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What is the internal mechanism for diopter adjustment? (1 Viewer)
- Thread starter tenex
- Start date
The focussing leses can be regarded as part of the objective. These may be either converging (+ve.) or diverging (-ve.). Examples of binoculars with positive focussing lenses are the Zeiss SF, Meopta B1s and the old Swarovski SLCs and ELs. Among those with negative focussing lenses are the Zeiss HTs, Swarovski EL Swarovisions and Kowa Genesis.
To focus a binocular towards infinity a negative lens is moved closer to the objective elements, i.e. forward and a positive focussing lens rearward towards the prisms.
To set the dioptre the right focussing lens is either operated independantly or the left focussing lens is decoupled.
John
PS:- The Kowa Genesis, of course, lacks a central dioptre adjustment. This is carried out with a helical adjustment of the right eyepiece.
To focus a binocular towards infinity a negative lens is moved closer to the objective elements, i.e. forward and a positive focussing lens rearward towards the prisms.
To set the dioptre the right focussing lens is either operated independantly or the left focussing lens is decoupled.
John
PS:- The Kowa Genesis, of course, lacks a central dioptre adjustment. This is carried out with a helical adjustment of the right eyepiece.
Last edited:
tenex
reality-based
Thanks John, that's just what I suspected for the diopter and it makes sense.
I can confirm that both my UV 32 and SLC 56 have negative focusing lenses that move toward the objective at infinity. (There was a third possibility too: the old Zeiss Dialyts moved the actual objectives to focus! I was very surprised when I learned that, having used one for years... looking into the other end of course. That may have been how they handled diopter adjustment also, since it was on the other end of the hinge?)
I can confirm that both my UV 32 and SLC 56 have negative focusing lenses that move toward the objective at infinity. (There was a third possibility too: the old Zeiss Dialyts moved the actual objectives to focus! I was very surprised when I learned that, having used one for years... looking into the other end of course. That may have been how they handled diopter adjustment also, since it was on the other end of the hinge?)
This meant that the Dialyts (I had 10x40 for 17 years) were effectively an air pump as the objectives moved to and fro in the tubes displacing air, which led to all kinds of strange changes to the feel of the focus when I used them in an airliner at high altitude and then on the high veld in South Africa, depending on how effective the grease around the objectives was working as an air seal at any one moment.
Lee
Interesting isn't it, Lee, to see the developments over the past decades?
Initially all scopes and binoculars were focussed by moving the oculars and the next step after your Dialyts was to put protective plane glass in front of the moving objectives to maintain a constant internal volume (very old 8x30 Swarovski SLCs and the 8x30 Zeiss Diafun).
A 7x42 Swarovski SLC of mine has a very weak converging lens in front of a focussing doublet and recent designs have a two or three element fixed objective with a weak +ve. or -ve. focussing lens.
Most current scopes have plane glass to seal the scope body - the Swarovski ATX/STX have two - so instead of "wasting" two air/glass surfaces perhaps in future manufacturers could put the field flattener in the scope body.
John
Yes John it is and as a general nature observer (as opposed to someone specialising in birds) one of the most significant changes has been the decreasing of the close-focus distance from 5 metres or more down to around 2 metres with many models at around 1.5 metres. For me this has been a more significant change than the improvement in sharpness at the edge of the field of view in some models. And the second most significant change IMHO is the shift from folding rubber eyecups to adjustable-height eyecups although for sure this has been done with a quite varied degree of success.
Lee
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