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Why is there a sweet spot?

Karmeck
Explorer
Why can't all of the lens be a sweet spot? Why not just make the sweet spot bigger and cover up the blurry part?
21 REPLIES 21

TwoHedWlf
Expert Trustee


Even glasses have a sweet spot, try looking at the edge of your glasses while looking forward. You will get a lot of chromatic aberration and distortion. Its how optics work .. concave/convex etc ... there is a sweet spot. 


It's EXTREMELY obvious I find with blue LEDs.  The buttons to open the doors at my work have a blue light ring around them.  Just by turning my head and looking through the edge of my glasses that blue ring can shift about a handwidth to the side.

LZoltowski
Champion
@TwoHedWlf  yeah it was odd to adjust to that at first (lived in denial for many years until headaches started so I got my glasses late I'm 34 and got them 2 years ago) ... even had slight issues walking around as they altered my perspective. The brain, such a beautiful adaptive machine it is ... adjusted and compensated for that over time. I bet after a time the same will happen for VR optics .. your brain will just get used to it and fill in the blanks.

Funnily enough I had the same issue with 3d glasses in cinemas, dont think about them twice anymore.
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crim3
Expert Protege


I am actually interested how this technology --- https://www.avegant.com/ could be implemented in a VR headset. It projects the image directly into your retina using millions of mirrors. People have reported the inability to see pixels in those things.


It's DLP technology, the one used in projectors. Instead of a bulky, power hungry and hot white light bulb and a spinning color wheel, the Avegant Glyph uses colored laser LEDS that blink at the appropriated rate to make the same work that the spinning wheel.

You can't see individual pixels because FOV is small.

It's not good for wide FOV VR HMDs because the DLP chips are too small. They actually are a kind of displays that instead of letting light go through them, like a LCD display, they reflect it with their "millions" of micromirrors.

A smart gadget nonetheless, but IMO it's an error to advertise it as a retinal projection display.

comixcroz
Expert Protege

crim3 said:



I am actually interested how this technology --- https://www.avegant.com/ could be implemented in a VR headset. It projects the image directly into your retina using millions of mirrors. People have reported the inability to see pixels in those things.


It's DLP technology, the one used in projectors. Instead of a bulky, power hungry and hot white light bulb and a spinning color wheel, the Avegant Glyph uses colored laser LEDS that blink at the appropriated rate to make the same work that the spinning wheel.

You can't see individual pixels because FOV is small.

It's not good for wide FOV VR HMDs because the DLP chips are too small. They actually are a kind of displays that instead of letting light go through them, like a LCD display, they reflect it with their "millions" of micromirrors.

A smart gadget nonetheless, but IMO it's an error to advertise it as a retinal projection display.


What exactly is the product they are selling?  Does it have any type of headtracking so you can looking around in a 3d space?  Or are you just watching movies, etc?  

FingerMcPokeye
Heroic Explorer
My understanding (which could be wrong) as illustrated in a janky mspaint diagram...

8p7iezz5966d.png

Choronzon
Adventurer

@comixcroz

I was interested in this until I realised headtracking was only possible playing games via PC - everything else is facelocked, including watching films. Plus it has a terribly small FOV. Plus after all the PR speak the picture is not as good as everyone hoped, judging by user reviews on the Avegant site.

Sarlin
Adventurer
Look up "Light Refraction" and you'll get a better idea.  Or if you take a pencil and place it in a glass of water.  Light shifts when going through different media.  Visible light is also different wavelengths. Astronomers use the dopler effect (race car going by) to measure distance to stars and if they are moving towards or away from us.  Light is pretty amazing when you think about it. /enter particle (photon) vs Wave debate.

comixcroz
Expert Protege


@comixcroz



I was interested in this until I realised headtracking was only possible playing games via PC - everything else is facelocked, including watching films. Plus it has a terribly small FOV. Plus after all the PR speak the picture is not as good as everyone hoped, judging by user reviews on the Avegant site.


Interesting, so from the sound of it it's not really trying to be immersive, more convenience, etc.   It probably needs to be tried but I'm having trouble imagining how it would work.  Especially if it has a small FOV and is headlocked. 

There may be huge potential though in the right hands.  

Tinindil
Expert Protege
isnt the photon both a wave and a particle, and it infact behaves in a way where it is able to be potentially in many locations at once until it is stopped, or measured (usually at same time)

hence the pin hole test

FingerMcPokeye
Heroic Explorer
Shortest explanation:  Travels like a wave.  Interacts like a particle.

Slightly longer: The photon when travelling does not have a defined location.  It has a probability of being in a location.  As tiny as a photon is when measured it's about a meter in diameter when traveling.  When it's location is measured (smacking into something for example gives you the location) then the waveform collapses and the probability of it's location gets reduced to one possibility.

The pin hole test that Tinindil mentions stems from the single slit experiment. 

In the single slit / pin hole you shine a broad beam light at a small slit.  The light goes through the slit but not in a single beam.  It gets refracted and fans out from the other side of the slit.  If the slit is very wide, little refraction occurs and it goes through very beam-like.  If the slit is narrow it gets refracted a lot.

Refraction is really just changing the vector/velocity of travel.  With that in mind in the small slit we know the photon (or electron..) position very well, but because of heavy refraction the accuracy of the velocity is low.  When the slit is wide the velocity is well known but not the position.  We can measure velocity and location to high accuracy but they are mutually exclusive.

To have your head asplode, look at the delayed choice variation of Young's double slit experiment...basically implies that time is an utter bullshit concept made up by the human mind.