Why do we have fresnel lenses?

[Roaster]

The reviews I'm seeing say the lenses are VR's biggest failure.  Rift and Vive both.  I was told the lenses were highly optimized for the screens.
I can live with delays. I don't care about the cost. I can live with more weight. I don't care about the games list at launch. I do care about image quality and clarity, and would simply pick the unit with the best show.  How are these light glare artifacts acceptable?
Would reducing the brightness help?  Can the lenses be replaced with some custom solution?

[Lucky_D]

Remember you are looking at a Gen1 Commercial product.  Remember your first flat screen?  The image quality was garbage, there was motion blurring, screen tearing, etc.  But it was a Gen 1 product.  Oculus is the same, this is the Gen 1 product, and as such we, the early adopters are helping build the product and improve it.  If this is not a role you wish to play or you are expected a highly polished Hi-Def solution, then you may want to wait a year or two.

[Roaster]

My first flat screen was a 42" plasma at 1080 and I was blown away every time I turned it on.  I bought the DK1 and 2 because they were the best available at the time, and will do the same for the current gen units.  I just naturally want the best, and these fresnel lenses seem like a terrible compromise to achieve some goal ... something other than clarity. 
My question is, why fresnel lenses?

[maxpare79]

And since CV1 uses more and smaller grooves then the VIVE the God rays seem to be affecting it more, which I believe is why it has been reported that the screen of the CV1 was dimmer then the VIVE...

Playing with contrast and brightness should help with the God rays... Games with this problem need to implement ingame brightness and contrast controls

On the ED forums there are 3 clips showing it and it doesn't seem as bad as some people make it out to be... Pictures of it seems to make it appear worst the it is.. But I can't wait to test it for myself

[Lucky_D]

If you want the best then this is not the product for you.  VR headsets are not where you want them to be on the image quality and will not be for several years.

[Roaster]

A slightly frosted diffusion layer would seem to be better at reducing SDE without the effect of a "Cross-Screen Filter" as used on a camera.  The solid lenses were not that bad. 

[Zoomie]

It sounds like Oculus opted for more finely faceted Fresnel lenses, and went hybrid (contoured) to maximize the pixels used from the underlying Samsung displays.  The result is a more rectangular FOV to use as much of the display area as possible.  The FOV, while smaller, has a higher density of pixels in the focal area - which is why people observe less SDE.  Unfortunately it seems like more Fresnel facets means it's prone to the light blooming people are reporting in very high contrast scenes.

Vive chose to use only a circular portion of the square Samsung (assumed) screens, but to magnify them more than Oculus' hybrid Fresnel lenses.  The result is a larger oval FOV in each lens, but with a visible SDE due to lower pixel density in the focal area.  The fewer facets of the Vive Fresnel lens also means there are visual artefacts that manifest as concentric distorted rings - although most people say they're barely noticeable when you're moving.  Because the Vive lens is Fresnel, it is also prone to the light blooming rays same as the Rift.  However, some users are reporting they're less obvious on the Vive due to fewer ridges in their standard Fresnel.  

Despite the Rift having a measurably lower FOV than the Vive, most people who have used both report the overall FOV feels very similar, and also that SDE is very comparable between the two headsets.  

[KingK76]

Roaster said:

A slightly frosted diffusion layer would seem to be better at reducing SDE without the effect of a "Cross-Screen Filter" as used on a camera.  The solid lenses were not that bad. 

No...  This IS NOT the case.  I used this method to reduce SDE on my DK2 and while using that method (i used screen protectors) it DID reduce SDE (and blurred the image heavily) but it also added a VERY unwanted side effect.  It's hard to describe in text but when the image on the display moves a certain aspect of the image appears to stand still.  It is VERY distracting and I would not suggest that approach to reducing SDE.  Anyway if with current technology you think Oculus AND HTC chose the lenses they did to combat SDE then trust that that is the best way CURRENTLY possible.

[KingK76]

Roaster said:

My first flat screen was a 42" plasma at 1080 and I was blown away every time I turned it on.  I bought the DK1 and 2 because they were the best available at the time, and will do the same for the current gen units.  I just naturally want the best, and these fresnel lenses seem like a terrible compromise to achieve some goal ... something other than clarity. 
My question is, why fresnel lenses?

Did you pay $20000 for that Plasma?  If you didn't then you were not using a "FIRST GENERATION" Flat screen Plasma.  I would wager to guess that when you bought your first Plasma the model you purchased was a few generation in.  First Gen sucked, and they only lasted a year or so because the screen burn-in was SO bad.  Look it up.  And yes I wrote Twenty THOUSAND dollars.

[w_benjamin]

Fresnel lenses are designed to bend light, similar to a magnifier, except instead of a continuous curve designed to bend light to a single focal point, they have steps that are designed to bend light into a cylindrical shape. 

The effect is that you can take something that is wider than your field of view and condense it.
Each step in the lens bends a certain amount of light at a specific angle..., the more steps in the lens, the higher the resolution of the image seen through it.

If you were to look at an image using only the pixels you can see with the naked eye at the range of an HMD display, it would look terrible.

In summary, the lens takes a larger display and shrinks it down to allow more pixels into the image that you can see.

Because of this, the distance of the display to the lens as well as the angle of the steps has a large impact on the perceived FOV, while moving your eye away from it..,. not so much (you'll still see just as much, but it will look smaller.)