Sun filter for 350p Flextube

[Stephen196360]

Hiya guys

I've got a Sky-Watcher 350p FlexTube 

And I'm after either making

Or buying sun filter for the front of my scope 

The problem is its 400mm wide

And I can't seem to find either the filter film

Or a ready made filter that fits my scope 

Has anyone got some solar film 500mm wide

Or equivalent 

Or information were to get some from

Kind regards steve 

[Naughty Neal]

 Baader AstroSolar A4 ND5.0 Safety Film Sheet - Rother Valley Optics Ltd

The RVO link has the same 1m x 0.5m  film as below.

Baader AstroSolar 1.0M X 0.5M ND 5.0 - Widescreen Centre (widescreen-centre.co.uk) 

Edited April 1 by Naughty Neal

[Steve Ward]

A 100-150mm offset filter will be more than adequate unless you are lucky enough to have near-perfect seeing from your location.

Without that quality of seeing the 350mm full aperture will be completely overkill .

[Louis D]

I would recommend making an off-axis aperture mask out of stiff foam board with the circular opening between spider vanes and covered with solar film.  That way, you'll have an unobstructed view, so there won't be any secondary shadow to fight while solar observing at larger exit pupils due to your scope's long focal length and fast f-ratio.  With the off axis aperture mask, you'd end up with a  roughly 135mm f/12.2 unobstructed solar scope.  Yes, it will be a huge 5.3 inch APO.

I see you already have a truss shroud which is extremely important during solar observing.

[Stephen196360]

Hiya guys

Thanks for the info 

However I'm a little in the dark about offset terms etc

Could someone give a technical drawing etc on the construction or explain exactly what I need

Kind regards steve 

[Steve Ward]

https://astrosolar.com/en/information/how-to/how-to-make-an-inexpensive-filter-cell/

[bingevader]

Made a few of these now, you shouldn't need a technical drawing, no technical skills here!

The above instructions are good.

If you make the offset diameter just smaller than the space between the spider vanes, as Louis D says, you should only need an A4 sheet of film, which would be quite a saving.

 

[bingevader]

Sorry, picture's a bit huge!

On my 8" dob (and the 10" that this picture is from), I have a cover that fits the top of the tube.

The offset is a hole covered by a cap (top left) that reduces the diameter of the 'scope and is offset from the centre to avoid the 2° mirror.

You'll basically be replicating this, but with a cover that fits over the diameter of the tube and with a smaller, offset, hole covered with the solar film.

As I said above, I'd make it bigger than the one in the picture, to fill the space between the spider vanes.

The one I've made for my 8" dob, to cover the hole in the cover is too small really.

The full size ones I've made for my 90mm and a 150mm in school are much better.

[Louis D]

6 hours ago, Stephen196360 said:

Hiya guys

Thanks for the info 

However I'm a little in the dark about offset terms etc

Could someone give a technical drawing etc on the construction or explain exactly what I need

Kind regards steve 

Here's an article about making an off-axis aperture mask.  It should give you the general idea of what is going on.  You would just cover the mask opening with solar film for solar observing, and securely mount the mask to the tube opening.

[terrain_inconnu]

An open tube reflector (even with a light-shroud) is a bad (i.e. risky) choice for doing solar. See a relevant discussion here.

Edited April 3 by terrain_inconnu

[Carbon Brush]

I fully agree with the idea of off centre masking, if using a newt (or other large) scope.
I also agree that a small refractor or mak, or similar, are a better choice for ease of use.
However, we do not know if the OP has another scope & mount available, or if his budget will stretch to this.

An A4 sheet of Baader film is £23. Other materials to make a safe filter holder are probably free from the shed/garage.
The leftover film can be used later for a refractor, or convert binos for sunspot viewers, etc.

HTH, David.

[Naughty Neal]

I do whole heartedly agree with all recommends to use offset , if the ota came with an aperature cap then likey it will have an offset cover already.

My small z130 has the offset aperatue cap though for white light I use a achromat.

I answered though as that is what Stephen  enquired about.

Edited April 3 by Naughty Neal