The first focal plane (FFP) between the objective lens and the positive lens is also the second focal plane (SFP) between the positive lens and the eyepiece. On these two focal planes, the target image can perfectly coincide with the marking image without being affected by parallax.

The biggest difference of Riflescope between the two focal planes is that the FFP is in front of the magnifying and adjusting part of the sight, while the SFP is behind the magnifying and adjusting part. That is to say, FFP marking image and target image will be magnified together, while SFP marking image will not. When changing the magnification, the FFP marking is synchronized with the target, and the scale on the marking can always maintain the same angle measurement no matter it is 5 times, 15 times or 25 times; while the SFP marking can only measure the accurate angle at a specified magnification (now many manufacturers often set it at 10 times for convenience). Once changing the magnification, it needs to rely on the conversion formula to correct.

Although the FFP marking design is far better than the SFP design, the cost is much higher. Therefore, only high-end models of sight will use the FFP design in the market. Moreover, FFP marking will become too thick or too thin after being synchronously amplified, which may affect the aiming. If we don't use graduated marking or fixed multiple collimator, then FFP design has no advantage.

Shooting in low light (such as hunting animals that only come out during the short period of dawn and evening) or with too strong background light often occurs when the contrast is too dark to see the marking. In order to deal with this situation, some sight glasses will have the function of "reticle illumination", that is, to set an additional light source to irradiate the marking line to increase the reflective amount. The marking lighting design can be either light from the outside with optical fiber or by radioisotope (usually tritium). However, most riflescope products on the market still use battery powered led to provide light source.