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CyndiBop (Cyndibop)
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Username: Cyndibop

Post Number: 1
Registered: 7-2007

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Posted on Saturday, July 21, 2007 - 5:50 pm:   Edit PostDelete PostView Post/Check IPPrint Post

I don't know if it's totally on-topic.
I'm not very tech-minded, sorry, all I want is to find the best solution to watch my iPod movies through a pair of video-glasses.
There are some models, I think there're others too:

but I'm unsure on which to buy!!
I don't know really what to do because I know I would take the worst model for the highest price.

As for the models, like this

which displays the 3d function, what I have to expect from exactly? They make me see my iPod movies in an 80" screen in 3d format?
I would get also a pair of video-glasses with normal LCD screens, the point is that I don't want them to tire my eyes or just to offer a larger but poor resoluction image.
I'm sorry, there're lots of things I would need to ask you but my english isn't really good, and I fear to write idiotic things.
I just hope any of you can suggest me the best model, as overall quality to see in the best possible way my iPod clips.
I thank you a lot in advance!!!! I hope to find a kind person to help me!
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Andrew L. Ayers (Cr0sh)
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Username: Cr0sh

Post Number: 13
Registered: 2-2007

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Posted on Monday, July 23, 2007 - 4:49 pm:   Edit PostDelete PostView Post/Check IPPrint Post

When choosing an HMD (head mounted display), there are a variety of factors to think about before purchasing, but there are really only a few "critical" factors which you need to concern yourself with:

- weight
- field of view (FOV)
- resolution
- cost

As with everything else, there are tradeoffs between all of these, and choosing the right set of tradeoffs will depend on your application. For instance, watching a movie is a different application than endoscopic surgery, both of which are completely different from using an HMD for a 3D FPS - like World of Warcraft, for instance.

Typically, the greater the FOV, the more the HMD will weigh, and the more it will cost. However, the greater the FOV, the poorer the perceived resolution of the HMD (because there are fewer pixels per degree of resolution).

First off - what is a "field of view" (FOV)? I will attempt to illustrate this: Look straight ahead, then imagine a cone or a pyramid, with the apex of the shape at the point of your iris (your eye), and the base of the shape out in front of your, with the base parallel to the "plane" of your face (I hope you at least have a minor understanding of geometry, or this explanation will not make any sense). Please note a couple of things: 1) the pyramid/cone shape is also known as a "view frustum", 2) in reality, the apex of this shape is actually at a "point" on your retina, and not at the surface of your eyeball - but for our purposes of illustration, it doesn't matter.

In this example, notice that there are two (2) of these cones/pyramids (because you have two working eyes, hopefully). The angle between the sides of the cone/pyramid (as measured at the apex of the object) is the "field-of-view". If you can imagine all of this, you should understand that for most humans, the eye has a very wide FOV (hence, the reason for "peripheral vision", which is the outer edge of the FOV). Furthermore, the two FOV's (for each eyeball) overlap. This is what allows for stereo vision in humans (for mainly "close" objects, of course). Also, this overlap can increase, obviously, as your eyes turn inward to examine close up objects.

Now, if you notice, in everyday life - you have this fairly insane resolution of your eye (which is actually "interpolated" resolution - your eye actually twitches a lot, and the brain makes up for it, making you perceive a still image with more resolution than what the retina has for rods and cones), coupled with this huge overlapping field of view (slightly smaller in the vertical direction than the horizontal, mind you) - giving you the feeling of being "in" the world: ie, you are "fully immersed".

This is what the term "immersion" means when talking about HMD's and FOVs - the closer you can get (in an HMD) to what you see in the real world, the closer you can get to feeling "like you are there" (until you experience it, you don't know just how limited our current computing experience really is - think "waking dream controlled by computer/user interaction" - and you have some idea). Immersion takes more than just a large FOV, but it is a big factor.

Now, a small FOV will look "constrained" - for an extreme example, look down a pair of toilet paper tubes (assumming you have toilet paper in your country - if not, a couple of sheets of rolled up paper approximately 10cm long each will do as well). This approximates a small FOV (about 20 degrees or so).

