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Erläuterungen zu diesen US-AUDIO Seiten der 1950er Jahre

Die hier stehenden amerikanischen Artikel aus 1959 (aus der US-AUDIO) sind teilweise sehr gewöhnungsbedürftig, weil sie erstens aus einer längst vergangenen Zeit stammen und zweitens, weil dort in den USA ganz "anders" gedacht wurde als bei uns in Old Germany oder in Europa.

Vergleichbar mit unseren deutschen Hifi-Magazinen etwa ab 1962 ist jedoch, daß auch diese Zeitschrift ihre Anzeigen- Kunden und -Leser (be- oder ab- ?) werben mußte. - Weiterhin sind die Dimensionen des amerikanischen Kontinents mit den unseren hier in Europa nicht vergleichbar. - Ein Redaktions-"Trip" von New York nach Los Angeles oder Chicago oder gar in die Wüste nach Las-Vegas zu einer der CES- Audio- "Shows" war - auch mit dem Flugzeug - immer noch eine Weltreise. Und jede Ausstellung oder "Messe" wurde als "Show" deklariert. Und natürlich, in USA musste alles "Show" sein, um beim Publikum einige Aufmerksamkeit zu erzeugen.

Der Autor Edward Tatnall Canby schreibt jeden Monat "AUDIO"

Sowohl in den monatlichen EDITOR's REVIEW's als auch in den monatlichen ETC's lesen wir ein Stück amerikanischer Gesellschaftsgeschichte vom Ende der 1950er Jahre. Dazu gehören auch die frühen monatlichen Schallplattenbesprechungen, in denen sehr viel Wissen rund um die Musik, die Gesellschaft und die Hifi-Technik eingeflochten wird.


AUDIO ETC ("Edward Tatnall Canby") - Kolumne


  • "It is with a great deal of pleasure that I read your recent article pertaining to stereo photography. I, too, am the owner of a stereo camera ...."
  • "I read with ... interest, on page 10 of the January (1959) Audio, of your success with stereo projection. I have enjoyed stereo pictures for years ... but have tried unsuccessfully to get a recommendation, even from the Eastman Kodak Company, on a projector. I think you would please many Audio fans if you would tell us what equipment you use ..."
  • "So you also are keen on colour photography! (This from England.) I'm just starting to play with stereo pictures ... I've not yet got around to projecting them ..."


When your "Stereo-Sound" sounds never ....

Well, there you have a few yelps of delight from an obviously frustrated minority and, you see, it's just as I said. Stereo photography, big biz has decided, is not for the Great American Public, and so, down with it; the People say, NO. But some of them, in small, anguished voices, still say yes.

With a pious hope that our own stereo sound will never, but never, be reduced to this sad state (as per the January Audio, ETC.) I bow to the inevitable, invoke my useful escape clause -  that "etc" in its alternative meaning of et cetera - and herewith toss a few ideas to the ravening hordes of stereo camera bugs. I'm probably the only guy left who has a kind word to say in print for stereo. Stereo pictures, that is. And I am dead-certainly the only person who has ever come out for stereo projection in a magazine about audio. Deny that if you dare.


Projection, in fact, is what's on my mind but first a bit of foreground.

Anybody can look at stereo through a viewer, and get the best possible stereo in this imperfect world. Nothing can beat it. Only those who have (a) one eye or (b) two eyes that habitually don't operate together (one goes psychologically blind) will find themselves constitutionally unable to get a stereo effect.

The second category, I've found, includes a remarkably large number of souls, most of whom don't even know they lack stereo vision. They always exclaim how pretty the pictures are and it's only when you quiz them very specifically about certain perspective details, like say, a branch of a tree that seems to be hitting you in the eye in the foreground, that you uncover a certain vagueness.

Pretty soon you begin to suspect that something isn't right, but it is amazing how hard it is to pin down the stereo-less pair of eyes. It's like color blindness, which even in this day of red and green traffic lights can go unsuspected for an astonishingly long slice of life in many people.

