Everything You Need To Know About Telescopic Sights
The Ocular Lens
This is the lens that is closest to your eye and it is often fitted with a screw in, screw out facility, which enables the shooter to focus the scope for their particular eyesight. In some cases, shooters who wear glasses can dial in the scope so that the need for the glasses is removed whilst shooting.
Every scope is also designed with a certain amount of eye relief. This eye relief is the distance that you will need to place your eye from the ocular lens to get a good un-blurred sight picture and it can range from anything from one to four inches. Scopes like the MTC Connect can be perfect for a new shooter as they are a short eye relief scope and this makes them easy to use and set up, since the shooter’s head position is less critical.
All scopes have a reticule, which could be a simple cross hair (30×30 ret) or a mil-dot or half mill-dot or the fantastic MTC SCB reticule. The reticule is extremely important as it is what you will be using to aim your rifle. The 30×30 ret is perfect for high power rifles as the rounds essentially fly on a flat trajectory. However, air-rifle pellets fly in an arc and because of this you need multiple aim points. Scopes like the MTC Viper and Hawke half mill-dot series are perfect as each line of the reticule will correspond to a set distance to where the pellet will strike.
Magnification – first and second focal planes.
At the ocular end, you will often find the magnification ring; which is quite simply a lens that enables you to make the image look closer or further away. Now, you may hear shooters talking about first and second focal planes. The basics of it are this; if your scope has a 1st focal plane, when you increase the magnification, the reticule will also increase in size along with the image. If you have a 2nd focal plane, the reticule will remain the same size and only the sight picture will get bigger. The vast majority of HFT and hunting scopes are 2nd focal plane.
If you are a hunter or a plinker, then 10x magnification is perfect as it will give you a clear sight picture out to 50 yards and a good depth of field.
The Objective lens
At the far end of the scope is the Objective lens, which can range from under 30mm to over 60mm in diameter and as a general rule of thumb, the smaller the objective lens, the larger the depth of field that you can see. The objective lens primary function is to gather as much light as possible and give you a good sight picture.
In between the objective and ocular lenses is the tube which usually comes in either 25mm or 30mm sizes. Within this tube is the reticule, which is usually etched onto a lens or-in some cases can be a wire filament. You also have the picture reversal apparatus, without which, your targets would look upside down. The whole scope is then filled with nitrogen, so that it will not fog up on a cold day. Attached to the tube are the windage and elevation turrets and the scope will usually have adjustable parallax at either the objective lens end or mounted on the side.
What is Parallax or, more importantly, what is Parallax error? Well, to explain it is fairly simple. Hold your hand out in front of you and raise your index finger so it is pointing towards the ceiling. Close one eye and, with your arm outstretched, move your hand so that your finger covers a point on the wall (your finger is your scope’s reticule and the point that it is covering up is the target). Now, move your head left and you will see that even though your finger has not moved, when your head is to the left, your finger/reticule is now to the right of the target. So, now move your finger back to the left so that it is covering up the target again and move your head back to its central position and your finger should now be to the left of the target. More targets are missed through PX error in HFT then any other form of error. To compensate for this, most quality scopes have Parallax adjusters, which will enable you to set your scope with a parallax of 40 yards for a 40 yards target and no matter how much you move your head about, your cross hairs should remain on the target. The problem is though that not all targets are at 40 yards, but can instead vary from say 8 to 45 yards and as you are not allowed to adjust your scope in HFT, you have to find a happy medium.
Depth of Field
This is one of the most important parts of your scope’s make up and buying the wrong sort of scope for the shooting that you want to do will cost you time and money. If you are going to hunt or shoot Hunter Field Target you will want a scope with a large depth of field. The way to check this is to take your scope and set the Parallax for about 25yards and place the magnification on 10x. Look at a target 45 yards away and adjust the Parallax until the 45yard image becomes slightly blurred. Then look closer and closer until the image becomes blurry again. A good scope like the Hawke Panorama or the MTC Viper should have a clear image from 45 yards down to about 15 yards. If you want to shoot Field Target, then you will want a scope with 2 to 3 yards DOF, these types of scope have large objective lenses and high magnification and you use the parallax adjuster to dial in the range.