Parabolic reflector shape

[Aston]

Hi all, I'm hoping to make a spotlight that will send a beam of light into the sky on a small budget, for my reflector i was going to use a satellite dish covered in Mirror Vinyl Wrap, however the focal point of my dish seems too far away (527mm (aprox 20")), so that got me thinking, what is the ideal depth of a parabolic reflector for an anti aircraft search light or Hollywood type spot/ searchlight? Thank you

 

[LEDphile]

For an omnidirectional source (typical lamp), deeper reflectors capture and focus more of the output from the lamp and give you less spill in the beam (so are more efficient at making a beam). You can get away with a shallower reflector if you use a directional source (think Cassegrain reflector)

 

[Aston]

For an omnidirectional source (typical lamp), deeper reflectors capture and focus more of the output from the lamp and give you less spill in the beam (so are more efficient at making a beam). You can get away with a shallower reflector if you use a directional source (think Cassegrain reflector)

Yes, I think my dish is too big and too shallow so I've bought a parabolic shaped fire pit, I think this will suit my needs better, thank you

 

[knucklegary]

I own an old Webber BBQ,, you're welcome to have it 😎