reddogg blogg

I have broken down choosing a new television into three basic categories; Size, Quality and Price. Of these three basic factors there is typically some compromize between them, even in the extreme case of a real movie theater.

Size does matter, at least within the scope of a home theater. Size is the largest factor affecting your level of immersion. Immersion is the state of being deeply involved or engaged; absorbed and I contend that size is the most important factor people use to determine thier choice of “TV”. Certainly if you look at the CRT rear projection TV’s of the last 10 years people were making huge sacrafices to gain size. Not the least of which is off axis picture quality, which on some displays would render a completely unviewable picture.

Aside from just going with the biggest display you can afford or just going with an eyeball estimation of what looks like a good size there are two important ways to determine the optimal size HDTV or TV for you, Visual Perimeter and Visual Acuity. “Human visual acuity is 20/20 at any distance if the height of the recognized letter or object is such that the visual angle is five minutes of arc or 0.0833°. The visual angle is one of the most practical ways of expressing the quality of human vision. An interesting side note is that, although the total visual perimeter of the eye is approximately 140°, humans really use only the fovea centralis of the eye, the area of best visual acuity. This represents less than 1°, or about 60 minutes of arc. To maximize the eye’s perceived resolution, the eye remains in constant motion, bringing the part of visual interest to the fovea.”

Size and Visual Perimeter : You need two numbers to determine size based on visual perimeter, one is your ‘distance to the TV’ and the other is the ‘viewing angle’. With those two values you can calculate the screen size. Measure from your typical seating position(s) in the room to where you plan on putting the display. It is even good to give a range, for example the range I am dealing with is 5 - 10 feet distance from seating to the screen. The viewing angle is basicaly a measure of how much what you see is represented by the TV. Standards have been set by groups like SMPTE and THX Ltd in reference to viewing angles. THX specifies a recommened minimum of 26 degrees and recommended norm of 36 degrees and SMPTE coincidentally splits the difference at 30 degrees. Now I can take the average seating distance at 7.5 feet against the 30 degree viewing angle and input them into a calculator like the one at Collins’ Cinema. For me this results in a 55″ 16×9 display.

Size and Visual Acuity : In the past on large CRT RPTVs it was common to have a knowledgable salesman recommend a minimum distance you sit from your display. Recently as the number of lines, commonly called resolution, has increased and there is actually a maximum distance you can sit from your HDTV display. If you are purchasing a standard definition (SD, EDTV) display you can pretty much ignore this section. However there is little need to purchase higher resolution if you eye can not dicern the difference from your typical seating position. For instance, for a 50″ display you should be no further than 9 feet away to discern 720 lines and no further than 6 feet away for 1080 lines. An article in Sound and Vision Magazine has some great information on this particular topic.

(original post October 31 2006)