CurtPalme.com Home Theater Forum

[Advent Videobeam]

I want to measure the output of my vintage Advent from my avatar. How does someone accurately measure Lumens and use what calculations?? What device to use?? Measurement from the center screen or from the PJ CRTs? This unit can project a usable 7 foot diagnal image, albeit low brightness. Wikepedia states light output at 50 lumens which seems too low for such a large image size. A unit conversion web site translates the 30 foot lamberts Light output of 1000A stated in Original Advent Videobeam brochures into a value of 110 lumens. I'm curious to do my own measurements as that site is used for historical purposes. The 1000A was a higher end unit compared to the Advent videobeam 710, 750, 760 models which had smaller screen and or lower light output.

I'm going to soon upgrade the original Advent screen surface with DA-Lite's High power screen material that IS washable with a gain of 2.8 on a flat surface!! The curve of the original Advent screen form should add even more gain to that high performance material from Da-lite. It's a shame no one invented this earlier. I'm sure it would of made more older projectors much brighter and useful, saving them by extending their service life. I expect big performance boost with this screen upgrade.

I have another Da-Lite high Power screen used for a newer digital PJ box as my main unit, and super bright screen produced beautiful image results. The bright scenes in movies bounce off the screen and light up the room, my family was floored when I did this upgrade to main unit.

I'll post pictures when I get material and my unit is properly converged for best display results possible. Maybe this can boost screen brightness at least threefold? ---that would be awesome!

[Person99]

Project a 10% white window. Measure the light (in ft. Lambers) on a known 1.0 gain material. Calculate the Lumens. That is "Peak Lumens". ANSI Lumens is measured on a full white field with contrast set where you can tell the difference between 90 and 100 IRE. It is measured at 9 locations on a known 1.0 gain material and averaged. Then lumens are calculated.

Was 50 the ANSI Lumens? If so, I totally believe that as an EM 8" PJ has about 200 ANSI lumens. I'd guess your PJ has peak lumens of about 300. Assuming that 84" means a 4:3 screen, then I bet you are getting right around 3-4 ftL, which is a good bit shy of the 12-14 we shoot for!

[ecrabb]

Don't forget gain, though Dave. The old Advents were sold with curved silver screens. Not sure what the gain on those was, but I'd bet maybe 3 or more. They had a pretty narrow viewing cone. At 3.0 gain, that would put your 3-4 ftL figure at 9-12 ftL, which isn't probably far off reality.

From my memory (admittedly, it was a LONG time ago), my dad's old Advent had to appear about as bright on the little curved screen as my G70 does now. I think I'm pretty close to 12. The silver screen was nice back in the day. We used to watch TV all the time with the lights on eating pizza on Friday night. Rockford Files... ABC Sunday Night Movie... those were the days.

SC

[Person99]

Good point.

[kal]

So to answer your original question: The device to use is a "Colorimeter". To see which is the lowest price reliable one recommended, see the first link in my signature.

Kal

[kal]

So to answer your original question: The device to use is a "Colorimeter". To see which is the lowest price reliable one recommended, see the first link in my signature.

Kal

[Gino]

I thought you'd want to use a luxmeter? I know you can use a colorimeter, but luxmeters often give you the lumen or ftL reading on their inbuilt display.

[David_Web]

Yes you need to use a lux meter.
Then multiply the value with the size of the lit up area in m^2

I would divide the area into 9 parts and measure 9 points and multiply each point with 1/9 if the total area.
lumen = lux*m^2

You could use luminance to show the light the screen would spit back at you but it would only be relative.
If you know the properties of the screen you could calculate the lumen needed to make that luminance but it's a little more complicated.

[Advent Videobeam]

Hello Ecrabb,

It's good to here from you again. It's cool your Dad actually had an Advent! What model did he have??

I keep correspondance with an engineer formerly from advent that's still in the CRT A/V industry. He says the original screen has a gain of ten when FLAT. I tried to deny it at first, but the screen is such an important part of an Advent having a great picture= the screen GAIN. I have devised serveral screen surface replacements, and the intial tests look great. I'll post some screen shot pics of Advent in action when calibration is done.

Most screens with high gain have a limited cone viewing area. I tried a sample of the expensive Supernova screen material. Similiar to the advent screen concept of a silver screen surface, has a gain of 5.8 as a flat surface. Someone at Advent really knew screen technology!!


