# How should go about making a Bat Signal ala Batman to shine on a water tower? **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2011, 1:45pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953 "2011-11-05T13:45:24Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![zamboni](https://avatars.discourse-cdn.com/v4/letter/z/4bbf92/32.png) [@zamboni](https://boards.straightdope.com/u/zamboni)\ **Post date:** [November 5, 2011, 1:45pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/1 "2011-11-05T13:45:24Z")
We have a high wattage light and that’s about it. What type of material should I make the stencil out of? We have tried but the light was defused and the image was blurry. The light may need to be stronger and the stencil needs to be away from the light a bit. The water tower is a vertical cylinder. ---
**Author:** ![Grumman](https://avatars.discourse-cdn.com/v4/letter/g/43a26b/32.png) [@Grumman](https://boards.straightdope.com/u/Grumman)\ **Post date:** [November 5, 2011, 2:16pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/2 "2011-11-05T14:16:18Z")
To make this work, you’d want a “dense” light source - it’s not how much light it’s putting out, it’s how close to an idealised point source it is. The image is blurry because each point on the water tower is being lit by more than one point within the light, so the stencil only blocks part of the light instead of all of it. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 5, 2011, 2:30pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/3 "2011-11-05T14:30:37Z")
Basically, you need a movie/stage light: A focusable spotlight with a Fresnel (‘frey-NELL’) lens, which allows the beam to be focused without much diffusion. The ‘stencil’ is called a ‘gobo’ or ‘cookie’ – ‘gobo’ for ‘goes between’, and ‘cookie’ for ‘cucoloris’. In my mind, an ‘gobo’ is for casting specific shadows and a ‘cookie’ is more for random patterns, but the terms seem to be somewhat fluid. These can be made from just about anything. I use 1/4" foam-core. You can also use plywood. Remember that if you are casting onto a cylinder, that you will need to adjust the ‘Bat Signal’ to that it looks normal when projected. The caffeine is only now taking effect, but I think you would need to ‘compress’ it on the gobo so that it spreads out onto the cylinder when projected. You might also take into account the angle of elevation. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 5, 2011, 2:52pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/4 "2011-11-05T14:52:50Z")
Find an old slide projector at Goodwill. Make a Batslide out of aluminum foil. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 5, 2011, 3:02pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/5 "2011-11-05T15:02:12Z")
Oh, about the gobo… For a ‘Bat Signal’ you’d probably want to use glass. That way you could paint or apply the silhouette to it without having the ‘supports’ necessary for a cut-out. I said ‘apply’ just now. If you paint, then you can’t change it. If you make a cut-out that can be applied to the glass, then you can modify it os use different shapes. About the lights… My most powerful light is a 4K (4,000 watts) ‘cyc’ light, which is used for illuminating a ‘cyclorama’ background. Or if you’re an indie filmmaker, it’s a good flood. I have two 2K spots with Fresnel lenses, but for what I’ve done I usually use 1K open spots and 600w or 250w open floods. Remember that illumination is inversely proportional to the square of the distance from the source to the target. So you’ll either need a powerful light, or you’ll need to be fairly close to the tower. Lights get hot. My light kits have frames for holding gels. The frames hold the gels, specifically designed for use with studio lights, about six inches from the lights. When I use a cookie, I put it on a C-stand a couple of feet in front of the light. Nothing has melted yet. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 5, 2011, 3:03pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/6 "2011-11-05T15:03:13Z")
> [@beowulff](#): > > Find an old slide projector at Goodwill. Make a Batslide out of aluminum foil. Or you could just do that. :smack: ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [November 5, 2011, 3:12pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/7 "2011-11-05T15:12:26Z")
> [@zamboni](#): > > We have a high wattage light and that’s about it. What type of material should I make the stencil out of? We have tried but the light was defused and the image was blurry. The light may need to be stronger and the stencil needs to be away from the light a bit. The water tower is a vertical cylinder. How far is the water tower from your projection point? ---
**Author:** ![zamboni](https://avatars.discourse-cdn.com/v4/letter/z/4bbf92/32.png) [@zamboni](https://boards.straightdope.com/u/zamboni)\ **Post date:** [November 5, 2011, 7:45pm UTC](https://boards.straightdope.com/t/how-should-go-about-making-a-bat-signal-ala-batman-to-shine-on-a-water-tower/601953/8 "2011-11-05T19:45:55Z")
Thanks for the input, the distance is roughly 40 feet.