Wenn "sie" nichts sehen, dann halte ich einfach meinen Mund ....

I usually shut up and say no more when I begin to realize that a given person simply is not seeing stereo. That's the only tactful thing to do.

After all, if they can't tell the difference, why be brutal. Some stereo newcomers are so very polite that it may take you a dozen pictures to find out that they are actually seeing everything double, and unregistered.

These nice people, after oohing and aahing about the beautiful photography and the lovely colors for ten or fifteen minutes, are apt to disclose, purely incidentally, that of course they are closing one eye - aren't you supposed to do that?

"Why, I see double if both eyes are opened. I thought it was so you could rest one eye at a time. . . ." Amazing what sheeplike virtues some people have! And no wonder stereo photography was sold down the river by the big operators. Even sheep protest, eventually.


The only proper type of viewer is that which has a built-in house-current light supply, via a small 80-volt bulb and a rheostat to adjust the amount of light. The bulb may be small but its light is still enormously more powerful that that of the battery-powered viewer light, the flashlight type. Once you've used the plug-in house current system, you'll never go back to batteries except for emergencies or extreme portability.

There's a major trouble with the plug-in light. Its color is wrong. Too yellow. (The flashlight bulb is beautifully white, at least for the first few minutes, before it begins to run the batteries down). When you reduce the light's brightness via the silly "volume control" (ein früher Dimmer), the color gets "yellower" (ohweh = gelber !!) still.

The only proper rheostat position is wide-open, at full voltage. I have a simple "solution" for this, speaking quite literally. Take out your bulb and dip it in blue ink, let it drip off and dry. Then you'll have a fine, soft, blue-white light that is exactly right.

True, the bulbs blow sooner (you'll need a half-dozen extras on hand) and the ink tends to turn dark. But you can wash it off and start again any time. With the inky bulb you'll finally get away from those yellow-orange sky effects that mar stereo viewing in so many viewers. (Why don't they make a blue bulb? Too much trouble, I guess.)

Es gibt noch zwei Rädchen an Deinem DIA-Betrachter

You'll note two adjustments on viewers, that for the separation of the lenses and that for focus. They can throw any new user into a tizzy, unless you demonstrate them one at a time. Start with a fixed focus - i.e., don't mention it at all - and have the viewer wiggle the separation lever
until he begins to find a good resting place that joins the two pictures comfortably. (Be sure the slide is in all the way, the two pictures aligned; better try it yourself first, to be sure.)

Then when conjunction is accomplished - if you get that far - point out the focus knob and let him play with it. After that, don't move anything. And if the pictures just won't join, or the person starts saying how lovely, with that vague, uneasy smile that says trouble is being concealed, just quietly change the subject. (..... dann leite über zum Wetter oder zum Abendessen).

Maybe it's time for dinner; or have you seen my new stereo hi-fi system yet? Pardon me - T mean heard. Xo use going on if the patient evinces symptoms of anastereoitis.


The viewer, one-person-at-a-time, is the only way really to see stereo. The viewed image is far superior to the projected image in a number of ways. It is sharper and clearer, but also, more important, it is relatively much larger; it fills a far greater area of the visual field.

A stereo picture inside a viewer is, let's say, roughly equivalent to a nine-foot-square image on a screen at about ten feet. Huge. Details are infinitely better in the resolution via the viewer than via projection, and (with Kodachrome) details are the very essence of good stereo.

To be able to recognize a person at a distance of a quarter mile via a stereo viewer is really something, but the magnification and the sharp detail (via a good lense) makes it quite possible. Same with distant mountains, pin-point houses across a Avide valley, distant signs, etc.

Incidentally, I use only Kodachrome.

