grijuraj Posted August 28, 2011 Share Posted August 28, 2011 Hi Friends, Is there any way to manually calculate ansi-lumens per sq meter based on throw distance and short and long throw lenses???http://www.blue-room.org.uk/public/style_emoticons/default/blink.gif Link to comment Share on other sites More sharing options...
badweasel Posted August 28, 2011 Share Posted August 28, 2011 Hi Friends, Is there any way to manually calculate ansi-lumens per sq meter based on throw distance and short and long throw lenses???http://www.blue-room.org.uk/public/style_emoticons/default/blink.gif Install Blendcalc and enter the screen size and projector light output. Click on the Luminance menu option. If you really want to get to grips with the math, send me a message. Cheers, Dave Shepherd Link to comment Share on other sites More sharing options...
AHYoung Posted August 28, 2011 Share Posted August 28, 2011 Hi Friends, Is there any way to manually calculate ansi-lumens per sq meter based on throw distance and short and long throw lenses???http://www.blue-room.org.uk/public/style_emoticons/default/blink.gif Theoritically its a simple matter of dividing the total lumens by the area and factoring in the F number of the lens at that particular setting, Whilst we are at it lets factor in the gain of the screen surface for the mean viewing angle of the audience. Blendcalcs a nice app, but its basic and doesnt give actual real world results as it doesnt take the lenses optical efficiency into acount, as a projector for example fitted with a 0.8 lens will throw out 60% of the light of the same unit further back fitted with a standard zoom at its widestsetting. You could assume that the manufacturers have measured the projector output with their most efficient lens and weight things from there as the max and min F number of each lens is generally published, but the maths is beyond me... There is no reason that such an app coulndt be written, but id like to see the algorithm for How bright / much splill etc from the windows, stage lighting etc which youd need if its an all purpose will the projector be bright enough app... Link to comment Share on other sites More sharing options...
Pete McCrea Posted August 28, 2011 Share Posted August 28, 2011 The throw distance shouldn't affect the Lumenance - the lens simply focuses light, so assuming perfect conditions and the same screen size the levels should remain constant as the throw changes. Obviously we don't work in perfect conditions, but with decent glass there should be very little change in light levels on the screen Link to comment Share on other sites More sharing options...
AHYoung Posted August 29, 2011 Share Posted August 29, 2011 The throw distance shouldn't affect the Lumenance - the lens simply focuses light, so assuming perfect conditions and the same screen size the levels should remain constant as the throw changes. Obviously we don't work in perfect conditions, but with decent glass there should be very little change in light levels on the screen Have to point out that this is wrong, thre throw distance has a massive effect on luminance due to the fact that as the distance changes you will be using a different lens in a different setting. Any lens will be considerably more efficient at the widest setting rather than the narrowest { tele setting}, its Very noticable and generally most units give about 30% more output at the fat rather than thin end. Also different ratios of lens have different efficiencies . a wide angle or 0.8 lens lets through a lot less light than a standard zoom lens at wide . Depending on what projectors you are unsing, you can maximise the brightness by simply choosing the most efficient lens at the most efficient setting and rigging at that point, its obviously not allways so easy, but if you have the option, it can make a massive difference. lets not get started on screen gain and viewing angles, but in the real world you cant just devide the screen area by the max number of lumens, you could do so and divide the results by a figure derived from the f number of the lens in the particular setting, but im no optical mathamsyst, Link to comment Share on other sites More sharing options...
lite_lad Posted August 29, 2011 Share Posted August 29, 2011 its Very noticable and generally most units give about 30% more output at the fat rather than thin end. But surely the light cant just disappear? if the screen is the output is the same size at the end(i.e. rigging a wide angle closer to the screen, and a narrow angle closer) then surely the brightness will be the same? Link to comment Share on other sites More sharing options...
J Pearce Posted August 29, 2011 Share Posted August 29, 2011 Wider angle lenses have more glass in them. Glass isn't 100% transparent, so more glass means more loss. There are other matters to consider as well, but the primary losses are caused by the extra glass in the way. Link to comment Share on other sites More sharing options...
eheart Posted August 30, 2011 Share Posted August 30, 2011 Yeah, play with the Luminance option to obtain what effect you want. Link to comment Share on other sites More sharing options...
rgye Posted August 30, 2011 Share Posted August 30, 2011 The clue is in the aperture (the F number) of the lens. Manufacturers publish these in the lens specs, along with the focal length. Fixed focus lenses have a fixed aperture value (eg Sanyo W01Z is F2.5). Zoom lenses have a range of values that vary with the zoom setting (eg S20 standard zoom is 1.7 to 2.3, M01Z long throw zoom is 2.0 to 2.6) etc. The smaller the F number, the brighter the image for a given image size. Link to comment Share on other sites More sharing options...
grijuraj Posted August 30, 2011 Author Share Posted August 30, 2011 Hi guys, Thanks for all your advice and feedback...it was really helpfull Regards Griju Link to comment Share on other sites More sharing options...
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