760nm filter for IR??

[Scruit 0]

I attached a 760nm filter to my new BW camera and it still sees a lot of light during the day, even with the illuminator off.

 

I got the focus and everything set up during the day, knowing I'd have to adjust it at night one time. Well, night is here and the image is dead black. Can't see the any reflection back of plates from the 850nm illuminator or anything.

 

I thought that an 760nm filter would allow 850 through? Maybe it does and I just need to play with the lens settings. But it seems that 760 allows through too much light during the day and causes a huge focus shift.

 

 

Am I supposed to be able to see refelction off a reflective license plate using an 850nm illuminator and a 760nm filter? Or should I use an 850nm filter?

 

And would the 850nm fix the focus shift issue between night an day?

 

Lens is a>75mm zoom lens from computar and I have it set to about 30mm. The license plates I want it to see are 80' away from teh camera and illuminator. Illuminator is 'rated' for 120'.

 

I'll probably find I can set it up fine at night but then by daytime it'll be messed up again...

 

Think I'll take the sony camcorder in ightshot mode the the IR blocked to see if I can 'see' the illumintor working

[Scruit 0]

I adjusted the lens when it was pitch black. Here's what I get...

 

For this test I parked my car in the drive where I want the camera to read the plates. Then I took two spare plates and mounted them at the furthest left and right that a plate would ever be (ie front of a older Pontiac Grand Prix = far right. Back of a UPS truck = far left) That's where there are 3 plates.

 

The day shot: (would the 850nm lens recude the amount of light in this picture? I was expecting there to be almost zero visible light)

 

 

 

The night shot (with hi-beams on to see if the camera is dazzled by the headlights like the old camera)

 

 

Being a public forum I scrubbed out the actual license plate numbers, I left a few digits so you can see how much it picks up.

 

 

 

I need to see how badly out of focus it is in the daylight tomorrow.

[rory 0]

what type of IR illuminator and which camera?

 

but no, an 750nm filter, or an 840nm filter, will not cut out all light.

 

BTW, most of us here, that are in the biz, would just buy a ready made LPR camera..

[Scruit 0]

what type of IR illuminator and which camera?

 

but no, an 750nm filter, or an 840nm filter, will not cut out all light.

 

BTW, most of us here, that are in the biz, would just buy a ready made LPR camera..

 

Illuminator: Panvigor 120', new, $49.99

Camera: No-name BW CS mount 1/3" Sony CCD, used, $20

Lens: Computar 12.5 >75mm zoom, CS, used, $30

IR filter: non-name 760nm, new, $10

 

Total cost = $110

 

How much is a proper LPR camera? I thought they were $800+

 

The 850nm filter should filter out more of the visible light, and reduce the focus shift?

[rory 0]

thats a no name IR btw ..

 

and a proper LPR camera would cost over $2000 retail.

 

using a fixed lens, would stop any focus shift, not the IR filter.

if anything the IR filter would cut out extra light/glare.

 

here are some REG-L shots

http://www.bahamassecurity.com/ExtremeREG/

[Scruit 0]

What is the distance between the camera and the license plates in those pictures?

 

It would be great if I could move the camera closer to the car, but the problem I have is the layout of the front driveway. For the first 50' it's about 50' wide so it's impossible to cover cars that drive to the garage doors to the front AND cars that drive around the back of the house instead. More than 50' from the house the driveway is one lane.

 

So my options are

 

(1) to use a zoom lens and film cars that are >50' away (about 80' is the thinnest part of the the driveway)

 

or

 

(2) to bury some wires in the ground and have a camera mounted 50' down the driveway.

 

[Scruit 0]

Also, I noticed that the brake lights on my car are not all visible under IR.

 

My car has 5 brake lights... One regular bulb per side, one LED bulb per side and a single hi-mounted brake light. When I drive away from the house you cannot see that the LED bulbs in the video.

[rory 0]

What is the distance between the camera and the license plates in those pictures?

 

they are close, it's an entrance to a gated community.

thats a 16mm fixed lens version.

http://www.extremecctv.com/product_detail.php?producttype_id=6&page=1&product_id=72

 

Rory

[CollinR 0]

I'm impressed, strong work man!

 

 

Where did you find your filter?

[Scruit 0]

What is the distance between the camera and the license plates in those pictures?

