Test
Results
Art. –Nr. PEN-XO-2.5
Pentax XO 2,58mm
Sharpness:
At the center perfect up to the diffraction limit of our measurement
equipment, but half the way out a little bit, but measurable, worse.
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.
Contrast:
At 2,58mm focal length you can not expect a really famous contrast. Also
Pentax has to respect physics, but for this short focal length the contrast is fine.
Aberration:
Very slight cushion distortion.
Eye Relief:
Not the right one if you have to wear glasses. The eye relief of 3.9mm is
really tight.
Mechanical Quality:
That’s nothing we have to report on earnestly for Pentax eyepieces.
Small, but perfect.
Summary:
An eyepiec for highest
magnification on fast telescopes. Sharpness outside of about 15° from the optical
axis is not perfect at all. I strongly recommend to test an eyepiece of this
short focal length on your own telescope, as magnification is really at the
limit where more magnification will not lead to more visible details.