LASER imaging using CCD !!!!

[pooja]

Hi everybody,..

I am trying to image a target at around 350 m during night time using
a continous wave (810 nm) LASER diode ( power of 1.8 W).
Two cylindrical lenses ( a convex and a concave with their axis in
perpendicular diections) are used to get a laser beam divergence of 30
X 24
degrees.

An Infra Red enhanced ( for 810 nm wavelength) , 1/2 " CCD camera is
used for imaging.

The camera settings are as follows :

1.Auto Iris mode.
2.Back light compensation ON.
3.FL off
4.Auto Exposure mode.
5.Super AGC
6.gamma factor of 0.45

A 20X Zoom Lens ( working on the focal length range of 15 mm to 300
mm) is used .


Though the camera is IR enhanced, I'm unable to detect any target in
dark condition say at around 7.30 p.m.
However, at a distance of 20 metres the camera picks up the target
with good clarity.


Am I missing any other system setting ???? I look forward for pointers
in this regard.

TIA

Pooja.

 

[pooja]

Hi all,..


I have tried using a ND filter during day time to focus at 20 m and
300 m range. With the same settings, the image of the target looks
dull during night time even after lighting the target by 1.8W LASER
diode ( 810 nm).

Do you still feel Zoom Lens is the limiting factor ???

Is there any other parameter that I'm overlooking ??

TIA

Pooja.

 

[pooja]

Hi all,..


I have tried using a ND filter during day time to focus at 20 m and
300 m range. With the same settings, the image of the target looks
dull during night time even after lighting the target by 1.8W LASER
diode ( 810 nm).

Do you still feel Zoom Lens is the limiting factor ???

Is there any other parameter that I'm overlooking ??

TIA

Pooja.

 

[Some Guy]

Did you overlook posting your question in alt.lasers?

I discovered that group a few weeks ago. The folks there seem to be pretty
friendly, and their specialty touches on your problem...

Not that I want the thread to go away or anything Just thought you might
get a more relevant response from people who study lasers.

Is there any other parameter that I'm overlooking ??

<snip>

 

[Jim Meyer]

Hi everybody,..

Though the camera is IR enhanced, I'm unable to detect any target in
dark condition say at around 7.30 p.m.
However, at a distance of 20 metres the camera picks up the target
with good clarity.

Pooja.

Your lens may focus IR wavelengths at a different distance than
it does for visible wavelengths. If the clarity issue is poor focus,
try adjusting the focus using only IR illumination.

Although your CCD is IR enhanced, your lens may have coatings or
actual filters that remove the IR wavelengths. A lot of lenses
intended for visual wavelengths and solid-state sensors have these
filters. Since IR and visible wavelengths don't focus at the same
spot at the same settings, if the camera is used for visible
wavelengths and there is substantial IR present, the image you get is
degraded unless the IR is filtered out.

Jim

 

[ctsbillc]

Is this really 1.5 W?

That is a ginormous amount of laser light.

eyeball frying power.

Bill C

 

[Harry Conover]

Is this really 1.5 W?

That is a ginormous amount of laser light.

eyeball frying power.

Bill, that's true if it's focused down to a point, but when it's
radiated over a wide area of illuminatin it's the same 1.5-W (at least
a fraction of) that put out by a glower or a small light bulb with an
IR filter.

I've often wonder what could be accomplished using a scanned IR point
focused source in syncronization with a sensor, still I have still to
see that done. If it has been done by some means, the results probably
are classified.

Harry C.

 

[Zak]

I've often wonder what could be accomplished using a scanned IR point
focused source in syncronization with a sensor, still I have still to
see that done. If it has been done by some means, the results probably
are classified.

I've seen pictures a LONG time ago - in some computer imaging book I
suppose.

Maybe not classified - night vision amplifiers are much harder to detect.


Thomas

 

[Some Guy]

Did you overlook posting your question in alt.lasers?

I discovered that group a few weeks ago. The folks there seem to be pretty
friendly, and their specialty touches on your problem...

Not that I want the thread to go away or anything Just thought you might
get a more relevant response from people who study lasers.


<snip>

I see he took my suggestion, and posted to alt.lasers... the answer he got
there was (paraphrased of course): Why are you using a laser? You are
diverging the beam so as to illuminate a wide area, and an IR LED has a
naturally diverged beam, and you can get a much stronger IR LED... or put a
bunch of them in parallel... same effect, much lower tech. You only need a
laser if you are trying to illuminate a point, as opposed to a field.

 

[[email protected]]

Your lens may focus IR wavelengths at a different distance than
it does for visible wavelengths. If the clarity issue is poor focus,
try adjusting the focus using only IR illumination.

Jim & Pooja:

In my experience as a photographer:

-1-- SOME telephoto 35mm camera lenses have a special mark to indicate the correct focus when using IR
(color or B&W) film.

-2--Depending upon the f/stop and focal length of the lense, focus is much more critical for a short
distance beteween subject and camera than for a long distance. -- See most any BOOK (Basic Organized
Ordered Knowledge <grin> ) on 35mm photography (depth of field).

Fred

 

[ctsbillc]

Oh, a point (if anyone is still monitoring this thread)

Using a very narrow band source will give rise to interference patterns,
specularity, and thus using LEDs which have a broader spectral output may be
a better approach for this reason also.

Bill

 

[pooja]

Thanks everybody.....for all ur help...!!1

Pooja