Foot lambert question

My 8500Ub which probably puts out under 500 odd lumens easily lights up my 153" 16x9 screen...so that would be a 133" wide for a 2.35:1 screen so 120" wide will be no issue. I believe the Sony doubles the lumen output of my Epson in best mode so there you go.

16' back from the screen you could save on the screen and go with the Seymour Xd material and put the saved money towards A JVC???? X55 or the X35 and a lumegen mini? I believe the JVC's have lens memory and automated focus, not sure if the Sony has lens memory???

Just a thought

First off, use eliteprojectorcalculator.com. It was built by one of the more senior members here and I've found it to be more accurate and easier to use since he uses values from actual tests, not the manufacturer's rated specs (which are almost always wrong).

Anyway, I get 18fL with a 14' throw, 0.9 gain screen, and 120" wide 1.78 screen. Do you want a CIH (2.35:1) screen or a 1.78? If you want a CIH screen that is 120" wide (meaning you will have a smaller 1.78 image in the middle of it) then I get 18fL when zoomed out to 2.35:1 and 27fL when zoomed in to watch 1.78:1.

What is the lumen rating of the desired projector ?

Art

With a new bulb. What will you get with 200 - 300 hours on the bulb? A little over 12 ft lamberts which will be just fine. .

The problem with calculators is that they do not take into account bulb hour aging at all and often to not accurately account for throw distance reduction which is a log function and not linear. Some calculators do a better job here than others. But whatever result one ends up with, I would reduce the ft lambert results by 30% to get what you will actually get after a few hundred hours of bulb use.
Edited by mark haflich - 11/12/12 at 1:09pm

Don't believe the numbers that they say you have to have. I have a Panny 4000 and the projector central calc says with my set-up I have 8FL, so acarding to that it should be unwatchable..... Well we love it and the picture is great. Actually still running in ECO mode and have I think around 900 hours on it, just the other day I was thinking it may be time to jump it to normal mode to get a little more light back out if it.

The thing is that you might not realise what you are watching at: I bought a lux meter a few years back and was surprised to work out that I was only getting 5-6fL from my HD350 (RS10) yet I thought it was bright enough as it seemed bright compared to my previous AE3000 so I don't know how little fL that must have been putting out. At least I could open the iris up on the HD350 to get 12-14fL and to be honest at first it seemed too bright, though I got used to it after a few films. It just shows that without a meter it's hard to know for sure what you're getting. I now use the lux meter to check the output occasionally and open the iris a click as necessary to maintain the light output at 12-14fL. Mine was only about £60 too, so not exactly expensive compared to the projectors I've owned. I'll use it to set my new X35 when it arrives, so I won't be one of those owners who goes on about how much better their new projector is than their old one, when in fact it could just be due to a newer lamp...if you see me raving about how good it is, then it will be based on a level playing field.

Ahh 9 feet. That might pose a problem for the Xd material. I start to see the weave of the screen at around 10 to 11 feet on bright backgrounds and I definitely see it at 9 feet. Nine feet is awfully close, ever think of trying to bring the front row back to 12 or so odd feet? (seven feet between rows?)

If your guests experience is important maybe the new JVC with the 4K e-shift2 and the Enlightor 4K screen if your budget can swing it. and that setup should easily light up a 130" wide 2.35:1 screen.

The Sony is supposed to be a really nice projector. I'm debating myself between the HW50 and a new JVC, either the X-55 or X-35 with a Lumegen mini.
Edited by Crabalocker - 11/12/12 at 12:36pm

I'd have to agree with those that say lower light levels are sufficient in a dark environment. I get about 4 ftL in my setup and only occasionally think it could use more brightness. A vast majority of the time, more brightness never even enters my mind.

