The Zeiss Fero Z51 / Orion 80 is a German surplus scope used with the HK G3 and several other less common Cold War era German weapons. Though bulky compared with modern night vision these Gen 2 scopes work sufficiently well to meet the requirements of many users at a affordable price point and is sturdy enough to be used on 7.62×51 rifles. The biggest difference I see when comparing side by side with a set of Gen 3 goggles is that the Z51 does not work in the very darkest situations, such as a moonless night, unless an IR illuminator is used. If there is lunar illumination or in an urban environment with even a small amount of light the Z51 works quite satisfactorily for a sub $500 scope. An excellent write up by user Wilhelm on HKPro forums covers the contents of these Z51 scope sets in detail, a link can be found at the end of this article.
For users who do not have an HK pattern rifle it is quite simple to replace the original mount with an adaptor which allows it to be fitted to a common picatinny rail. My personal preference is for either UTG or Monstrum low profile risers which are typically under $15 on Amazon. I have used these mounts extensively with both the Zeiss Z51 and Hensoldt Z24 scopes on a wide variety of rifles for nearly a decade with no complaints. If a more “prestigious” brand is desired the only option I’m aware of are the ARMS #7 or if quick disconnect is desired ARMS #19. As I have been quite satisfied with the performance of the inexpensive mounts and the reputation of Dick Swan in the firearms industry I have never bothered to try the ARMS mounts.
In the 2010-2015 time frame the Z51 scopes were in stock from a number of dealers however in more recent years they seem to have dried up. The best looking were unissued sealed scopes sold by Dan’s Ammo for approximately $500 shipped, these included a limited number marked as “US Property”. Though these scopes were in mint condition I have found them to be the most problematic which I will address later. They are still the best of all the scopes, just be prepared to crack them open to tune them up. A variety of other surplus dealers such as Copes Distributing and Midway also sold them for $400-600 and, in my experience, are well used but fully functional scopes.
Recently scopes have been available from dealers such as HK Parts in “Premium” packages for $1495 that promise zero time tubes and metal parts have been refinished black. From looking at the pictures they appear to be quite similar to the unissued “US Property” scopes sold by Dan’s for under $500. I’m not inclined to pay such a significant premium just to try these out however if anyone has experience I would be interested to know more. Additionally a number of scopes have been available from several dealers on Gunbroker for reasonable prices. In mid 2016 Veronesi Gun Works had Gunbroker auctions which typically went for under $300. The scope I received was in rough shape with neither on/off shutter or focus mechanism functional, several of the assembly screws were quite loose and my impression was that it may have been cobbled together from parts. Fortunately the tube was in good condition and the mechanical issues were relatively straightforward to remedy. Most recently in the fall of 2017 “Backyard Bunker” has been selling “broken” scopes on Gunbroker for $119. As a source for spare parts this is, in my opinion, an excellent option. The only other source of scopes that can be scavenged for parts that I am aware of is HK Parts with sells them for $299.95.
Initial disassembly of the Z51 is accomplished by removing the five hex head screws which are located approximately four inches from the front of the scope with a 2mm hex wrench. Once the screws are removed the front of the scope, which contains the focus elements, can be be removed from the rear which contains the image intensifier. . Depending on the age of your scope this may require a slight amount of effort as there is a blue-ish grease that is used to seal the halves together and can stick them together. Try and avoid moving the focus elements in the front of the scope as it can complicate ensuring it focuses correctly later. When you disassemble the scope you will need to do it in the cleanest possible environment that is free of dust. A can of compressed air is very useful for blasting any dust away however be careful as some will leave a residue on the optical elements if caution is not used.
The two issues I have seen most commonly are with the power/shutter knob and with the focus knob. In both cases the root cause is due to the hardware being insufficiently tightened inside the scope. As I alluded to earlier this has been a problem with every “unissued” scope that I have tried out. When disassembled the gears which are meant to make these adjustments simply “slip” on their shafts. The older scopes have a small bead of what I assume is some variety of thread locker that seems to be lacking on the newer scopes. Whether this represents a change in manufacturing process or is a field modification to the older scopes which remedies a common fault I do not know. What I can say is that in my experience the unissued scopes typically do not function correctly without some work where the used ones seem to have been sorted out.
