Calculating mounting distance - how to do it properly? - AVS Forum
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post #1 of 30 Old 05-05-2013, 11:03 PM - Thread Starter
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hey guys I'm sure this is an incredibly stupid question. Putting all the pieces together for my first projector and I want to make sure I calculate everything right..



I uploaded this silly photo to explain what I'm asking. Do I calculate the projector distance from ceiling to ceiling.. or towards the middle of the screen or top? or what? If that makes any sense

Thanks
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post #2 of 30 Old 05-05-2013, 11:46 PM
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I would suggest posting your room dimensions and the projector you are planning on buying, then we can help you.

Take a look at the various projector calculators out there.
Which projector is it for?

This is a complex set of factors for someone new to the game, how and where you mount the projector is based on numerous factors.
The overall clearance of your head or seating area, the limitations of the projector's Vertical Shift range, the limitations of the projector's Zoom and Throw range. And the side effects that using any of the most extreme ranges can cause.

In other words, the answer is it depends.

www.eliteprojectorcalculator.com is an older version of software that I'm about to replace, and might be a little confusing to a new person. Projector Central has a calculator.


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post #3 of 30 Old 05-06-2013, 12:44 AM - Thread Starter
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Hello.

I'm pretty sure I am getting the mitsu HC7800D

It's a bit of a smaller room. 11 feet long, 9 feet wide, 8 feet tall

What I was hoping to do was ceiling mount it about ~10.5 feet back from a 9x8 foot wall for a 100 inch screen. I was planning on getting a Sableframe 100 inch which comes in at 7.65x4.475 feet so enough room to be mounted on my 9x8 wall.

According to that link you gave me (very useful by the way) everything should fit , correct? Seems as though I can mount the screen ~ 2 feet off the ground which is where I wanted it to be at and everything should fit.

Does using 1.5 lens zoom as opposed to no zoom affect picture quality?

I know this is kind of squeezing it tight but it's also a temporary set up.. planning on moving to a bigger house in ~5 months where I'll make sure to have more space.
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post #4 of 30 Old 05-06-2013, 06:20 AM
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Best position will vary, but normally, the middle of the zoom range is a good place to start. A good post on the topic. http://www.avsforum.com/t/1226740/does-zooming-degrade-picture-quality#post_18132593
Generally, having it closer to the screen with a larger zoom results in a brighter image and a little lower contrast, while further away less bright, and more contrast. Place it where you need, within the zoom capabilities of the pj, and adjust it if necessary.
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post #5 of 30 Old 05-06-2013, 07:37 AM
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With your screen size, you will not need the higher brightness associated with close throw mounting, mid position would give the worst of many worlds compromising brightness which you do not need with your small screen, giving up maximum contrast (remember there is no straight line relationship as to how brightness and contrast fall off as you move away from the respective extreme, its a log curve and going to the middle is bad because the curves have leveled off pretty much, calculators often assume straight lines or attempt to create a curve based on user measured observations with their crack light meters and measuring techniques, using a log curve and obtaining the f stop at both ends of the throw baffles them, sometimes). Plus the lens works best at long throw keeping the image closer to the lens center and by being smaller in exit size allows more use of lens shift with out image degradation. The answer for you is simple and not complicated. Longest throw. Distance is measured horizontally from front of lens to screen plane. To make clear. measure parallel to the ceiling and floor. Hope this helps.

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post #6 of 30 Old 05-06-2013, 10:56 AM
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The baseline measurement ALWAYS starts from a user or reviewer measurement, so no choice but to base it off a "measurement", unless the MFR supplied a precisely accurate number (which they do not). You cannot achieve accurate results just by adding a LOG equation to a user-based measurement (you just stated the reason why yourself, your post assumes we have a number that does not exist - an accurate measurement, but this is not supplied to us that make calculators). Think about this point VERY carefully before we have to go over this again...

I'm not mad if I sound that way (you know how posts can sound sometimes), I am just stating why things are the way they are smile.gif

You note a calculator needs to work this way or that way, but at the same time you state that the user or reviewer measurements are wrong. All the data comes from these measurements whether I like it or not, because the MFR data is farther off than the user data, there is no valid measurements to start with.

Since we've now established there is no "PERFECT" measurement, therefore your example is trying to correct a number that started out as being a bad "baseline measurement" by the user with a log function, so it doesn't work out right that way. We can't start with a bad number and correct it with a function, we must first make the source of the data as error-free as possible, that is the #1 thing any equation has to focus on in this situation, averaging. Basically, a simple log system would have to use one of 3 numbers which then has no weighting of the number, an averaging system can weight the numbers to at least some small degree. A combined system with using the log as part of the weighting is possible, but not really worth it right now, it's unlikely to increase the accuracy of the results by enough to be worth the trouble, as the X factor is lamp variance and lamp hours (and measurement technique and equipment) which is a larger error than the weighting of the LOG against the 3 measured results.

