Which type of lens is recommended?

[titopuente]

Hello everyone,

I want to build a portable image projector that I can use to project an image on a building on a large format. The image would be created with a gobo and the lights would come from a powerful LED flashlight. Which type of lens would you recommend me for this type of application? Which one would be best or which one would be the cheapest to do the job? I can print the adapter on my 3D printer for holding the gobo, the flashlight and the lens together and also if need be, to add some sort of focus capabilities to it. I was thinking of the lens from an old CRT retro-projector TV? Or perhaps, a lens with a ratio of at least 1.5 to 2 as minimum? Any suggestions would be helpful before attempting to buy something.

Many thanks in advance!

[visualopsins]

Welcome titopuente. Somebody will be along shortly with som suggestions for you. Guessing a lens from slide projector.

[DConvert]

If it's only a silhouette of a gobo then I would think a Fresnel lens should be adequate. That should simplify the mounting & avoid excessive cost.
If the Gobo is more like a color slide then a more highly corrected lens would be an advantage & a suitably sized projection lens may be a good option

[titopuente]

I was thinking too of a projector lens. But should I look for a specific throw ratio? The one available on marketplace as we speak are these vintage ones but I can't find the specs for them (throw ratio).

[Raxar]

throw ratio is not your concern. its a fixed value base on fov. you can find the optimal focal by looking at the image circle and distance to the projected screen. any good film or slide projector lens can do the job. your main concern would be if need to tilt the lens you need bigger image circle. if might help if we know the size of the gobo and the degree of tilt and the distance to the building.