The passion for all things optical started for me more than 45 years ago as a young lad looking through my Dad’s binoculars whilst out sailing and marveling at the objects that were so far away, but being brought right close and clear for me to see in such detail.
This interest in optical instruments grew and eventually led me into a career in optics. From my early days of study and training associated with the British Ministry of Defence in navigational and observation systems, through to a 20 year relationship with major European optical manufactures onto where I am today, I still have a great passion and interest in all things optical.
The Rifle Scope
The scope in various forms has been with us since the early 1600’s when a Dutch inventor
Hans Lippershey was accredited to the first known telescope. Then over the years there were numerous developments of optical lenses, the most significant was the achromatic lens (two part lens – Crown and Flint). Although patented by John Dolland in 1753, it was in fact an amateur optician Chester More Hall who in 1733 proved Newton’s statement incorrect “that chromatic aberration correction through a lens was not possible”. This significant development in optics allowed for wavelengths of light, which have different focal properties to diminish the effects of light scatter to be more controlled and thus reduce chromatic aberration. This then led onto the apochromatic lens, which coincidently was developed and patented by Peter Dolland (John Dollands son) in 1763. These developments in lens correction and the increase of uninterrupted light transmission lead us into the basis for all optical systems of rifle scopes, as we know today.
The rifle scope first appeared around 1835 and was developed by an American, Morgan James in collaboration with a John Chapman who discovered his invention. This led to the first commercially available sight, which was called the ‘Chapman James Sight’. These long tube scopes had no adjustments for height or windage and were constructed using thin copper or brass sheeting which was malleable and thus able to be rolled to form a tube like construction and then soldered down the joint seam. The lenses were then inserted and this became the rifle scope as we know it today. This in turn was then mounted onto the rifle. The optical power was low, probably around 1 – 2 x magnification but the point was that the huntsman could now view his subject more clearly. Then around 1853 a William Malcolm started to produce scopes using achromatic lenses, together and incorporating windage and elevation adjusters for the outside of the tube. This was a huge improvement for the rifle scope. These scopes along with those that were produced by Lee Amidon (The Vermont Sight) were the standard scope used during the American Civil War.
Then as further advancements in optic design evolved, so too did different manufactures which brought on the onset of different designs and styles of scope bodies. As the optical manufacturing quality improved so too did the sighting mark (reticle).
The first types of reticules that were used in the earlier Malcolm scopes were just a rudimentary fine wire vertical post soldered onto a brass ring and inserted into the tube. They then found that by adding a horizontal wire, which crossed the post, gave the marksman a better orientation. This improvement to the reticules and their design had great effects on both sides of the campaign during the Civil War.
The reticle, which was first produced, used primitive materials such as spider webs or even horsehair to obtain the sighting cross. Then with the advent of the industrial revolution, materials were able to be produced with greater accuracy and treated steel wires of less than 1/25inch (.040mm) were used.
However, as the improvements to the optics were made and larger lenses were introduced to increase light transmission, so to did it create a problem with heat build up inside the tube and hence cause the reticle to distort. The larger lens or objective is similar to a magnifying glass. The light enters and converges at a focal point and we all know how hot that focal point gets when the sun shines and your hand is in the way.
Although the first etched reticle was around 1700, the accuracy and fine detail required for a scope did not evolve until the mid 1800’s. There were a few different ways in which to produce an etched reticle. The first was by hand, using a diamond blade and then filling in the scored line with graphite and then coating it with a form of clear lacquer. Later they started to produce reticules using chemical etching, which made the outline more defined, thus producing finer detail. This process used bitumen coated onto the glass and then using a rule to draw a finite line or mark onto the bitumen. This small piece of glass sometimes no bigger than 5 mm in diameter, would then be dipped into hydrofluoric acid and then washed in alkaline solution. The bitumen was then removed to reveal the finite lines, chemically etched into the glass. After polishing, the etched line was in filled to define the mark of the outline and then covered in a clear non- reflective lacquer. This process was further developed by the British prior to WW1 and was then applied to an array of different optical devises with great success. From binoculars to range finders and gun sights, which incorporated the first forms of the Mill dot style reticle for improved accuracy and determining the range of the target, hence the word graticule. This followed with the development of the photographic etching, which is a more complex process, which greatly improved the designs and styles of the scopes that are in common use today.
The laser etched style reticle, which can be found on most modern scopes of today. Up until only 10 years ago precision glass reticules were only commonly available on your more expensive brands of scopes, however we are now seeing them being fitted to the lower end brands. The advantage is that they are obviously more stable and less susceptible to any shock treatment within reason or heat distortion.