In the case of the power knob it is necessary to “time” the gearing for the scope to operate correctly. Initially the knob should move the light filter frame sufficiently to actuate the switch which powers up the scope yet leaves the intensifier aperture covered by the filter, you should hear a very slight click when the switch is depressed. This allows the scope to be used in periods of twilight without damaging the intensifier. Correct timing of the knob will raise the filter frame to fully expose the intensifier aperture when turned clockwise. It should be possible to correctly “time” the gear internally however the knob can be removed by two small set screws. Use caution to not over-tighten the nut which secures the adjustment gear on the shaft as it can be easily sheared off. I recommend using Loc-Tite and lightly tightening and allowing to fully cure before reassembly.
The focus knob requires a bit more attention to achieve best results. My preferred technique is to secure the adjustment gear with careful tightening to avoid shearing the shaft along with a very small amount of Loc-Tite. After that I remove the two set screws on the adjustment knob and with a bit of careful prying remove the knob. Travel of the knobs is limited by a steel post in the scope body, that post is often bent on older scopes which represents the frustrations of generations gone by. One solution is to help is to simply pull the stopper steel post to allow maximum range of travel. The “wing” on the focus knob will still limit the travel and from my examination of the workings of the focus mechanism I cannot see any potential issues from the additional range of adjustment. With the focus knob removed my preferred technique to set the focus is to take the scope outside and utilize any convenient star. Use a pair off pliers to turn the focus adjustment until the star is in focus and mark the position with a sharpie. With the scope set to infinity install the knob with the “wing” as far clockwise as possible Use caution when re-installing the focus knob set screws as I have broken off a torx wrench tip. If this happens it’s irritating but not an emergency, a single set screw will often hold the focus knob sufficiently tight and if you are feeling bold a drop of Loc-Tite will ensure it is secure.
Another common problem I have seen with the Z51 scopes is specks of stuff in the field of view. Some of this could have occurred while fixing the other problems with your scope. The good news is that you can probably fix it, the bad news is that you can jack up your scope if you aren’t careful. In all likelihood those black specks you see are not damage to your intensifier tube but are instead bits of dust on the face of it. With careful cleaning it is possible to clear things up, but it’s also quite easy to make things worse. If you are to try this you will need to have a room available with clean air and as little dust as possible. After disassembling the scope it’s simply a matter of examining the surface of the tube and removing any and all contaminates. In many cases it is possible to simply use a can of “compressed air” to blow the specks off. If you encounter specks which are more stuck in place I recommend using alcohol and a lens cleaning cloth. I personally prefer cans of 99.95% pure from MG chemicals which is available on Amazon to prevent any residues from remaining. Use extreme caution if you attempt to clean the shutter mechanism as it extremely fragile.
If you do clean the filter mechanism and break it there are a couple paths you can take. If it’s not badly broken you can use epoxy and carefully secure the pieces. It will look like crap but surprisingly it won’t impact the view through it much and obviously once the shutter is fully open it will not matter. If you choose to repair it with an intact shutter from a broken scope it is relatively straightforward. Start by removing the small circuit board immediately beneath the shutter. Then remove the small gear which moves the shutter followed by the three hex head screws of the underlying frame. Use caution with the top center screw as it holds a small copper electric contact that is prone to popping off. After the parts are loose it is then possible to slightly lift the underlying frame and slide the shutter off. Re-assembly is simply a reverse with care to correctly “time” the gear to ensure that the shutter actuates the on off switch correctly.
Another quite common issue is that the retaining straps for the front lens cover are often broken where they mount to the body of the scope. If you wish to correct this I have head good results using a needle and thread to sew it back together and then add a drop of superglue. So far mine fixed in this way have held up.