Type of Lenses
Video Camera Lens –
Are primarily designed for the
CCTV applications providing maximum light level and a recognizable
image. Hence, they are suitable only for lower-resolution inspection
tasks. Lenses are available in a focal length from 8.5 mm to 135
mm.
This lens is typically a C-mount lens. This mount can be used with
sensors that are 0.512" (13 mm) or less in size. However, due to
distortions at the lower focal lengths, it is recommended that the
sensor size does not exceed 0.128" (3.25 mm) for an 8.5-mm focal
length lens, and 0.256" (6.5 mm) for a 12.5-mm lens.
35-mm Camera Lens –
Are primarily designed for 35-mm
photographic film. Their larger format provides a better image but
their design is optimized for larger distances. They mount to the
standard CCTV camera trough a C-mount adapter.
This lens is typically a U-mount lens. This mount is suitable for
sensor not exceeding 1.25" (31.75 mm). The short focal lengths should
not be used with sensors exceeding 1" (25 mm).
Microscope Lens –
Are designed for small FOV (2
– 4 mm) and for viewing objects at short distances. They also mount
to standard CCTV camera through a C-mount adapter.
Zoom Lens –
Is a lens that has adjustable focal lengths
over some range. Although zoom lenses may be more convenient,
they have smaller apertures and usually more distortion than similar
fixed-focal-length lenses.
Macro Lens – Allows focusing
on very close objects without loss of definition and without the
need for front or rear attachments. As it is optimized to work at
a magnification near 1, it is usually used for magnification between
0.1 and 10.
Telecentric Lens
– This lens provides constant magnification
for any object distance. They are usually used for precision gauging.
The disadvantage is that the first element must be as large as the
FOV.
Close-Focusing Attachments – Adding a thin meniscus lens
of 1-, 2-, or 3-diopters power in front of the camera lens shortens
the object distance of a standard lens. The new object distance
(d is given in meters)
can be calculated by using the following equation:
While 1-D and 2-D attachments are
generally satisfactory, the 3-D attachment causes distortion, even
when the main lens is stopped down considerably.
Extension Tubes –
The focusing distance can also be shortened by inserting extension
tubes of different thickness between a camera and its lens. The new
object distance can be calculated by using the following equation:
where f is a focal length, and E is the thickness
of the extension tube. It is also possible to combine an extension
tube with a diopter attachment.
Tele-Extenders – Instead of using an empty extension tube,
a much greater change in image size can be obtained by using a telenegative
attachment (tele-extender). These attachments serve to double or
triple the image size without altering in any way the previously
determined object distance. They are typically available at 2x and
3x power As the extender rings usually cause a reduction in depth
of field and resolution and increase distortion, it is recommended
not to exceed the 4x power.
For more information, please contact
High-Tech Digital Technical Support.
310-265-8203
support@high-techdigital.com.
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