johnnylawes Posted October 4, 2007 Share Posted October 4, 2007 Hi,I was just wondering whether it is possible to get 2degree lenses for profiles, or to get profiles which already have 2degree lenses, to be used for gobo projection over a long distance. Or does anyone know any other ways or projecting a gobo over around 250 meters. Thanks in advance for any help. Link to comment Share on other sites More sharing options...
sparkyweb Posted October 4, 2007 Share Posted October 4, 2007 blimey 250m throw. More importantly than the lens, what is the source going to be???? I have heard of 5 & 10deg but nothing less. Link to comment Share on other sites More sharing options...
Dmills Posted October 4, 2007 Share Posted October 4, 2007 Possibly one of the long throw followspots? You will need a hellishly rigid mounting and I would expect that even things like thermal expansion of the metalwork to move the image an appreciable amount. Also consider the effects of the diffraction limit of the optics! Regards, Dan. Link to comment Share on other sites More sharing options...
Bryson Posted October 4, 2007 Share Posted October 4, 2007 I've never seen anything smaller than 5 degrees. I guess you could talk to HELL or someone and see if they could custom-make something, but I suspect that 2 degrees will be beyond the technical limit of feasibility. Even if possible, I doubt it'll be cheap! Also remember that over 250 metres you're up against the inverse square law, so it would have to be very, very bright to register. You'd probably also need a telescope-type mounting to be able to position it with any kind of accuracy.Are you sure you can't get it any closer? How detailed is the gobo? Could you print it "small" in the centre of the gobo and use a 5 degree? Link to comment Share on other sites More sharing options...
johnnylawes Posted October 4, 2007 Author Share Posted October 4, 2007 Thanks for your replies. I may try putting the image small on the gobo, but looks like I'll have to tell the people who want me to do it for them that it isn't really possible. The problem is there is a large stretch of water in the way, so unless I can get a boat (which obviously wouldn't be stable enough) I can't make the distance any smaller. Link to comment Share on other sites More sharing options...
Bryson Posted October 4, 2007 Share Posted October 4, 2007 A still lake? Alton Towers sucessfully use raft/pontoon type things for their lake. A fast-flowing river might be more of an issue. Link to comment Share on other sites More sharing options...
Wuddy Posted October 4, 2007 Share Posted October 4, 2007 Have a look at the Robert-Juliat Lancelot, zoom follow spot/effects projector. 4000watt HTI, 2 -5 degree zoom, beam diameter at 250Mtr = 9Mtr. Link to comment Share on other sites More sharing options...
Bryson Posted October 4, 2007 Share Posted October 4, 2007 4K HTI? Crikey! That might well do it. Good spot*, Wuddy! * = Pun totally intended Link to comment Share on other sites More sharing options...
scjb Posted October 4, 2007 Share Posted October 4, 2007 Laser projection? Or out of budget parameters?! Link to comment Share on other sites More sharing options...
DavidLee Posted October 5, 2007 Share Posted October 5, 2007 Also remember that over 250 metres you're up against the inverse square law, so it would have to be very, very bright to register.Wrong! This is a common misinterpretation of the inverse square law, which defines the decrease in intensity with distance for a given beam angle - NOT the intensity of ANY source at a given distance. Assuming the same lamp, the same loss within the optics and neglecting optical absorption of the air (that is intensity limited only by the inverse square law), a 2 degree profile would give exactly the same spot size (8.7m diameter) and intensity at 250m as a 40 degree profile at 12m - or indeed any lantern giving the same spot diameter. In other words: given the above assumptions - the intensity of light is simply defined by the area of the spot over which it is distributed and not the distance of throw. In practice the long-throw lantern is likely to be less efficient but this is due to optical design and absorption and NOT the inverse square law. David Link to comment Share on other sites More sharing options...
Grahame Posted October 5, 2007 Share Posted October 5, 2007 Might be worth talking to Northern Light in Edinburgh - I think they have some kind of customised follow spot for the 'lone piper' ending of the Tattoo at Edinburgh Castle, and that has a similar sort of throw.I'm talking off the top of my head here as I've never worked the Tattoo, but I've heard about this. Maybe some other BlueRoomers have more knowledge of the Tattoo than me? Link to comment Share on other sites More sharing options...
sparkyweb Posted October 5, 2007 Share Posted October 5, 2007 A daft thought, if the projection is 250m over the water, where on earth are the punters going to be?????? Link to comment Share on other sites More sharing options...
pscandrett Posted October 6, 2007 Share Posted October 6, 2007 A daft thought, if the projection is 250m over the water, where on earth are the punters going to be??????One presumes the punters could be punting on their punts on the water. I'll get me coat. Link to comment Share on other sites More sharing options...
Ben Lawrance Posted October 6, 2007 Share Posted October 6, 2007 Mark beat me to it. I was going to say the same. Now, my maths off the top of my head isn't great, but whats 9mtrs going to look like from 250mtrs. Surely there will be a focus issue as well? Link to comment Share on other sites More sharing options...
boatman Posted October 6, 2007 Share Posted October 6, 2007 How about a bit of lateral thinking. On what are you projecting? Is it possible that you could use rear projection from a much shorter distance behind the object? Link to comment Share on other sites More sharing options...
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