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Author Topic: Of lumens and throw ratios David E. Nedrow Master Film Handler Posts: 368 From: Columbus, OH, USA Registered: Oct 2008 posted 12-09-2009 12:22 AM                        OK, our micro-loan came through. Phew! Now I can get the walk-in cooler to sell beer. Oh, and a video projector. It's pretty much down to the Sanyo PLC-XF46 or XF47. Before I make the buy, I wanted to check here for input. We have a 107 foot throw to a 26x14' screen, but need to plan on a future upgrade to 38x16'. The XF46 is a 12,000 lumen projector, while the XF47 is 15k. We've used the XF46 in the past to run some video presentations and it seemed fine, level wise. Is there some formula for calculating the lumens needed from the projector -- understanding that you're not actually going to get the max/ rated output on the screen? And to verify, the throw ratio is the throw distance divided by the screen width? So for a 26' screen at 107', the ratio is 4.1. And 107' to a 38' screen is 2.8. So, I need a zoom lens capable of providing a ratio of between approximately 2.8-4? Sanyo has a number of lenses available, but I think the LNS-S03 is the one I need. It has a throw ratio of 2.6~3.5:1. Anyone want to take a look at their lens chart to double check me? Sanyo Lens Table I'm also still considering suggestions for different projectors if anyone wants to chime in. -David  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-09-2009 08:48 AM                     Be careful! If you're using this for pre-show lamp cost can kill you. When selecting any projector always check lamp costs from at least three sources. Be sure that these lamps are keeping within your budget...  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-09-2009 09:13 AM                        Are you using top masking or side masking? You need to figure out your screen sizes for the various image formats. With video, you will most commonly be dealing with 4x3 (1.33:1) and 16x9 (1.78:1) images, so you need to be able to zoom the lens to fit both sizes. If you could accommodate 1.85:1, 2:1, and 2.35:1, that would be even better. You need to figure the width that each format will be on your screen and then calculate the needed throw ratio for each one. As for brightness, footlamberts = lumens per square foot. Therefore, you want to get at least 16fL per square foot of screen area for each format. In practice, no video projector is ever as bright as the specifications say, so you should really double the lumen requirement. This will be an issue as the bulb ages. In practice, a 10k lumen video image is plenty bright for a 17x30' 16x9 image. A 7k lumen unit will look slightly dim on that size screen. You might want something brighter if you intend to use it to show advertising or powerpoint shows with the house lights up.  |  IP: Logged David E. Nedrow Master Film Handler Posts: 368 From: Columbus, OH, USA Registered: Oct 2008 posted 12-09-2009 09:39 PM                        Thanks for the input. We may install a ceiling mounted projector midway down the auditorium for generic use, and reserve the Sanyo for actual shows and presentations. I think I'll go with the PLC-XF46N, since it's looked fine when we've rented it before (at $1100 with lens). My big thing is trying to figure out which lens to get. It doesn't look as though there is one that completely fits the bill, but I can only afford one. We have four-way masking, so the screen is pretty flexible when it comes to format. I'm also thinking of installing the projector at the front of our projection soffit, which reduces the throw to about 80'. I have to shoot a laser and see if we'll clear it when projecting 35mm on the new screen to be installed next spring. -David  |  IP: Logged

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