Maths for calculating screen brightness. - AVS Forum
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post #1 of 42 Old 01-22-2014, 09:45 PM - Thread Starter
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Projector experts, what is the formula for working out how bright the projected image will be? I am involved in a project where the owner wants a 4740mm x 2000mm screen! If my maths are correct, that will be over 200inch on the diagonal. He has a SIM2 (D80) and will use an A-Lens (probably one of my MK5s). I am just having a doubt this projector will cut it. Screen will be same 1.16 gain as SmX.

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post #2 of 42 Old 01-23-2014, 06:09 AM
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Brightness = Lumens * gain / screen area

Or to figure out how much light output you need (Lumens) you swap that around a bit:

Lumens = brightness * screen area / gain


So by my math, that's 187"x79", 100 sqft. So if you shoot for DCI 16ftL, that's 16 * 100 = 1600 Lumens I probably wouldn't figure any gain for the SMX material, I think they may have gotten over 1 by not counting the open area of the screen.

I found this review of the D80E, which says it's about 500 Lumens:
http://www.avsforum.com/t/988572/my-sim2-d80e-review

That would mean about 5 ftL on the screen, yeah, I'd say that's probably too dim.

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post #3 of 42 Old 01-23-2014, 10:21 PM - Thread Starter
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Thanks for that. So a projector up grade for him then.

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post #4 of 42 Old 01-24-2014, 05:37 AM
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Too bad there aren't any "good" options that aren't really expensive frown.gif

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post #5 of 42 Old 01-24-2014, 12:11 PM
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I was doing a calibration for a guy and the recording rate for 100% white seemed quite slow compared to what I was used to, so I got my light meter out to measure the lux at the screen. The fL figure came out at around 3 before any screen gain was used in the equation, yet he was quite happy with the image. His room had total light control and the image didn't look as bad as I would have thought at that level of reflectance.

It's surprising how bright an image can look even at low levels in the right conditions - unless you're used to something much brighter. Even so, it's nice to be able to start at a higher level so you have the option to dim it down if you want. Back catalogue DVD definitely needs more cinematic levels of reflectance or compression artefacts can become visible. Each to his own of course.

There are brighter, cheaper options, but they're usually office projectors with lower contrast and no processing, so an external scaler or HTPC are needed for decent video reproduction. It's what we used to do in the early days of digital projectors before ones with decent processing and contrast started to come along at reasonable prices. Something like an Optoma EH501 (first 1080 I stumbled on via google) with a scaler may be better than the Sim2 in some respects - without seeing and comparing, I couldn't say, but at those prices, could be worth a go. Depends on the clients budget of course.

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Who says Cameron is "right" and why do we care about him so much - lol!

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post #6 of 42 Old 01-27-2014, 05:00 AM - Thread Starter
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I will take my gear to his house tomorrow evening to take a few readings on his current screen, then present him with the facts. It might get interesting.

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post #7 of 42 Old 01-27-2014, 01:52 PM
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I'd like to know what readings you get too

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post #8 of 42 Old 01-28-2014, 06:04 AM - Thread Starter
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Not good. The screen in his room is about 120" on the diagonal and he wants to go over 200". The image looked tealified and when I measured it at RGB255 (white), red was only about 40 percent verses green and blue which were both over 110 percent and it only measured 3.5FL :eek

It was not all bad because once I broke the bad news and his wife learned she could get a 3D projector to replace this one, instant WAF smile.gif

Will be curious to see if she is still smiling when she learns the price of the anamorphic lens tongue.gif

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post #9 of 42 Old 01-30-2014, 02:03 PM
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Any news on how the prices went yet? smile.gif

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post #10 of 42 Old 01-31-2014, 04:08 AM - Thread Starter
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Quote:
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Any news on how the prices went yet? smile.gif

Gary

No not yet. I meet with them next week to discuss their new 3D/5000 lumen beast I found for them. I guess I will throw in a MINI3D just for good measure too.

Slightly OT, I have a new toy to test (play with) in my cinema. It is a new laser/LED hybrid from Optoma, so will be interesting to see if this grey scale tracks better than the last one I got my hands on (the Veiwsonic). Not sure what throw this is, but just hope for three things -
1. throw out to at least 2.0:1
2. 3D @ 144Hz (DLP Link? Fingers crossed)
3. It scales for CIH in 3D like other models do.

