solar observing with a newt

[ponytale]

I am thinking of adding baader film to my f5 newt, it is an open truss tube type the mirror has a short tube extension of 200mm and the secondary is in an open cage, do i have to put film over tube end near primary mirror or over the open end by the secondary / i am worried about stray /flashes of sunlight that may get into my eyes ,will baader film work below the secondary or will it reflect light back to my eyes ?

do i need to make a shroud for solar observing

i hope this is not a silly question, but i am sure some one will reasure /help me,

[Bizibilder]

You MUST put the solar film over the extreme end of the tube and you will have to make a proper, secure and lightproof shroud for your scope. It simply isn't worth the risk of losing your eyesight by getting things wrong.

To be quite honest I wouldn't use an open truss type design for Solar work as the risk to your eyesight is too great should you not get the shrouding correct. It may be better to get yourself a small refractor (and a solar filter!) and use that. It will be quite safe.

[Nova]

Only silly questions are the ones that dont get asked. The film goes over the open end by the secondary but not sure if you need to do more with an open truss to add additional protection. One of the SGL members did a great safety video on youtube for solar observing but I cant for the life of me find it

EDIT

Here it is http://stargazerslounge.com/beginners-help-advice/151264-safe-solar-observing-video.html

[angusb1]

I'm sure more knowledgeable people will respond to this as well but my understanding is that you can use a sub-aperture mask for solar observing with the solar film across that. Because the sun is very bright you do not need the full aperture of an F5 scope, rather you can get a "slower" f ratio by masking off all but a small area of the aperture. This will give you a narrower light cone and greater depth of focus as well as making it easier to convert your scope between a solar and night-time setup as you just remove the mask when you want to use it at night. Also the smaller aperture will be unobstructed by a secondary if it is away from the central axis so the light goes past the secondary on its way into the scope. This should improve contrast in comparison to the same aperture with a secondary obstruction.

In theory the primary should not reflect any light anywhere but up towards the secondary due to its shape so you shouldn't need to shroud the tube but I'm open to correction about this.

[Peter Drew]

Probably the best route is as Angus suggests. You should be able to achieve a 3" unobstructed aperture on a Newt your size, this will show you everything that's visible in white light. Contrast would be better if the tube was shrouded but I don't think there is a safety issue with stray light not associated with the front aperture.

[Moonshane]

I don't think there's any issue for you but what about someone standing a little further away? could they see the sun's reflection in the mirror?

[Peter Drew]

I think not, if the scope is centred on the Sun, the angle of incidence still equals the angle of reflection.

[Moonshane]

smart Alec

I never mind being proved wrong as long as I know why - now I do!