Re: Turbulence and diaphragm


giorgio mengoli wrote:
Someone has direct experiences or documentations or you draws that speak of the technique of
diaphragm of the telescope amateur to contain, at least partly, the effects
negative of the seeing?

The effects of seeing are well documented in the later chapters of
"Making your own Telescope" by Jean Texereau.

There are two other items you might be interested in::A) off axis
aperture mask, B) Gaussian Aperture

The off-axis mas is a device placed over the front of a telescope that
reduces the aperture, and makes the telescope less capable of
'resolving' the atmosphereic blur. Some like these, I do not. They work
in bad seeing, but when the atmosphere clears up for moments at a time,
the unmask telescope outperform the mask ones.

A Gaussian Aperture is a mask that sits on the front of a telescope
that reduces the amount of light entering the outer edges of the
telescope. Idealy the limits resemble a Gaussian curve (Bell curve). In
practice, one only needs to reduce the light at the very edge of the
aperture by 60% (40% of the light remains) to get a good effect. This
gets rid of the Point-Spread function effects on the airy disk and
gives a nice clean spot without diffraction rings. It also eliminates a
good precentage of the light entering the telescope. A Gaussian
Aperture can be approvimated with a series of screens cut to different
internal apertures and placed over each other in such a way that light
is reduced in proportion to the off axis distance.

.

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