Without knowing WHO's measured result of several is more accurate, and which of each of those measurements are more accurate at each point (closest, mid, farthest), then there really isn't a simple solution right now at the moment other than basic percentile averaging.

Using a log by itself based on one measurement (or even one averaged measurement) would be an even faultier way of doing it, the reason being is because it reduces the sample size of the percentile averaging of the LIMITED data I have available, and it does so more than it actually corrects the error. I could even work out a way to get a true standard deviation by doing a lot of measuring tests with different equipment, but as noted, there are more important things at the moment.


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post #7 of 30 Old 05-06-2013, 12:22 PM
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Sorry to go OFF TOPIC.

Instead of going over this again, I will now just keep referring to this post. Now logged in notepad.

Let me simplify and hopefully I'm done with this smile.gif

1) User takes measurement at 400 lumens at closest throw...
====Option # A) We use a log function to correct that, but by doing so we ignore his other measurements (because they disagree with the LOG function)...
====Option # B) We use multiple numbers from multiple sources, a percentile averaged measurement that is based upon averaging the "middle" of multiple measurements from MULTIPLE reviewers, and throws out measurements that deviate too far.

How can a log function that STARTS out with 1 of his 3 measurements be more accurate than the average between the three measurements (or rather the percentile average of 3 measurements between 5 people), it cannot, it's impossible (think carefully now). The reason being is because if his last 2 measurements at mid and farthest throw are off, then his first measurement has more odds of being off then the average between three, therefore the log function has worse odds than averaging the three. Since we NEVER start with a perfect number, and we are ALWAYS trying to average a person's measurements, then we always hit this same problem, a log function can only work if the first measurement is more accurate than an average of multiple. With three measurements at three points we are reducing measurement error, with 1 measurement we are increasing it (your example).

Now why does Option B work better, yes Option B might show in the calculator itself a different depiction of LUMENS change as you move the slider from the baseline, but that is because you are seeing averages of measurements. I admit this concept is somewhat complex, but I have some background in statistics, so now let me re-explain it like this...

We do not BASE the equation on the accuracy of the changing of the lumens between when he moves the slider, we base it on universal averages, because what we care about is the accuracy of the end-result between averaged measurements at a GIVEN THROW, which is based on all 3 points being averaged, not just based on a small sample of data. Even if I average multiple reviewers at a single point, the concept is the same, as the whole it can be off more than the log can correct it. The curve is not based on a LOG because it is based on an average of multiple reviewers at each point, simple.

Your example uses Garbage In, Correct Results out, when it is Garbage In - Garbage Out. You have to fix the garbage, modifying garbage does not = accuracy. The way to fix garbage is by averaging, ok sorry I'm done...


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post #8 of 30 Old 05-06-2013, 01:32 PM
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Every zoom lens is manufactured to a specific F stop at long and short throws and all zoom lenses at non constant aperture follow a log function between the extremes. One can easily measure the exit image size at long and short throws and all one needs is the specified f stop at one end if that's all one can get. The manufacturers have this info and I would expect that they will supply it upon request. Several calculators show the effective F stop at both ends and obviously they got them from somewhere. Whether they use a log function for F stop and lumens out at throws in between I don't know. Please do not view this as a criticism of your very fine calculator. You and your calculator a valuable asset to us all and your calculator and posts are very much appreciated and are valuable to boot.

Now. Back to the question asked by the TO. Do you concur with my recommendation and the logic behind it?

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post #9 of 30 Old 05-06-2013, 01:33 PM
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The manufacturers do not supply this data with lab measured results for multiple projector modes, no projector calculator has this data (PJC uses data from the manual or their own measurements). Their data is not consistent by any stretch.

I deal with statistics half my life in programming. Re-read it again. F-stop has nothing to do with this, I know what F-stop is. Give me an accurate first measurement (again does not exist).

Garbage in, Garbage out. Without an accurate initial measurement, we cannot modify it to be more accurate, no matter what formula we apply (other than averaging). Also looking at the F-stop equations, they have too high variance between the measured results of the reviewers vs. the equation. This variance matters because we are starting with a MEASURED result from a reviewer or user (because we have NO choice )... You cannot ignore the other reviewer's measurements and still use one of the measurements at as basis at the same time (well you can but it's not as accurate).

If the manufacturers had data to give me, I would take it, but I don't.