Grainy color films are taboo in stereo - the magnification (via viewer) is enormously too great and you can practically count the dots. Kodachrome has no dots: it is a dye picture and, if I'm right, has practically infinite detail resolution. It is absolutely amazing to look at a Kodachrome 35mm picture with the naked eye and see how incredibly tiny are some of the clear details that can be seen and resolved via the huge viewer magnification.

Incidentally too - while I'm at it - I use Kodachrome not because it gives a true color value but because the exaggerated Kodachrome colors are absolutely first rate for dramatic emphasis in the peculiar stereo visual medium.

Stereo-Dias im Vergleich mit Stereo-Sound

This is an interesting point and has a direct analogical relation to the same thing in sound recording. In stereo pictures, there are many missing elements  - motion above all, but also the more subtle sense of actual happening, of life itself, including the accompanying sounds. The picture has depth, but is still a picture. For emphasis and dramatic force, then, a stereo picture - any sort of picture - must make up for the lack by plugging, exaggerating what it has. That's where the art comes in. Same thing in recording.

Kodachrome rightly plays up color values (though with good color balance) and legitimately gives a heightened sense of drama to good stereo photography. In the same way, close-up mike technique, blown-up volume on solos, on opera singers, solo instruments with orchestra, distorts "reality" but adds legitimate drama and force to reproduced sound, for a truer emotional projection of the musical effect. So I'm all for Kodachrome's color, though many people deplore it, just as I am all for dramatic mike techniques in recording, though they are far from literal-minded.

  • Anmerkung : Das stimmt nur so lange, wie man den Vergleich mit dem AGFA Chrome 100 nicht hatte. Denn der Kodak Film war immer sehr blaulastig.


Back to the stereo viewer.

It is best for one major reason above all others - it is the only form of stereo viewing that does not distort the optical values of the pictures. It sees virtually what the camera saw, the depth and width in proper relaition, and this even though in some cases the point of infinity - the sky, or background - is actually at a distance of only six inches or so.

In effect, you look at a small model of the actual scene in these cases; but it is an accurate model with the basic spatial relationships essentially correct from side to side and front to back, give or take a bit of false curvature.

In a viewer rightly built and rightly used the infinity point for your eyes is at infinity, and all nearer points are very nearly where they should be. Your "model" is as large as life. (Differences between camera eon-figurations and viewer optics account for these effects.)

Social or Antisocial

So - today's big question - why project? (die Projektion) Why, if projection fuzzes up the details, grossly distorts the spatial effect most of the time, gives far too small a picture, requires messy glasses that cost too much (Polaroid's tight little monopoly) and generally hurts the eyes beyond bearing -  why bother?

For only two reasons. One is overpower-ingly important. Stereo projection is social. Two or more people may enjoy a picture at the same time. I've coped with as many as sixty.

Viewer stereo is strictly antisocial. One person at a time, exclusive, solitary - or just a plain nuisance, when several people are trying to get into the act.

If you've stood next to a joyful friend, buried in your stereo viewer, who keeps shouting "Oh, and what's that little thing up there, and who's this, down in the right hand corner?" when you haven't the faintest idea what picture is being looked at, you'll know what I mean.

Or if you've seen a flock of avid souls tearing your pictures apart, pushing them in and out of the viewer, upside-down, backwards, reversed, greasy fingers always squarely on the film surface, dropping slides on the floor and stepping on them in their eagerness to be next in line . . . well, that's antisocial viewing. It's anti-you, more than anything else. It hurts.

Beschrifte Deine DIAs - aber kurz und knapp

So stereo picture makers tend to develop into hermits. They retire to a safe, lonely place and lose themselves happily in their solitary hobby.

Wonderful, but not for parties. Even one extra is trouble enough. I have two suggestions here - before I get to a second pro-projection argument. First, write brief captions on your slides, and do it on the slide face that must be towards your eyes. Make them short, readable, simple. It's hard enough to get people to look out of their viewer anyhow - it hurts the eyes; the quick change from the inner infinity focus to the outer close-up is tough on most people and they won't read your titles at all unless prompted. But if you say to them, "Just put the slides in with the captions facing you and right-side-up"  - then they'll more or less have to read them. And you'll have a minimum of upside down, backwards pictures.

