Dobsonian and Sun observing

[Sneezy24]

I'm just about to order an 8" Dobsonian (almost certainly Revelation - visit to Astrofest will confirm that or Skywatcher).

I will probably have a go at observing the sun at some point (if it ever appears again), I've read lots about Baader film, and how to make a full filter, but I'm sure I read something about using just a 3" hole (with Bader film!) - between the secondary supports?? Not sure how this works! Anyone got a diagram/picture so I can get my head round this?

Sorry for the Newbie question!

Mick

[GuillermoBarrancos]

For large apertures you have something like this: http://www.teleskop-express.de/shop/product_info.php/info/p6251_Astrozap-Off-Axis-Glass-Solar-Filter-for-Tubes--232-238mm.html

Tho when I had the 8inch SCT I used a full aperture Baader filter without any problems. It wasn't too Bright for me.

[Sneezy24]

Thanks for that.

I assume you could make something similar using Baader film over the smaller hole?

[GuillermoBarrancos]

Thanks for that.

I assume you could make something similar using Baader film over the smaller hole?

Most safe is to make a full aperture filter first and then stop it Down.

[Sneezy24]

Good idea, thanks. I suppose I can then play with size/position of the hole.

Mick

[Peter Drew]

A 3" aperture off axis filter will be perfectly adequate for solar obsevation, make sure you use the ND5 variety. The aperture should be placed such that it provides an unobstructed lightpath between the spider vanes. 

[rwilkey]

Hi Mick, when you get your Dob, you will see that the plastic dust cover at the front has what appears to be two circular caps, well, one is fixed and one can be unscrewed, giving a stopped down view to the mirror, it is behind this hole behind the cover itself that you tape the Badder solar film firmly to the back.  When you replace the cover over the front of the telescope make sure the hole with the Badder film is over the freer part of the telescope insides, not over the secondary mirror side and that will be enough for you to look at the sun in white light.

[Avocette]

Hi,

I have done as Robin mentions above, taping the Baader film across the small hole onto the rear of the main tube cap. However, I found that after a few months the film already showed signs of perforation around the edge of the small hole through the tube cap. My feeling is that this was due to the filter material acting as a drum and flexing everytime the small cap was removed or replaced, and perhaps even when the whole tube cap was removed or replaced. So my advice is to be super vigilant if you use the Baader film in this way and be ready to replace it when (rather than if) it starts to perforate. 

[Eastridge]

We built solar film to cover the whole 10" aperture  but leave the main cap on just using the small hole Robin refers to, belt and braces I guess but means we have both and no chance of sunlight in at the edges of the main cover causing an issue.