Rob

Ones eyes get used to low ft lambert levels. Just a few years ago, the best set ups were FP CRTs, three 9 inch tubes. And with a 110" D 1.78 screen with 1.3 gain, 7 ft lamberts would be pretty bright. When you are at low light levels to start adding a bit more tends to be quite noticeable. The old rule about quadruppling the light to make it appear twice as bright. So of you start with say 5 ft lamberts which many of us had in the FP CRTS, get 20 ft lamberts woulkd be twice as bright. If you start out today at 20, you would need 80 to look twice as bright so the dimmer you are the more you will appreciate a tad mor light.

It does appear that the Sony's are quite a bit brighter this year.

Issues with Lumens Calculations
It would be great to have an "exact" lumens number in a calculator and logarithmically increment it, but realistically a simple percentile averaging method is better because so many of the reviewers have pre-production units or are not being careful on how they measure. Percentile averaging between varying throws helps throw out bad averaging from multiple basis points and squeezes the error lower than an incrementing log function because you have 3 points of averaging instead of 1, and the limited source data we have available to us has a far larger error than the modification error between the three throw points. Then there is also lens complications, lamp variance, lens shift and other things which contribute another error margin to a pure log function (because using % averaging of measured results at differing throws helps counter this error because of randomizing setup variables, not the least of which is also MFR lamp variance and slightly varying lamp hours at when each measurement was taken). So it's all a messy averaging system at best.

This is why I left the fields open so users can enter their own numbers, and I would always suggest ALSO using the numbers from your favorite review site instead of only using mine (at least for now). I can think of some better ways to do it, which would involve building some complex statistical averaging system that combined logarithmic functions and percentile averaging and weighting systems, but if you have to choose one method to keep it simple, then you use percentile averaging over log. I also have better things to do than to mix mathematics which eventually gets to the point that you are dealing with chaos theory in a simple projector calculator.

Now if someone wants to help me build a time machine instead of a projector calculator (we can go back and cleanup the forum), then I'll be glad to dive into chaos theory and the butterfly effect.
Edited by coderguy - 11/13/12 at 12:49am

It would be a whole new world if the calculators specified a margin of error for their calculations. I do think that where the manufacturers make the effective F value of their lens known at the extreme ends, the slider for throw number position could be made a log function. If this were done we would see rather large lumens loss as one moved away from closest throw. The existing calculators to some extent fool some into putting their projectors at mid throw to maximize some net sum of on off and lumens. The calculators don't show for the most part the on off related to throw position. The fall off there is just as severe. Me thinks one needs to chose what one needs the most and mount at close or far, normally choosing far for best projector operation, sharpness, less geometric distortion, less hotspotting etcMiddle position mounting tends to give a lower net than either extreme.

Most calculators give an optomistic assessment of what the projector will do with a new lamp. I'd love to see a box that gave expected footlam,berts with some bukb wear. Something like the calculator calculates a ft lambert readiung of X for you. In real life after some bulb use expect a ft lamberts of .7 times X. Your calculator is a real good one and allows user import rather than relying on best case manufacturer wishes for ad purposes. I am on the road for the next two days, will continue this later.

Does the overall surface area of the screen play a factor? My common sense says yes. A 200" screen @ 9fl has got to appear brighter than a 100" screen with the same fl just because of the sheer size of the screen. So if ones goal is to achieve 14fl on a 100" screen, then there has to be a sliding scale for the surface area to fl . Or is this already taken into account?

Your eyes can deceive you but your eyes don't lie. If you start at 24fl and it decreases to 10fl over time, your eyes will deceive you into thinking the image is now too dim. But if you were to start at 12fl, then it will be around 6fl before your eyes deceive you. Psychology has to play a part as well. The same way you can make warm water feel cold or make cool water feel warm.

