Monocentric 5mm

Hello,

I would like to share experience with this eyepiece.

I bought a 5mm Monocentric TMB eyepiece (in Paris). While image is very crisp and perfect at the center of field, eyepiece shows a serious astigmatism at the edge of the field and a mild one near half of the field (Sorry to say but exactly as described in Sky and Telescope). In fact only 15° (half of the field) is usable. This eyepiece is not unusable on the moon. Usable on planets if on optical axis (itself not perfectly centered).

Is that normal or a defect ? What is your experience ?

I am using it with F/7 scopes.

Regards, Laurent

This problem has occurred before, although the stated policy of TMB and APM is they will replace any defective eyepiece. Getting in contact with either the the retailer from whom you purchased the eyepiece originally, or APM who is the European distributor of these eyepieces, is the proper first course of action. Keep us posted as to your experiences.

Walter