3D Effect vs screen size & Viewing distance - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 5 Old 03-22-2017, 12:01 AM - Thread Starter
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3D Effect vs screen size & Viewing distance

Hi all:

I've been trying for half a day to get more information regarding this topic, but to no avail.

I read this on Optoma's website:
"
Why use a projector for 3D?

It is a widely accepted fact that the bigger the image, the greater the 3D effect - for the best results it is essential to fill your field of vision, without having to be too close to the screen. Even a huge 50” TV can only create a window on the 3D world, whereas the immersion & excitement created by a massive 150” projection screen makes you feel like you are part of the action!
"

I currently own a 3D PC monitor (23"), and a 3D projector that projects out a 86" screen. I have noticed the following relationships (when viewing 3D movies):
- The smaller the screen, the lower the 3D Depth effects
- The nearer you are to the screen, the lower the 3D Depth effects
*Assuming that the source 3D material is identical.

So if I were to believe my anecdotal experience, I find that to get the best 3D depth effect, I need as large a screen as possible, coupled with being as far away from the screen as possible.

Is this correct? is there any information on the web that supports my theory?

Thanks!
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post #2 of 5 Old 03-23-2017, 06:06 AM
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Quote:
Originally Posted by limestone View Post
Hi all:

I've been trying for half a day to get more information regarding this topic, but to no avail.

I read this on Optoma's website:
"
Why use a projector for 3D?

It is a widely accepted fact that the bigger the image, the greater the 3D effect - for the best results it is essential to fill your field of vision, without having to be too close to the screen. Even a huge 50” TV can only create a window on the 3D world, whereas the immersion & excitement created by a massive 150” projection screen makes you feel like you are part of the action!
"
So if I were to believe my anecdotal experience, I find that to get the best 3D depth effect, I need as large a screen as possible, coupled with being as far away from the screen as possible.

Is this correct? is there any information on the web that supports my theory?

Thanks!
A large screen makes objects look closer to life size, therefore giving more realism to the image. There is a sweet spot of distance from the screen that will give you the best 3D depth effect. If you move too far back, the 3D effect becomes somewhat stretched. Too close, and you get a flattened 3D effect plus crosstalk or overlap of Left and Right images in your shutterglasses. You will rarely find that you can get close enough to fill your field of vision. Plus you will loose sharpness and definition within the image. I have a 16:9 screen 159" diagonal, and I sit about 17 feet away and it's perfect. If I watch 3D movies that fill the whole screen, then I get a very immersive effect. If I watch 2.35:1 widescreen movies, then not as much.

Overall, I would agree that bigger is better, but you have to consider the brightness capability of the projector as well. For good 3D on a large screen, you need a projector that can do 2,300 or more lumens of brightness. But it's all subjective. You will find that sufficient brightness for 3D is the nemesis to getting a large screen and projector that will satisfy you. My projector is rated at 2,500 lumens and my screen gain is 2.4 times what a normal screen would be. However, I have a special screen that is hard to find, and most screens are going to be 1 to 1.2 gain, and that limits your size to about 120" for a bright image that is satisfying. It's always best to read the projector forums and find out what projectors and screens people are buying that are giving them a great 3D image.

If you are getting your first projector and want a big screen, then I would recommend the Optoma 142x, which has an excellent 3D picture and is rated at 3,000 lumens at a very reasonable price. Search Amazon. You can also get a 150" screen for reasonable--search that as well, and get one that has a high review rating.

Others on this forum will have their own opinions as to what is the perfect projector and screen, so be prepared for more confusion. The projector/screen I suggested costs around $1,000 and is a great way to get into large screen TV without chewing up your budget. If the screen turns out to be too big and not bright enough, you can always mask it to a smaller size with black velvet material you can get at most cloth stores.
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post #3 of 5 Old 03-27-2017, 08:32 AM
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The base propositions are correct :
- The bigger the screen the stronger the 3D effect
- The closer to the screen you watch, the lesser the 3D effect

But the explanations are incorrect. The field of view thing is actually the opposite.

