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Quote:<hr>For those wondering about the Zoom vs. PQ question...
The AE-700 has a zoom lens with differing f-stop values at each end of the zoom range. Thus, for any fixed image size, that image will be dimmer at maximum zoom than it is at maximum wide angle.
Calculations...
The lens is rated at f1.9 (at max wide) to f3.1 (at max zoom). Dividing 3.1 by 1.9 gives 1.63. Squaring 1.63 gives 2.66. This is the amount the lens decreases in brightness between f1.9 and f3.1, equivalent to about 1.5 stops.
Putting this in concrete figures: the lens at f1.9 is 2.66 times brighter than it is at f3.1. Conversely, the light at f3.1 is 37.5% as bright as it is at f1.9.
Practical implications...
In my case, I found that I could achieve the image size I wanted (100 inches wide) by placing the projector at the back of my viewing room, 8 metres (~26 feet) from the screen. However, I had to use maximum zoom to do this. The image was just too dim at maximum zoom.
I moved the projector forward about 3 metres (~11 feet), resulting in a projection distance of 5 metres (~16 feet). Zooming the lens back, to once again achieve the 100 inch picture I wanted, gave me the extra stop of brightness I needed to make the picture more comfortable to view.
This has nothing to do with the "inverse square" law of optics related to point sources of light. It is a function of the limitations inherent in the zoom lens design. It doesn't mean it's a crappy lens. Many very expensive photographic zoom lenses have the same drop in brightness along their zoom range. A lens that had less drop-off would probably double the price of the projector.
On filtering...
I've found that I can use the Lee Filters "Pale Salmon" (filter #153, 1/2 stop) in place of the "Light Salmon" (filter #109, 1 stop). This means my projected image is 1.4 times brighter straightaway (the difference between the 1-stop and half-stop attenuation of brightness between the filters). Changing filters, coupled with the decrease in projection distance and consequent winding back of the zoom factor, my image is now probably 2 to 2.5 times brighter than it was yesterday, at the same 100 inch size.
Nice.
As I was going to use a projector trolley for my HT setup, wheeling it in and out of service as required (necessary to pass the Rolling Pin Test and actually live to enjoy my projector), the change of plan in projector-to-screen distance (placing it in the middle distance of the room instead of at the back) referred to above, doesn't affect me too much in a practical way. <hr></blockquote>
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