Swarovski Tech Blog Reveals How Scopes Work
The Swarovski Optik website features a blog with interesting technical articles. In the “On Target” series of blog stories, Swarovski has provided a handy explanation of how optics systems work, with exploded diagrams of rifle scopes, spotting scopes, and binoculars. CLICK HERE for Swarovski Optics Blog.
Resource tip by EdLongRange. We welcome reader submissions.Scope Terminology
Focusing Lens
The focusing lens is an adjustable lens inside the optical system for focusing the image at different distances…. In the case of rifle scopes, apart from focusing, the focusing lens also facilitates parallax compensation.Diopter Adjustment
For rifle scopes, the reticle can be focused using the diopter adjustment on the eyepiece, thereby correcting any visual impairment. [Editor’s Note: Movable eyepiece diopter adjustment is not offered on all rifle scopes. It is a useful feature on Swarovski and other premium scopes. This allows shooters who need eyeglasses to get a sharply focus image even without wearing corrective lenses. Of course shooters should always wear ANSI-certified eye protection. With the diopter, folks who need correction can use inexpensive, non-Rx safety eyewear instead of expensive prescription safety glasses.]Reversal System
The purpose of the reversal system is to reverse the image by means of prisms in binoculars and telescopes, and lenses in rifle scopes….The lens reversal system is needed in rifle scopes to control the variable magnification and move the exit pupil[.]
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Tags: Diopter, Reversal Lens, Rifle scope, Spotting Scope, Swarovski Optik
Pretty much every scope that I have seen has an adjustable eyepiece. Some have fine threads that require multiple turns to traverse the full range of adjustment, which precludes any simple index system. These usually have a lock ring, and the eyepiece is rigidly attached to the scope when it is tightened. Other scopes have adjustment systems that have much faster pitch threads and complete their full range of motion in a turn or less, allowing for the use of an index system. These are usually secured more loosely with a spring providing tension against the threads, and although this would seem to be less secure, good results have been obtained using both systems.
Both styles allow considerable range of adjustment by moving the eyepiece lenses together, as a unit.
Being able to adjust a scope so that it can be used without corrective lenses presents the temptation of shooting without any protection. This is an unsafe practice that is all to commonly done by people who seem to be intelligent in all other respects, but in this one area, evidently are not.
Boyd,
You raise some good points about eye protection. Most common eyeglasses do NOT have ANSI-certified impact-resistant lenses. Eyewear with actual glass lenses can shatter dangerously on impact. That is why it’s better for someone with non-impact resistant eyeglasses to remove them and use safety eyewear instead. The Diopter adjustment will allow most folks (those who don’t require extreme correction beyond plus or minus 3.0) to see the target sharply.
Of course, you can also order custom Prescription eyewear that IS impact resistant. Such prescription safety glasses are not inexpensive.
Have you noticed that you can do the same thing with a fine threaded eyepiece? It just takes so many turns to get to the extremes that there is none of the snapping in and out of focus, because the change is so gradual. What you are doing is working with the entire set of lenses between the second focal plane (typically) and the retina, including the eyepiece, corrective lenses, and the eye’s lens, to focus on the plane that the reticule is in. Recently, I have been using an auxillary lens that screws onto the back of the eyepiece that not only increases magnification, but holds the field of view the same, and actually increases the sharpness of the image…for MY eyes.