Riflescope focal planes


35
43 shares, 35 points

First focal plane or second focal plane? The choice is easy – once you know what it all means!

Every rifle scope out there has a purpose. Some can be considered multi-purpose but one scope cannot usually fulfil all your requirements. The reticle may be too thick, there may not be enough elevation in the turret, the design may not have enough power in the zoom, or perhaps there’s no reference marks in the reticle when some are obviously required.

Looking for the best telescopic sight for your needs can be a tricky experience when you’re not armed with the knowledge.

One choice you have is between having the reticle in the scope’s first or second focal plane. This makes a big difference to how you use the scope and is an important but often overlooked aspect of choosing optics.

Before I get any further into this article, I’ll state outright that I will not be talking about scopes in the lower price range of $50-$250 as they present their own set of problems, most of all being that they’re just cheap pieces of rubbish.

A good quality centrefire rifle requires a good quality scope. The glass should match the rifle. Too often I have seen a good, competitively priced rifle such as Tikka T3 topped with a $200 scope. This is like putting retreads onto a late-model Monaro.

Focal Planes

Reticles in modern variable-powered rifle scopes are installed in two different ways.

Scopes with first focal plane (FFP) reticles are becoming more popular for tactical and long-range shooters as they provide contestant values in the reticle throughout the variable power range. FFP scopes are more expensive due to costly and time-consuming design and production.

Scopes with second focal plane (SFP) reticles remain popular with target shooters and other shooters who want the reticle to remain the same size throughout the variable power range. The reticle does not clutter the image at maximum power settings.

First Focal Plane

First focal plane scopes have the reticle installed towards the front of the erector tube or forward of the magnification lenses. The reticle is very near the centre of the turret housing. When the magnification is increased, the reticle increases in size along with the image you are looking at.

Two illustrations below provide a good example. Figure 1 shows a 10cm grey target at 100m viewed at 10x magnification. The target is 1 milliradian (or milrad) in size. Figure 2 shows the same 10cm grey target viewed at 20x magnification. Both the target and reticle have doubled in apparent size, but the target is still 1 milliradian in size.

Focal planes 2

Second Focal Plane

Second focal plane scopes have the reticle installed towards the rear of the erector tube or rearward of the magnification lenses. The reticle is fixed near the ocular or eye piece. When the magnification of the scope is increased the image size increases, but the reticle size remains the same. The value of the reticle subtensions change as a result.

If the value of the subtensions are set to “true” milliradian value at 10x, then when the power is increased to 20x (that is, doubled) the value of the milliradians is halved. Each scope manufacturer will explain in the user manual their true milliradian power setting. For example, Nightforce NXS always have theirs at maximum power and Leupold have theirs at 10x.

An example is shown by figures 3 and 4 (below). Figure 3 shows a 10cm grey target at 100m viewed at 10x magnification. The target is 1 milliradian in size. Figure 4 shows the same 10cm grey target viewed at 20x magnification. The target image has doubled in size but the reticle has remained the same size. The value of the milliradian reticle has now halved, or in other words, two milliradians now equals one milliradian.

Focal Planes 3

Advantages of FFP scopes

The value of the reticle always stays the same through the power range. The constant value of the reticle allows the shooter to:

1. Maintain the match between the reticle value and the turret value (milrad turret and milrad reticle)

2. Calculate the range to the target knowing the values of the reticle and size of the target

3. Calculate the size of objects or targets knowing the values of the reticle and range to the target

FFP scopes are advantageous for long-range hunters, tactical shooters, snipers, multi-distance shooters using spotters and any other shooter who requires a measured reticle pattern.

Advantages of SFP scopes

1. As the reticle stays the same width with an increase in image size, this reticle will not clutter the target when on very high power settings.

2. SFP rifle scopes are usually cheaper for the same make.

SFP scopes are advantageous for target shooters (benchrest and F Class), shooters who prefer to use the scope to observe bullet holes in the target, and shooters who prefer plain-style reticles.

Your Choice

Narrowing down the choice and setting boundaries early on will help you find your ideal scope. Deciding on FFP or SFP rifle scopes to suit your requirements will eliminate problems down the track.

There are other factors that come into selecting your rifle scope, such as variable or fixed power, milrad or MOA, external turrets or internal turrets, glass quality and so on.

Glen Roberts is the chief instructor at Precision Shooting Australia


Like it? Share with your friends!

35
43 shares, 35 points

What's Your Reaction?

super super
6
super
fail fail
20
fail
fun fun
18
fun
bad bad
16
bad
hate hate
14
hate
lol lol
12
lol
love love
10
love
omg omg
6
omg

0 Comments

Send this to a friend