Who adds the twinkles...and why?

[meta]

Consider http://antwrp.gsfc.nasa.gov/apod/ap051225.html

The largest stars have diagonal "twinkles" in X shapes shooting out from them, with "haloes" of glow. I have to believe that these aren't an artifact of the telescope, but are artificially added by someone.

So my question is... who adds the twinkles, and why?

I understand that the media might want their astronomical pictures jazzed up with fake twinkles and lens flares and the like, but I'd have thought the audience for APOD would want to see an accurate depiction of the actual subject.

I dunno, this has been increasingly bothering me of late. Am I alone?

[craterchains]

Who?
God does. Just look up and say thank you.

Norval

[harry]

Twinkle twinkle little star
How I wander what you are
Up above the world so high
Like a Twinkle in the sky


Merry Xams
and a Happy New Year

smile its good for the IQ

[jgabany]

Hi:

The twinkles are an artifact of the telescope's optical system. This image was taken with a 20 inch cassegrain reflector telescope.

A picture of the telescope can be viewed at the following URL:

http://www.cosmotography.com/images/rc_secondary.jpg

The inset diagram illustrates the path light takes to reach a focus with this telescope design.

Notice that the secondary mirror is held in place by four sets of brackets. As light passes around these brackets, the twinkle artifact is introduced.

[Axel]

The Mercedes-Benz people ought to fund a telescope with three brackets.

[BMAONE23]

What should be done id to suspend the central mirror in the middle of a clear flat smooth glass plate then the artifact problem will not be a factor.
It is a good way though, to differentiate between foreground stars and background galaxies.

[jgabany]

Hi:

Schmidt and Maksutov Cassegrain telescopes take the approach you mention- the secondary mirror is attached to the underside of a clear lens that is placed at the opening of the scope.

These kind of telescope designs are some some of the most popular in the world- Meade and Celestron have sold hundreds of thousands over the past 30 or more years.

While this removes the twinkle artifacts (also known as diffraction spikes, by the way) it introduces other issues caused by forcing the light to pass through a piece of glass before stiking the primary mirror.

Unless the large lens at the front of the scope is carefully made, subtle color smearing, a slight loss of light and loss of details can be introduced to the image.

I have owned several telescopes by both these fine manufacturers but, through experience, concluded that I would rather have the twinkles. :>)

[S. Bilderback]

The quality of the glass support would have to be incredible to prevent optical distortion. Glass isn't a rigid material (large mirrors and lenses need support), so maintaining structural integrity, vibration dampening from tracking movement and wind, and one more hardware to keep clean makes it impractical.

If you would like to design a stable mirror support using a harness of thin, high-tension carbon fibers you might have something.

[BMAONE23]

Maybe you could utilize the militaries new transparent aluminum as a single 1/4" thick piese with a slightly thickened and shaped center that was mirrored. Thin, Light weight, and one piece.