Lens Zoom VS. Throw Distance question

Usually most projectors don't have a throw ratio of 1.0. Going from memorary the Sony has a minimum throw, the closest one can place the projector and still fill the screen of 1.37 times the screen width (1.78 aspect screen) or so and a max throw of 2.23 times the screen width. I didn't look them up but they are posted in the threads. I am probably slightly off. The closest throw maximizes brightness and minimizes on off while the longest throw minimizes brightness but increases on off. Generally, if one has sufficient brightness and this depends on screen size and screen gain, long throw is preferable because optically that is where the lens performs best, the image occupy an area the is or is close to the sweet spot. The area of the lens which is flat instead of curved or less curved. Also screens with gain work better at long throws which has to do with the angle the light hits the reflective layer of the screen. With a specic throw distance, there is only one correct zoom setting and visa versa. They go hand in and hand, and picking one mandates the other.. Hope this helps and if you don't understand this just give me a call and I would be glad to explain further.

BTW Always stay at least a few inches away from the closest or the farthest throw to allow ffor a little measurement mounting area and the fact that manufacturers tend to push the lens throw numbers to a little beyond where the lens for other factors might perform better.

Te brightest will be at short throw. Throw distances depend on the width of the screen and can be any number between the long and short tyhrow range time the screen width. Suppose your screen is 7 ft wide. The closest throw would be 1.37 (or whartever the actual number is) times 7ft. That will give you the brightest picture but not the best. For a small screen you will not need the extra brightness. The dimnest but perhaps the best picture would be at mounting at long thrw, 2.2 or whatever times the screen width. The trade off between maximum brightness and maximum contrast is not linear between the two extremes. It is a log function. Rather than make me type, please just call and I will walk you through it all and answer the questions that will arise you being a newbie.

Mark, can you explain the on off part? Are you referring to contrast?


Tothjm, good choice with the hw50es!

The on/off contrast, one of the holy grails of projector performane goes up as one zooms the picture smaller. depending on the zoom ratio, the long throw multiplier divided bt the short throw multiplier the more the contrast will increase. conversely the more the light amount transmitted through the lens will decrease. The black reference level, more black as that level decreases, will also lessen because there is less leaking light at black because just like any light at long throw, less light can get through, the screen area of course remains the same, less light, same area, better blacks. With a small screen, just set it up at long throw, everything except maximum light out will be better and at small screen size you don't need the extra light.

The on/off is called "Contrast Ratio". It's the ratio of darkest to lightest and generally describes the "dynamic range" of the image.

The higher the contrast ratio, the more depth or realism the image has. High contrast ratio can almost appear 3D sometimes. Low contrast ratio looks washed out. Until recently CRT projectors were the holy grail of display devices that could give nearly infinite contrast ratio (due to the technology employed).

Low contrast ratio on the left, high on the right:





Not the best of examples but it gives a rough idea.

So normally what people want to do with digital projectors is to install as FAR BACK as possible (to increase contrast ratio) while maintaining an adequate level of light on the screen. For front projectors 14 foot lamberts of light is recommended (measured with a meter) though this can go lower and still appear ok if your room has very dark walls (bat cave). Digital projector bulbs dim over time so this has to be taken into consideration too.

Kal

Thanks for jumping in. I think your and my consecutive posts are the only two posts in the entire history of AVS to use the term holy grail without quoting each other.