Using a Thermal Clip-On with Second Focal Plane (SFP) vs. First Focal Plane (FFP) Scopes: What You Need to Know

When it comes to combining a thermal clip-on unit with your daytime scope, one key consideration often overlooked is whether your scope utilizes a SFP or a FFP reticle. These differences are critical to understanding how your setup will perform—especially when your clip-on is mounted on a Picatinny rail in front of the daytime scope.

FFP vs. SFP: The Basics

Let’s begin by briefly explaining the difference:

• FFP (First Focal Plane): The reticle size scales with magnification. When you zoom in or out, the reticle grows or shrinks proportionally with the target image. This means your holdovers and subtensions remain accurate at all magnification levels.
• SFP (Second Focal Plane): The reticle stays the same size regardless of magnification. As a result, your subtensions are only accurate at one specific magnification—usually the highest.

Why It Matters with a Clip-On

Now, consider a setup where the thermal clip-on is mounted in front of the scope using a Picatinny rail mount. In this configuration, perfect coaxial alignment between the clip-on and the scope is practically impossible. This misalignment will be especially pronounced if you are using a 20 MOA or greater angle base with a second focal plane scope. Such bases angle the scope downward relative to the barrel, while the clip-on remains parallel to the barrel. As a result, the optical axes of the clip-on and the daytime scope are not only non-coaxial—they aren’t even parallel (as shown in the image below).  Even when using standard Picatinny scope rings and the misalignment is small, it can still have real consequences:

• When you zero your thermal clip-on to your scope at a certain magnification, everything may look good.
• However, with an SFP scope, when you change magnification, the image size changes, but the reticle stays static. This amplifies any small misalignment between the clip-on and the scope, causing the point-of-impact (POI) shift.
• The more you adjust magnification, the greater this shift becomes. How misalignment influences the point of impact will be very different for every combination of the rifle, the caliber, the daytime scope, and the scope mount because it depends on many factors. However, to understand something like an average, consider the following test: a Vortex Razor Gen II HD-E 1–6×24 SFP scope installed on Picatinny rings with a Hogster-C clip-on attachment in front fixed on a LaRue Picatinny Mount was zeroed dead-on at 100 yards at 3× magnification. Changing the magnification to 6× caused a vertical shift of about 2.25 inches downward at 100 yards. Notably, the original zero returned when magnification was set back to 3×.

Solution for SFP Users: If you're using an SFP scope and a Picatinny-mounted thermal clip-on, the best practice is to zero the clip-on at the specific magnification you plan to use for shooting. If you want flexibility across different zoom levels, you’ll need to store multiple zero profiles in your clip-on device—one for each magnification setting. Bering Optics thermal clip-ons can store up to four separate zero profiles.

Better Practice: Use a Throw Lever Adapter for Coaxial Alignment

To minimize these issues, a better setup for SFP scopes is to use a custom-size throw-lever adapter that mounts the thermal clip-on directly onto the objective bell of the daytime scope, ensuring perfect coaxial alignment. In this configuration:

• The reticle remains accurately positioned relative to the thermal image display of the clip-on attachment, eliminating misalignment and minimizing zoom-induced point-of-impact shift to only a slight deviation caused by the discrete nature of the clip-on’s adjustment increments when the perfect zero lies between two steps resulting in a slight POI shift in the range of something like 1/8 of an inch at 100 yards.
• Changing magnification does not introduce any significant point-of-impact shift.
• You maintain a reliable hunting zero across all zoom levels.

What About FFP Scopes?

With an FFP scope, the magnification changes the size of both the image and the reticle in sync. That means:

• Any slight misalignment at the time of zeroing does not grow with magnification changes.
• Your point of aim remains consistent, regardless of zoom level.
• Even if you’re slightly off zero (say, a quarter-inch high), that offset stays the same for that distance at any magnification.

Still, for long-range shooting—even with FFP scopes—we strongly recommend using a throw-lever adapter. In our tests, this configuration produced exceptional results. For instance, while testing the pre-production Super Yoter C clip-on unit for Bering Optics, we achieved consistent hits at 1,100 yards using a through-lever adaptor for the coaxially-mounted setup. In contrast, the same unit on a Picatinny mount delivered respectable hunting accuracy up to 200–300 yards, suitable for most AR-platform hunts, but not ideal for precision long-range engagements.

Best Overall Setup

If you're looking for the most precise, reliable configuration for combining thermal and daytime optics, the clear winner is a First Focal Plane scope, paired with a thermal clip-on, mounted coaxially using a Custom-sized throw-lever adapter.

This combination ensures maximum accuracy and consistency across all magnification levels.

Turnkey Solutions from Basic Precision

To make this setup accessible, Basic Precision offers fully integrated day-night hunting solutions, including:

• A FFP daytime scope,
• A custom-fit adapter that mounts like a glove
• A thermal clip-on from Bering Optics
• A proper size and height scope Picatinny rings or 20 MOA Picatinny Base options 

Each bundle is optimized for a specific shooting range and application. Customers can select the combination that best suits their style—from mid-range AR-platform setups to precision long-range bolt-action configurations.

👉 Explore Bundled Thermal Solutions Here

With these plug-and-play kits, hunters can hit the ground running with confidence that their thermal and optical gear are fully compatible and zeroed for an uncompromised performance.