[FoRK] Re: [Wearables] So, what is wrong with HITL/microvision?

Wed Jan 9 07:16:55 PST 2008

----- Forwarded message from Ozan Cakmakci <ozan.cakmakci at gmail.com> -----

From: Ozan Cakmakci <ozan.cakmakci at gmail.com>
Date: Wed, 9 Jan 2008 09:36:16 -0500
To: Blair MacIntyre <blair at cc.gatech.edu>
Cc: "wearables-list at media.mit.edu" <wearables-list at media.mit.edu>
Subject: Re: [Wearables] So, what *is* wrong with HITL/microvision?
X-Mailer: Apple Mail (2.753)

I was hoping that there would be some set of wearables applications  
that can benefit from 20-40 degree fields of view range with compact  
physical size (within a few cm^3), full color (450-650nm), high- 
quality (20% MTF + <5% distortion), cheap to produce (<100 USD),  
decent pupil size (let's say 3 to 8mm pupil*) & eye clearance (~15mm  
or greater), see-through optics.

 >40 degree see-through + all of the constraints above within the  
eyeglass form-factor (or as close as we can get) ? We probably have  
to work harder or loosen some of the specs.

To answer your question though, I don't know the exact number for how  
big the fov can get for a single mirror geometry. We submit an  
abstract at the society of information display conference to study  
this aspect.

Ozan

*I would like to say that even 4mm is challenging with these specs.

On Jan 9, 2008, at 8:09 AM, Blair MacIntyre wrote:

