Pros and Cons of making a projection tv

[Darren Nemeth]

Weather is getting nice outside over here in Michigan. Time to make the speaker stands I have been planning on and a couple more projects.

Among one of the projects on my mind is a projection TV as I have been reading about in these forums.

I have some basic questions before I start.

Truthfully, how good is the adverage picture quality of these?

Is the LCD pannel refresh rates good enough to enjoy a movie without distraction or is there a "stammer"?

Are the blacks dark or greyish? It is hard to tell looking at the many images posted here.

Is Lumnivision the way to go or is there other designs that work just as well?

Please forgive me if some of these are in the FAQs. I think I read them all.

Thanks in advance.

 

[Guy Grotke]

some answers

Q. Truthfully, how good is the adverage picture quality of these?

A. It can be fantastic, if you do it right and have a S-video connection from a digital cable box, satellite decoder, or DVD player. My 15" LCD projector has 1024 by 768 pixels: Broadcast TV is more like 320 by 485 pixels!

Q. Is the LCD pannel refresh rates good enough to enjoy a movie without distraction or is there a "stammer"?

A. I think all the 15" LCDs you could start with have response times way too fast to leave trails behind moving objects. Smaller or older LCDs might have a problem with this. Look for a panel with <30 msec response time. There is another effect through, even with a fast panel: There are some small "pixelization" artifacts that you would not be able to see with a slower display technology. This occurs during fast pans in the source image, so it may actually be an artifact of MPEG decoding. I only notice it if I look for it on purpose, but it does bug some people.

Q. Are the blacks dark or greyish? It is hard to tell looking at the many images posted here.

A. Depends on your LCD and optics. 350:1 contrast ratio looks pretty good, but is not quite as good as a CRT display that can actually go down to luminance = 0. But it is still probably better than the maximum contrast available in most home theaters, just from ambient light. Do you watch in total darkness with all your walls painted flat black? If not, then ambient light and light from the screen will bounce off the walls and return to the screen again. That lowers the contrast. Another real issue is that a digital display with 8 bits per color has a step size of 1/256 of full-scale. So the first step above zero is 1/256 of the brightest possible image. Eyes are log devices with much finer response at low illumination levels. Another cause of "greyness" in black areas is the use of a bad projection lens. Lens aberrations can scatter light from illuminated pixels over a large are of the image. But keep in mind that lots of people enjoy their 100:1 contrast ratio OHP panel images.

Unasked Question: How do DIY images compare to those of commercial projectors?

A. Not nearly as bright. You can make a beautiful image with a good DIY projector, but you will never want to watch it with any lights on, or during the day unless you have good blackout curtains.

 

[Crazed_climber]

Guy nice answers do you mind if I use this on the site im building? Its kinda a free guide/info about diy projectors
PS: you'll get full credit

 

[Guy Grotke]

blanket permission

Anything I post on a public forum, may be quoted on a public website, as long as proper attribution is included. That does NOT mean it is all correct! I am a professional programmer, not an optics engineer, so the things I post about DIY projection are just my opinion. Anybody reading them should check other sources, etc. before spending money based on what I wrote.

That said, please feel free to search all the threads for my postings and collect them on your website, if you like.

 

[Crazed_climber]

Thanks man,
I read over your post and it looks correct to me. If and/or when I use it I will give you full credit.