If this is done correctly the top of the adaptor will lie about 2 mm below the rim of the
clamp all round. Now screw in the clamp screws a little till the flexure folds of the clamp
begin to squeeze the flaps of the adaptor. Insert your eyepiece at this stage and continue
to tighten the clamp screws till the eyepiece is held in place.
Eyepiece eye relief – limits of usability
Even if an eyepiece has a diameter than can fit the standard AF51 clamp (with or without
the thin adaptor) it must also have a suitable level of eye relief in order to be used with this
clamp.
In the tests that I have done with the 13 eyepieces shown in figure 5.1, all the eyepieces
can be imaged properly by the camera sensor even if they have a very short eye relief but
not all of them can be so imaged with the standard AF51 eyepiece clamp. This is because
eyepieces with a very short eye relief cannot be brought close enough to the camera lens
to get the full field of view into the camera with the standard clamp. For those eyepieces
with short eye relief, therefore, some custom adaptor will again need to be made or
acquired by the user (they are not supplied with the camera).
To give you an idea of whether the standard clamp will work fully with a particular
eyepiece I have tabulated my results with the 13 eyepieces tested. Manufacturers use
various methods to measure eye relief distance and not all eyepiece models quote this
eye relief value. For that reason, instead of trying to list a manufacturer’s listed eye relief
value I made my own surrogate measurement, which I call the ‘eye point’ distance,
defined as the distance away from the top-most solid part of the eyepiece where the disc
of light coming from the eyepiece is the smallest when a specimen is in focus on the stage
with a x40 objective (figure 5.4).
All measurements were made on a PUMA microscope with its Abbe condenser and
Kohler illuminator in situ. I stress this setup because I have found that the same
measurement technique made with the same eyepiece on a different microscope gave
slightly different results for this eye point measure.
OptArc AF51 Camera Page 52 of 99 User Guide v1.02
