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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

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”

Auto

1.3

2.8-12 mm

102.2~23.7

PLEN-0205

LEN-210

1/2”

Auto

1.6

8-80 mm

46.6~4.7

PLEN-0203

PLEN-0205

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.

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.

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.

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

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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