Using a Telescope for a Searchlight

Light Magic

Newly Enlightened
Joined
Oct 9, 2021
Messages
3
Location
California
Greetings Bright People from a forum newbie!

I joined to see if I was the only one that has discovered that putting a bright flashlight into the eyepiece hole of a reflector telescope (10" Dobsonian) created an incredibly coherent sharp edged beam that throws hella far? Green LEDs create an awesome beam. I'm interested in the brightest green LED that could fit into my 2" hole. I'm using this LUMENSHOOTER A8Plus and it is pretty awesome, especially the green LED. I'm interested in using this at festivals that feature a bunch of glowy LED magic at night.
 

Illum

Flashaholic
Joined
Apr 29, 2006
Messages
13,053
Location
Central Florida, USA
Its not a new phenomenon, after all you're aiming a light source at a concave mirror which then works backwards. I have a Celestron 10" strut dobsonian. I use it for astronomy, its too cumbersome for spotlight duty. but yes, on foggy nights that was something that I've done as far back as when Surefire M3T incandescent were carried regularly.
 

sven_m

Newly Enlightened
Joined
Jul 11, 2009
Messages
100
Location
Southern Germany
Old thread reanimation is fun:
  • pro: Telescopes are perfectly fine for max spot lux, that is "throw numbers" on the paper: They have a good opening diameter (4 to 12 inches). Now, as only this diameter and the luminance of the source account for max lux, you could reach more than 10 Mcd with 10 inches (and up to roughly 1 Mcd with 4 inches) with a typical high luminance LED (200 cd/mm²). Given perfect adjustment of the light source: This source needs to be in the focal point of the telescope mirror or lens. That means removing the telescope ocular and perhaps even removing the flashlight lens or mirror.
  • contra, evil drawback: the very long focal length means that lumens is, well..., more than sad. You have less than reasonable lumens. While you have fine lux with good adjustment, you will always have an extreme thin pencil beam. A MaxaBeam is almost a flood light in comparison. And without good adjustment you might think it doesn't work at all.
In practice this unfortunately means that you usually have no good use of these tiny max lux with the naked eye.
Notable exception: You have binoculars or another telescope to magnify the spot in a great distance :- )
 

idleprocess

Flashaholic
Joined
Feb 29, 2004
Messages
7,197
Location
decamped
Huh. Maybe I could do something interesting with that old cheap telescope that I've held onto for 30+ years.
 

Latest posts

Top