Don't write "View towards the Southwestern corner of the Sierra Madre range, taken from our little summer cabin on the slopes of Mount Dinky doodle, July, 1958." (You won't have room anyhow.) But compress : "Sierra Madre. Cabin. 1958." That does it.

Secondly, if you are showing pictures to a friend in person, the thing to do is to have your own viewer (that's where my old battery-powered viewer comes in handy). Look at each picture yourself first, in the viewer; then pass it on to your friend with I its image fresh in your mind. This works
wonders. You can even do it with two people, in tandem, if you hold back each new picture until both have seen the preceding one.


To return to where I was - the second good reason for stereo projection is utterly simple. For all its faults, with all its grave difficulties, it can be made to work - if you are lucky. You can be social, and you can do it successfully. You can entertain from six to sixty simultaneously and emerge with a good passing grade of blessings and a minor proportion of curses, plus a few blissful sleepers - somebody always takes advantage of the darkness for a quiet snooze. If stereo projection works at all, it's worth the time and trouble.

But, boy, do you have problems en route. The first is to get a stereo projector over the loud objections of the photography dealers, who will tell you. of course, that it is hopelessly impractical and they wouldn't touch a stereo projector with a fifty-foot pole.

The second is to get a stereo screen, which must be silvered, since beaded screens will not work. The third is to get stereo glasses. Plastic ones, fragile as air, a blasted nuisance at best and they cost around 20 cents a pair. I use 'em. Glass ones cost a mere of $3 or so apiece, which will put you in the broke category before you even get started.

I have one glass pair -  for myself. At least it doesn't fall off my nose when I'm trying to work the projector. The rest are plastic, some of the clip-on type, some entirely frameless (wear your right arm out holding 'em - I use these on kids) and a few with plastic side-arms that keep falling off. Phooey! They do make things hard for you.

If you like to buy a Stereo-projector

Whether you can still buy this sort of equipment, as things now stand, I don't know. When a commercial boomlet like stereo collapses, it busts wide open. (Again, keep my moral in mind.) Maybe you can't find any of it and the discussion is academic. But the chances are that you'll find what you want if you persist. The reputable stereo makers - those from the pre-boom days - still make cameras, notably the Stereo Realist people, and if you look hard, and brave the dealers' displeasure often enough, you'll locate the rest even if it has to be in the second hand market.

My first stereo projector was nearly a total flop.

My first stereo projector, a pure boom product and a disgrace to any industry (like some of our present gimcrack stereo phonographs) was nearly a total flop. It was an outrageously crude bit of expensive gadgetry. For $100 or so you got a shaky pair of 300-watt optical systems in a giant framework, intended tantalizingly to project stereo on a screen or, via a reflector, onto a rear-facing ground glass about a foot square.

The ground glass was useless (too small for good viewing, even by one or two people) and the machine itself was so flimsy that if you picked it up too hastily the frame buckled and the ventilating fan blades sideswiped their crude mountings with a screetch.

It was pinned together with those little flat pieces of metal split in the middle that pass for nuts in gimcrack construction. What's more, 300 watts per "channel" was not enough for projection (with those lenses, anyhow). And the picture adjustment controls promptly stripped their gears, letting one picture suddenly drop down a foot on the screen each time a cog slipped.

But I had seen possibilities (I must have been the only person who did). I went forth again, licking my wounds, and got me a real prize. The "Nord stereo projector", costing me half as much, was smaller, neater, lighter, with two 500-watt bulbs and plenty of screen illumination. (You need a lot because of the double loss in the two pairs of Polaroid filters, one in the projector, the other in the glasses you wear). It was solid, rigid, adequately ventilated and with good controls - an excellent machine.

