I have noticed many CCTV cameras have a ring of LEDs around the lens - but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)

On 21/10/2014 10:54, DerbyBorn wrote:
I have noticed many CCTV cameras have a ring of LEDs around the lens - but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)

They have a reasonable range and the cameras are pretty sensitive so
that they don't need much light to form an image. The total IR output is
a bit less than that of a 1W LED torch and with a wider spread. 20m is
typical working range for small ones and 40m for the better ones.

You don't have to have the LEDs on but in the pitch dark they can be
useful on a moonless night. Rain or snow backscatter is more of a
problem than anything else with the lights being near the lens axis.

--
Regards,
Martin Brown

In article 6,
DerbyBorn writes
I have noticed many CCTV cameras have a ring of LEDs around the lens - but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)

I think they are a bit ****, I'd much prefer a proper low light camera
rather than one of those fakes. They do still exist but it is near
impossible to find them as the false claims of the LED based ones swamp
the real ones.

It comes down to doing your homework, looking at proper reviews of the
camera sensors themselves and choosing a camera that uses one of the
proper low light ones eg. Sony Super HAD CCD sensors used to be
excellent for sensitivity but may have been surpassed now. I see SONY
EX-View also gets a mention now.

On the scatter back problem, this doesn't happen as you will find there
is a foam grommet surrounding the lens in contact with the glass that
cuts out any internal or external reflections and the LEDs are (just)
far enough away and their beams narrow enough that external reflections
do not occur.

--
fred
it's a ba-na-na . . . .

On Tue, 21 Oct 2014 09:54:34 GMT
DerbyBorn wrote:

I have noticed many CCTV cameras have a ring of LEDs around the lens
- but behind a front glass (Saw this on a drone which made me
wonder....) Can the LEDs be of any use given the sort of useful
distance that the camera is expected to focus on? Does having the
LEDs behind the front glass cause scatter off dust and moisture to
ruin the image. Are they just a gimmick?
(a bit like using a flash on a camera at a stadium concert - see
Inverse Square Law of Light)

The built-in LEDs don't suffer from scatter, as described in another
post, but if you put the camera behind a pane of glass, then you will
see nothing using the LEDs, it will just reflect off the inside of the
window.
I have a camera in my two-car garage, and with the built-in
LEDs, I can tell that there is a car on the far side of it, or not, but
there is no detail. Much better than flash at a concert, no question.

--
Davey.

Martin Brown wrote:

Rain or snow backscatter is more of a
problem than anything else with the lights being near the lens axis.


Or, at certain times, millions of tiny insects flying around just in
front of the camera. It looks amazing though.

Bill

On 21/10/2014 10:54, DerbyBorn wrote:
I have noticed many CCTV cameras have a ring of LEDs around the lens - but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)


On most of them the lens has a shield to stop the leds reflecting back
into the lens.

They can be designed to illuminate from 5m to 120m but not at the same
time. You decide what when you order the camera and lens combination.
Wide angle lenses need wider illumination and have a shorter range.

On 21/10/2014 11:26, fred wrote:

On the scatter back problem, this doesn't happen as you will find there
is a foam grommet surrounding the lens in contact with the glass that
cuts out any internal or external reflections and the LEDs are (just)
far enough away and their beams narrow enough that external reflections
do not occur.


That sounds like a cheap camera.
All of mine have a tube which passes through the front glass to stop the
leds reflecting back from either surface.

An external IR illuminator is a better bet as that stops number plates
reflecting back and swamping the sensor.

On 21/10/2014 11:26, fred wrote:
In article 6,
DerbyBorn writes
I have noticed many CCTV cameras have a ring of LEDs around the lens -
but
behind a front glass (Saw this on a drone which made me wonder....)
Can the LEDs be of any use given the sort of useful distance that the
camera is expected to focus on? Does having the LEDs behind the front
glass
cause scatter off dust and moisture to ruin the image. Are they just a
gimmick?
(a bit like using a flash on a camera at a stadium concert - see Inverse
Square Law of Light)

I think they are a bit ****, I'd much prefer a proper low light camera
rather than one of those fakes. They do still exist but it is near
impossible to find them as the false claims of the LED based ones swamp
the real ones.

It comes down to doing your homework, looking at proper reviews of the
camera sensors themselves and choosing a camera that uses one of the
proper low light ones eg. Sony Super HAD CCD sensors used to be
excellent for sensitivity but may have been surpassed now. I see SONY
EX-View also gets a mention now.

On the scatter back problem, this doesn't happen as you will find there
is a foam grommet surrounding the lens in contact with the glass that
cuts out any internal or external reflections and the LEDs are (just)
far enough away and their beams narrow enough that external reflections
do not occur.

I'm disappointed that it's difficult to find low-priced IP cameras that
work well with just moonlight.

I've yet to find a consumer-priced IP camera that can outperform a
10-year-old Philips Toucam Pro webcam in low-light conditions.
Some IP cameras even appear to have built-in noise reduction software,
that removes the possibility of improving low-light performance by doing
off-camera frame-stacking.