SingAstro

It is a 48mm threaded filter, but I think you need a step down ring for it .

If it is USD$21 like what Debash said, I would not mind , but if it is very expensive, then really got to consider .... hehehehe.....

Pleased to meet you too

Thanks Debash :D ... so I guess just quoting this address for them will do? :D http://www.telescope.com/shopping/product/detailmain.jsp?itemID=98&itemType=PRODUCT&iMainCat=3&iSubCat=257&iProductID=98 Jeremy, I would be delighted if we can combine shipping :D. want me to write the ema...

Sure, why not .... if you want to use my V-Post ... I can do it too .

You can get the Celestron other brands of Oxygen III filter from them as well

OPT do, but Orion don't. ..... I have to send items to Vpost for things from USA to Singapore which does not accept orders from overseas. I was thinking along the line where Orion ship out the filter directly

yaoting (male hor .... most people tot I am female because my name sounds like a girl's name ..... especially since my name in Hanyu pinyin is the same as my female cousin )

sorry, what I mean is how do you know the exit pupil as in how to measure the exit pupil. I had never measure the exit pupil before

how do you know?

But Debash, I surfed OPT website, it is stated as USD$99.95 for the 2" version and USD$79.95 fro the 1.25" version for Ultrablock :(. They will only send to a USA address as well. I know Amazon is selling the 2" Ultrablock for $80 though :D. I am looking for a 2" edition as I am ...