2"filter with a 1.25" EP

[JJDOBBER79 (Jas)]

Hi, quick question. Can I use a 2" filter with a 1.25" EP. I have a 2" 30mm threaded extension tube but when I use this with my XW10 I cant reach focus. Does anyone know of any other way to do this. Or someway I can reach focus using the extension.

[alistairsam]

hi,
if you have a 1.25inch to 2inch adaptor, the filter can be screwed onto the 2inch adaptor at the telescope end. Its threaded for 2inch filters and won't use up too much back focus so your focus won't be affected.

like this
http://img530.imageshack.us/img530/6521/2infilter.jpg

Cheers
Alistair

[JJDOBBER79 (Jas)]

thanks alistair. I have one of those but it is not threaded. I think I will buy a new one.

[astro744]

To focus do you need to go further in or further out? If out then just pull the eyepiece out a bit and tighten. You can get parfocal rings than lock around the barrel to give you the correct distance each time. See http://www.scopestuff.com/ss_par1.htm

I've not seen an XW up close only a picture so are you saying a 2" barrel is screwed into the wider portion of the eyepiece? If so then this should got into the focuser all the way and you would in fact get the eyepiece in further in 2" mode. If you were using your eyepiece in 1.25" mode would you actually have the eyepiece out a little further (typically 5-10mm depending on 2"-1.25" adaptor although I know some adaptors are quite thin).

Note if you are going to get a new threaded 2"-1.25" adaptor you need to make sure you will have plenty of clearance inside so that the 1.25" barrel of the eyepiece does not hit your 2" filter.