[visionlist] Focal distance / accommodation distance HTC Vive Pro

[Woods, Russell L.]

Maarten and Daniel,

That’s the power (focal length) of the eye lens.  In addition, you need the distance between the lens and the display surface.  With those two, you can calculate the vergence at the eye (= apparent / optical distance).  That will give you the first order approximation.  The step beyond requires measurements of the curvature of the lens surfaces and knowledge of the refractive index of the lens.  With thick lenses and short distances, it can make a bit of a difference.  Though, for most purposes, focal length and distance to object are sufficient for a simple system like this.

best wishes,

Russell

P.S.  I too hope that I am not embarrassing myself   :)


> On 11 Oct, 2021, at 11:36, Maarten Wijntjes - IO <M.W.A.Wijntjes at tudelft.nl> wrote:
> 
> Like this, which is actually an old oculus lens from the first developers kit. 
> 
> <focal distance.png>
> 
>> On 11 Oct 2021, at 17:31, Maarten Wijntjes - IO <M.W.A.Wijntjes at tudelft.nl> wrote:
>> 
>> Dear Daniel,
>> 
>> Shouldn’t it be in the range of some cm’s as it projects the screen in front of the eyes to far away/infinity? I thought a simple test for focal distance measurement is to project something with it that is far away, e.g. a lamp on a high ceiling or a window. The distance between the lens and the projection plane (e.g. table with white paper) is the focal distance. 
>> 
>> I hope I am right and did not make an optical fool of myself in front of the vision list community ;)
>> 
>> Maarten Wijntjes
>> 
>> 
>> 
>>> On 11 Oct 2021, at 13:50, Oberfeld-Twistel, Daniel <oberfeld at uni-mainz.de> wrote:
>>> 
>>> Dear list,
>>>  
>>> we’d like to determine the focal distance in the HTC Vive Pro headset, in order to use exactly this distance for tests of visual acuity before the actual VR experiment. An internet search produced a variation of estimates, ranging from 0.75 m to 2 m or even infinity. So we are wondering if someone here made optical measurements of the Fresnel lenses inside the Vive, to determine the effective focal distance of the display.
>>>  
>>> Best
>>>  
>>> Daniel
>>>  
>>> ---------------------------------
>>> Prof. Dr. Daniel Oberfeld-Twistel
>>> Johannes Gutenberg - Universitaet Mainz, Experimental Psychology &
>>> Laboratoire ICube UMR7357 Université de Strasbourg
>>> Wallstrasse 3
>>> 55122 Mainz
>>> Germany
>>>  
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