Review – Atom Optics 4-16×40 AO – Part 1

One of the things I have wanted to try my hand at for a while is a product review. As it happens, the people at ‘In Your Sights’ thought this was a good idea too, and have given me an opportunity to have a go. They sent me a scope which they think would be ideal as a budget option for HFT. My job is to find out if they are right.

The first thing to do was work out how I could make this review different to others. I didn’t want to copy anyone else’s style, or write something generic or vague.
I had a read through some magazines and online articles, to see what was already out there and an idea started to form. It seems to me that offering opinions on a scope’s performance is fine, as long as the writer has the experience to pull it off. I definitely don’t have this level of experience so my opinion wouldn’t be worth much. Instead I’ve planned this review to be more of a technical test. Occasionally I might stray into giving an opinion, but on the whole this will be based on repeatable experiments. 

There are some aspects of scope design and manufacture that I don’t have the ability to test. For example I can’t test the lens coatings, efficiency or brightness. Maybe in the future I can work on this, but for now I’ll do what I can.

This review was going to be released all in one go, but there were some problems on my part. Firstly I spent more time playing with measurement methods than writing or shooting. So some of the tests aren’t finished yet. Also when I do start writing I have trouble keeping it short. The first part will give a good overview of the scope, the second is for the more demanding tests:

Part 1

  • Packaging and Contents
  • Construction
  • General Measurements
  • Objective
  • Eye Relief
  • Magnification
  • Reticle
  • Initial Impressions

Part 2

  • POI and recoil
  • Shockproof?
  • Fogproof?
  • HFT
  • Conclusion and final thoughts

I am always keen to get feedback, so if there’s anything I have missed please let me know, and I will try to include it in Part 2 and any future tests. From my side, I will give all of my feedback to the manufacturer and let you know what they say.

Part 1

As per the title, this review is of the Atom Optics 4-16×40 AO scope. Sold by ‘In Your Sights’, the price (at the time of writing) is £49.99.

On their website is a list of what you can expect to receive in your parcel:

Rifle scope mounts
Flip-up lens caps
Cleaning cloth
CR2032 Battery
Allen Key

And the quoted specification is:

One piece aluminum
Shockproof and Fogproof
Nitrogen filled
Etched glass reticle
Green multi coated lens for optimal clarity
Dual illuminated Mil-dot reticle  (Red & Green)
Fast focus eyepiece

Weight: 719g
Magnification: 4-16
Objective Diameter: 40mm
Tube Diameter: 25.5mm / 1 inch
Eye relief: 2.95-3.03 inches
Reticle: Mil Dot
Length: 380mm

Packaging and Contents

To be sent out for posting, the scope had been wrapped in bubble-wrap, and then a generic plastic postage bag.
The outer packaging is a glossy paper sleeve covering a thick cardboard box. The sleeve is a simple design with bold colours, reflecting the theme of the website and the brand. Sliding the sleeve off reveals the main packaging which is a fairly plain, black cardboard box. Standard for most scopes in this price range.
I missed the original delivery so had to make a trip to the collection office. When they handed over the parcel the first thing I noticed was the scope moving around inside. The box looks like it is a standard item which fits their whole range,  meaning everything except the largest scope they sell will have room to move around. I checked the scope over thoroughly, but it showed no signs of damage in transit. It might have been helped by a bit of extra packaging inside, although I would prefer more.

Inside the box are all of the items mentioned on that list above. Nothing was missing and all pieces were in good condition. Again there was no damage. So far, so good. 

Something worth mentioning here is the instruction booklet that you will find tucked into the box. At best it’s a good laugh. At worst it’s misleading and might give someone cause to send the whole lot back again. It seems to be a very generic leaflet provided by a factory in China. A lot of the content is gibberish, partly because it refers to features that don’t even appear on the scope. For someone who buys this as their first scope, I would suggest searching the internet for more precise instructions.

The cleaning cloth is expected, and would only be notable by it’s absence. It appears to be lint free, so will probably work just fine.


One piece aluminium? Yes. The main scope body appears to be one piece aluminium as stated. The finish is a low gloss satin black paint, very typical of most scopes. Markings on the objective and magnification rings are in white, and the nitrogen port is covered with the usual sticker.

As a basic test I rubbed over the paint and the markings with a soft cloth and 3 common liquids that a scope might be expected to come into contact with:

  • Plain water = No effect
  • Gun oil (in this case Armistol from Decathlon) = No effect
  • Furniture polish with beeswax (which I use to buff up varnished stocks) = No effect

Let me know if there are any other substances you want me to try this with (withing reason please!), and I’ll see what I can do. Although to be honest, I don’t expect anything short of paint thinners to actually cause a problem. 