> Cool stuff, ozan.  How big an fov can you hope to get?  I do AR,  
> not HUD-based wearables, so 24 diagonal is not really useful;  40  
> is barely useful, much higher will be necessary in the long run.
>
>
> ---
> Blair MacIntyre
> Associate Professor, School of Interactive Computing, GVU Center
> Georgia Tech, 85 5th Street NW, Atlanta, GA, 30308
> (please excuse the terseness, this was sent from my phone)
>
> On Jan 9, 2008, at 7:45 AM, Ozan Cakmakci <ozan.cakmakci at gmail.com>  
> wrote:
>
>>
>> On Jan 8, 2008, at 9:52 PM, Blair MacIntyre wrote:
>>
>>> On Jan 8, 2008, at 8:28 PM, Adam Oranchak wrote:
>>>
>>>> Robin Lee Powell wrote:
>>>>> I remember, and I'm sure some of you do to, Back In The Day when
>>>>> HITL said they'd have full-resolution 24-bit colour in  
>>>>> something the
>>>>> size of a grain of rice or whatever for a few hundred dollars.   
>>>>> IIRC
>>>>> "the day" was 1995 or so.
>>>> Well, you just stepped into a realm that I am intimately aware of.
>>>> (Yes,
>>>> you cheeky ones, I said "intimately!") It just so happens that all
>>>> those
>>>> specifications neglected to tell you that the image was crap,  
>>>> that if
>>>> the display moved out of alignment from the wearer's eye by a
>>>> millimeter
>>>> off you lost half the image, that the corners were dark and
>>>> pin-cushioned and that the 8 bits of red depth of one pixel  
>>>> appeared
>>>> over the 8 bits of green produced by a pixel 10 pixels away. Oh
>>>> yeah, it
>>>> cost $20K.
>>>
>>> Wow ... tell us how you really feel, Adam.  Don't hold back.  :)
>>>
>>> Of course, never having used the original one, and having owned and
>>> used a more modern $3.5K version of VRD (the "nomad expert
>>> technician", I would suggest that readers take what you say with a
>>> grain of salt.  I found the Nomad to be very nice.  Yes, there are
>>> issues when you move rapidly, but aside from that, I found the image
>>> quite good, the exit pupil large, the field of view better than most
>>> other displays in that price range.
>>>
>>> I won't bother listing my "credentials", though.  I don't do HMD
>>> optics, I just use them.
>>>
>>> All that said, to actually answer the first question:  rumor has it
>>> that they will have a small, full-color prototype delivered to the
>>> military this year.  I'm anxious to see it, as I still believe that
>>> the VRD is the most promising approach to usable, high-res, wide- 
>>> field-
>>> of-view HMDs out there.   All other approaches seem to require  
>>> lots of
>>> big crap in front of your face, which just won't cut the mustard  
>>> with
>>> the general public.
>>>
>>> cheers,
>>>  blair
>>
>> There is another promising approach which is not studied  
>> extensively - limits of a single mirror. We are trying to look in  
>> the direction outlined below with Adam's help on industrial design  
>> and opto-mechanical design.
>>
>> Starting to believe that an alternative ideal solution to not  
>> requiring big crap in front of your face is to use a single free- 
>> form off-axis mirror as a magnifier. Free-form to say that  
>> rotationally symmetric aspheres are unlikely to perform in this  
>> geometry. Off-axis to say that there is no single axis around  
>> which the system is symmetric.
>>
>> I'm unsure how the optics would have a lower element count than a  
>> single optical element + the microdisplay. Given the lack of space/ 
>> volume to place the optics, lower element count designs seem to be  
>> helpful. Additionally, such a configuration has no moving parts  
>> which is desirable.  Single mirror has no dispersion so color  
>> correction is not needed. We just fabricated a single free-form  
>> mirror that is designed for 24 degrees full field diagonal with  
>> 20% light at the Nyquist frequency of the modulation transfer  
>> function (MTF). It is being assembled right now, we will know more  
>> soon. I don't know too much about molding free-form parts but I've  
>> heard people say that it can be mass manufactured for about a few  
>> dollars. Yes, there will be issues with manufacturing tolerances  
>> but I believe they will not require invention for their solutions.  
>> This would potentially let people get into the <100 USD/hmd range.
>>
>> We have to optimize the mirror surface (coefficients describing  
>> the mirror) across a particular field of view to get the best  
>> image quality possible (<5% distortion + 20% light at Nyquist as  
>> determined by the pixel spacing on the microdislay). The geometry  
>> of a single mirror + microdisplay is highly constrained from an  
>> optimization point of view. There are not that many degrees of  
>> freedom to optimize to achieve the goal of good image quality.  
>> Tilt of the mirror is set to an absolute minimum to reduce the  
>> angles of incidence on the mirror. In such a configuration, the  
>> shape of the mirror seems to turn into the major optimization  
>> variable. The consequence is that how we describe shape becomes  
>> important. Free-form usually means Zernike or x-y polynomials for  
>> the description of shape. We are finding out that we might need to  
>> change the basis for describing locally anamorphic pieces along  
>> the mirror surface. We have been experimenting with optimizing the  
>> radial basis function network representation (RBFN) with a  
>> Gaussian basis to represent the mirror surface. Initial results  
>> indicate that you gain 20% MTF compared to standard descriptions  
>> of free-form shapes such as anamorphic aspheres, Zernike  
>> polynomials and x-y polynomials (we had a submission pending with  
>> optics express which just got accepted this morning :). The  
>> surface will remain manufacturable through diamond turning as long  
>> as the rotationally non-symmetric sag from the best fit sphere is  
>> kept within a few hundred micrometers. This seems to be the case  
>> for the specific configuration of a single element magnifier  
>> described using an RBFN description. Another concern is alignment  
>> tolerances but we learned through fabricating dual-element  
>> magnifiers that the alignment tolerances are not as bad as people  
>> think they are. Anyway, what can we do with the gain in  
>> performance (MTF) if we go to a different surface representation?  
>> It may be traded off with a larger exit pupil size or a larger  
>> field of view. Establishing the field of view and pupil size  
>> limits of a single off-axis mirror seems relevant to this problem.  
>> In terms of improving brightness, people are thinking about new  
>> microdisplays that differ from LCD, OLED or a laser based source.  
>> It seems that the brightness of microdisplays might increase  
>> considerably within the next 5-10 years.
>>
>> Thank you,
>> Ozan
>>
>>
>>
>>
>>
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>>

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[FoRK] Re: [Wearables] So, what *is* wrong with HITL/microvision?

[FoRK] Re: [Wearables] So, what is wrong with HITL/microvision?