Copyright P. J. Smith

But permission is given to distribute this material in unaltered form as long as it is not sold for profit.

 This design is for an Abbe or Orthoscopic design which uses modern optical glasses.

The efl = 15 mm.

Eyerelief is 17 mm and users should find the finished eyepiece very comfortable to use at the total apparent field of view of 52 degrees even for spectacle users.


To achieve the long eyerelief some slight definition loss will occur at the edge of the field. Three radii have been held common to make for easier construction but the temptation to make more radii common has been resisted. This practice is common in cheaper commercial designs which is reflected in a poorer image. Some astigmatism has been introduced but it will be much less than often found in similar eyepieces.

There is no doubt that even better performance would result from the use of these glasses if eyerelief was reduced. This is a good example of a design which sacrifices something for the benefit of spectacle users. But even non spectacle users want to show off their images to others and have little comprehension of how badly the results are compromised by inadequate eyerelief.

The spot diagram box sides are 50 microns.

 Defocus because of curvature of field amounts to about 2 diopters although the eye will not notice some degradation at 26 degrees off centre..


Dotted line represents 1 minute performance limitations.

 The performance on axis is excellent down to about F:5. Even at F:4 it is quite good but some slight loss of definition will be noticeable off axis.


Radius of curve-------Thickness------------ Glass------------ Semi-width

efl = 15 mm.

Four different lap sizes are required. Unfortunately two curves are so steep that surfaces must be polished singly. The others will fit 3 or more per lap.

Two of the glass types are more expensive but are not uncommon. These glasses will suffer from climatic degradation unless cared for properly but this is normal for high performance eyepieces.

Centring, especially for the steeper curves, must be done well to take full advantage of the design.