Pentax XO 5.1mm
Perfect up to the edge. At 5mm it is simply not possible to get a better result.
x-axis: distance from optical axis in °, y-axis: resolution in arc minutes
Apparent Field of View:
The measured apparent field of view is approx. 42°, somewhat less than the 44° given by Pentax.
For a 5mm eyepiece: outstanding! That’s real an eyepiece for planetary observations.
If you are very precise: a small field curvature may need to shift the focus from the center towards the edges. But this will depend on the telescope in use also.
Not the right one if you have to wear glasses. The eye relief of 3.6mm makes it like driving a Ferrari: pure power without any comfort.
That’s nothing we have to report on earnestly for Pentax eyepieces. Small, but perfect.
Surely an eyepiece for purists. Structures on planets, which you will not identify with this eyepiece, you won’t get with another one. The absolute sharpness combined with highest contrast makes this eyepiece clearly a high-end one.