I've trouble seeing unclipped images through high magnification eyepieces. Is the position of the holder incorrect?
BBC Sky at Night Magazine's Scope Doctor Steve Richards solves your astronomy ailments.
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:
- A basic guide to eyepieces
- BBC Sky at Night Magazine eyepieces reviews
- What eyepieces are best for observing nebulae and star clusters?
Email Steve your astronomy queries to firstname.lastname@example.org and they could be answered in a future issue of BBC Sky at Night Magazine.