Re: [APML] H-alpha solar photography nightmare

[Chris1011@aol.com]

In a message dated 10/7/2002 10:42:51 AM Central Daylight Time, vega@ulisse.it writes:


> I wonder: where should such a disk be placed? I guess that:
>
> 1) it should be put so as to get its borders perfectly in-focus in the field 
> of view when the Sun itself is;
> 2) it should be of the same apparent size as the Sun's disk, which of course 
> varies slightly as time passes (time scale something like a few days?).


I've seen people glue a penny on a thin stick which protrudes out the side of an old eyepiece. The disc is placed at the focus point of the eyepiece. You can then move the stick around to block the sun with the disc of the penny. It does not have to be the exact same size, bigger is preferred. You will then be able to uncover a small wedge of the area that you want to observe. The Baader coronagraph comes with 6 precision machined occulting discs which are attached to a glass lens placed exactly at the focus of the telescope. A projection lens then transfers the first image to a point behind the assembly where you can then view it with an eyepiece or a 35mm camera. A built-in diaphragm allows the user to eliminate any glare that gets past the occulting system, and renders the background sky very dark for maximum contrast. 

Roland Christen