Embroidery hoop - which size?

[moffer]

Just made a dew shield out of a foam mat. Trouble is it's losing shape at the open end so will be buying a plastic embroidery hoop to cure the problem.  Not sure what size hoop I need for my 200p dob, 8" seems the obvious choice but thought it best to check first. Also, thinking of stitching it to the foam unless someone can suggest a better way of holding it in place.

[Bizibilder]

I think you will need the hoop to be "tube sized" which is more like 9" diameter?  There is some slack in the hoops but not much.  I have several foam mat dew shields and they hold their shape quite well with no reinfoecement.

[Steve Ward]

I needed a 9" hoop for the full size Solar filter I made for my 200PDS if that's any help .

Best bet would be to measure the dew-shield and then visit a haberdashery and compare the 8" and 9" against your measurement .

[LukeSkywatcher]

I needed a 9" hoop for the full size Solar filter I made for my 200PDS if that's any help .

Best bet would be to measure the dew-shield and then visit a haberdashery and compare the 8" and 9" against your measurement .

I think this is a good plan. The OD (outside diameter) of an 8" scope is slightly more then 8", but a good bit less then 9". You want something that goes on and off easily enough. Ive made a dew shield for a 130mm scope and a set of 20x 90 bins ,using a camping foam mat (who hasnt). I cant say that they has lost their shape. Maybe you need thicker foam? 

[moffer]

The foam is 5mm thick so probably a bit on the thin side. Thing is I had it given to me, it's light in weight and black, most camping mats I've seen are sky blue. I've used velcro to join the foam so can adjust the diameter to suit the hoop - a 9" hoop should be ideal. Don't think there's any need for a hoop on the scope end as the foam stays in place just fine.

Thanks chaps