Hand of the maker

[mmcirvin]

The makers of kitschy commercial religious art of the Christian persuasion should be grateful to the telescope builders of the world for so often putting the secondary mirror struts in a cross shape.

Comments

[thette.livejournal.com]

Backstory?

[mmcirvin.livejournal.com]

It leads to lots of starry photos like this (http://en.wikipedia.org/wiki/Image:Pleiades_large.jpg), thanks to diffraction. Stars don't usually look like that to the naked eye, but the cross-shaped diffraction spikes have, I think, influenced a lot of modern iconography of such things as the Star of Bethlehem.

Hmm, that's a question worth investigating in itself--do depictions of Stars of Bethlehem with cross-shaped spikes coming out of them predate the invention of the telescope? It would be interesting either way.

[mmcirvin.livejournal.com]

Here's a nice one with T-shaped spikes (http://en.wikipedia.org/wiki/Image:L_Adoration_des_Mages.jpg) (like a tau cross, I guess) from the 1400s. I hadn't seen that before.

[mmcirvin.livejournal.com]

...More thoughts about this:

There are a lot of ways to see rays coming out of a star or other bright light. Just squinting will usually create the appearance of vertical rays, and anyone who's seen a lamp through a sheet or a piece of fabric is familiar with cross spikes. And, of course, prefiguring the cross in the Star of Bethlehem is an obvious enough visual trope that I wouldn't be surprised to see it appearing early on.

But I still think the spikes in telescope images have fed back heavily into the modern imagery.

[ikkyu2.livejournal.com]

According to wikipedia, which is always suspect, reflecting telescopes were invented in the 16th c. But I suspect various types of aberration in the lens of the human eye could account for as much of this as you wanted to attribute to it.

Coincidentally, yesterday I was just reading about tunable wearable optics (http://www.cvs.rochester.edu/williamslab/r_contacts.html) for correcting higher-order aberrations of the lens. Interesting stuff.

[mmcirvin.livejournal.com]

As far as I know, Isaac Newton invented the reflector sometime in the 17th. Most modern reflectors are some descendant or other of the Cassegrain, which was actually invented not much later.

[darius.livejournal.com]

I've wondered why the classical Greeks didn't invent it -- didn't they have the math, and the basic idea that light goes in straight lines and reflects at equal angles? Though that'd still leave you without a lens for the eyepiece.

[tau-iota-mu-c.livejournal.com]

Being able to grind a mirror to 1/16th of a wavelength is not easy. And the technique is *far* from obvious.

And besides, the greeks couldn't even get gravity right. Light things fall slower than heavy things, ptui spit!

[smashingstars.livejournal.com]

Ooh, I wish I'd known that back when I was on Ghost Hunters boards. Some really gullible people thought they'd seen some kind of "ghost star" in a photo, where I was sure a bright star (the ghost star! ooh, scary!) had been cut 'n' pasted in. The star that was pasted in must have been photographed by another camera with a different lens, since no other star in the photo had the same kinds of spiky bits emanating from it.

[mmcirvin.livejournal.com]

Not necessarily--it could be that the bright light was just the only one in the frame that was bright enough to show visible diffraction spikes, from whatever was causing them (maybe the camera aperture).

[mmcirvin.livejournal.com]

This page has a caption for another Pleiades image (http://cseligman.com/text/stars/starclusters.htm) in which the photographer actually ran strings across his telescope to make pretty cross spikes--the secondary mirror was set in a transparent plate, so they wouldn't have appeared otherwise!

[tau-iota-mu-c.livejournal.com]

I originally wondered how you could run strings across a binary telescope to decompile the secret passphrase from it.

And now I wonder if you can can come up with any funky shapes (I dunno, a graphic of a cat chasing a laser pointer?) using different strings, although you'd need to somehow compose a fourier transform of your funky shape to have it come out right, if I remember the theory of diffraction spikes correctly.

[mmcirvin.livejournal.com]

You'd pretty much need something like a hologram placed across the mouth of the telescope. That's what a hologram is--a diffraction grating constructed so as to make an arbitrarily funky image in the diffracted light.

[nexstarman.livejournal.com]

Six-pointed stars come from telescopes with three vanes. And maybe from use of an iris with x number of blades?

[mmcirvin.livejournal.com]

I was going to make a joke about how such photos would figure prominently in Cylon religious art. But I couldn't find a good picture of an old-school shiny Seventies Cylon shot through a six-pointed star filter, the way they used to do it all the time.

[mmcirvin.livejournal.com]

Though I did find this. (http://thewisdomofadistractedmind.blogspot.com/2007/10/these-days.html)

[antikythera.livejournal.com]

Aah, I've seen that. It's in Toronto and we googlemapped exactly where it is. ^^

[mmcirvin.livejournal.com]

And, yes, I've seen six-pointed stars with my Canon S2 IS by shooting bright lights with the aperture stopped down as narrow as possible (while I was trying to shoot fireworks).