I've been loaned this unit not only to test for the company that sells them, but to be sure the hole pattern is compatible with my Projector Station. One of their guys got to see it today and thinks it rocks.

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post #11 of 42 Old 01-31-2014, 05:56 AM - Thread Starter
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1. throw out to at least 2.0:1
NO! mad.gif Apart from this short throw design, this projector has SOOO much going for it. it is sharp, it is bright and the colours look good. I have not set the colorimeter up on it yet, but i did give it a quick calibration using the THX Calibrator BD and I'd own this (apart from the throw being too short). It is VERY quiet being Laser/LED, no lamps cool.gif

2. 3D @ 144Hz (DLP Link? Fingers crossed)
Didn't have glasses to test tonight. I could not find the DLP Link setting in the menu either, so maybe this is the RF type.

3. It scales for CIH in 3D like other models do.
YES!biggrin.gif Not only does this scale for CIH in both 2D/3D, it even has a mode "anamorphic lens - none, fixed, moveable". How good is that?
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post #12 of 42 Old 01-31-2014, 06:56 AM
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I know Zombie thinks DLP link is bad, since it kills contrast, so he'd be happy if it was RF. Is this the HD90/HD91? I didn't think that was a hybrid though.

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post #13 of 42 Old 01-31-2014, 09:28 PM - Thread Starter
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Quote:
Originally Posted by stanger89 View Post

I know Zombie thinks DLP link is bad, since it kills contrast, so he'd be happy if it was RF. Is this the HD90/HD91? I didn't think that was a hybrid though.

I think your right, straight LED, not a hybrid. Apart from the very short throw, I do like it.
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post #14 of 42 Old 02-01-2014, 06:55 PM
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Quote:
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It is VERY quiet being Laser/LED, no lamps
It's not the lamp that makes the noise. It's the fans. LED needs fans, too. No fans?
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post #15 of 42 Old 02-02-2014, 06:56 AM - Thread Starter
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Your right, it is the fans that make the noise. Because this LED projector does not really produce much heat, the fans don't need to be same type used in projectors with a UHP lamp and why it is quiet.

I've only had a short time with this so wonder what i could do once I work it out.





Goes back tomorrow and I'll miss it.

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post #16 of 42 Old 05-26-2014, 02:20 AM - Thread Starter
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OK I thought I would update this thread rather than start a new one.

The projector being used on this project is an Optoma
Quote:
Originally Posted by CAVX View Post

No not yet. I meet with them next week to discuss their new 3D/5000 lumen beast I found for them. I guess I will throw in a MINI3D just for good measure too.

Slightly OT, I have a new toy to test (play with) in my cinema. It is a new laser/LED hybrid from Optoma, so will be interesting to see if this grey scale tracks better than the last one I got my hands on (the Veiwsonic). Not sure what throw this is, but just hope for three things -
1. throw out to at least 2.0:1
2. 3D @ 144Hz (DLP Link? Fingers crossed)
3. It scales for CIH in 3D like other models do.

I've been loaned this unit not only to test for the company that sells them, but to be sure the hole pattern is compatible with my Projector Station. One of their guys got to see it today and thinks it rocks.



The screen is 4740mm x 2000mm and there is still a bit of alignment work to do, but on a full white field, I measured the image brightness at 23FL! It will drop a bit after calibration.

Sorry for the crappy pic, but all I had on me today was my phone.

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post #17 of 42 Old 06-10-2014, 09:49 AM
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Quote:
Originally Posted by CAVX View Post

OK I thought I would update this thread rather than start a new one.

The projector being used on this project is an Optoma


The screen is 4740mm x 2000mm and there is still a bit of alignment work to do, but on a full white field, I measured the image brightness at 23FL! It will drop a bit after calibration.

Sorry for the crappy pic, but all I had on me today was my phone.

So you are getting 25fL on a 19' wide screen ?

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post #18 of 42 Old 06-12-2014, 05:22 PM - Thread Starter
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Quote:
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So you are getting 25fL on a 19' wide screen ?

Art
The screen is 4.740m wide. My calculations are 15.5 feet wide and 23FL on a full white field. Yes this is bright.

Again another crappy snap on a phone, but this is freaking awesome when sitting at just 2x the image height (4m back).


