Does my Spotting Scope accept Astronomical Eyepiece & Filters?
July 5, 2019
Using Astronomical Eyepieces and Filters with Celestron Spotting Scopes
One of the features that makes Celestron’s Regal M2 ED, TrailSeeker, Hummingbird ED, C90, and C5 spotting scopes much more versatile than other spotting scopes in the marketplace today is the compatibility of these spotting scopes with 1.25” astronomical eyepieces such as the Celestron Luminos, X-Cel LX, and Omni eyepieces.
All Celestron 1.25” mount Luminos, X-Cel LX, and Omni eyepieces can be used with the above-mentioned spotting scopes to provide higher levels of magnification or wider fields of view, not to mention the superb optical performance these prime eyepieces offer in combination with the precision optical design of these spotting scopes. However, it is not recommended to use an eyepiece with any spotting scope that would produce a numerical level of magnification greater than twice the measurement of the scope’s objective diameter as measured in millimeters; e.g., a spotting scope with an objective lens of 80mm in diameter should not be combined with an eyepiece that would yield a level of magnification greater than 160x.
To determine the level of magnification for Celestron spotting scopes in combination with Celestron eyepieces, a handy chart has been created for easy reference.
A Special Note About Filters and Barlow Lenses
While the zoom magnification eyepieces that are included with Celestron spotting scopes do not accept 1.25” astronomical eyepiece filters, eyepieces such as the Celestron Luminos, X-Cel LX, and Omni models certainly do, and they can be used with filters when used with the above-mentioned Celestron spotting scopes. However as spotting scopes generally have shorter back focus lengths than astronomical telescopes, and as the addition of a filter to an astronomical eyepiece increases the overall length of its mounting tube, the eyepiece’s plane of focus may be found to be beyond the position at which the spotting scope will be able to reach focus at optical infinity when so mounted with the filter attached. In terrestrial applications, this will generally not be noticeable, but it may become so in some astronomical observing circumstances. For more information on Zoom Eyepieces, click here.
It should also be noted that while Barlow lenses that feature 1.25” mounting tubes will physically fit the eyepiece mounting port of these Celestron spotting scopes, their long tube length makes them optically incompatible with the shorter back focus lengths of the scopes, therefore they should not be used as focus will not be able to be achieved.