Hi Folks
This may be a no-brainer to most of you, but despite some web search efforts, I have never been that happy with advice on how to attach my Bahtinov mask to my refractor until I read a couple of sites that suggest using sewing rings/hoops. Basically the idea is to attach your focusing mask to a sewing hoop then slide the hoop easily and securely over the end of your scope. The hoops are easily found in craft stores, or stores like Lincraft or Spotlight. So for the uneducated, like me….
Taking note of the outer diameter of my WO Megrez 90 and my 72 mm guide scope, I purchased several hoops that, with some shimmying, would fit snugly over the ends of these scopes. Each hoop has an outer and inner ring – the outer ring was discarded to reduce weight. I then ordered several wonderfully made acrylic Bahtinov masks from Mike (aka ozstockman) http://www.iceinspace.com.au/forum/s...ad.php?t=47090, with outer diameters the same as the outer diameter of the inner hoop rings. I then simply used double sided tape to attach each mask to the wooden rings (you could use PVC glue instead). Finally, I found that some 6 mm self-adhesive Raven weather strip stuck to the inside of one of the rings allowed the Bahtinov mask to fit snug and centered to my 72mm guide scope.
For the 90 mm scope, a larger ring was used, but the ring only just fit over the end of the scope so a little sanding was required to the inner ring. This also allowed me to glue some 10 mm black velvet ribbon to the inside of the ring so the mask would slip on and off of the scope smoothly and easily – not to mention, protect the end of the scope from any scratches. The end result was a perfect fit of the Bahtinov mask to my Megrez 90 scope.
There are many different sewing hoop sizes so I’m sure you could find one to suit most scopes. I found the method above provided an accurate lightweight solution to attaching the masks effortlessly to the scopes.
Like I said.... this may be a common approach, but for those of you like me who were unaware of using sewing hoops for attaching focusing masks, then I hope this helps.
Thanks Ric, I'll be interested in knowing what improvements you might make.
I've found that as long as the scopes are pointing up (and they always will be with the masks on) the masks will not move at all while slewing. And as there is no velcro used to hold the mask in place, there is no accidental movement of the scope when slipping a mask on or off.
Hi Steve, the improvement I was thinking about is to glues some more hoops together onto the single one that I use now and add some depth.
The felt and stripping are a great idea to make it fit more snug.
At present I use only one hoop which is around 5mm in thickness with bit of tape holding it in place. It does the job quite well but there is definitely room for improvement.
Thanks Rob - I'm a bit pedantic so I would probably find electrical tape just as effective!
Ric.... I didn't think to put two hoop rings together for depth. This would certainly make it more secure on the front of the scope. By the way, FYI.... I dropped into Lincraft to get some felt for the inside of the sewing ring and brought the aluminium scope cap into the shop with me. I thought the scope cap was felt lined only to be corrected by the Lincraft staff member that it was actually velvet not felt. They didn't keep any suitably thin felt anyway but they had heaps of velvet ribbon in a range of widths - all of which were quite thin so it wont reduce the inner ring diameter too much.
