Quote:
Originally Posted by julianh72
You should be VERY careful if using a Collapsible Dob to view the Sun. (I wouldn't recommend it at all.)
In theory, as long as it is pointed directly at the Sun, with a full aperture solar filter in place, then the filter will cast a shadow over the whole primary, and it is just the same as using a closed-tube Newt.
However, think about what happens as the Sun tracks off-axis. (And with a manually guided Dob, this will happen continuously, or if the scope is bumped off-axis.)
You could start to get some direct sunlight passing through the open tube and striking the primary. As it will be a few degrees off-axis, the reflected (focussed!) beam shouldn't be directed to the secondary / eyepiece, but it may well strike the solar filter adjacent to the secondary. I would imagine the focussed sunlight from just a few percent of the primary could burn a hole in a plastic film filter in just a second or so, or crack a glass filter in not much more time, and then you could be in all sorts of trouble!
At best, you might only scorch or burn part of your scope (or set fire to your hair); at worst ....
I think a black-out shroud is HIGHLY advisable!
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oh yes don't get me wrong - I agree a shroud is
highly advisable
i was just pointing out that is
possible without a shroud, the OP suggests that it wasn't. my circumstance was a one off for the transit of Venus haven't done it again since. it tracked fine all day as i did a two star alignment pre dawn. these scopes track very well if set up carefully.
the good news is that there are now affordable options available (back in 2012 the only options were a couple of hundred dollars and from o/s - if you weren't really game to make your own).
http://www.myastroshop.com.au/products/accessgen.asp
i haven't tried one but probably will.