The "A Lens"

Just a quick question: What are you using to measure the fL as that seems pretty low compared to what I'm getting from an X35. My screen is narrower at 112" but the same gain at 1.5. I'm using minimum zoom and getting 14fL when using my Isco II lens and -9 on the iris in low power. I found that the fL readings using my i1 display Pro enhanced meter were low compared to my calculated fL based on a lux meter reading at the screen. This is due to the directional nature of the screen making it hard to get an accurate light level reading with the i1D3.

I found that there wasn't much difference between zooming brightness and using my lens either. This is likely because I'm at minimum zoom and there is a big change in brightness as the projector is zoomed at this end. There is likely a big change in contrast too, hence why I keep the lens. I wouldn't base getting a lens on expecting a huge difference in light output due to the effect of the projector's aperture altering the light output as it zooms. When I checked with my old HD350 it was something like 78 lux (lens) verses 74 lux (zoomed), so not even worth worrying about as you'd never see that difference even side by side IMHO.

The throw is going to be around 2.0 using these figures, so pincushion will be worse than I suffer (negligable) at 2.8 but well above the usual target of 1.5+

138" wide 2.35:1 is 103" width without the lens. 17' throw is 204" so I make that 204/103= 1.98 throw.

If it wasn't for the noise issue, I'd say just stick without the lens and buy a lamp when it dims too much, or do the same in low lamp and just accept a dimmer image. I meant to ask, but I'm presuming that you've opened up the iris (aperture) as well?

Maybe not the best meter in the world as the range we need is it's lowest range and no decimal places, but I doubt it's that much different to mine (yes the calculation is the same as I use, down to the x1.5 for screen gain).

I've just open the iris more and stay in low lamp, the change in the contrast shouldn't be that bad verses wearing out the lamp quicker and the noise factor. I thought you were maybe at max iris already.

Another 'cheat' is to use HDMI standard and clip all above 235 which will gain you a little light over enhanced and allowing up to 255. A compromise that I use is Superwhite and I clip at 245 to allow for a small amount of headroom (especially if some processing in the Lumagen causes over 235 in some circumstances).

ftL = fc * screen gain (e.g. 1.5 for UM 150). Your figures are not Lumens, or if they are you have something seriously wrong.

Lumens = fc * area of projected image (in square feet)

He has got something wrong...in the RS4810 owners thread he confirmed someone else with the same meter found that the meter wasn't accurate and his fL has been measured as being 28fL not 10fL. Cheap meters might be worse than no meter at all...
Edited by Kelvin1965S - 1/13/13 at 9:57am

Sorry I mixed you up with someone else who has been using that same meter. He found that the meter was completely inaccurate and measured 10fL when a calibrated meter confirmed he was really getting 28fL.

Apologies for the confusion.

It looks like you might not have a problem with your projector, perhaps just with the meter.

There you go. Conversions from fc to ftL and then to Lumens is easy. I'm not familiar with the Ev.