The down side is that they can collect microscopic particles on the surface that may be floating in the tube and hence obscure the field of view. Another common problem they are susceptible to is the easy occurrence of water marking, due to temperature changes in the tube. The standard wire reticle, which is fabricated mostly from either one or two metal sheets or wires, is not as robust and is susceptible to heat change and furring, caused be electrolysis when two dissimilar metals are used in construction.
The detail and information we can obtain from a reticle today is exceptional. The reticle below is a Bone and Crocket commonly used in Leupold scopes and no more than 15mm in diameter.
The Scope of Today
There have been significant improvements over the years in lens development and corrections with the introduction of multi coatings and changes to the compounds of the glass, together with the way they are ground and polished. These improvements have significantly improved the physical properties of light transmission even further especially when the light on the subject you’re observing is poor. We have also seen over the last 30 years improved angles of observation, longer eye relief, etched reticle systems and illuminated reticules. There has been the adjustable objective to elevate parallax disorders, to more recently the addition of a side-compensating lens for easier parallax control. There is even the possibility that duel range monitoring through the eyepiece will be a reality one day. All these developments, together with other functions and features enhance the observer and better still attain greater accuracy for the shooter.
Basic Scope Maintenance
One of the most common misconceptions when buying a scope, is not only its light gathering capabilities, reticle type, ease of use etc., but more often the question asked is it nitrogen filled. We know that when moist warm air hits a cold surface i.e. a lens, it forms small water droplets. This is fine when it’s on the outside of the glass, but when it’s on the inside it causes fogging. This is when nitrogen is used, as it is an inert gas, heavier than air and together with less than 1 PPM H2O it has a greater density and is thus less susceptible to temperature change. Also due to its high purity nitrogen is drier than air and it is less likely to cause corrosion and prevent moisture damage to the coated lens surface.
All scopes are like balloons – they are susceptible to temperature change and consequently pressure loss over time due to expansion and contraction. So in other words there are very few scopes in the 30 years I’ve been repairing them that I could say have a reasonable nitrogen tight seal.
So as you see the scope is always exposed to temperature change both internal and external. There are certainly ways to prevent any moisture present from causing further damage. One of the best is silica gel either available in a container or a small bag. Just remember “Moisture and Optics Do Not Mix”
Never Spray Oil on Your Scope
I have received many scopes where the owner has thought they were doing the right thing by spraying oil onto the steel tube to prevent it from rusting. As mentioned before there are very few scopes with a nitrogen tight seal, therefore it is important that oil is not sprayed onto the tube or where other parts join the tube i.e. windage and elevation adjusters. Once a combination of moisture and oil has got onto the lens set inside the scope, it is imperative that it is looked at as soon as possible, to avoid further damage.
Windage & Elevation Adjustment
I recommend every once in a while to give the windage and elevation adjusters a bit of a turn. You can count the number of turns you do either left or right and return them back to the central position. This is just to give the components a bit of a work through as the grease inside becomes hard over time. You may have to do a bore sight prior to use depending on the quality of the scope. On another note with the windage /elevation there are a number of scope manufacturers that use an opposing spring to compensate for the adjustment. This spring can soften over time due to the consistent pressure being exerted on it. So if the scope is not going to be used for an extensive period it is worth backing off the windage/elevation adjusters.
Never clean your lens with your handkerchief. Always gently blow to remove any grit or particles with your mouth or preferably use a puffer brush (available from camera stores). It’s these small particles that cause the minute scratches on the coated lens and if not removed, just get rubbed in again and again and thus change the refractive order of the lens.
Once clean, a gentle spay of isopropyl alcohol (lens cleaner) will remove any film or grease. Lens caps are always a good option when walking through the scrub to help stop dirt getting onto the lens and also (providing a cap with no colour cover screen) stops the suns rays from entering the tube and causing heat build up. At the end of the day the objective lens is just like a magnifier lens.
Optical Repairs Services
We have been offering a comprehensive range of optical repairs for over 30 years. We repair and overhaul a wide range of optical devices, which include both vintage and more current types of rifle scopes, binoculars and the like.
We also specialize in repairs of large telescopic gun sights, laboratory microscopes and even precision refractor heads as used by your optometrist to measure the refractive disorder of your eyes.
We predominantly specialise in the older European optical devices, however we will gladly look at most problems to see if they can be repaired or overhauled and all evaluations are at no cost.
Our customers over the years have come from wide and far. UK, Canada, USA, South Africa, New Zealand and we have also carried out work for the Australian Maritime Service, Australian Federal Police, QLD Governor General and a number of Specialised Hospitals and Clinics associated with Eye disorders both in Australia and overseas.
This article appeared in print in the Diesel & Dust Magazine. Download the print version here: opticalrestoration