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post #10 of 30 Old 05-06-2013, 01:47 PM
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Obviously there are lots of variables to determine the lumens entering the lens. I am saying the lens mass produced will all have approximately the same F stops, different of course at the zoom extremes. The F stop will determine how much of the light entering will get out and varying the zoom will have the same cut on light out from short throw to long throw regardless of the light in. The starting point say at short throw will widely vary based on a variety of other factors such as bulb to bulb variations etc but the lens' effect will remain constant.

Anyhow this is a friendly discussion. What do you think of my recommendation to the TO?

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post #11 of 30 Old 05-06-2013, 01:48 PM
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Quote:
Originally Posted by mark haflich View Post

Now. Back to the question asked by the TO. Do you concur with my recommendation and the logic behind it?

Sure, I agree...

On the lumens problem, I thought about it for hours and hours, the data I do not have is perfectly accurate starting data from MFR modes, and then you must verify the LOG actually can apply more accurately then the averaging, but it won't (not in the way I get the data). I don't have access to enough of these projectors myself to do all the measuring myself or high-end enough equipment, so I'm going to keep it this way for the foreseeable future.

I really don't think the manufacturers have any data to give that they took time measuring all the modes (even if they did, I don't have it). So I have not attempted to apply it because I do not have the data to apply it to.

Also, are you 100% sure the F-STOP formula works correctly across multiple projectors without unknown variables varying the results greatly?

The reason I ask this last question is because at a quick glance there are many measurements from reviewers that average within 20% of each other, but at the same time they average > 30% to > 50% from what the F-Stop formula would tell us (even in relative terms). This is problematic and I would have to get to the bottom of it before I would even consider using it, but then we are back to PROBLEM A - where I get my data from will not properly average using F-stops.


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post #12 of 30 Old 05-06-2013, 02:50 PM
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The F stop is based on the area of the glass used. f stop is a log function A F stop of 2.8 is exactly half the area of a F stop of 2.0. So if one were to measure the exit area at short throw one could measure the exit area of the long throw to calculate the reduction. the problem is what is the starting f stop at short throw/ One needs to know the design f stop at one end.. this is totally independent of operating mode which involves gamma curves, temperature, aperture setting etc. But lens f stops are design absolutes.

The variability on light out at an extreme is caused by other factors such as the bulb and bulb hours etc.

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post #13 of 30 Old 05-06-2013, 03:25 PM
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Right, but unless I can get more universally equal and precise data between the closest throw numbers, then I still will just average all of the numbers, because it's still the same problem, 3 measurements from an imperfect source is better than one across the entire throw average brightness.

I would also argue that getting numbers from multiple reviewers that are within a given range as a weight has a higher likelihood of accuracy then even comparing MFR results between different MFR's, even if the MFR's will claim to give accurate numbers in a given mode (which we all know they do not). I would still have to verify it with some system, regardless of where it came from.


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post #14 of 30 Old 05-06-2013, 03:30 PM - Thread Starter
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Thanks guys you really narrowed it down for me . lol.
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post #15 of 30 Old 05-06-2013, 03:33 PM
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What are your primary uses for the PJ?

Sports, Movies, Gaming, etc??

Give us % breakdown of viewing content.


Quick and Easy Shelf Mount Method for both one projector or dual stacks

Web Calculator v023 & v025
- Quick Peak at the new upcoming calculator
**Current Projector Calculator** -- http://www.eliteprojectorcalculator.com

Coder's Top Projector Picks of 2012 --http://www.avsforum.com/avs-vb/showthread....

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post #16 of 30 Old 05-06-2013, 04:00 PM - Thread Starter
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Quote:
Originally Posted by coderguy View Post

What are your primary uses for the PJ?

Sports, Movies, Gaming, etc??

Give us % breakdown of viewing content.

Probably like 60% movies 20% sports 20% gaming
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post #17 of 30 Old 05-06-2013, 04:21 PM
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See what you started.... LOL
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post #18 of 30 Old 05-06-2013, 04:38 PM
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Look at the Sharp xvz-30000 and see if it will fit (sorry dont have that one in my calc ATM). I think the Sharp is better than the Mits from what people have said in the forums. Though the Mits has more accurate color, but I doubt that's a good reason for a newer user to PJ's, it's more of a purist trait (depends).

As far as calculators go, the numbers are close in most cases (and even closer on the next release), but I can tell you it's not fun having to go to 3-5 different places to gather lumen data in the first place smile.gif

It's not hard for my calculator to win an accuracy argument when the other calculators don't even show what mode the projector is in or the baseline lumens, and they only REPORT one undisclosed PJ mode. Someone being hard up on how the PJ adjusts the % of reduction or increases it, well that's all because the users can easily go to X/Y reviewer site and it's more compatible with this UI entry method (and the reasons I stated above, it won't magically get more accurate). Etc... Etc...


