Time warp: Rear Projection TVs

In between the venerable CRT TV and modern plasma or LCD TV, there was a briefly popular display technology called RPTV – the Rear Projection TV.

To be fair, it hasn’t completely disappeared, but it will because just about everything it could do, plasma and LCD can do better.

RPTV came about because people wanted a big TV picture, and you simply couldn’t get a big one with CRT tellies. Once we did see one glass tube TV that offered a standard definition 97 cm widescreen picture. It was well over 600mm deep and weighed 92 kg! It was not the least bit practical in the home.

RPTVs first appeared in the 1970s, but you weren’t likely to see one of those in your home. They were too big, too bulky and too bad. Analog TV didn’t scale up very well to a large screen, so having a big screen in your lounge room gave you a fuzzy, noisy picture. We didn’t even have colour until halfway through the decade!

However, in the 1980s and 1990s they became useful in clubs for showing sporting events to large numbers of people.

As time went on, even analog TV gradually improved and smaller size RPTVs began to be viable. At a time when a large TV had a screen size of 66 cm in 4:3 aspect ratio, a 110 cm RPTV was impressive. At the same time, improvements in design allowed them to be thinner, so that they weren’t too bulky when pushed up against a wall.

Finally, in the late 1990s the DVD arrived, followed soon after by digital TV. Only with RPTV could you enjoy a large video image with decent quality. At this point the plasma display was just starting to appear, and cost tens of thousands of dollars, and the large screen LCD TV was still some years off in the future. For home theatre, RPTV ruled.

So what was an RPTV? It was simply a projector in a box. It bounced its image from a mirror so that it struck the rear of a translucent screen. Its electronics flipped the image so that it looked the right way around to the viewers.

But what kind of projector? Initially there was only the CRT projector: three glass tube CRT guns, one each for red, green and blue. Like regular TVs, these had the advantage of easily producing excellent levels of black, but they were rather weak. Since brightness was a problem, the translucent screen was designed to direct the light more or less directly forward. If you looked down at the screen from an angle, the picture was quite dark, so the vertical viewing angle was narrow.

And in almost all cases, these were limited, like most regular TVs, to SDTV resolution.

Later all the different front projector technologies migrated into the boxes of RPTVs: LCD, DLP, LCoS. Each had similar advantages and disadvantages to their front projection versions. In general, DLP gave better black levels and richer colours than LCD, but cost more and could generate the dreaded ‘Rainbow Effect’.

LCoS (Liquid Crystal on Silicon) was just a bit too late to appear in more than a very few models.

Brighter than CRT RPTVs, they could still get away with less powerful lamps than those used in front projectors, so they typically had a lamp life of 8,000 hours rather than 2,000.

But even though newer designs reduced the depths of their cabinets to only 200 to 300 millimetres, in the end they could not compete with plasma and LCD panels, which start at 120 mm and can now be as slim as 30 mm.