I’m very excited to have just built a working Google cardboard. I’ve been looking forward to VR since it first became visible in the mid(?) nineties. And now that I’ve tried it for the first time, I can say that I am more excited about it than ever. It is awesome. I’m looking forward to playing with the SDK when I have a bit of free time, and I already have a couple of projects in mind.
Like everyone else, I couldn’t find suitable lenses, since the Durovis Dive lenses recommended by Google sold out almost immediately. I spent a morning looking around the internet for something suitable in the UK and found a few places that sold 25mm diameter biconvex lenses with a 40mm focal length, as recommended (e.g. Thor Labs), but they were about £20 (~US$30) each (and obviously you need two), so this added quite a bit to a cardboard box project I didn’t even know was going to work.
After a bit of thought, I realized that simple magnifying glasses were biconvex lenses! The tricky thing is that magnifying glasses are sold by magnification rather than focal length, but, thanks to Wikipedia’s page on magnifying glasses I found the conversion factor I needed, which is MP = 0.25/f + 1, where MP is the magnifying power and f is the focal length in metres. Working this out, gives a magnifying power of 7.25 for a 40mm focal length. So, knowing this, I headed over to eBay.
The nearest thing I could get were some jeweller’s magnifying glasses (they might be sold out now, but any similar ones will do) with a 6x magnification and a 25mm diameter lens. The lenses were the perfect diameter, easy to pop out, and gave a focal length of 5cm. This slightly longer than specified focal length required a bit of extending of the distance between my lenses and the phone inside the Google cardboard, but since everything is made of cardboard, this wasn’t too hard. After a bit of adjusting (via extra cardboard and some tape), I managed to get the focal length right. The moment everything jumped into place in 3d in those cardboard goggles was amazing – well worth the effort. And the Google Maps app alone is fantastic – I took a flight over the west coast of the USA yesterday. They’ve also updated Streetview on Google Maps to support cardboard, so a bit of 3d StreetView tourism has been fun, too.
Congratulations, Google, on an awesome project (and on causing a worldwide shortage of 40mm biconvex lenses).