Tech Tools / Calculator
Gobo Projection Sizer
Find projected image diameter or required field angle from throw, with artwork and usable-gate notes.
Planning aid only. Generic lens geometry only. Gate size and artwork diameter must be verified; no gobo format or fixture compatibility is implied. Verify equipment specifications and on-site conditions before the show.
Setup
Results
How to use this tool
The full projected field diameter is D = 2T tan(θ/2). If artwork uses only part of the usable image gate, its diameter is D × artwork/gate. In inverse mode, the desired diameter refers to the artwork itself.
Required angle = 2 atan[(desired diameter × gate/artwork)/(2T)]. The selected field angle is only a proxy for the optical gate: lens specifications and actual image circles differ. Use a test projection to confirm.
FAQ
Is gobo outside diameter the same as image size?
No. Use the usable image diameter inside the retaining ring, not the metal or glass outside diameter.
What about oblique projection?
This is a normal-incidence circular image estimate. Keystone, focus across an angled surface, distortion and shutter cropping are not included.
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