Caution is called for using any optical equipment to view the sun.
Direct viewing with a large filter in front of the objective lens is
safe. Filters near the focal plane are dangerous since they may crack
with overheating. Projection viewing is safe for the eye but may still
be damaging to equipment. Cemented lenses may have their cements melted
and elements separated. Lenses which are tight fitting in their barrels
may expand sufficiently that the elements burst under the pressure.
Simple, uncemented lens designs such as Huygens and Ramsdens are best to
avoid expensive damage. These are the types of eyepieces typically
provided with inexpensive scopes.
Chuck Norcutt
On 5/23/2012 3:46 PM, Moose wrote:
> On 5/23/2012 6:34 AM, Chris Trask wrote:
>> This one is more practical:
>>
>> http://www.cloudynights.com/ubbthreads/attachments/2722210-scherm1.jpg
>>
>>
>>
If you use frosted glass or plastic for the viewing screen you can
photograph it from behind. Difficulty in making this is finding a
refractor telescope with a 2-point finder mount.
>
> Needn't be a refractor, should work with a catadioptric telescope.
> <http://galleries.moosemystic.net/MooseFoto/index.php?gallery=Tech/Misc&image=IMG_0420croof30.jpg>
>
> I'm not sure it the tube is large enough for the finder mount on
> mine, but the design is certainly simple. Fortunately, I don't feel a
> need for one. I guess I got it out of my system 40 some years ago.
> :-)
>
> Folded Optics Moose
>
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