Mein Projektor war ein Auslaufmodell

Unfortunately, it was being discontinued. The stereo boom was already about to die. Just in case, the Nord stereo projector was made by the North Star Specialties Co. of Minneapolis. Maybe you can dig one up (wir sind immer noch in 1959 und es gab da kein Internet), or persuade the company to turn out a few more. This was a fine example of a legitimate consumer product orphaned, so to speak, by the ruthless overexploitation that killed the stereo boom. We could see the same in stereo sound.

My only complaint about the Nord is that I haven't figured a way to operate it without getting a blast of hot air in my face from the ventilating slats on top -  not to mention a bright beam of light. Maybe it's just because I'm left handed. I don't mind too much, as long as my guests are happy with the pictures.

Stereo-Brillen ??

Glasses? I offer you little hope, but maybe you can locate some in one or another store. I keep picking them up, a few at a time. They still sell, here and there. If you're desperate, you can stage a raid on one of the current revivals of those dreadful 3-D movies ("The House of Wax"  - was that one?) and collect the glasses they pass out there. Or you can always get the 3$ glass models.

Screens? No problem except in cost. Silvered screens aren't hard to get. But be sure to get the biggest screen you can possibly afford. This is vital for stereo projection. I don't recommend any stereo projection on a screen less than 50" square. That's big, though bigger is even better. You can probably get a "stereophile net" discount if you're lucky, about as in the audio field. I did.

Depth Distortion - sehr ähnlich zum Hören

And so - stereo projection. First of all, you must understand that the stereo picture on the screen is variously distorted, at times to an almost ludicrous extent. The optics involved are just plain cockeyed.

Not easy to figure out in detail for most of us, but one thing is immediately clear as you move about your stereo room. There is a single theoretical point where distortion is reasonably minimum and that is the spot where you are as "close" to the picture as you would be inside the stereo hand viewer.

A nine-foot picture at ten feet - or a four-foot picture at about five feet, roughly speaking! All other, more distant positions offer compromises, and it isn't just a matter of brightness and image-size, either. Distortion of perspective is fantastic.

As you move away from the stereo screen, the sidewise dimension seems to get smaller. So does any screened picture. The further back you sit, the smaller the picture.

Nur zwei Dimensionen bei der konventionellen Projektion

Now in the conventional projection, you are dealing only with the two flat dimensions and the entire picture on the screen is reduced strictly in proportion.

The only distortion you find is the relatively slight effect of watching your pictures from one side, at an angle. Not too serious until the angle becomes acute, as we know from movie theatre experience.

In fact, the main practical difficulty is a loss of brightness in the image. We can take the sidewise distortion aspect without even noticing it.

But stereo projection is utterly different. It involves the third dimension - depth. And in the projection, that dimension never varies in apparent measurement, regardless of your distance from the screen! As you move back in the room, the sidewise and up-and-down size of the picture decreases, but the depth remains exactly the same.

Therefore, a stereo picture from a distance has a violently distorted and grossly exaggerated depth. By "gross" I mean a lot. For if your picture is reduced (as you see it) to one quarter size, the depth dimension is relatively quadrupled. A picture of a square plot of grass shows as an oblong, four times as long in depth as in width - and a city block is four blocks long. Nearby backgrounds, recede to near-infinity, foregrounds are monstrous.

I'll never forget my first stereo projected picture, in a large lecture hall! It was of the Taj Mahal, and the ratio of dimensions from where I sat was about 1:16. The photo showed a huge, wide plaza that stretched about ten miles back and at the far end was a tiny little building as big as your thumb. That projectionist didn't have the faintest idea what he was doing.

Close-up Window

So you will begin to see where all this leads to. If you are to have something near a 1:1 relationship between the dimensions in your picture, you must be really close to the screen, so that the sidewise dimension is big enough to match the unchanging front-to-back one. As I say, that means right down in front.