The objective and magnification rings were initially stiff to turn. I struggled to do it with just finger tips, and had to use more of a full hand grip. After a couple of cycles turning them all the way up and down, they loosened off. Now they can be turned easily with a fairly light grip, but still feel tight enough to not move in use. Compared to 4 other scopes I have to hand (ranging from £30 to £150 RRP) the effort is very average. 

Green multi coated lens? I’m going to have to take the manufacturers word on ‘multi-coated’ because I have no way of checking. What I can say is that there is definitely at least one green coating. You can tell by holding the scope in the light and checking the colour of the reflection. This was tricky to photograph but I think I managed it (just). You should be able to see the green tinge.

Nitrogen filled? I have no direct way of testing this. However the ‘fog test’ should give us a clue. That will come in Part 2. During normal use so far, there have been no issues with the lenses fogging up or going cloudy.

Etched glass reticle? Without taking the scope apart I can’t say for sure. However directly comparing the reticle with some of my other scopes, it does give the appearance of being etching. What makes me say that is looking at where the mil-dot portion of the reticle, meets the thicker bars. There is no connection here, i.e the mil-dot portion seems to be floating in the middle of the scope. As far as I know, this can only be achieved with etching. Let me know what you think.

Dual illuminated mil-dot reticle? Check and check. There are definitely mil-dots there and the illumination works (once you fit the provided battery). Photographing this didn’t really show much. I’ve taken some pictures in the dark to show what you can expect. One thing I like is that the colour only extends as far as the mil-dot portion of the scope. Some budget scopes I’ve seen flood the whole view and don’t seem well thought out.

Fast focus eye-piece? Yes, no locking ring is required on the ocular lens. Three full turns of adjustment are available which moves the ocular ring a total of 12mm. It is smooth to turn and didn’t need loosening up like the other adjustments. 

There are three removable caps (all aluminium and the same colour as the main body). On the left (as if you were looking through the scope in use) is the battery cover. This was easy enough to remove and the battery contacts on the underside are lightly sprung.  Fitting it back on again was a bit tricky due to the fine threads. As long as this is done carefully it shouldn’t be a problem.

The caps for the windage and elevation turrets need to be removed before adjustments can be made. 5 equally spaced grooves give purchase to your fingers, and fit in with the styling of the objective bell. 
As a quick test I removed and re-fitted one of them 50 times, and the other I took off just the once. The photo below shows the threads on both. On the left is the cap that was removed once only. On the right is the cap that was fitted 50 times. Although this was a boring test, it shows that these can happily be taken on and off multiple times.
I plucked the number 50 out of the air. Should I have done more? Let me know in the comments.

The turrets themselves turn easily with a very positive click as they engage. Each turret is clearly labelled with a direction arrow indicating ‘Up’ and ‘Right’.

The turrets are also numbered, but I couldn’t see anything to use as a reference point. In this photo you can see the paint dot reference point for the illuminated reticle.

I counted what I call the ‘usable clicks’. By this I mean the amount of clicks of adjustment that are the same effort to turn. Further adjustment is possible but the effort to turn the turret increases, indicating you are near the end and should stop. Forcing further adjustment can damage the scope so isn’t advisable.

Windage Adjustment = 315 clicks
Elevation adjustment = 295 clicks

Something I’ve not tested here is how accurate each of the clicks are. Are they really 1/4 M.O.A? The answer will be in Part 2. Unfortunately I didn’t manage to get my big vice out in time for Part 1, and the scope needs to be held very steady for this test.

The lens caps are a nice feature on a scope in this price range. They are a two piece construction. The main body being a rubbery sleeve which pushes onto the end of the scope. The whole weight of the scope can be held up by the cap, so I would say the fit is good. The actual lens cover is spring loaded and flips up as you pull or push on the plastic tabs. Not the most sophisticated mechanism but it works. I’ve opened and closed one of them 100 times in a row with no issues. This probably isn’t enough to cover the life of the scope, so I might increase this if I get the chance.

The only minor problem is with the front cap. This fits over the grooves in the adjustable objective body. This means it can be fitted in 5 ways, so depending on which parallax setting you use the cover is unlikely to flip up vertically. A tiny niggle but something that could be annoying to the OCD user. However this is the only scope in this price range that I have seen with flip up covers. Most come with the usual bikini style. That’s a real selling point for In Your Sights.


Weight was measured on my digital scales, which were zero’d before every measurement. The results were:

Scope only = 673g
Front lens cap = 34g
Rear lens cap = 16g
Mounts (pair) = 107g
Total = 825g

The scope plus lens caps are 723g. This is only 4g more than the weight stated on the website. Although the website doesn’t state exactly what is being measured, I’ll give the benefit of the doubt here and say its almost bang on.
The scope alone is roughly 120g heavier than my current favourite HFT scope (I don’t currently use lens caps). Is this an issue for a budget scope? Probably not. Some people actually prefer a heavier set-up as it helps reduce the felt recoil of springers. 