First off - you won't find an HMD offerring anywhere close to "real world immersion" FOVs, until you start to move into $25,000+ (US) range. Even at these extreme price points (most such units are sold to companies and governments for simulation and military usage), you will only start to hit "real world" immersion - but in most cases, that is more than enough. Some of these HMDs, though, are rather large, and use multiple LCD or OLED panels, and weigh quite a bit more than what is sold on the consumer market.

What you are likely to find on the consumer market are HMDs with either 640x480 or 800x600 panels, one per eye (although, there are some out there that use one for both eyes). The optics will typically allow for around 22-30 degrees FOV (although this is typically measured diagonally - instead of in separate horizontal vs vertical measurements - so, to get the true field of view, you will need to also know the aspect ratio of the displays used - typically 4:3 - then do some basic trig - to figure out the real FOV - this is done for marketing reasons).

You then need to divide the resolution by the h/v FOV - you will probably find that for these HMDs, there will be anywhere from 30-40 pixels per degree of resolution (ie, for each degree in the FOV, there will be 30 pixels). Please note that such resolution is considered "legally blind" - in other words, if you were to hook a video camera up to this HMD, put on the HMD, then point the video camera at a standard eye-chart at the standard distance, you would be very lucky to read the second line down.

This isn't to say you couldn't enjoy a movie on such an HMD. Furthermore, note that even with the lower resultion, and the small FOV, your eye and brain will attempt to compensate and fool you into thinking the image is larger than what it really is (and maybe even sharper than what it is). This is a natural response of the visual system - which helps in the case of HMD usage.

Lastly, try to get an HMD that offers "fixed at infinity" focus (most do, nowadays). This will lessen the eyestrain (even so, I still reccommend limiting usage of an HMD to 30-45 minutes - or less if you feel tired). Eyestrain can still be an issue. Also note that you shouldn't drive or do other similar tasks for 20-30 minutes after using an HMD, until your eyes/brain readjust to "the real world". Try to get an HMD that allows for "inter-ocular" spacing (ie, adjustable for different eye-spacing widths). Such a feature tends to raise the price of the HMD more, but makes for a more comfortable viewing experience, and lessens eye strain. Try to also get one that has the least weight - particularly "nose weight". Four (4) ounces may not seem like a lot, but it is a quarter-pound of weight, and if most of that is resting on the bridge of you nose, it can become very uncomfortable very quickly (which is why most professional HMDs use head straps and counterbalances to make wearing them for extended periods more comfortable).

Finally - about the "stereo 3D" - for watching movies, this isn't a necesary feature. If you were to use the HMD for gaming, or other such usage (such as specially formatted video), where the video output can be configured to show a different view for each eye (to more accurately simulate a real world experience), which the brain combines into a single stereo view - then this feature would be a nice addition. However, for regular videos on an iPod, it isn't necessary - you will see a monocular (ie, same image for each eye) view. So, only get it if you think it is something you will use (and, if all the good HMDs you find have it, then consider it a bonus).

I hope this information helps you to make a more informed decision. I can't reccommend any recent models of HMDs, simply because I haven't tried any. I suspect other readers who have will post a response in this thread, though. Just remember to compare the specs, and realize that each manufacturer/seller is attempt to sell you something, and will probably not give you all the true facts to make an easy decision. Email them, ask for true specs:

- resolution of screens
- number of screens
- inter-ocular spacing of screens
- horizontal and vertical FOVs
- eye-relief
- etc

Then use those numbers to determine what the true values of the HMD are, not just the marketing numbers. This is the same trick as selling CPUs by MHz, or selling a 19 inch monitor with a viewing size of 17 inches (ie - including the bezel size in the dimensions).

Good luck!
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CyndiBop (Cyndibop)
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Username: Cyndibop

Post Number: 2
Registered: 7-2007

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Posted on Monday, July 23, 2007 - 8:28 pm:   Edit PostDelete PostView Post/Check IPPrint Post

thank you! I thank you a lot! You've been very nice!

Now I didn't get the whole message yet, I will read it better the next hours, it's not that easy for me, but thanks, thanks a lot

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