View Full Version here: : Filters and scope size

21-03-2007, 03:47 PM
Hi there

Posted this Q in another thread but suspect it may have become buried... (http://www.iceinspace.com.au/forum/showthread.php?t=17831)

I've been wondering if there is a minimum aperture for scopes/binos that O-III HB filters could be used with? Eg. would 100mm BT45 binos or an 80mm refractor be too small?

I guess my question is whether there is much light loss with these filters?



Peter Bobroff
21-03-2007, 09:16 PM
I have used the OIII filter on an 80mm refractor, great view of the Veil Nebula.

I have a setup to fit OIII and UHC filters on to 7x50 binoculars - interesting but not too serious.

I think you can use them on anything.

Peter Bobroff
21-03-2007, 09:22 PM
I haven't found the HB filter nearly so useful. I use it only on the Horsehead and have found that a 14" to be the minimum. However friends of mine swear they can see it with smaller scopes.

22-03-2007, 05:47 AM
I wouldn't get the HBeta - it's useful only on one or two objects, and even then I believe a big aperture is required.

An O3 or UHC filter can be used on any size scope and will be useful on any size scope, but if using it on a small scope just remember that it will cut out some light, and with smaller apertures you want all the light you can get!

22-03-2007, 07:51 AM
Thanks, Peter and Mike - appreciate the advice.


Don Pensack
28-03-2007, 08:21 AM
So long as you keep the magnification under 10X/inch, there is no minimum size scope in which these filters are usable. I've used them in 50mm binocs.