Unfortunately my vernier calipers were not big enough to use for this, so I have used a metal rule instead. I think this is perfectly acceptable for this measurement as it won’t be that critical. Results are:

Ocular lens all the way in, no caps = 365mm
Ocular lens all the way out, no caps = 377mm
Ocular lens all the way in, both caps = 381mm
Ocular lens all the way out, both caps = 393mm

The stated length of 380mm is somewhere in the middle of these measurements. Again, the website doesn’t state exactly what is being measured. 
Obviously the actual length will depend on the users ocular adjustment, and preference for lens caps on or off. 

Tube Diameter

This was measured with vernier calipers, and in four places. Two in front of the turrets and two behind the turrets.

Location 1 = 25.54mm
Location 2 = 25.54mm
Location 3 = 25.54mm
Location 4 = 25.53mm

The website actually stated a diameter 25mm when I first received the scope. However as this is a 1 inch tube, the measurements I took were spot on. I happened to mention this to my contact at the company, and the listing was updated straight away to read ‘1 inch’. This definitely shows willingness to listen to feedback, and I think we all appreciate that.

Objective Diameter

This seems like an easy measurement to take, but I’ll hold up my hands now and say I messed this up several times. Maybe in the future I’ll write a post about my test methods (the many failures and eventual success, but that would take up too much space here). The basic idea is to shine a light through the scope and measure the effective diameter of the circle of light produced.
I also measured the outside diameter of the objective bell, and lens cap. This could be useful if you want to know how close to the barrel the scope might get.

Effective objective diameter = 39.9mm
Outer diameter of scope, no cap =  57.1mm
Outer diameter of front cap = 61.6mm

The measured objective was only 0.1mm smaller than stated on the website. This amount might just be the accuracy of my measurements. Either way I would be more than happy with this. I have heard stories of some budget offerings not giving the claimed objective, but that’s not a problem here. 

Eye relief

This was measured in a similar way to the objective diameter, except this time the light was shone through the front of the scope. At the rear of the scope a black cardboard box was moved forward and back until the circle of light became perfectly clear and focused. This was easy to see with a multi LED torch as there are multiple small circles of light that come into focus all at once. 

However, this is only the true eye relief for that particular magnification. Therefore this test was done several times. At minimum and maximum magnification, and minimum and maximum ocular adjustment. Parallax adjustment was left at 100 yards throughout.

4x mag, ocular bell in = 60mm
4x mag, ocular bell out = 57mm
16x mag, ocular bell in = 79mm
16x mag, ocular bell out = 76mm

The claimed eye relief is 2.95-3.03 inches, which converts to approximately 75-77mm. Again the website does not state the exact conditions that their measurements are valid for. But their claims fell within the envelope of my measurements. So we can assume their claim is valid, we just don’t know what settings were used.

Some measuring attempts


A.K.A the new bane of my life and the reason this review has taken so long.
I knew that measuring this would be difficult, but I under-estimated just how hard it would be to get accurate figures. After quite a few failed attempts, I now have a method which I am fairly happy with, and which is very repeatable. However there is an element of user error caused by the actual measuring of things. For this reason I have calculated roughly what my user error is, and also provided the maximum and minimum magnification based on this.

DISCLAIMER: This bit is kind of important. Measuring magnification is hard, no other way of saying it. It is also subject to some variables that I hadn’t previously considered. Because of the way scopes are constructed, messing with the adjustable ocular and objective lenses WILL affect the actual magnification delivered. The number you see on the magnification ring is more of a guide than hard fact. This means people with different eyesight, and therefore different scope settings, will get different results. These changes aren’t obvious enough to spot with the naked eye, but become apparent when you start taking measurements. There are also the errors that come with a person (i.e me) trying to measure things precisely.

In order to make the tests repeatable I have decided to use a parallax of 100 yards, and the ocular ring exactly halfway through it’s adjustment. The results I give below are my findings only and may not fully represent the scope’s actual performance. I have done my utmost to give you accurate results, but take it with a pinch of salt.

That’s the boring bit out of the way, so now the my results. The numbers are a bit meaningless without comparison, so I have also tested two other scopes (£30 and £150 RRP). As a reminder, the scope on test retails at £49.99.
Each graph shows a blue line which is the claimed magnification, and a red line showing what was measured. The closer the red line is to the blue, the better the scope has performed.

