DIY White Light Solar Filter for 8” Dob

[PeterStudz]

Having purchased a ready made solar white light filter for my 4.5” Newtonian last year and enjoyed observing the sun, I decided I’d like something similar for my Skywatcher Skyliner 200p Dob. At the time I was new to all of this and didn’t feel confident with making my own.

This started life as round paper mache box from Hobby Craft for £5. I’m lucky to have a Hobby Craft close to me. It’s a wonderful shop…

https://www.hobbycraft.co.uk/search/?q=round box paper mache

And a 20x29.5cm sheet of Baader AstroSolar Safety Film from FLO for £22, although I see that it’s now £25. This sheet doesn’t quite cover the full aperture (you need some to stick down at the sides) but it’s large enough…

https://www.firstlightoptics.com/solar-filters/baader-astrosolar-safety-film-nd-50.html

I made sure that I followed the instructions that came with the film. Eg the use of double sided sticky tape to hold the film down and not fitting the film tight.

I had thought that the 25cm box would be ideal for my 8” Dob. But I didn’t realise that the size was the outer dimension of the lid and not the internal diameter. It was a really snug fit. Now you could get away with this, and it might actually be easier, but I had a design sketched out which needed a bit of a gap for some tabs. So, I used the box lid and made it longer by sticking a couple of strips of veneer (which I already had) into the inner part of the lid. With some 2mm black craft foam this was now a tight fit on the end of the OTA. I’m not keen on relying on a tight fit so for security I put some holes in the tabs which fit over the adjustment knobs of the secondary spider. The foam tabs being stuck down with Evo-Stik impact adhesive.

A circular hole of 185mm diameter (as much as I could get away with) was cut using a sharp knife into the box lid. This was painted white on the outside with black trim. 

I then made a cell with another piece of card, added some card tabs or “ears” so that when I dropped the cell into the lid it would be an accurate fit. For me gluing “ears” is far easier than trying to cut the whole thing to an accurate fit. This was painted with blackboard paint on one side with double sided sticky tape on the other. 

The film was carefully stuck to the tape on the black card cell. Following instructions and ensuring that the film wasn’t tight. More double sided tape was added to the round box lid and the cell plus film dropped and stuck down. I then finished off by adding flocking material to the inner sides which were scraps left over from flocking the OTA. Blackboard paint would work just as well but I didn’t want to risk dropping any onto the film. 

That’s it. I’ve used it a few times now and it seems to work well. It’s certainly not going to fall off.

As I mentioned before - you could get away with cutting down the box rather than using the box lid. And a cut down box will make a tight fitting rear dust cover as shown in the pictures (shown unpainted).

And every solar filter needs a safe storage box. I made one out of a lager 29cm Hobby Craft box, painted and decorated.

[vineyard]

Ingenious.  I'm toying with the idea of using these cake boards to make the retaining rings: https://www.amazon.co.uk/Culpitt-Round-Cards-Silver-Boards/dp/B09RKM257Q/ just need to figure out the holding cylindrical cardboard contraption.

Excellent idea of the hobby boxes to store them carefully in.

[wookie1965]

Where did you get the chair from please

[PeterStudz]

1 hour ago, wookie1965 said:

Where did you get the chair from please

I got it locally for £10 via Gumtree. For the 200p it’s easily adjustable to the full length of travel. It’s also handy inside the house. My daughter uses it as an art stool too.

I believe it’s an old IKEA screw stool that’s called “Ringo”. No longer sold. Have a look on the likes of eBay and Gumtree. There were a lot made so they do come up second hand quite a bit. And a quick search on Gumtree comes up with two for a total of £15, or £7.50 for one. Of course it’s near Birmingham but it shows that they are around. 
 

Pair of ikea ringo height adjustable stools 

Edited October 21, 2022 by PeterStudz