zonino Posted March 16, 2006 Share Posted March 16, 2006 Hi all, last week I was doing a gig where I hired in a second XF30 in addition to the venue's XF30 to do double side projection, rather than central. So I could get the same image size I read off the front of the installed lens, F=2.0-2.8 to the hire company, they said they didn't have one of those but could get a 2.0-2.6. all fine I thought! when the projector arrived 6 hours before the gig, I set it up and got a very large image compared to the in house XF30, ie, at least 4 metres wider! and when the maths is worked out this seems to be about right for hte hired in lens. in the end the problem was "fixed" by using 2 scalers to get it down to fill the size of the screen Does anyone have any idea why this might be? the general thinking so far is that the house lens has been modified but if anyone has any other thoughts they'd be appreciated, thanks Link to comment Share on other sites More sharing options...
pumphouse Posted March 16, 2006 Share Posted March 16, 2006 The figure you got off the lens was the F-stop range, and not the zoom range. F-stops are a rather esoteric lens property used more by photographers, and this relates to the ratio of the aperture of the lens divided by its focal length. This is partly related to what you needed, which was the projection zoom ratio. The zoom ratio gives the relationship between the screen width and the projection distance The hire company would work on a zoom ratio range figure - and that's what they sent you. The alarm bells should have started ringing when the numbers weren't quite the same. Projector manufacturers make a limited range of lenses, usually covering a variety of zoom ratios eg 1.3 - 1.8:1, 1.9-2.6:1, 3.0 - 7.0:1. They wouldn't make a lens of 2.0 - 2.6:1 and one of 2.0 - 2.8:1 as the lenses are expensive to develop and manufacture. A typical lens for a reasonable size projector such as yours costs around £2k. Manufacturers don't usually put the zoom ratio on the lens - just the F-stop range which confuses people. The hire company should really have spotted this and warned you, but maybe you didn't get the right person. Hope this helps a bit. If you want an explanation of F-stops then run it through google, but don't expect to understand it unless you are a keen photographer. Jason Link to comment Share on other sites More sharing options...
zonino Posted March 16, 2006 Author Share Posted March 16, 2006 there was another figure on the lens that I also quoted to them, however I can't remember what that was at this moment in time! Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.