£30 Scope

Atom Optics 4-16×40

£150 Scope

From those graphs we can see that the Atom Optics scope holds up quite well. It does’t match the more expensive scope, but remember it is only 1/3 of the price. Minimum zoom is closer to 5x than 4x. Obviously this isn’t quite what is claimed. However if you are buying a variable scope, what are the chances of actually using 4x? I would bet pretty slim.
Maximum magnification falls slightly short of the claimed 16x, delivering around 15x.

The cheaper scope really shows that you get what you pay for, struggling to get anywhere near it’s claimed magnification. The line of the graph is actually quite straight which leads me to believe the mechanism inside is working well, i.e not binding or catching on anything. If this scope was marketed as a 6-18×50 it would be almost perfect. But they don’t, so it isn’t. 

The more expensive scope looks very nice on the graph, almost matching the claimed magnification the whole way up from 4x to 12x. If I tried this test using different objective or ocular settings, I think it could be made to match perfectly. Maybe this level of precision is too much to ask for in a budget scope, but it gives a useful comparison to show where the extra money goes.

To be honest I was expecting the Atom scope to be closer in performance to the £30 scope than the £150 one. The results show a different story though. Personally I use two levels of magnification on my airguns. 6x zoom for general plinking with my older rifles, and around 10x for my HFT setups. The Atom scope would happily fill both of those roles, although a bit of fiddling may be required if you are searching for an exact magnification.


This was the part of the scope that surprised me the most. All of my other budget scopes up to about £80 RRP have fairly thick and clunky reticles. This is fine for general plinking, but can become an issue with HFT when you are aiming at 15mm kill zones. This scope has a much finer reticle than I was expecting and nudges the scope a bit closer to being a good starter choice for HFT. I’m aware that this is starting to sounding like an opinion and I said this would be factual! So I’m moving swiftly on to the mil-dots.

The next test is to determine at what magnification the mil-dots are ‘true mil-dot’. If you look online there is usually some discussion about what the meaning of true mil-dot is, but to keep it simple I am using:

1 mil-dot = 3.6 inches at 100 yards

My target for this test is exactly 10 yards away. Therefore 1 mil-dot at this range is equal to 1/10th of 3.6 inches (or 9.144mm). Then all we need to do is adjust the magnification until the mil-dots on the scope line up perfectly with the mil-dots on the target. Simple. The photos below show the general idea.

On this scope the mil-dots line up at an indicated 9x magnification. According to the magnification graph above, this is roughly 10x actual magnification. Plenty of manufacturers aim for true mil-dot at 10x mag. So either this is a coincidence, or this reticle is actually quite good. I’ll let you decide which.

Too much magnification
Not enough magnification
Just right

One possible issue is a small speck on the lower half of the reticle, shown in the next picture. I’m assuming this is dirt from the factory when it was assembled. A shame because otherwise it seems well made with good attention to detail.

Initial impressions

This scope hasn’t been put through it’s paces on the potentially more destructive parts of the test (coming up in Part 2), but I’ve started to form some impressions:

  • It does seem well made. The adjustments are all tight and stay where they should be. The threads on the caps look good and didn’t cause any problems with multiple on/offs
  • The magnification is close to the claimed specification and easily provide what I consider to be a good usable range. Some budget scopes struggle with this.
  • IR works well and is not gimmicky
  • Reticle is a pleasant surprise and finer than expected. Although a speck of dirt slightly lets it down
  • True mil-dot is at 10x zoom. A popular option, although the supplier don’t advertise this
  • On the whole, the manufacturers claims are accurate
  • So far, this could be a contender for a budget HFT scope

Although I have already planned Part 2 of this review, please feel free to leave comments with suggestions for further tests. If possible I will try and get them into Part 2 for you. Also let me know if you like the format and style of this review.

The scope can be purchased from In Your Sights at the following link. Remember, using code TheAirGunBlog119 will get you 10% off anything on the site.


Thanks again to ‘In Your Sights’ for providing the scope and giving that very generous 10% discount. Check back here for Part 2 where we really test the scope out. (By the way, if you like springers, you should enjoy part 2….)



13/11/2017 – A representative from In Your Sights has already got back to me regarding two of the issues I’ve raised. 

  • Insufficient packaging allowing the scope to move around inside the box
    ‘We are now making sure that the scope are padded to make sure there is no sliding. Additional bubble wrap has been added as well. In the next 12 months we will be looking to have properly sized slot packaging.’
  • The user manual
    ‘We are working on a printed one which will also be online as well. I am also considering making some videos to help illustrate some of the key points.’

If you have any other points you want me raise please let me know. They are very fast at responding so you will get an answer.

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1 Comment on "Review – Atom Optics 4-16×40 AO – Part 1"

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Joseph Hallare

Considering this is your first optical review it is expected to run a little longer because you have to establish your testing parameters and still find the happy medium where you are properly evaluating in an objective manner.