It's a shame these other high gain screen materials didn't come out sooner for the older PJs . The original screen was easily damaged and soiled, not servicable. The whole effort of replacement surface arised when my screen surface was damaged in a few areas. The screen is dirty too and no real way of cleaning that aluminum surface was revealed when screen border plastic was pulled back showing what the screen surface SHOULD look like.

Does anyone have any old GOOD screen shots of these Advents in good working condition to post here please. David webb, that last part of math is M(m is?) (what does symbol mean?)times two?? please explain and clarify so I can do calculations with measurements.

Thanks

[David_Web]

m^2 is meters squared.

Let's say that your screen is 1 meter high and 1.8 meter wide. It will have a surface area of 1 * 1.8 = 1.8m^2 = 1.8 square meter.
Let's say that the projector managed to put out 100 lux in average on the entire screen. That would be 100 lux * 1.8 square meter = 180 lumen.

It should have been: lumen = lux/m^2 and as I understand it it should be read: lumen = lux per square meter.

[rickycleung]

I have an old Minolta fash/day light electronic meter that are used for photography. Its a functional meter in the past. Can this light meter used to check PJ Lumen? What kind of reading I look for in the light meter that it can check Lumen?

[David_Web]

You can't check lumen with any light meter apart from an integrating sphere.
However you can calculate it as shown.

Your meter could be used to measure ether lux or luminance depending on how it works.
Do note that it will not be very accurate as the lux or luminance at the screen is not that high.

This should get you on the right track.
http://www.fredparker.com/ultexp1.htm#EXPOSURE%20FACTOR%20RELATIONSHIP%20CHART%20B

[rickycleung]

[tse]

Screen size in square feet x footlamberts = lumens

Use a light meter that measures footlamberts like:

http://se.konicaminolta.us/products/industrial_light_meters/ls_100/index.html

Scott

[David_Web]

That is not an integrating sphere but it sounds like a light meter. What unit does it show?
It might not do very well in a dark room though unless you can change it's sensitivity.

[Advent Videobeam]

Helllo everyone,

I have been pleasantly surprised to recently find a Zenith 810 CRT PJ I owned years ago still working!! Zenith really made great TVs and this have zenith CRTs and zenith service modules. Modules may have been replaced, doesn't look like it and no repairs evident. It's amazing since this has a 1986 date code. I haggled and picked this up at a charity which had a high price on it. I almost passed it up for this reason. I mentioned to saleperson these have little to no parts still available, he was motivated and sold it to me for $20! I purchased this same set from a private A/V dealer 12 years ago for $600!

It was great, I had it set up for a 100 inch image, setup in special cabinet to hold it at right height parallel to the wall projected. I touched up convegergence as much as possible.
Reliable and never failed, I eventually sold it to a real estate person when moved for a fair amount since se twas setup nicely. I realized the same set at home when displayed the same CRT wear as years ago and same control setup. I removed the cover to attempt to find adjustments and do good dust cleaning due to age.

I discovered each CRT can be accurately focused when other two are masked. The slowly adjusting the U.S. Lens accurately for that projected image size. With the focus properly setup and razor sharp , the convergence I can't find adjustments to move the 3 colors horizontally image wise for the different image sizes tthe lenses allow for? Can someone chime in who has one OR can help, the modules have a lack of control labling period.

the Green CRT is strongest, Picture is awesome, I'm ACTUALLY using my videobeam screen w/ zenith PJ til my advent unit is fixed with small amount of image distortion.

This has wear but is relatively as bright as the videobeam 1000A w/ good tubes, maybe 2 to 5 times bighter? Seems in ball park as my older advent set, how do they measure lumens? I recently saw a sony d50htu pj for sale, the shopping dots comm site staed this PJ has only a spec of 160 lumens, the picture is fantastic tho. Not a world of difference in terms of brightness between this zenith and my ancient beast. The wikepedia post of 50 lumens I believe is FALSE for videobeam. When operational, a 40 watt lamp washing out some of the image --could be on Opposite of screen, which is not preferred.

Anyone visiting bright and sunny CA can see my videobeam which I believe 50 lumens. The original screen surface is redone in silver reflective paint to keep gain charactistics while allowing surface to be cleaned w/ a damp cloth.

I'm really interested in a measuring standard and equipment used for this number.That Sony Lumens seem pretty low, I'm sure the image is near flawless.