Solar observing

[Astro-Nova]

Seen projecting it on a sheet of paper. Is solar observing not bad for the optics? Anyone done projecting?

Seen solar filter for 30.00 I want to get if Im able to see venus sun transit.

I dont think I want to use projection, i dont feel its as personal as looking through the scope, obviously with solar filter.

[garethmob]

the usual and cheapest way is with a baader or seymore solar filter (the baader is more neutral seymore is red) but both you see the basic sun spots and granulation

the filter takes away 99.9% of the suns rays and heat from the scopes optics so its save providing its secured on perfectly

iv seen projection systems, mainly on TAL scopes but im not sure how they work

[iwatkins]

It's actually 99.999% or ND5.0.

Projection works by using a telescope as normal, including an eyepiece but focusing the exiting light onto card/paper at a short distance. Recommended to only be used on refractors. Also would not recommend using such a system in public. Just too easy for someone to put their eye to the eyepiece while your back is turned.

If you want to share the view, much safer with solar film over the front then take in turns at the eyepiece, or share by using a camera instead of eyepiece and show on a laptop. You can then use this method on any telescope design, not just refractors.

Cheers

Ian

[Bizibilder]

There is a further problem when not using a whole objective solar filter and that is that both the Sun's light and heat are concentrated into the scope. Any parts that are either plastic or lenses that are cemented (glued together) will be damaged by the heat. Glass lenses themselves may shatter of sunlight/heat are focussed onto them.

Baader film (ND 5) in a properly made holder is safe to use both visually and photographically. The ND 3.8 is only for photographic use.

[4lefts]

another thing to remember is that, from the uk, we'll be very lucky to see any of the transit - doesn't it finish at 5:30 in the morning or something?

for the solar filters, flo sell ready made ones from baader filter film too.

[Moonshane]

it will be seen for about half an hour if the NE horizon is clear as the sun comes up. I use a Baader filter and it's great and safe

[callump]

I have used the projection method a lot in the past - to be honest I feel safer looking at the projected image than through a white-light filter. Though I now use an h-alpha solar scope (Lunt) primarliy

My first projection device was just a screen held on a threaded rod some distance behind the eyepiece, with the rod attached to the tripod head, where the scope attached too. This worked o.k. but was a but prone to vibration. I was also worried about people trying to look through the scope at public events, so I did not use it much for that.

My second projection device was an oblong box made from foam board, with a window towards the back to view the disk of the sun through. This worked much better, was less prone to vibration, provided some shade for the view of the sun, and the eyepiece is shielded so that its difficult or almost impossible to look through it, and if you tried you would probably push the scope away from the sun in the process.

In the June 2012 Sky and Telescope there is a good article about building a 'sun funnel', which is another projection device but the view of the sun is through the screen at the back of the funnel.

You can read about this at http://cdn.transitofvenus.org/docs/Build_a_Sun_Funnel.pdf

I have not experienced any particular problems with heat build up in my refractor (Borg 76ED), or eyepieces. Newtonians are not recommended unless stopped down, and dont try it if you have a cat (literally).

Callump