Or, alternatively, further back, with a LARGE screen, the projector far enough away to fill it to the maximum. You must at once throw out all your ordinary conceptions of picture projection, start thinking from scratch. In this medium, you don't look at the screen; you look through it - or sometimes in front of it.

Since you look through the stereo screen, this immediately poses another new conception. It is, of course, a window, not a flat surface. The window concept is essential in your stereo thinking.

Deine Bildwand ist wie ein großes Fenster

Now, how big must a window be, to see out of? If you will visualize for yourself the "size" of an actual window, related to your own inner field of vision, you'll see at once that an ordinary home movie screen, maybe three feet on a side and ten or fifteen feet away, is like looking outdoors from your living room armchair through a six-inch hole in the wall, more or less.

Your overpowering need in such a circumstance (given a pretty view to look at) is to get up closer, make the window seem bigger. Or to cut a larger hole in your wall and stay in the same place.

One odd feature of this aspect. You'll find that you can walk right up to a stereo screen and look at parts of the picture (into, I should say) from only two or three feet away. The only limitation is the graininess of the screen surface and the fuzziness of the projected image itself.

This is due to a curious psychological fact. If the depth dimension is less than the sidewise one - if the picture is wider than it is deep - you are not aware of distortion.

We are entirely used to this situation. We see it as a sort of low-relief effect, a step between normal depth and no depth at all, i.e., the ordinary "flat" picture. We accept partial depth and, indeed, find it very natural and satisfactory. But just try a wee bit of exaggerated depth and your eye goes crazy. Dreadfully distorted!

Pointing to Hifi-Stereo

- Which only goes to show that in this particular area, as in our own area of reproduced music, the objective facts of "hi-fi" reproduction must always be tempered by the strange interpretations of the human mind. If it seems good to us, then it is good. As old readers know, this has always been my philosophy concerning "hi-fi."

Setting Up my screen - affordable

You now have the basic material to anticipate my own variety of stereo projection set-up. I threw out my first screen, normal room size, and got me a 50" x 50", the largest I could dig up in regular stocks. I would prefer something at least six feet by six, but haven't the loose cash to sink into one.

Worauf zu achten wäre ....

Take the longest possible throw you can find, between screen and projector, in your home - usually a diagonal, possibly involving a hallway. Put the projector back, the screen forward, and a bit high. Fill the screen full-size, even slightly larger, cropping off a few minor details around the edges. (You can lift the projector occasionally, if need be.) It won't matter if the viewers in front have to look uphill a bit.

Your chairs should, as always, be clustered around the center line (mount the projector high, too, to send the beam over the taller heads) BUT, put everybody up forward. Concentrate the entire audience well in front of the projector.

Put the majority, if you can, near or beyond the point where the size ratio is 1:1 - which means practically at the screen. Resist people's natural tendency to sit around the back and sides of the room. They'll get that six-inch window effect and the distorted depth. Put all the kids on the floor, practically at the foot of the screen. They'll love it. Keep the picture BIG, for each and every member of your audience.

Das obige gilt für alle außer Dir selbst

Except, of course, yourself. You have to be back at the projector, and you'll have a job trying to focus and blend the pair of pictures at this disadvantageous distance. Try to stand in front of the projector and reach back towards it. Not easy! Leave a space so you can walk forward a few feet to view the effect at a better nearness.

And there you have it. I won't impose on our audio friends much further except to suggest a couple of adjustments that are vital. The projector has, in addition to a joint focus knob (like a ganged stereo volume control in "our" stereo), a separation control, spreading the two pictures sidewise, and an up-and-down adjustment, to register the inevitable misfits, where one picture comes on the screen higher than the other. It takes a lot of knack to operate these quickly and surely. And the focus must be adjusted constantly, too , for accurate detail in the relatively enormous enlargement you are producing for your viewers - much greater than with "flat" screen projection. Three knobs, all to be juggled at once.