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post #19 of 30 Old 05-06-2013, 05:51 PM
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Quote:
Originally Posted by DreamAgain2 View Post

.... Do I calculate the projector distance from ceiling to ceiling.. or towards the middle of the screen or top? or what? ...

The distance is usually measured horizontally, as shown in your top illustration. Usually from front of lens to screen. But always check the manufacturer's installation instructions.
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post #20 of 30 Old 05-06-2013, 06:29 PM
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Once again, to narrow a precise answer down.


Distance is measured parallel to the floor or ceiling, the shortest point between the plane of the lens front and the plane of the screen, as the 11 ft in your diagram.

Given your screen size and intended projector but it really doesn't much matter here exactly what projector, mount at the longest throw possible for your projector given the space available. The longest distance would be your screen width (87 inches) times the maximum long throw which for your projector is 2.1. If you don't have that distance available move it closer. When I say longest, always mount an inch or two closer to make sure it all works given any slight measurement inaccuracy or projector to projector minor throw variances. The closest you can mount the projector to your screen would be 1.4 times 87 inches. That's it. There is simply nothing else to say.

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post #21 of 30 Old 05-06-2013, 06:35 PM - Thread Starter
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Quote:
Originally Posted by mark haflich View Post

Once again, to narrow a precise answer down.


Distance is measured parallel to the floor or ceiling, the shortest point between the plane of the lens front and the plane of the screen, as the 11 ft in your diagram.

Given your screen size and intended projector but it really doesn't much matter here exactly what projector, mount at the longest throw possible for your projector given the space available. The longest distance would be your screen width (87 inches) times the maximum long throw which for your projector is 2.1. If you don't have that distance available move it closer. When I say longest, always mount an inch or two closer to make sure it all works given any slight measurement inaccuracy or projector to projector minor throw variances.

Thanks, makes sense. It seems for now I'll probably buy a 100 inch screen, mount it and run the image at ~90 inches. Will this work out alright until I move?
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post #22 of 30 Old 05-06-2013, 06:42 PM
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Yes, that will work until you move, you can fill the screen as much as you can, you will probably get a little larger than that (but I forgot how deep the projector is from front to back).


Quick and Easy Shelf Mount Method for both one projector or dual stacks

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Coder's Top Projector Picks of 2012 --http://www.avsforum.com/avs-vb/showthread....

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post #23 of 30 Old 05-06-2013, 08:15 PM
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I agree with Coderguy about the Sharp 30k versus the Mitsubishi HC7800D. I owned the Mitsubishi (two actually, the first needed to be returned. it was defective). Both units had a horrible dynamic iris. It was unusable. Way too intrusive, it kicked in late and there was tons of pumping during 95% of all scenes. With DLPs you need a good dynamic iris to stay competitive with other technologies to achieve even modest (by todays standard) black levels and contrast. You won't have this issue with the Sharp. Considering you can't use the one on this specific Mitsubishi model for all practical content I'd highly recommend the Sharp over this model if you want to buy a DLP model. Heck, I'd even recommend the BenQ W1070 over the Mitsubishi. The only thing I'd recommend the Mitsubishi for would be as a "3D" only projector.
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post #24 of 30 Old 05-06-2013, 08:29 PM
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Your diagram shows 11 ft to the pole holding the projector mount BUT throws are measured from the front element of the lens. Fitting the projector within the 11 ft you have and having at least a little distance from the back of the projector to the rear wall will mean you will have a maximum throw of about 9 ft available. Have to look up the projector dimensions to figure exactly. divide that distance by 1.4 and that will give you the maximum projected width. A 90 inch diag screen is about 80 inches wide. 80 x 1.4/12 is about 9 ft 4 inches and I don't think asfter you mount the projector you will have quite that. To figure exactly look at the dimensions of the projector and the center point for the mounting pole. You have to add the throw distance to the length of the projector plus a few inches at the rear depending on how the hot air exhaust is..With a rear exhaust or intake you might need as much as 10 inches behind the projector so look it up in the online Mits manual and figure it out..

