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Isonomia wrote:
> One solution I'm considering is using solar filters for astronomy and
> I quote (http://www.greenwich-observatory.co.uk/acatalog/
> Solar_Filte.html): "BAADER AstroSolar film has become the natural
> first choice for white-light solar observation. It's optical qualities
> are excellent, enabling you to see high-resolution images with a
> natural colour."
>
>   
I used similar material during the trials with my spiegelboog in 2005 
(check my website www.dehilster.info on the spiegelboog page, fig. 14. I 
am the observer at the far right holding the spiegelboog with a piece of 
foil attached). The only downside of these filters is that they are very 
reflective (as you can see on fig 14), so when you mount it at a 
distance from the telescope you will have a lot of reflection from 
behind you interfering with the direct dim image. You can compare it to 
holding aluminium foil at an arms distance. It is foil and hence not a 
flat surface, so light gets reflected from all directions towards your 
telescope and will at times hide/suppress the direct image of the sun. 
This foil should be mounted directly on the telescope to avoid 
reflection, as we did on the theodolite, but then you will probably not 
be able to see the horizon...

Nicol�s

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