Maths for calculating screen brightness. - Page 2 - AVS Forum
Forum Jump: 
 10Likes
Reply
 
Thread Tools
post #31 of 38 Old 06-18-2014, 01:51 AM - Thread Starter
AVS Special Member
 
CAVX's Avatar
 
Join Date: Aug 2005
Location: Brisbane, Australia
Posts: 8,354
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 31
Quote:
Originally Posted by Gary Lightfoot View Post
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.
The system uses an OPPO95 (which he already owned) connected through Yamaha CX5000 (pre-pro) to the projector. I wanted to install a MINI3D but was over ruled by the bean counters with a "lets see it first". As I said, when I first tested this, it was not good, yet on this size screen, it seems to be doing OK to the point that I would be happy with the image given the size and brightness. I think its black levels could be on par with the BenQW6000 I am currently using on a much smaller (1/4) size screen.

I didn't want to go the "data" route, but decided to give this a go because it does have a true 1920 x 1080 chip, does 3D (via DLP Link) at 144Hz and has lumens to spare. Normally I would have avoided a data grade like the plaque. And yes, given the results so far have been positive, it does allow those with the desire to go big and bright an affordable means to do so now.

Quote:
Originally Posted by Gary Lightfoot View Post
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).
I'll calibrate first, then decide if the projector needs the ND filter. I agree it will make the blacks better. I just don't want to kill off the bright whites at this size if I don't have to.

Quote:
Originally Posted by Gary Lightfoot View Post
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.
We got the sound system up and running so tonight is the first watch. I will be interested in his feedback. He was totally blown away the other day as was his wife before that.

Quote:
Originally Posted by Gary Lightfoot View Post
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
I'll look into it, thanks.

Mark Techer

I love my Constant Image Height system!

Last edited by CAVX; 06-18-2014 at 01:54 AM.
CAVX is offline  
Sponsored Links
Advertisement
 
post #32 of 38 Old 06-18-2014, 02:10 AM
AVS Special Member
 
Gary Lightfoot's Avatar
 
Join Date: Jun 2000
Location: Surrey, UK
Posts: 4,437
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 36
Thanks for the feedback Mark.

The Optoma certainly seems to have paid off - not everyone is a black level junkie, and if you need to fill a larger than normal screen, these type of pjs seem to be a good alternative. I think Art was quite happy to go from stacked G90s with the black levels CRTs can provide, to a Sim2 that could fill the scope screen at a size he wanted but with lighter blacks. This is much the same but staying on more affordable levels for the average pocket.

What was the image like initially that gave you reservations, and are there any negatives compared to the usual home cinema projectors we'd usually go for when comparing on a like for like basis?

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.
Gary Lightfoot is offline  
post #33 of 38 Old 06-18-2014, 05:50 PM - Thread Starter
AVS Special Member
 
CAVX's Avatar
 
Join Date: Aug 2005
Location: Brisbane, Australia
Posts: 8,354
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 31
I know that capturing an an image on a digital device like a phone may seem to alter the percieved image brightness and black levels, but the black on the CAVX test pattern was pretty black. Not JVC DiLA black, but pretty decent. And for the price, this system seams to be working well.

I still want the HD91 LED projector for my system.

Mark Techer

I love my Constant Image Height system!
CAVX is offline  
post #34 of 38 Old 06-21-2014, 11:53 AM
AVS Special Member
 
ellisr63's Avatar
 
Join Date: Jul 2002
Location: In the Home Theater
Posts: 1,933
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 108 Post(s)
Liked: 228
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).

Is that in the ECO mode? I used the calculator and it came out to 40fl for that size screen.

Denon 4520ci, 3 JBL 2360As/EV DHA-1s, 3 1/4 Pie bass bins, MiniDSP 2x4s, 4 Klipsch HIPs, 2 Klipsch KP3002s, PS3, XBox 360, 3 Intel NUCs, Monoprice Redmere, Monster HTPS7000, 2 SUPER SPUD subs, Panasonic AE8000u, 2 Danley DTS10 subs, & Yamaha P7000s.
ellisr63 is offline  
post #35 of 38 Old 06-21-2014, 12:43 PM
AVS Special Member
 
Gary Lightfoot's Avatar
 
Join Date: Jun 2000
Location: Surrey, UK
Posts: 4,437
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 36
If Mark calibrated the projector, that could quite easily mean a loss of 40% of the advertised lumens which are often the maximum achievable lumens before any adjustments are made to make the image give an acceptable video image. If you reduce that a further 25% going from high to eco mode, then 23fL is probably not that far from the truth if we start with 5000 lumens.

If you measure most projectors out of the box, you will find that they are never giving the advertised figures. I think JVC are one of the few that advertise real figures rather than max achievable.

Gary
ellisr63 likes this.

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.
Gary Lightfoot is offline  
post #36 of 38 Old 06-21-2014, 03:59 PM - Thread Starter
AVS Special Member
 
CAVX's Avatar
 
Join Date: Aug 2005
Location: Brisbane, Australia
Posts: 8,354
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 31
I'll be calibrating the projector tomorrow. I will save the files and post the results.

Mark Techer

I love my Constant Image Height system!
CAVX is offline  
post #37 of 38 Old 06-24-2014, 07:54 PM
Newbie
 
neoridium's Avatar
 
Join Date: Dec 2013
Location: Australia
Posts: 9
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Liked: 10
After reading through this topic I made a little excel document to help me calculate everything just by changing
Aspect ratio, screen height, screen gain and either Lumens or Brightness. This is for people like me who use the metric system and I thought I would share it
Attached Files
File Type: zip Screen_Brightness.zip (8.3 KB, 3 views)
neoridium is online now  
post #38 of 38 Old 06-25-2014, 02:28 AM - Thread Starter
AVS Special Member
 
CAVX's Avatar
 
Join Date: Aug 2005
Location: Brisbane, Australia
Posts: 8,354
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 31
Thanks for that.

So after spending a few hours on this system, on BRIGHT ECO mode I still get 23FL.

I will need to take more measurements as the colours (CIE diagram) is not showing close to reference even thought the colour on screen looks quite amazing. Grey Scale tracks fairly flat.

The biggest problem I have with these Optoma projectors is that the projector changes the user controls for each different input including my PC set to output 0-255 Vs an OPPO also set for 0-255. Frustrating to say the least.
ellisr63 likes this.

Mark Techer

I love my Constant Image Height system!
CAVX is offline  
Reply 2.35:1 Constant Image Height Chat

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off