In showing pictures (you will have checked them over ahead of time, if you are a better man than I), start with the up-and-down alignment. That hurts most when it is out. As the picture appears, quickly move the up-and-down knob until some visible point in both pictures is level  - say a mountain top or the peak of a house roof, or a human head. Look over the top of your glasses, so you can see both images. This is the absolute first necessity  - and virtually every picture will need adjustment. The two pictures overlap dizzily - but they must be on a level with each other.

Second, quickly adjust focus, if needed. Many films tend to "pop" with the sudden heat and must be re-focussed, a problem common in all projection.
Third, SLOWLY adjust the sidewise separation of the picture for optimum effect. And thereby hangs my final pointer.

Push-pull Perspective

In the pair of stereo pictures no two points are precisely the same. Join together a post in the foreground so the two pictures coincide on the screen, and the mountains in the background will be separated a couple of inches in the actual images. Join the mountains (infinity) and the posts will stand apart, as you look without glasses. These differences, of course, constitute the stereo element itself, the depth-producing effect, and they correspond very closely to the differences in phase between Channel A and Channel B in our stereo sound signals. They can't all be in phase at once - or the two photos would be identical, as would our two sound channels. A striking and interesting parallel here, to think about.

There is even "phase reversal" in stereo photography. If you mount your picture wrongly left to right - "reverse the speakers" - you will get inverted depth. Trees are at the back of deep slots in the sky, which is in the foreground. Mountains are cardboard cut-outs standing in front of the clouds above them. (Black-and-white, or shadow perspective remains normal, of course, and the two types fight each other. Same is true of stereo sound in reversed phase. Some effects are more or less normal; others are reversed, inside out.)

How (to return) do you know which parts of the overlapping images on the stereo screen to make coincide? Should the background match, the two pictures actually hitting the same spot on the screen? Or foreground objects? You have a very wide range of choice, via the separation control. (It moves the lenses.) And you have a fairly wide range of choice in the viewing itself. The eye is remarkably adaptable.

Think of it in this simple way. You are looking through your screen, into depth -  you may even look in front of it, at a virtual image in the air. The screen itself is merely an accidental point, the frame of the window, the window glass.

Endlich zum Ende des Artikel

The point at which your two images coincide is always seen at the screen. Other points are in front or in back, according to their natural separation.

Therefore, if you wish your infinity to be where it belongs - through and beyond the screen - you must make some of the nearer points coincide. With projection's exaggerated sort of perspective, some nearby points may be too close for the eyes to join - you have to push them back a bit.

As you turn the separation adjustment (sliding the overlapping pictures together or apart by about a foot or more in normal viewing) the screen-point, in the viewed picture, is nearer or further. Bring them closer together (looking at them outside of your stereo glasses) and you move the entire picture forward. You can put your mountains right at the screen if you want, the rest floating in front of them, sort of miniature; but don't do it.

The best technique for average pictures is to choose a nearby object, perhaps eight or ten feet away from the camera, and join its two images so they coincide on the screen. Then all the rest of the picture will fall into place, most of it behind the screen, with infinity in its proper distant location. The eyes can take a certain amount of nearer foreground in front of the screen without noticing it.
If, however, there are violent contrasts, with some objects very near - a close-up leafy branch, a person's arm - you must push the whole picture further back, or the exaggeration will be too much for the eyes and the pictures won't join. Wider separation. Same with close-up pictures of people, minus distant background: push them back behind the screen, via wider separation.
You'll quickly find that in most ordinary outdoor pictures you can take a quick look (outside your glasses) at the background, spread its points apart about two or three inches, and infinity will be where it belongs, the rest in place. But you must be ready for quick adjustments.

And if your two loudspeakers seem to spread that string quartet out into a twenty-foot line of players five feet apart, if the stereo Steinway sounds as if the keyboard were forty feet wide, then slide your two speakers closer togeth -  hey! I've slipped into the wrong kind of stereo.

From here on, we'd better keep them well separated.

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