What is the difference between a SLR lens and a focal plane?

The screw filter used in the front-end SLR camera lens is different from the aperture at the front end of the bayonet hood, but the focal plane needs the hood to block stray light, and a square filter is installed, and the apron, hood ring or bayonet behind the hood must be close to the front end of the lens, so the front end of a group of lenses is often the same aperture, so it is time-saving and labor-saving to replace the focal plane.

Internal and external scaling. Many SLR cameras use external zoom, and the lens barrel expands and contracts when zooming. On the focal plane, contact-following focusing gear ring, hood barrel and filter are used, which is not suitable for telescopic lens barrel. Therefore, the displacement of the lens group must be completely realized inside the lens, and no trace can be seen outside, so internal zoom is usually used. Moreover, the focal plane often adopts focus chasing and focus shifting, which needs to solve the respiratory effects of the lens, so the design of floating lens group is adopted.

Focus/aperture ring and pin. The positions of the focusing gear ring and the aperture gear ring of each focal section in a group of focal planes are matched with each other, and it is not necessary to adjust the position of the follow-up focus or the three-axis driving motor when replacing the lens, which saves time and labor. SLR camera lens usually has no toothed ring used with the follow focus system, and the focusing and aperture rings are textured designs, which are convenient for operators to hold.

Manipulate. The focal plane emphasizes more accurate focusing and smoother control than the SLR lens, so the focal plane has a large focus ring stroke and a thin aperture ring, and adopts a segmented aperture design.

Aperture value. The aperture index of the focal plane is different from the F used by the SLR lens, and T is used for marking, for example, CN-E24MM T 1.5LF ... That is to say, it is not only calculated by a simple formula such as the F aperture value, but the actual light input marked by strict testing, and the deviation is much smaller than the F aperture value.