The screen size effect is all about geometry.
Stereopsis (the sense of depth using stereoscopy) is caused by your brain sensing differences in your eyes angles relative to one another.
The more angle difference, the further your brain believe the object is from the original screen depth.
The big issue with movies is that they are shot and mastered once and cannot be modified. This means that the separation of objects between the eyes is a fixed number of pixels in the image, which translates into a fixed percentage of the screen size.
By increasing the screen size, the same separation of an object in pixel becomes a bigger distance on the screen surface. Therefore, your eyes will move more relative to each other, and you will perceive a stronger 3D effect.
This also affects games but in a different way : since games' 3D effect is generated dynamically, the 3D effect can be tuned in real time. Games usually have a user customizable setting that allows changing the amount of separation (a customizable 3D strength setting). The higher the setting, the more the objects in the scene separate between the left and right eye, therefore the more angle between the eyes and the stronger the 3D effect.

There is a limit though : if you increase separation to the point of getting your eyes diverging when watching at objects that are far in the distance, then your brain will detect something is very wrong and violently break your sight so that you can search for an other object to focus on (it's like a computer crash and forced reset).
Movie directors know their films will be projected on giant cinema screens, therefore they tend to be very conservative on object separation. This is why 3D movies appear to have plenty of depth at an IMAX cinema, but become all flat when viewed at home on a small screen.
The same applies to objects coming towards the viewer in front of the screen, although the separation limit is much more variable from person to person.
Some people have a larger capacity to go cross eyes than others : think about people who read inches from their eyes vs people who are used to reading at an arm's length (it's not the most exact analogy but you get the idea : the maximum out-of screen separation is not as strictly defined as for depth).


The sitting distance to the screen effect is more complicated : it is about how our brain actually measures stuff.
The thing is : our brain is extremely poor at measuring absolute distances.
It is pretty much the exact same phenomenon as with all our other senses : we humans are incredibly poor at measuring the world (be it distances, sound pitch, smells, or even heat), unless we have something to compare it to.
However, we are very good at comparing things : you could argue that our senses depend on comparison. This is also why it is so easy to create illusions that foll us so easily. (the very way we make images for pretty much everything is a big optical illusion).

The same applies to stereopsis : our brains are incapable of measuring the absolute angle between our eyes. We sense depth by continuously measuring the differences in movement as our eyes scan across the entire image.
The more things you are able to look at, the more depth-difference measurements you are able to make. This constant scan of the image is performed unconsciously. Our eyes actually have only an extremely small field of view with enough detail to see properly. But we are able to see an entire picture with little effort thanks to this constant unconscious scan of the image. Beyond that, peripherial vision has very poor capabilities (insufficient for proper 3D).
This constant scan at high detail only works within a very small field of view (the small area of the screen you are looking at), for your eyes to see beyond this tiny field of view, it takes a conscious decision to move your eyes, which takes effort and breaks temporarily the continuous process of stereopsis.
--> Every time you consciously need to move your eyes you reset the 3D effect.

By sitting closer or further away from the screen, you change how much of the image your limited high detail field of view your eyes are exposed to without having to consciously decide to move your eyes.
The closer you sit to the screen the smaller the field of view, the less stuff your eyes are capable of scanning unconsciously, the more effort it takes for your brain to obtain a 3D effect.
By sitting further away from the screen, your eyes will unconsciously scan a much bigger area of the picture, sensing more difference in depth, giving you a more important 3D effect.

This effect is the reason why wide angle shots can provide enormous 3D effect with minimal separation, while close-ups usually look completely flat.

If you combine the two (large separation of objects + sitting far enough from the screen to have the entire picture in your field of view) : you get maximum 3D effect.

THERE IS ABSOLUTELY NO LINK between the real life size of an element and it's 3D effect.
You can perfectly combine the 2 techniques (high separation and large field of view with lots of objects at different depths) to increase the 3D effect to create stronger 3D than reality.
Video games are a great way to experiment such "too much 3D effect" scenes because some of them tend to have higher than natural field of vision (or a user customizable fov slider), and you can tune the amount of separation to any value you want. Such a scene feels distorted (if you are in such a situation you may experience vertigo just from looking straight through a long corridor), but is perfectly watchable.

As a side note : this is how every "in your face" pop-out 3D scene in movies are done (these scenes are totally artificial, they usually have higher than usual fov and use long continuous objects that allow your eyes ton continuously climb and descend the entire length of the scene space to reduce the amount of separation needed. If these were shot and reproduced at reality accurate separation levels you'd go cross eyed and you'd be unable to watch them).

