I have trouble seeing unclipped images through high magnification eyepieces. Is the position of the holder incorrect?

Steve says: "It is unlikely that the ‘clipping’ you’re observing is caused by the positioning of the eyepiece in the eyepiece holder.


However, eyepieces incorporate a field stop which consists of a metal or plastic ring that defines the edge of the field of view as part of their design.

If correctly placed at the focal plane within the eyepiece, a field stop produces a well- defined circle which avoids a gradual drop-off in the fidelity of the view.

The field stop limits the apparent field of view of the eyepiece which in turn limits the true field of view observed through the telescope.

If you know the diameter of the field stop, you can calculate the true field of view through the telescope in degrees by dividing the eyepiece field stop diameter by the focal length of the telescope and then multiplying the result by 57.3."

Some other useful guides that might help:


Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.


Astronomer Steve Richards
Steve RichardsAstronomer and author

Steve Richards is a DIY astronomy expert and author of Making Every Photon Count: A Beginner’s Guide to Deep Sky Astrophotography.