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post #25 of 30 Old 05-06-2013, 08:35 PM - Thread Starter
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Originally Posted by Seegs108 View Post

I agree with Coderguy about the Sharp 30k versus the Mitsubishi HC7800D. I owned the Mitsubishi (two actually, the first needed to be returned. it was defective). Both units had a horrible dynamic iris. It was unusable. Way too intrusive, it kicked in late and there was tons of pumping during 95% of all scenes. With DLPs you need a good dynamic iris to stay competitive with other technologies to achieve even modest (by todays standard) black levels and contrast. You won't have this issue with the Sharp. Considering you can't use the one on this specific Mitsubishi model for all practical content I'd highly recommend the Sharp over this model if you want to buy a DLP model. Heck, I'd even recommend the BenQ W1070 over the Mitsubishi. The only thing I'd recommend the Mitsubishi for would be as a "3D" only projector.

I actually found a used 7800d from a friend for a super cheap price. i figure since this is my first entry in to the world this will be a good chance to get my feet wet. I'm spending more on the screen than I am the unit lol!

down the line i'll definitely pick up a better unit though.
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post #26 of 30 Old 05-06-2013, 08:37 PM - Thread Starter
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Originally Posted by mark haflich View Post

Your diagram shows 11 ft to the pole holding the projector mount BUT throws are measured from the front element of the lens. Fitting the projector within the 11 ft you have and having at least a little distance from the back of the projector to the rear wall will mean you will have a maximum throw of about 9 ft available. Have to look up the projector dimensions to figure exactly. divide that distance by 1.4 and that will give you the maximum projected width. A 90 inch diag screen is about 80 inches wide. 80 x 1.4/12 is about 9 ft 4 inches and I don't think asfter you mount the projector you will have quite that. To figure exactly look at the dimensions of the projector and the center point for the mounting pole. You have to add the throw distance to the length of the projector plus a few inches at the rear depending on how the hot air exhaust is..With a rear exhaust or intake you might need as much as 10 inches behind the projector so look it up in the online Mits manual and figure it out..

Thanks good info. I'll make sure I mount it properly with enough exhaust space and stuff. From what you guys are sayin i'll get a ~85 inch screen in this room which is fine. I'll go ahead and get a 100 inch screen and hide the extra with drapes for now. When I move I'll make sure I plan accordingly to properly use my full 100 inches.
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post #27 of 30 Old 05-06-2013, 08:50 PM
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You should get around 90" to 94" screen on the safe side out of the 100", maybe a little more.

I have a sinus headache (which I seem to get often lately).

OK so I looked at the measurements, it is 13 inches deep and about 16" wide.
The vents are side to side, just like the Mits hc4000.

So basically take off 16 inches (13+3) from your measurement since the cables go in the back.
The projector has a 1.4-2.07 throw ratio based on my calc.


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post #28 of 30 Old 05-06-2013, 09:52 PM
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JFYI or just for the record:

There are some closest throw to farthest LUMENS numbers in my calculator that are incorrect, because I got too lazy to average them all in Excel or had incomplete data, so I threw a "that's close enough" number together. I am being more diligent this time in the next version, though it was still usually close enough.

The point of my posts though, is that either method used doesn't actually fix the data (whether it be a log to calculate the mid- far throw, or taking an average of all 3 points, or applying a log weighting to displace the average). The correct way would be to apply the F-STOP LOG as a weight against the reviewers 3 measurements, which basically means taking into account the closest and farthest throw measurements and partially displacing ("averaging") that number into what the expected LOG would be across the range (if the F-STOP LOG is truly 100% error free formula, I don't know yet). Now although something like this last method is best, it also would complicate the UI and the math code. In programming, math code is a lot more intense than on paper because you have to interact with things. I'm not in a hurry to complicate the math averaging further by adding an F-STOP LOG as a partial displacement formula. Adding a plain F-STOP log from one number would NOT be an improvement, it would be a setback, but averaging an expected F-LOG into the 3-points could be worth it (but not at this very moment, too much other work to do).

It is really not something I have as a high priority, since I am more concerned about adding more projectors right now and just fixing the data that is there (getting it averaged better).


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post #29 of 30 Old 05-06-2013, 10:32 PM
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When you say 100 inch screen, we interpret that to be a 100 inch diag, 1.78 aspect ratio screen. The height of that screen is 49 inches and its width is 87 inches.

Mark Haflich
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call me at: 240 876 2536
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post #30 of 30 Old 05-06-2013, 10:37 PM
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Right, the vents are on the side, so he doesn't need extra clearance, and the PJ is only 13" long/deep. The min throw is 1.4, so 90" easy, maybe 94" to 96" depending how tight he squeezes it in.


Quick and Easy Shelf Mount Method for both one projector or dual stacks

Web Calculator v023 & v025
- Quick Peak at the new upcoming calculator
**Current Projector Calculator** -- http://www.eliteprojectorcalculator.com

Coder's Top Projector Picks of 2012 --http://www.avsforum.com/avs-vb/showthread....

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