Light fantastic

By Marcus Wilson 30/03/2011 5


D’oh. Missed the exploding meteor last night. From the news reports it sounds like a pretty impressive sight.  (N.B. I like the comment on the stuff.co.nz article that says "Faster than a plane = definitely over 10000 km an hour. I don’t know how many planes this guy has travelled in, but doing 10000 km an hour would certainly make a trip from Auckland to London a lot less stress.)

Actually, last night was spent trying to teach our most adorable catty-puss some finer points of mouse-catching etiquette:

1. When one is a cat it is perfectly acceptable to catch small rodents. However, all felines should note the following:

2. All games with one’s catch should be undertaken outside. Taking one’s toy into the house to play with is considered bad manners.

3. After use, it is polite to kill one’s mouse. Bringing it inside in a deceased form and presenting it to one’s owner as a gift is acceptable; leaving it half-alive scrabbling about the kitchen floor for one’s owner to discover later is poor form.

Somehow I suspect the message hasn’t got through.

Back to astronomy. A couple of nights ago I glanced out of the window to see Orion (upside down of course) looking back at me. At least, I think it was Orion; it was hard to tell because I didn’t have my glasses on. What I actually saw was a few glowing splodges in the dark sky, roughly making out the shape of the constellation, with a brigher splodge up and to the right, which I assumed to be Sirius.  My eyes are certainly getting worse as I get older. (Though, Waikato drivers should be pleased to here that on putting my glasses on the stars return to their point-like form.)

Each splodge can be considered the ‘point-spread function’ for my eye. This optics terminology describes how a point source of light, like a star, is mapped imperfectly onto a sensor element (my retina). The broader the point-spread function, the worse the eyesight. It’s a useful thing to know, because you can then model how any picture would appear to your optics. What you’d do is a convolution of the unblurry image with the point-spread function, that is, apply the point-spread function at every point. 

The reverse process ‘de-convolution’ is possibly more useful – if you can work out exactly how an image is being blurred, you can work out what to change about its optics to make the image sharp (i.e. design an appropriate ‘lens’ for it.) 

For those who know about such things, convolutions are easy to do numerically with Fourier Transforms.


5 Responses to “Light fantastic”

  • Marcus said…
    For those who know about such things, convolutions…

    I do my software development in Java, so my Java algorithm implementation of convolution, I use the IIR digital filter algorithm (Infinite Impulse Response) rather than (fast) fourier transform. To me, IIR based convolution is a little bit faster than fourier based convolution.

  • Anyway, I thought that the following paper on the use of IIR (Infinite Impulse Response) digital filter may be useful to researchers who are involved in DNA sequence detection & Genomics, which appeared in the proceedings of Digital Signal Processing Workshop, 2004 and the 3rd IEEE Signal Processing Education Workshop.

    “Identification of CpG islands using a bank of IIR lowpass filters [DNA sequence detection]”
    http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1437966

    • Sounds like you should be keeping your own blog given the number of comments that are coming in. Do you?

  • Marcus said…
    Sounds like you should be keeping your own blog given the number of comments that are coming in. Do you?

    It is a tempting idea, but I also have an interest in politics. This means that I will write blog posts in politics (assuming I have a blog) which have no relevance to science if it is to be syndicated to SciBlog. Lets say that my blog won’t be syndicated to SciBlog for some reasons. If I write on science topics then no one knows about what I write about (since I suppose that my followers/readers are those that are interested in politics only).

    This is the reason I come here to SciBlog to make comments and share scientific knowledge. SciBlog has been around for 2 years & I suppose I never had any interest in coming here to make comments. I started commenting here, when I came to read about David Winter’s blog post on Ken Ring. I’ve commented on the Ken Ring earthquake predictions in other NZ local political blogs, but I found that the majority of readers don’t seem to grasp the scientific concepts that I cited or commented on. I believe that I naturally fit-in here at SciBlog. I wouldn’t want to venture away into each individual blog that are being syndicated here, since some or most may be outside my domain knowledge/expertise/interests.

    I know that SciBlog allows guest post, but I’m more interested if they allow people to post about research papers (just a summary of each or just their abstracts) that may be of interest to readers here. Either research papers those haven’t been registered in the radar of others (even though they may be concepts that have been around in a few years) or papers that show new scientific applications of existing ideas or papers with completely new ideas. If this is allowed, then I’m happy to contribute. Perhaps this will stop me from polluting other blogs here at SciBlog with my frequent commenting.

  • Peter Griffin, I have a suggestion if you want to explore it to see if it is possible.

    How about making a general thread for science debates available here at SciBlog? Say, one general debate thread a week? This will allow anyone to post messages on any scientific topic. The good thing about this are:

    #1) others will feel free to discuss anything that they have thought about but regular blog topics/messages covered by SciBloggers here don’t address (or have touched) them.

    #2) it will act as alerts , since anyone who stumbles across a scientific topic (or something related to science) somewhere, can raise them here (or point a link to source), so scientists in that specific field can explore those heads up further.

    #3) other scientists, who don’t have blogs (like myself) can post messages in there without the feel to hold-back since posting too many messages in one’s own blog (by others) will irritate them.

    Just a thought.

    Cheers.

Site Meter