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How to Adjust the Back Focus for TCM-5311
Category Type
Configuration Note
Camera Model
TCM-5311
Firmware Version
N/A
Publish Date
2009/09/03
Last Review
2009/09/23
Knowledge Type
Video Quality –Correct Focus
Function Type
Hardware - Lens
Contents
Introduction of Back Focus
The Purpose of Adjusting Back Focus
The Compatible Lenses for TCM-5311
The Procedure of Adjusting Back Focus with PLEN-0203
The Procedure of Adjusting Back Focus with PLEN-0205
Demo Videos of Back Focus Adjustment
References
Introduction of Back Focus
TCM-5311 is a high class camera that has a
built-in back focus ring, by which it is
convenient to fine tune sensor position in
order to achieve the ideal distance of the
sensor from lens.
By rotating the back focus ring it is
possible to slide the sensor back or forth
inside the camera. The back focus ring is
shown on the image 1.
Once the back focus has been adjusted properly, the lens has been successfully
adapted to camera, and there is no need to re-adjust the back focus thereafter. All
the following adjustments are done on the lens itself by changing focal length (zoom)
and front focus, depending on the camera location and the distance to the
monitored object.
Image 2: Back Focus
Back Focus
Image 1: Back Focus of TCM-5311
2
The Purpose of Adjusting Back Focus
For the cameras with changeable lens, there may exist some positions in the zoom
scale which cannot be focused at all. Which means that the practically usable focal
length will be shorter than shown in specifications. However, with the help of
correctly adjusted back focus you can benefit from the maximum possible scale of
focal length of the given lens.
By adjusting the back focus we can achieve following:
Make the maximum possible zoom range focusable
Maximize the depth of field for each zoom position
Enhance the focus in the corners of the image
In other words, properly adjusted back focus can achieve optimal performance of the
camera and the lens.
The Compatible Lenses for TCM-5311
Although it is possible to attach almost any C or CS mount lens available, there is a
risk that an uncertified lens does not give satisfying result. Two lenses are
recommended for TCM-5311. Below you can see the specifications of those lenses.
Lens name
Old name
Size
Mount
Type
Iris
Aperture
Focal length
Angle (HOR)
PLEN-0203
LEN-207
1/3”
CS
IR
Auto
1.3
2.8-12 mm
102.2~23.7
PLEN-0205
LEN-210
1/2”
C
IR
Auto
1.6
8-80 mm
46.6~4.7
PLEN-0203
PLEN-0205
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The Procedure of Adjusting Back Focus with PLEN-0203
Depending on the type of lens used, the ideal back focus position will be different.
Also, the lens type will determine the starting position for lens focus and zoom.
Below are the step-by-step instructions of adjusting back focus. Before starting the
adjustment process, login to Web Configurator and display the live video from
TCM-5311 camera.
Back Focus Adjustment:
Procedure
Action View
Camera View Result
Rotate the back focus ring to the
left, until the end. The positions
of zoom and focus are still
random at this point.
Set zoom to widest (W) and its
corresponding focus to nearest
(N). We are now at one end of
zoom scale and we trying to get
perfect focus there. Point the
camera at an object 75 cm away
(2.5 feet). The object is out of
focus.
Slowly turn back focus to right,
until the object will attain focus.
It means the camera can attain
focus with widest zoom angle of
the lens. The adjustment of back
focus is complete.
Now that the back focus adjustment is complete, there is no need to adjust it again.
The sensor is now at ideal distance from lens, allowing the whole range of zoom to
be focusable.
The following steps are done by adjusting zoom and focus of the lens, depending on
how far the actual monitored object is at the camera site and how big you want it to
appear on the screen. In the following table, two example scenarios are provided.
4
Lens Zoom and Focus Adjustment:
Procedure
Action View
Camera View Result
Case 1: We need a zoom-in view
from a distance.
For testing, put the camera
several meters away from the
object.
In order to zoom-in, change
zoom angle to telephoto (T) and
then slide focus towards infinity
(∞) until you get clear focus.
Case 2: We need a wide view
over the site.
Change the zoom angle to
widest (W) and then slide focus
towards nearest (N), until you
get clear focus.
5
The Procedure of Adjusting Back Focus with PLEN-0205
PLEN-0205 is a lens with very deep zoom with the focal length of 8mm - 80mm. Due
to its different structure, its wide zoom angle is focused with “Far”instead of “Near”.
For better understanding of this difference, you can refer to the graph at the end of
this document.
Back Focus Adjustment:
Procedure
Action View
Camera View Result
Rotate the back focus ring to the
left, until the end. The positions
of zoom and focus are still
random at this point. Point the
camera at an object 100-200m
away.
Set zoom to telephoto (80 mm)
and its corresponding focus to
FAR. We are now at one end of
zoom scale and we trying to get
perfect focus there.
Slowly turn back focus to right,
until the object will attain focus.
It means the camera can attain
focus with deepest telephoto
zoom of the lens. The
adjustment of back focus is
complete. The fine tuning can be
done later with zoom and focus if
needed.
Now that the back focus adjustment is complete, there is no need to adjust it again.
The sensor is now at ideal distance from lens, allowing the maximum possible range
of zoom to be focusable.
The following steps are done by adjusting zoom and focus of the lens, depending on
how far the actual monitored object is at the camera site and how big you want it to
appear on the screen. In the following table an example of wide angle focusing
process is shown.
6
Lens Zoom and Focus Adjustment:
Procedure
Action View
Camera View Result
Case: Widest Zoom (8 mm)
Point the camera at an object 4-5
meters away, which is the
minimum recommended working
distance for such lens.
Adjust the zoom to widest angle
(8 mm). For better tuning of
focus, it is recommended to
leave a bit space at the end of
zoom scale, for example set
zoom to 9-10 mm.
Move focus slowly towards left
until the focus is obtained. The
camera is now set for a wide
angle view and with a very long
depth of field.
Demo Videos of Back Focus Adjustment
After reading the instructions of back focus adjustment above, you can refer to
following videos for hands-on practice:
TCM-5311 back focus adjustment with PLEN-0203
TCM-5311 back focus adjustment with PLEN-0205
7
References
Below you can find the graphical explanation of the difference of two lenses. On both
graphs, the trend line shows the position of focus for each zoom position.
The mark shows the starting position for adjusting back focus. For the lens
PLEN-0203 the starting position is Wide (2.8mm) and Near (N). For the lens
PLEN-0205 the starting position is Telephoto (80mm) and Far. You may notice that if
we slide the zoom of PLEN-0205 all the way to 8mm, then we need only a small
movement with focus ring (around Far) to obtain focus.
2.8mm (W)
12mm (T)
PLEN-0203 Focus Scale
Far (∞)
Near(N) Zoom
Focus
8mm
16mm
24mm
32mm
40mm
48mm
56mm
64mm
72mm
80mm
PLEN-0205 Focus Scale
Zoom
Focus
Near
Far
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