I recently got a new 10" telescope which comes with a 2" to 1.25" reductor (something like whats seen here)

I have 2" and 1.25" eypiece, and want to buy a UHC filter, so my question is: if I buy the 2" filter, can I use it on the adapter when using the 1.25" eyepiece?


1 Answer 1


Many 2-in to 1.25-in eyepiece adapters have threads on the bottom for attaching 2-in filters. When using these you must be extremely careful that the barrel of the 1.25-in eyepiece does not protrude far enough below the shoulder stop to contact the filter. Some eyepieces have longer barrel extension, and can scratch or even crack the filter if inserted fully. To avoid this problem, some manufacturers do not put 2-in filter threads on the bottom of their adapters.

  • $\begingroup$ I've never seen a 2" to 1.25" adapter that wasn't just a short ring. A right angle adapter usually has threads that could be used. $\endgroup$ Commented Jul 27, 2022 at 15:48
  • 2
    $\begingroup$ I have a few inexpensive 1.25" adapters that all have a depth about 30 mm, and are threaded at the bottom for filters. Many eyepieces like plossls and orthoscopics, particularly at shorter focal length, have barrel lengths under about 25 mm, so would not pose a problem. More complex EPs with wider field and longer FL, and some Barlow lenses have much longer barrels. I agree that a diagonal is a safer place for the filter, but the OP is referring to a Dobsonian telescope that does not use a diagonal. $\endgroup$ Commented Jul 27, 2022 at 18:03

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .