<P> The telescope is focused correctly for viewing objects at the distance for which the angular magnification is to be determined and then the object glass is used as an object the image of which is known as the exit pupil . The diameter of this may be measured using an instrument known as a Ramsden dynameter which consists of a Ramsden eyepiece with micrometer hairs in the back focal plane . This is mounted in front of the telescope eyepiece and used to evaluate the diameter of the exit pupil . This will be much smaller than the object glass diameter, which gives the linear magnification (actually a reduction), the angular magnification can be determined from </P> <Dl> <Dd> M A = 1 / M = D O b j e c t i v e / D R a m s d e n \ mathrm (MA) = 1 / M = D_ (\ mathrm (Objective)) / (D_ (\ mathrm (Ramsden))). </Dd> </Dl> <Dd> M A = 1 / M = D O b j e c t i v e / D R a m s d e n \ mathrm (MA) = 1 / M = D_ (\ mathrm (Objective)) / (D_ (\ mathrm (Ramsden))). </Dd> <P> With any telescope or microscope, or a lens a maximum magnification exists beyond which the image looks bigger but shows no more detail . It occurs when the finest detail the instrument can resolve is magnified to match the finest detail the eye can see . Magnification beyond this maximum is sometimes called "empty magnification". </P>

When is magnification equal to unity in a converging lens