[info] [Wearables] So, what is wrong with HITL/microvision?

Wed Jan 9 15:17:06 UTC 2008

----- Forwarded message from Blair MacIntyre <blair at cc.gatech.edu> -----

From: Blair MacIntyre <blair at cc.gatech.edu>
Date: Wed, 9 Jan 2008 09:40:22 -0500
To: Ozan Cakmakci <ozan.cakmakci at gmail.com>
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 (2.915)

> 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.

I'd definitely imagine there is ... just not for me. :)

> >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.

Which ones? :)   All the alternatives are big, heavy and expensive, so  
loosening something isn't so bad.

Heck, if you can make anything with  > 40 degree diagonal that costs <  
$1000 and is descent quality (e.g., as good or better than the eMagin  
Z800) that would be great.

> 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.

good luck!!

>
> 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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[info] [Wearables] So, what *is* wrong with HITL/microvision?

[info] [Wearables] So, what is wrong with HITL/microvision?