Solar filter

[8kids]

I'm going to make one for my 300pds, all I want to know is, is aperture king when solar viewing or is smaller better?

Gary

[DirkSteele]

It is an interesting question. I have a full aperture glass solar filter for my 11" SCT, but I know quite a few people who say they have better results with scopes on the smaller end of the spectrum as the atmospheric turbulence is so prevalent during the day as to negate the usual benefits of a larger aperture and being smaller actually increases your chance of observing through a small tranquil slice of the atmosphere. I rarely observe the sun (filter was bought for the 2004 Venus solar transit) so I have not had the benefit of viewing through scopes of differing sizes to form my own opinion on this matter.

I am sure other SGL members will also have opinions as well. I look forward to reading them.

[Bizibilder]

It has been a long held theory that anything over 100mm (4") aparture gives no significant advantage in Solar observations due to the atmosphere being turbulent during the day and preventing a larger scope from benefitting from its additional resolving power. For your 300mm scope I would suggest a 100mm off axis solar filter - positioned so that the filtered light passes beteween the legs of the secondary mirror holder. You can make one from stiff cardboard - just make sure that there is no way it can come off the scope by accident. You could start by making a mini-filter using the scopes plastic cap if it has a small (60mm?) hole already in it. An added advantage with this method is that you can get more than one filter from a piece of film. Baader film is only 7.75" (200mm) wide for the standard sheets.

[8kids]

It has been a long held theory that anything over 100mm (4") aparture gives no significant advantage in Solar observations due to the atmosphere being turbulent during the day and preventing a larger scope from benefitting from its additional resolving power. For your 300mm scope I would suggest a 100mm off axis solar filter - positioned so that the filtered light passes beteween the legs of the secondary mirror holder. You can make one from stiff cardboard - just make sure that there is no way it can come off the scope by accident. You could start by making a mini-filter using the scopes plastic cap if it has a small (60mm?) hole already in it. An added advantage with this method is that you can get more than one filter from a piece of film. Baader film is only 7.75" (200mm) wide for the standard sheets.

That's what I was wondering, wether if it's worth making one as large as I can go or as you've just stated 100mm.

I think I'll just make one to fit between the spider vanes.

many thanks.

Gary.