Passive 3D, forever !
My Full-HD dual-projector passive polarised 3D setup. (really out of date ! I need to update it some day...)


Last edited by BlackShark; 03-27-2017 at 08:52 AM.
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post #4 of 5 Old 04-04-2017, 10:16 AM
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Quote:
Originally Posted by BlackShark View Post
By sitting closer or further away from the screen, you change how much of the image your limited high detail field of view your eyes are exposed to without having to consciously decide to move your eyes.
The closer you sit to the screen the smaller the field of view, the less stuff your eyes are capable of scanning unconsciously, the more effort it takes for your brain to obtain a 3D effect.
By sitting further away from the screen, your eyes will unconsciously scan a much bigger area of the picture, sensing more difference in depth, giving you a more important 3D effect.

This effect is the reason why wide angle shots can provide enormous 3D effect with minimal separation, while close-ups usually look completely flat.

If you combine the two (large separation of objects + sitting far enough from the screen to have the entire picture in your field of view) : you get maximum 3D effect.
Very true and well explained. I noticed this recently when visiting a friend and his setup is a 1080p 55" LG passive and seating was approx 18-20 feet back. It's very easy to notice the 3D effect at this distance and small screen size and resolution is very good. However, the immersive effect is lost at that distance. Objects appear to float off screen and into room and depth is maximized as well into the screen (which isn't a bad thing, it looks good like this too) but you don't flinch at objects coming out like I do on my setup which is 140" at 11 feet. In my setup, I feel as if I'm in the movie and not viewing it like a window on the opposite side of the room. That said, sometimes it is hard to focus on the entire picture and find yourself moving your eyes around to focus on certain things.

The bold text I quoted is very important, maybe the most important thing you wrote. Finding the sweet spot, but that may be determined by room constraints, if not then comfort may also come into play on distance from the screen. You put a screen and seats in a certain way because that's where they have to go, absent choice. Too close or too far, it's really subjective there for the viewer on comfort. In my setup 140" at 11' may be too close for some, others might enjoy it.

I've always enjoyed sitting in the back row of the lower section of theaters. That was always my sweet spot. But I haven't been to a theater since Interstellar and setting up my basement space for HT. 3D sweet spot is a little different but I think you get used to it wherever you end up on distance and screen size. If it's uncomfortable you have to change it and find what works for you.

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post #5 of 5 Old 04-07-2017, 11:20 AM
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Quote:
Originally Posted by tomtastic View Post
Very true and well explained. I noticed this recently when visiting a friend and his setup is a 1080p 55" LG passive and seating was approx 18-20 feet back. It's very easy to notice the 3D effect at this distance and small screen size and resolution is very good. However, the immersive effect is lost at that distance. Objects appear to float off screen and into room and depth is maximized as well into the screen (which isn't a bad thing, it looks good like this too) but you don't flinch at objects coming out like I do on my setup which is 140" at 11 feet. In my setup, I feel as if I'm in the movie and not viewing it like a window on the opposite side of the room. That said, sometimes it is hard to focus on the entire picture and find yourself moving your eyes around to focus on certain things.

The bold text I quoted is very important, maybe the most important thing you wrote. Finding the sweet spot, but that may be determined by room constraints, if not then comfort may also come into play on distance from the screen. You put a screen and seats in a certain way because that's where they have to go, absent choice. Too close or too far, it's really subjective there for the viewer on comfort. In my setup 140" at 11' may be too close for some, others might enjoy it.

I've always enjoyed sitting in the back row of the lower section of theaters. That was always my sweet spot. But I haven't been to a theater since Interstellar and setting up my basement space for HT. 3D sweet spot is a little different but I think you get used to it wherever you end up on distance and screen size. If it's uncomfortable you have to change it and find what works for you.
I read a review of a 3D title that mentioned in a few scenes objects came out a few inches from their face. I watched the same scenes on my 55 inch which I sit about 12 feet from the TV and it looked like the objects were a few feet from my face. I moved to six feet from the TV and now the objects were a few inches from my face.

Cinerama web site:
http://incinerama.com
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