Hi Alexis,

thanks for double checking, when I wrote this (not quite up to standard) post, I had the MC EP specs page open but obviously didn't scroll down far enough to the 24x/30x wide but only to the 27x/40x/50x and that is quite a bit narrower than the 20x/25x.

Both the 20x/25x and the 24x/30x wide do indeed result into a true field of 3 deg on 60mm bodies and 2.4 deg on 78/82mm bodies.

Same for the 16x/24x/30x DS - and a whopping 4.5 deg at 16x in the 50mm...

As for the 15x/19x (Type 7772) I did only find an old BH Photo Video page - but alas, no field of view data listed.

As for whether the 15x/19x can offer a wider true field than the 20x/25x or 24x/30x wide, we can make an educated guess... If the field lens diameter of any of the latter two EPs plus a mm or two for the barrel is close to the inner diameter of the eyepiece receptacle of the scope body, the true field is as wide as we can get... the formula given above is (while correct) not ideal for what we want to do...

afov in deg = tfov in deg * magnification = tfov in deg * telescope focal length in mm / EP focal length in mm = 57.3 deg * field stop diameter in mm / EP focal length in mm

Multiplying both sides by EP focal length in mm and solving for tfov in deg yields:

tfov on deg = 57.3 deg * field stop diameter in mm / telescope focal length in mm

which is much more useful in our case. It is easy to see that with any given scope body and thus a fixed scope focal length, field stop diameter and true fov are directly proportional and thus if the field stop diameter for an eyepiece is at the maximum dictated by the diameter of the eyepiece receptacle, the true field for another eyepiece can not get any larger.

Sorry for the maths...

Joachim