Telescope Reviews: how to mesure Eye Relief

Jack.

I read ALL your posts , but must admit that I do not always understand EXACTLY what it is you are trying to explain or ask.

As regards EYE RELIEF -- YES -- it IS important -- and it CAN be measured -- but at the end of the day -- once you have bought a binocular, or an eyepiece -- you own it , and are stuck with it --unless you sell it.

One of my binoculars -- a Japanese 15 x 70 has only 8mm eye relief -- far too short for perfection -- bit I STILL use that binocular -- and enjoy doing so too.

O.K -- we might lose a little field of view -- but in many cases THAT area of field of view is not very clear to look at anyway -- so I think that this whole issue can be made too much of in some cases.

As far as your previous posts go , I have an understanding ( correct me if I'm wrong ) that you have been experimenting with placing a lower - magnification "booster" directly in front of the "exit -pupil" in order to attain a GREAT magnification.

It is a thing I've tried many times -- and was in fact playing around with this earlier this evening.

It works better with a very low power binocular , or monocular , placing the objective lens EXACTLY in the prime position within "eye -relief" of the exit -pupil from the larger scope.

It helps if you stick to something VERY low power , such as a 3x monocular -- and much better if the objective of the monocular or " booster binocular" has an objective lens EXACTLY the same diameter as the OCULAR of the FRONT scope.

To achieve any kind of success with this , you need to have BOTH scopes / monocular / binocular MOUNTED STEADY and PEFECTLY ALIGNED -- and the higher the QUALITY of BOTH instruments , the more chance there is of a satisfactory result.

The end result is a magnification of the Original Scope MULTIPLIED by the magnification of the " booster".

It can be a great way of studying image quality and exit -pupil and of finding really fine -tuning FOCUS.

I tried this today , using my Zeiss 7 x 42 binoculars in front of my Zeiss 85mm Fluorite Scope ( set at 20x ) so the combined magnification is 7 x 20 = 140x !

By co -incidence -- the 42mm objective lens of the binocular is almost EXACTLY the same diameter as the eyepiece of the scope --and the eye -relief from the scope lens just happens to be "just short" of the "comfort zone" presented when the two surfaces are butted together.

In other words , if the "over -hang" of the 7 x 42 bino objective casing was about 3mm LESS -- so that the two glass surfaces came 3mm closer together , then I believe I would have as good a focus as possible for these "crazy" experiments.

It is interesting ( and surely perfectly explainable by someone with the technical knowledge ) that best focus is achieved when BOTH instruments are set EXACTLY as they would be optimum as if each were being used to look at the object independently.

I have never had what I would call GREAT success with these little experiments -- but some STAGGERING magnifications CAN be obtained by this crude method.

For example , using my 15 x 70s against the scope set at 60x , gives the theoretical magnification of 900x ( through a 85mm objective lens ) -- truly CRAZY for sure !

Regards -- and have fun -- Kenny.

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If everyone is thinking the same thing , no-one is thinking - General George S.Patton

Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera