optical lens characteristics/lens terminology explained

1,CS and CMount

The CS-mount lens has the flange back distance of 12.5mm.The C-mount lens has the flange distance of 17.5mm. The CS mount lens is only applicable to the CS mount camera， but theＣmount lens is ft for both C mount and CS mount cameras aslongasa 5mm Adapter Ring is used to match the CS mount camera

2,Flange Back Distance， Back Focal Length， Mechanical Back Focal Length

Flange back distance is the distance between the lens flange and the sensor focal plane.

Back focallength is the distance between the vertex of the rear lens element and the sensor focal plane.

Mechanical Back FocalLength is the distance between the surface of the lens frame and the sensor focal plane.

3, Depth of Field (DOF), Depth of Focus

The depth of field refers to the area within the field of view which is infocus.A large depth of field means that a large percentage of the field of view is infocus. A small depth of field means only a small section of the field of view is infocus. The depth of field is of following properties.

1) The larger the FNo.is， the wider the depth of field becomes.

2) The shorter the focal length is，the wider the depth of field becomes.

3) The longer the distance to the object is， the wider the depth of field becomes.

4) The backward depth of field is wider than the forward depth of field.

4, Non IR Len VS IR Lens

Day& Night cameras are normally used in near-infrared(NIR) or infrared(IR) at night. If we use a Non IR lens with a day& night camera，the image will be out of focus(shifting) at night. Our special optical designs with broad band co-focusing technology based on special glass material minimize light dispersion. As a result， refocusing is not required when the camera is used under NIR or IR. The special design makes the lens to deliver perfect focusing either under visible light or under IR illumination circumstances.