Racer_Rob Posted May 23, 2011 Share Posted May 23, 2011 I have a 36 degree Source 4 which I'm thinking of using to project a gobo over a fairly small distance. I need to know for a gobo of size A or B, from a 36 degree Source 4, x meters from the target surface, how big the gobo image will be. Also, how can I tell if the image will be sharp? Presumably if the light is very close to the target surface there won't be enough travel in the lense to focus it. Is it possible to calculate how close the Source 4 can be to the surface whilst staying sharp, does this have something to do with the focal length? Link to comment Share on other sites More sharing options...
Matthew Robinson Posted May 23, 2011 Share Posted May 23, 2011 I would imagine that you'd calculate beam throw in the same way that you would any other beam (ie: with the application of basic trig) and you can make the beam more or less focussed by using the focus knobs of the S4. Link to comment Share on other sites More sharing options...
Phill.Beynon Posted May 23, 2011 Share Posted May 23, 2011 Here's the quick way to find what size a projection will be at any given beam angle...just change the 5m distance to whatever yours is. If you need a VERY precise size then you may have to look at what size the gobo image is made as well, ie how much of the gobo it takes up, but that is precision beyond anything I've ever had to do, and would probably be easily changeable on site by hanging the lantern in a different way.Unless you're very close to the projection surface you won't have a problem with focussing. I've never had to try it though, so can't give precise distances, sorry! How short is a fairly short distance? Link to comment Share on other sites More sharing options...
jonathanhill Posted May 23, 2011 Share Posted May 23, 2011 Whatever you decide, you may be dissapionted with the results from a 36 degree Source 4, as due to the double lens (note no extra 'e') you get some undesired fringing and aberration effects in the beam. Most people use a 'B' size gobo in the gate, rather than an 'A' size gobo in the iris slot. I am fairly sure that the DHA/Rosco site has some information about image size of the various gobo types. Link to comment Share on other sites More sharing options...
Racer_Rob Posted May 24, 2011 Author Share Posted May 24, 2011 How short is a fairly short distance? It could be as little as 3-5m. I want to project a gobo of a window on to a double bed on stage and I want to make sure the window will come out a reasonable size relative to the bed. I am fairly sure that the DHA/Rosco site has some information about image size of the various gobo types.I've found this on the Rosco website for sizing gobo projections but using a bit of trig seems to work just as well. Over 5m it comes out at 3.1m beam diameter without gobo, so long as the gobo has thin edges that may just be alright. Does putting the gobo in the gate rather than the iris slot reduce this fringing effect? It doesn't have to have a perfectly sharp edge but if it would look unacceptably fuzzy then I may be able to hire in a few (I need it in serveral colours) 50deg S4 but the budget, as usual, is tight. Link to comment Share on other sites More sharing options...
tlc Posted May 24, 2011 Share Posted May 24, 2011 It doesn't have to have a perfectly sharp edge but if it would look unacceptably fuzzy then I may be able to hire in a few (I need it in serveral colours) 50deg S4 but the budget, as usual, is tight. If you need several colours consider using a data / video projectorthese work reasonably well if the image size you need is not enormous (and the lighting state is atmospheric not full up) Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.