Re: [ATM] about solar filters

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Harro,

> 1 - In what way shall I filter the sunlight? I have an old piece of
> Solarscreen but this gives a lousy low contrast. (I much prefer the
> oldfashioned eyepiece-filter, though dangerous. It gives a wonderful
> contrasty image!). I heard about the homemade Baaderfilter. Is this the
same
> as Solarscreen? Or is Baader much better.

Baader is, from all I have heard, second to none, and pretty cheap too. I
wouldn't settle for less (I don't in fact).

> 2 - Is it possible to give the telescope some corongraph-like features to
> see the ring of light of Venus while entering the solar limb? What's the
> best place to block the direct sunlight: in the eyepiece?

You wouldn't see Venus with a Baader filter on - and I for one wouldn't
consider looking into a telescope aimed anywhere near the sun without one
(and damn well secured in place, too).

> 3 - I was thinking about stopping the telescope with two holes opposite of
> each other, to create higher resolution. Mel Bartels advised me to do four
> holes, to obtain a highter resolution in all directions. My question:
should
> I bother about higher resolution? (Maybe it is better to use only one hole
> of 100mm. Four smaller holes could probably create four shifting images
> caused by bad seeing because of the heating effects of the sunlight...)

With one 100 mm hole mask, you'll likely get about all the resolution you
can use during daytime seeing. As for 4 holes - Steve Koehler recently
calculated a 4 hole mask on a 20" aperture with 15% secondary obstruction -
the result was comparable to a 16.6" with a 29% obstruction, so why bother?

take care,

Nils Olof

_______________________________________________
ATM mailing list http://www.atmlist.net/