Magnifying a display without compromising exit pupil

[zacherynuk]

Hello, I hope somebody can help me, or point me in the right direction... or perhaps just say "that's impossible - go down the pub instead"

I am currently looking into ways of upgrading a head mounted display, although I have had some good results using projected images, I would like to try and build an optical based solution.

The headset (an old VR4) uses LEEP style optics, which focus on 33mm diagonal display which is 17mm from optic; these optics provide excellent user comfort due to their exit pupil size (12mm), Field of View (60d) and eye relief (25mm).

I have acquired some high resolutions displays, which are much smaller, in fact 1/3 the size of the displays which the eyepiece optica are calibrated for.

So, if at all possible, I would like to be able to find a way of increasing the size of the image from these displays, 3X, so that we can use our current eyepieces. Initial tests have ruined the exit pupil and made the eyepieces hard to use.

I have thought about using a concave mirror with a beam splitter, perhaps with an additional field lens at the 17mm focal point. Or using one or two simple lenses, or even a freznal lens, but I fear all of these will reduce the eyepiece exit pupil.

I have attached some diagrams, with my ideas I don't think a beam splitter would allow enough light through, but I don't think a lens alone could do the job - and I don't know where to begin calculatng what lenses would be required.

Any and all help and advice is much appreciated!

Basic:
[URL]http://www.wastedspace.co.uk/hmd/tmp/SmallerDisplayDiagram.jpg[/URL]

[URL]http://www.wastedspace.co.uk/hmd/tmp/SmallerDisplayDiagramUsingMirror.jpg[/URL]

 

[Andy Resnick]

Hmmm.. this is a tough one.

Naively, you want a 3x image of the new display placed at the location of the original display, which I think is fairly straightforward with a simple magnifier- but I don't know if the exit pupil will remain the same size.

My suspicion is that it won't- the entendue (image height * angle of the chief ray) is conserved in lossless optical systems, so increasing the image height will decrease the brightness/exit pupil diameter.

 

[zacherynuk]

Hmmm.. this is a tough one.

Naively, you want a 3x image of the new display placed at the location of the original display, which I think is fairly straightforward with a simple magnifier- but I don't know if the exit pupil will remain the same size.

My suspicion is that it won't- the entendue (image height * angle of the chief ray) is conserved in lossless optical systems, so increasing the image height will decrease the brightness/exit pupil diameter.

Exactly. The eyepiece is made of three lenses, the canter one is the magnifier, simply adding to or replacing this with a stronger lens was my first thought, this and adding a single 10mm fl lens between the eyepiece and the display gives magnification at the expense of exit pupil and image quality – edges are blurred, for example and small movements of the eye away from dead-centre result in distortion.
I think I may be looking at this problem the wrong way round…