given such things as imperfect construction/alignment issues/whatevers. So, somewhere in that range depending on other parameters. For reference, about a 50 inch “focal length” gives an image of the sun about half an inch across IIRC. Also, for a given focal length, things start getting to can burn things burn level hot when the overall diameter of the mirror “system” is 1/4 th (or F4) the focal length. Make it 1/2 (F2) and now you are into solid burn stuff territory. 1/1 or F1 and its hot momma time. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 10, 2011, 10:01pm UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910/22 "2011-02-10T22:01:38Z")
> [@Kinthalis](#): > > Another thought: I was pretty worried looking at the kid in the video, as his hand came in pretty close to the “Death beam”. How much time in the beam’s focus point before you go from hand to charred stump? Meh. It charred the surface of the wood pretty rapidly, but didn’t seem to penetrate much. I could envision a good localized third-degree burn, but you’d instinctively jerk your hand away before doing deeper damage. Note that laser cutting is a fairly common industrial technique, and if you’ve seen videos of it, the cutting head moves pretty fast. The beam must have an awful lot of light concentrated in a very small area to be able to cut through metal that quickly. I could envision much more serious tissue damage if you were to screw up around one of those. ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [February 11, 2011, 3:14am UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910/23 "2011-02-11T03:14:52Z")
> [@LSLGuy](#): > > Doable, but waay more work than a youngster’s science project ambition can support. Attacklass would like to point out that she is a jaded 13, and while youthful, is not perhaps best characterized as a ‘youngster’. 😉 Actually, this would likely be next years project, we don’t have the lead time for this year for a project like this. > [@Kinthalis](#): > > Question: > > Why a bunch of little mirrors, instead of one large one like a telescope? I was going to say that if we drop a one centimeter mirror, it costs a nickle. However, I [just found a guy](http://www.greenpowerscience.com/SHOPARABLOICHOME.html) who sells parabolic mirrors for this sort of thing- [del]setting fire to stuff [/del] science and solar energy. This may be a game changer. > [@Sunspace](#): > > Just before the focus spot, put a diverging lens. Then there will be a parallel beam of concentrated sunlight leaving the collector. Add a couple of mirrors to bounce and aim the beam, and there’s your solar death ray! > > The tricky part is to figure out how much the diverging lens has to diverge. Not that I’ve spent a lot of time thinking about this or anything… :: innocent look :: Bwah ha ha ha, my time to rule the world has finally COME! I mean, cool, what a neat idea. I was thinking the parabolic thing might work well in the context of steam generation - the beams could converge at a point inside a column of water, for instance. If not, then lets go death ray. > [@Kinthalis](#): > > Another thought: I was pretty worried looking at the kid in the video, as his hand came in pretty close to the “Death beam”. How much time in the beam’s focus point before you go from hand to charred stump? She’s got another hand. Hell, maybe she can regenerate, like a starfish or a time lord. More seriously, a trip to the welding store would be required for eye protection and mitts. Maybe we can get steampunk welding glasses, just for style. I’m sure that and a top hat would go over well with the judges. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 11, 2011, 3:18am UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910/24 "2011-02-11T03:18:37Z")
You might be able to build a 1920s style one. 😉 ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [February 11, 2011, 3:28am UTC](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910/25 "2011-02-11T03:28:42Z")
I’m amazed we got to post #24 without this. The steampunk thing might have to defer to a 1920’s look. I just found[’Ask me about my death ray’](http://shop.webomator.com/retropolis/retropolis_pf/retro-future/Ask-Me-About-My-Death-Ray/_s_61224) T-shirts. [Previous page](https://boards.straightdope.com/t/considering-a-death-ray-science-project-is-this-video-real/570910.md?page=1)