Does HDTV Mean Big Screen TV?
© April 15, 1998 by David Broberg
As you’ve heard before, HDTV is not about more detail, it is about a larger field of view. A good analogy is to think of your TV screen like a window to a beautiful mountain-view. Your 27" screen represents a small window. If you remodel your house and make a big picture window, you don’t see the mountain any more clearly, but you see a bigger field of view and you see more information. This is how HDTV works.
The design limit for NTSC television has always been 7x picture height. That means that your ideal viewing distance should be 7x the height of the picture. Or about 9-1/2 feet for a 27" screen. Sit any closer and you will begin to see the line structure and the cross-color errors. For big screen TVs with good comb filters the accepted limit has been pushed to about 5x picture height. But many people still find this to be a "fuzzy" image and reject the notion of TVs that big, consequently only about 5 – 7 million homes enjoy NTSC Big-Screen TVs.
HDTV promises to change that by allowing a bigger "picture window" view which has a design limit of about 3x picture height (for the maximum resolution of 1920 x 1080). This means that the same viewer who was happy with the picture quality on his 27" TV at 9-1/2 feet away, needs a much bigger screen.
How much bigger?
I did some calculations (chart below) and they reveal that this customer now needs a 73" HDTV screen! This assumes the new screen is 16x9 and the customer will enjoy the same optical clarity from the same viewing distance as before. This is startling news to many people.
The consequence of these calculations is that there is really no need for HDTV screens smaller than about 55", unless of course you are sitting with your nose to the screen. Remember the 3x picture height design rule for HD? A 32" HDTV screen (as some companies are proposing) has an ideal viewing distance of less than 4 feet!
For another example, look at a typical big screen customer today: They may have a 50" (4x3) set with a comfortable viewing distance of about 12.5 feet. What can he expect when he upgrades to the HDTV? If he chooses a 60" model, he will still be sitting at 5x picture height and will have the same image size for 4:3 images, but he will be beyond the design limit (3x) of the display, instead of inside it. When he gets up to get close to the set, he will see more detail, not more distortion.
Here’s the chart. I hope this can be helpful in selecting your next HDTV.
| NTSC (4x3) Viewing Distance | HDTV (16x9) Viewing Distance | ||||||
| Diagonal Screen | 5x height | 7x height | Diagonal Screen | 3x height | 5x height | ||
| 80" | 20 feet | 28 ft | 73" | 9 ft | 15 ft | ||
| 70" | 17.5 ft | 24.5 ft | 60" | 7.35 ft | 12.25 ft | ||
| 60" | 15 ft | 21 ft | 55" | 6.75 ft | 11.25 ft | ||
| 55" | 13.75 ft | 19.25 ft | 40" | 4.9 ft | 8.2 ft | ||
| 50" | 12.5 ft | 17.5 ft | 36" | 4.4 ft | 7.4 ft | ||
| 45" | 11.25 ft | 15.75 ft | 32" | 3.9 ft | 6.5 ft | ||
| 40" | 10 ft | 14 ft | |||||
| 36" | 9 ft | 12.6 ft | |||||
| 32" | 8 ft | 11.2 ft | |||||
| 27" | 6.75 ft | 9.45 ft | |||||
This article may not be duplicated, reprinted or published in whole or part without express written permission from the author. dbroberg@hotmail.com
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