Measuring the eye

Our eyes are like windows, I’ve been told. We use them to look out at the world, and doctors use them to look into our body; a non-invasive health check. But our window is not really top-quality, which blurs the seeing in both directions. Glasses and contact lenses have long been used to better see the world. They correct low order errors, like defocus and astigmatism, and give improved vision.

Of course, some glasses just serve as inexpensive identity props, 

 more funky ones let you see wrackspurts.

For doctors to look into our eyes, we turn to imaging systems that compensate these aberrations and image the retina, blood vessels and other features in the eye. The efficiency of correction both ways depends much on how accurately the aberrations are measured.

In 1961 Mikhail Smirnov developed a subjective technique to measure the aberrations of the eye. The individual would look at two incoming beams of light, use the on-axis beam as reference and change the position/angle of the off-axis beam to try and fuse the two beams at the retina. This gave the slope of the wavefront and allowed step-by-step measurement of the eye’s aberrations.

Compressed Sensing and other stuff

Hey everyone..

I have registered for FiO 2011, and have started looking into the schedule. There are many events this year and I don’t want to put off looking at the schedule till the last moment and miss out on the more interesting ones. 

The first day, Sunday 10/16, 4-6pm, seems to have a very good What’s Hot in Optics session that should be interesting. Usually a start-off session like this provides a very good overview of things to come, so I will surely be there. 

Sunday evening (7.30-8.30pm) has meetings for OSA technical groups. I had signed up for a couple for groups and got emails from them inviting anyone interested to join the meetings. There should be discussions for areas like Optical Design and Instrumentation, Holography, Information Acquisition, Biomedical Optics, etc. Meetings like these help people get involved with OSA in these technical areas.

Monday has a great session on Compressed Sensing (FMM, from 4-6pm). Rebecca Willet from Duke is going to have a 45 minute tutorial style talk on compressed sensing for optical imaging; she mentions IR and focal plane arrays in her abstract. There is much work being done to minimize the data being sensed as well as transmitted. Her group works on compressed sensing, exploiting sparsity in the nature of data to obtain compression. She has worked on compression in the presence of Poisson noise, coded aperture imaging, multi-aperture imaging for thin imagers, and more. So the tutorial talk should be a good overview.

There are also talks from George Barbastathis' group at MIT, and some from David Brady’s group in this session that should be interesting. There is one by K. MacCabe that takes advantage of aliasing high spatial frequencies, folding them into the lower spatial frequency region which is more resistant to loss during defocus. In my opinion, turning around aliasing to your advantage is always brilliant! This session certainly promises to be very interesting.

Oh.. I just found an old video of Rebecca Willet giving a talk at some CS workshop at Duke; summarizes compressed sensing to some extent. Here are the slides for her talk, do check out the slides because the video below does not display them. Also, audio-video here are a bit out of sync, but with the slides it's a pretty good talk. Her talk at FiO will probably have more recent stuff, but this should give you a flavour of what to expect at the CS session.

 Ref: http://www.youtube.com/watch?v=J1P7-zVNibQ 

 

Ref:  http://www.youtube.com/watch?v=u5l-adNkRAA&feature=related

Ooh, just spotted this, Kevin Kelly from Rice seems to have a 30 minute talk (LTuC3) Tuesday morning, on their work on single pixel compressive imaging where they use a fast DMD to time multiplex and compress the object information and then capture only the minimum required on a single pixel! 

That's it for now. I'll post more about other sessions and events over the next few weeks. Cheers and thanks for reading!

Fun weekend, cool jellies!

Hey everyone!

The weekend was good. We did some fun things. Drove to Monterey, CA, and got stuck in lots of traffic en route. But the scenery around us was so beautiful, we loved the drive!! We were surrounded by some of the most fragrant tall Eucalyptus trees. Then slowly drifting past artichoke farms, we could see the artichoke-heads up close near the highway. Around Gilroy, we could smell Garlic!
 
At the Monterey Bay Aquarium, we saw the coolest jellies. These are called Comb Jellies. They propel themselves through the water using their hairy cilia. And light diffracts off their hairy-cilia-comb making an amazing rainbow! Check out this video from that exhibit (uploaded by someone with a fairly steady hand). And you can read more about Comb Jellies here.

Ref: http://www.youtube.com/watch?v=Lw5Q_w7ubxs&feature=related

I don't think the one below was at the Aquarium when we went, but I spotted the next video browsing through the aquarium website - the Bloodybelly Comb Jelly.

 Ref: http://www.youtube.com/watch?v=LbcnRVkzy8A

Nature is astonishing!

Cheerio and thanks for stopping by!