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post #19 of 42 Old 06-12-2014, 09:28 PM
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Quote:
Originally Posted by CAVX View Post
The screen is 4.740m wide. My calculations are 15.5 feet wide and 23FL on a full white field. Yes this is bright.

Again another crappy snap on a phone, but this is freaking awesome when sitting at just 2x the image height (4m back).

What projector are you using? It must be big bucks...

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post #20 of 42 Old 06-13-2014, 03:15 AM - Thread Starter
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Quote:
Originally Posted by ellisr63 View Post
What projector are you using? It must be big bucks...


It is an OPTOMA. Sorry for the bad pic and the fact that I don't have the exact model number on hand but this thing is a native 1920 x 1080 with 5000 lumans! Can you say LIGHT CANNON? I don't think it cost that much but it does 2D at 72Hz and 3D (with DLP Link) at 144Hz.

The interesting thing was this projector did not have a lens fitted to it out of the box. There is a choice of long or short throw lenses available and they have to be fitted on installation. This system is using the short throw option (1.5:1~1.9:1). The long throw option runs from 1.9:1 to about 2.4:1 and costs about 3x as much as the short throw option.

Above is the projector mounted to one of my Projector Stations with one of my MK5 "Aussiemorphic" Lenses. This A-Lens is one of just two with the new (JVC safe) optic coatings. The other lens with these is my own (got myself an upgrade ) anamorphic lens.

When I first tested this projector, I was pretty impressed with the sharpness but thought the CR was going to be bad, but on that size screen, the image is pretty amazing and now I wish I had a screen that size in my own system.

TR is about 1.85:1 and the screen was custom curved to match the pincushion using the DIY ray tracing method first described by Vern Dias.

To measure pincushion, you need the following -
1. Projector with anamorphic lens
2. A flat wall to project onto
3. A tape measure
4. A straight stick that is tall enough to have the light shine on it when one end is on the floor - typically a broom stick will work here.
5. a roll of masking or similar tape
6. an assistant (optional)

1. With the anamorphic lens in the light path, project an image onto the wall.
2. Place the stick in the centre of the image.
3. Place some tape at the base of the light beam.
4. Move the stick to the edge of the image. The light should now be projecting below the tape.
5. Move the stick out from the wall (stay 90 degrees to the wall) until the light is just above the tape (like how it was when you first applied the tape).
6. Measure the distance from the stick back to the wall to find how far your screen ends need to come out to correct pincushion.
7. Repeat test for other end to ensure image is the same (just for the sake of being geeky).

And there you have "Ray Tracing" for measuring pincushion without the complex (and expensive) computer software.

Next up is connecting the 3 way active speakers. I will be using 3 MINI DSPs for both electronic crossovers and EQ. The 7.1 channel will use a total of 23 channels of amplification.
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post #21 of 42 Old 06-13-2014, 09:58 AM
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I see that HD had this one... http://www.homedepot.com/p/Optoma-19...H501/205192804 This is not what you are using, correct? What does the one you have cost?

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post #22 of 42 Old 06-13-2014, 02:58 PM
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Quote:
Originally Posted by CAVX View Post
The screen is 4.740m wide. My calculations are 15.5 feet wide and 23FL on a full white field. Yes this is bright.

Again another crappy snap on a phone, but this is freaking awesome when sitting at just 2x the image height (4m back).
I'm skeptical of your meter's accuracy. Or your black level, or something. That works out to 2351 Lumens. My 3 Chip DLP isn't much over half that with a new bulb. That's more than Art's old HT5000 put out IIRC.
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post #23 of 42 Old 06-13-2014, 03:04 PM
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Quote:
Originally Posted by GetGray View Post
I'm skeptical of your meter's accuracy. Or your black level, or something. That works out to 2351 Lumens. My 3 Chip DLP isn't much over half that with a new bulb. That's more than Art's old HT5000 put out IIRC.
Looks like this:
http://www.optomausa.com/products/detail/EH505

About $3500

Not exactly an HT Projector but I'm sure it's bright.
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post #24 of 42 Old 06-13-2014, 05:36 PM - Thread Starter
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Quote:
Originally Posted by stanger89 View Post
Looks like this:
http://www.optomausa.com/products/detail/EH505

About $3500

Not exactly an HT Projector but I'm sure it's bright.
Yeah that would be it. As I said, during my initial testing, I really had a doubt about this projector but now that is set up (not calibrated yet) on the 2m tall screen, it is quite impressive. It wow'd the customer and that is really what matters in the end of the day.
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post #25 of 42 Old 06-13-2014, 05:38 PM - Thread Starter
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Quote:
Originally Posted by ellisr63 View Post
I see that HD had this one... http://www.homedepot.com/p/Optoma-19...H501/205192804 This is not what you are using, correct? What does the one you have cost?
No, not that projector.