The calc for ft lamberts is ANSI lumens out of the projector at a particular throw ratio times screen gain all divided by the sq fooot area of the screen. All calculators require you to plug enough scrren dimensions and aspect ratioto calculate the screen area in sq ft. Also required entry is the screen gain. These are fixed and do not change unless you decide to change the scren material (gain) or screen size. Thje big variable is the throw distance and how this decreases the light out of the projector as the throw number gets larger. You do need to know how much light does the projector put out at one given throw point and the effective F stop values of the lens extrememes. A simple log function formula can then be used to calculate how much light will the beast emit at any given throw point. This is a weak point of many calculators. One selects a projector and the calculator has embedded the maximim ANSI Lumens specified by the projector manufacturer and any effective F stop extreme points. Few use the correct log function equation using just a crude assumption of a straight line between the extremes. This is not a deal breaker but the use of the manufacturers ANSI number is. One needs to know how much light will your beast put out at your chosen throw position, operated at whatever gray scale white point temperature you will choose, and with some number of bulb hours. Most bulbs quickly lose 20 to 30% of their brightness very quickly. It is possible to use Coderguys calculator to account this by relying on your own entries for ANSI Lumens.You can use numbers posted by posters which may or may not be accurate. You can also do it roughly by taking the manufacturer's rated lumens decreasing it by say 30% for some bulb wear and decreasing between o and about 30% for throws that are anything but short. The roll off is a log and the light falls off quickly as you move away from short throw. If you are at mid or beyond, I would just do a 30% second reduction. Then plug that ANSI in. Don't worry, that number will probably be too high.


Earlier, some one posted that one starting at say 22 ft lamberts would notice a decrease that reached 10 ft lamberts. I would postulate that because the decrease occured over time one would not really notice it until they tried a new bulb. For the image to klook to your eyes as being half as bright, you would have to drop from 22 to 5.5. On the other hand, a reduction from 10 would have to go to 2.5. At 6, one would probably not notice a difference over time. Its a log thing again.

ahh, understood. I new there was a reason why I get my projectors as close to the screen as I can. My new JVC or Sony will be 3 feet further back than ideal (closest throw) so it can be mounted along side my BenQ. Hopefully I don't loose to large of a % drop in brightness. The HW50 and 900+ lumens in best mode is starting to sound a bit more attractive. Hopefully the X55 will be 800+.

yo... Just to clarify, my calc does give footlamberts with bulb wear, always has, user can even choose any hours or any percentage himself (see black boxes). It's in the main display in parentheses. The biggest drawback in my calc compared to others is the GUI is a bit crammed (also a couple lens shift bugs due to browser version issue w/ pixels), but once I get a chance to redesign I can fix that.


Edited by coderguy - 11/13/12 at 10:07am

I'm the opposite, though to be fair it's dictated by being a living room and I don't want an ugly projector hanging from my living room ceiling: My projector sits at longest throw, but due to some screen gain and not being as big as some of the typical ones on here (112" wide 2.35:1) I have enough brightness, so I prefer to maximise the contrast instead as this rises the same way that the brightness drops at least zoom. Side effect is that it helps with using an anamorphic lens as long throw reduces pincushion.

No rights or wrongs, but knowing the effect of projector lens aperture effecting contrast and brightness might help chose a preference.

It's the first time I've looked at Coderguy's calculator, but it seems much better than others I've used. The exciting thing for me is that I compared my existing HD350 (RS10) with the RS45 (I'm getting an X35/RS46 shortly) and it works out quite a bit brighter even at my long throw, so I think I'll be able to really close the iris down to max out the contrast even more than the difference between JVC's claimed contrast figures would imply.

Knowing and understanding is what's important, I honestly believe. This is what most people getting into projectors should realize.

I agree, Coderguys projector calculator is one of the best if not 'the best' I've seen.

+1. I think people try and go too big screen wise for a given projector. 10' wide is big. I like a bright picture though - I'm barely satisfied with my Lumis on a 118" wide screen with 1.25 gain ( and I only have about 500 hours on my bulb ), at 25 foot lamberts. With HD sources, you can sit a lot closer to your screen these days ( I'm about 12' from that 118" screen ), so rather then go bigger, go a little closer.

That's dim. And another good reason to own a light meter - like an AEMC CA813.