 

they are close, it's an entrance to a gated community.

thats a 16mm fixed lens version.

http://www.extremecctv.com/product_detail.php?producttype_id=6&page=1&product_id=72

 

Rory

 

When you say 'fixed', what are you referring to? Fixed focus?

 

I checked the lens again - it's actually a Fujinon H6 12.5Rx75mm.

 

It has manual adjustments for iris, zoom and focus. All of these adjustments will affect the focus. Which order should I set these in?

 

I have been adjusting the iris to the lowest light setting that gives me an usable image (ie if I go one click lower then the image goes dark). Then I adjust the zoom to get the field of view I want, then adjust the focus. I have to switch back and forth adjusting the zoom and focus to get a good crisp image in that shows the correct field of view. Adjusting the focus appears to adjus the zoom slightly.

 

 

At first I set this up during the day so I got a good The I waited until night and repeated the steps above. I had to open the iris another couple of settings. Now that it is morning again I need to go out and see what the image is like during the day. I'll write down the night settings before I mess around with it.

 

 

 

I got all this stuff from eBay.

[Scruit 0]

Checked the camera this morning, focus was fine.

 

I'm now conducting a 24hr test of the platecam. I have a capture card in my computer that is taking an image every minute for 24 hours

 

 

I should be able to produce a thumbnail gallery of the platecam in all light levels to ensure it's reliable 24x7.

 

My main concern is twilight/dawn because the IR illuminator has a photocell to turn itself off during the day, and I worry that it will turn off while there is not enough ambient light to see the plate.

[Cooperman 0]

I checked the lens again - it's actually a Fujinon H6 12.5Rx75mm.

 

It has manual adjustments for iris, zoom and focus. All of these adjustments will affect the focus. Which order should I set these in?

 

I have been adjusting the iris to the lowest light setting that gives me an usable image (ie if I go one click lower then the image goes dark). Then I adjust the zoom to get the field of view I want, then adjust the focus. I have to switch back and forth adjusting the zoom and focus to get a good crisp image in that shows the correct field of view. Adjusting the focus appears to adjus the zoom slightly.

 

At first I set this up during the day so I got a good The I waited until night and repeated the steps above. I had to open the iris another couple of settings. Now that it is morning again I need to go out and see what the image is like during the day. I'll write down the night settings before I mess around with it.

 

Hi Scruit,

 

First off, you should always carry out focus adjustments at maximum aperture. I'm guessing you've got the "Electronic Iris" function switched on in the camera, so even at maximum aperture on an overcast day, you should still get a reasonable image.

 

For the purposes of picking up vehicle plates, it is preferable to have the camera sited well away from the target area; so your 50' distance would be ideal, whereas a shorter distance generally would not be the first choice.

 

If you calculate the distance that a vehicle can travel in the 'field of view' you may find for example that the number plate is on screen from perhaps 60 feet distance down to 40 feet. If so, (this is an example) you should place an object 1/3rd of the distance into the 'recognition zone', so with this example, it would be perhaps 47 feet (ish) from the camera.

 

Focus on the object, then close the lens aperture a couple of stops ( to perhaps f 4 ), then assess the picture quality, both by day and night.

In practice, f 5.6 would probably give you a very good daytime image, but you would need lots of light to ensure a good night view (or move your illuminator closer to the target area).

 

As regards using IR pass filters, it will "standardise a variable" in terms of preventing the risk of focus shift that would have been present under different light frequencies, but ideally, if you were using an 850nM illuminator (for example) then you would want to use an 850nM pass filter to ensure that the maximum usable amount of IR is reaching the imager.

 

Although many people worry about focus shift when using either daylight or IR illumination with an unfiltered lens, in practice, simply stopping the lens down two or three 'f' stops is often sufficient to offset the shift phenomenon that is a characteristic of non IR corrected optics.

[Scruit 0]

Update:

 

 

I switched out the 760nm IR Pass filter for an 850nm filter, and adjusted the apeture. It was almost closed before (f16). What I did was open it all the way until the image was washed out totally (gave it a couple seconds for the auto iris to adjust) and then started to close it until I got a good readable image on a license plate that I placed in the driveway at the bottleneck. Wound up at f5.6 - As Cilla used to say; "Surprise Surprise"

 

I have marked the settings down as 'daytime', and will come back at night and check again.

 

I hope the open apeture doesn't make the camera susceptible to headlight blinding as it was before - hopefully the 850nm filter will reduce the visible light enough to where the camera isn't blinded.