I'm sure the RRP is about $5K+ here in AU.
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post #26 of 42 Old 06-13-2014, 05:39 PM - Thread Starter
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Quote:
Originally Posted by GetGray View Post
I'm skeptical of your meter's accuracy. Or your black level, or something. That works out to 2351 Lumens. My 3 Chip DLP isn't much over half that with a new bulb. That's more than Art's old HT5000 put out IIRC.
23FL was the measurement off screen as read by the colorimeter. I should have grabbed a screen cap.
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post #27 of 42 Old 06-13-2014, 05:56 PM
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Quote:
Originally Posted by stanger89 View Post
Looks like this:
http://www.optomausa.com/products/detail/EH505

About $3500

Not exactly an HT Projector but I'm sure it's bright.
Just dug up this one on projector central...http://www.projectorcentral.com/Optoma-EH500.htm $1483 street price... Makes me wonder if I should have went with this instead of the Panny 8000.

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post #28 of 42 Old 06-13-2014, 07:39 PM
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Quote:
Originally Posted by CAVX View Post
23FL was the measurement off screen as read by the colorimeter. I should have grabbed a screen cap.
That could be it. Not very accurate for luminance measurements, typically, but still seems high.. As you said, as long as the guy likes it...

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post #29 of 42 Old 06-14-2014, 02:29 PM
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I believe the brightness, but I'm surprised the black level/contrast is satisfactory.

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #30 of 42 Old 06-15-2014, 05:55 AM
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Hi Mark,

Sorry if I missed it, but are you using any form of image processing or is the pj doing all the work with BD connected directly to it (no processor or HTPC in the chain)? Going on what data projectors used to be like in the olden days, a processor or HTPC was needed for best results. This could be good news for those on a budget and with larger screens - it really can expand our choices for clients (or even forum members) on smaller budgets and I think by taking that leap of faith with a data pj you've actually widened our choices. I've often wondered if these newer 1080 data pjs could be used in the home in much the same way we did about 15 years ago, and I think you've proved that there is a place for them - given the choices and the costs I think you may have people like Art looking at a completely different product line for the norm. I actually think this is an exciting development.

Like Stanger, I'm a bit surprised the contrast looks OK as the pj is only rated at 2000:1 (the one I initially linked to was around 15000:1 with DB). That's the minimum spec for DCI IIRC, so should be fine I guess, but these days we're used to much more. Maybe if what you're seeing there is comparable to commercial theatres (relative black level wise as the pj is delivering higher fL), it's probably looks better than most of us would think, but an ND filter will reduce the white and black levels to more cinematic levels, and allow the lamp a longer lifetime because the ND can be removed as the lamp dims with age, or if a sports event is on and you want your mates round but don't want to be completely in the dark with them (oo-er missus).

What you could try before the customer gets too used to the brightness other than an ND filter, is an FL-Day filter and recalibration. It allows more use of blue and green, dims the image to more 'cinematic' reflectance levels and increases on/off contrast. I used them all the time on UHP lamped pjs because of how they could improve the image on those two points. Tell the customer the image he is getting is around twice the brightness of a commercial theatre (assuming the 23fL is ballpark) and just by using an ND see what he thinks - it may take a while for him to get used to the dimmer image but it's worth a try, especially if the FL-D is an option for them.

I find using a photopic lightmeter like those in the Tecpel range (can't remember the US equivalent - there are a few that are identical except for name and colour) you can get more accurate lux readings than using the usual calibration tools like a colorimiter. They aren't that expensive but are a very useful addition to our usual calibration tools IMHO. I used to velcro the head of the meter to the stand I had the colorimeter mounted to so could use both at the same time if necessary when measuring at the screen (rather than from it and using an offset file for better low level measurements).

Cheers

Gary

Quote:
Originally Posted by elmalloc
Who says Cameron is "right" and why do we care about him so much - lol!

I trust Gary Lightfoot more than James Cameron.
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Reply 2.35:1 Constant Image Height Chat

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