Drive-by shooting!

[wittaj]

While it can be done, PTZs are much more difficult to use for LPR because you cannot assign a fixed focus number like you can a fixed camera. Those that do will set it to the LPR mode well early so that it has something to focus on and then doesn't move it at all during the dark hours.

@bigredfish has slower traffic and can get away with it, but you would need the right conditions to get reliable LPR out of a PTZ. The focus issue is the hardest part.

 

[Cold-Lemonade]

@wittaj So am I correct in understanding that the PTZ camera's firmware does not allow the user to manually set the focus?

 

[bigredfish]

You can set a fixed focus point for a preset, but once it tries to track or zoom it’s on its own. I can only get away with using it for LPR because as mentioned cars are only going 10-15 mph with 30-40 distances and I have a street light to give it just enough light to focus when it gets to the LPR capture preset (initiated by a spotter cam in advance of the vehicle arriving there)

In most normal scenes, a PTZ isn’t going to be able to focus at greater distances and fast shutter needed to capture plates. And because you have to run such a fast shutter, it won’t be any good to you for anything else, it will be too dark

 

[Cold-Lemonade]

@bigredfish Sorry I am having trouble understanding. Would it work in the following context? Most of the time, the PTZ camera would stay in a fixed orientation looking at the street at an angle where I can see the passing cars' license plates. But sometimes, I would manually take control of this camera and pan/zoom around look at the delinquent teenagers making trouble on my block. When I am done using it manually, I would return it to the its prior fixed orientation where it looks at the street. I wouldn't have the camera track on its own. Would this configuration work?

 

[Parley]

As long as it is fixed and you do not move it, then yes you can. I have one of mine watching a segment in front of my house. I do have a preset to its home position in case I want to look at something else with it.

 

[wittaj]

But once you move it at night, then it won't have anything to focus on.

At night, we have to run a very fast shutter speed (1/2,000) and in B/W with IR and the image will be black. We need the fast shutter to capture the plate and take advantage of the reflective properties of the plate. All you will see are head/tail lights and the plate. Some people can get away with color if they have enough street lights, but most of us cannot. Here is a representative sample of plates I get at night of vehicles traveling about 45MPH at 175 feet from my 2MP 5241-Z12E camera (that is all that is needed for plates):

At that shutter speed you will not pick up the outline of the car, people walking by, etc. Just like at a shutter speed to capture people at night, the plate will be all white due to the reflective properties of the plate.

 

[Cold-Lemonade]

@wittaj -- But if I return it its preset position, as @bigredfish and @Parley describe, then I would be okay, right? Even at night?

 

[wittaj]

No because it will then not have anything to focus on unless you have enough light that it can see something to focus on like in @bigredfish example below. Most of us don't have enough light that our image is all black and an all black image will result in it trying to find something to focus on all night and then the image is blur when the plate goes by.

Now if you have enough light and the speed of the vehicles are slow enough, maybe?

Review-SD4A425DB-HNY 1/2.8" CMOS 4MP 25x Starlight Auto-tracking MiniPTZ

When I increase the track size target, it tracks the wrong person/area lol Example: infant and parent/ dog walker and dog/ stroller and parent, the camera would start zooming into dogs, infant, stroller etc and not zoom in "enough" to see both objects. As you know, these things are not...

ipcamtalk.com

 

[CaptainCrunch]

@wittaj -- But if I return it its preset position, as @bigredfish and @Parley describe, then I would be okay, right? Even at night?

With the fixed camera, you can tell it to focus at a certain setting, regardless of what the camera sees. If the ptz does not have that ability, the ptz will try to focus on what it does see. If it can't see anything, it can't focus. When a plate does come into view, the ptz will try to focus on it. But in all likelihood, the plate will be out of frame before that will happen.

Imagine it like this. You have a cup on the other side of the room. You have a machine that can launch a ball with repeatable precision of the angle and the power. Every time, it's the same angle and the same power. The likelihood of getting the ball in the cup is pretty good. That's the fixed lens. Now imagine if you could have the right angle but the power was random. You might make it in the cup but it's not nearly as likely. That's the ptz trying to focus. It'll probably start off focused either too close or too far and won't have time to correct itself.

 

[Cold-Lemonade]

Thanks. @bidredfish's test results are impressive.

I have a lot of street light because I'm in an urban setting. I think I probably have more than the ambient light in @bigredfish's tests because it never gets dark enough for the cameras in the front of my house to use IR at night. I wouldn't have his spotter cameras. I am on one-way street so I can leave it in one preset position when I am not using it manually to get a close up of the would-be criminals across the street. Does it sound like this PTZ camera would work in my use case?

 

[Cold-Lemonade]

@CaptainCrunch I follow your analogy, but if I understand @wittaj and the other comments, if there is enough light then it would be able to focus on the pavement. Right?

 

[Parley]

With my PTZ's I can set the shutter speed up to like 1/10000. IMHO you can set the focus and there is no reason for it to change if the camera does not move. Now mine may wander a little on the focus over time and all I have to do is hit the preset and it comes back into focus.

 

[bigredfish]

Daytime is easy, especially with spotters triggering far enough in advance to allow time for it to get to the capture point

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[bigredfish]

Nighttime IF you leave it positioned and have enough light for it to focus, maybe. But you can see its no good for anything else at night, so there's the tradeoff

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[wittaj]

@CaptainCrunch I follow your analogy, but if I understand @wittaj and the other comments, if there is enough light then it would be able to focus on the pavement. Right?

Yes but that is a big IF based on distance and speed of the vehicles.

If you are getting a PTZ anyway, then give it a try.

In my scenario with no street lights, if I set the PTZ up to get plates, if I move it around, then I need to slow down the shutter to be able to see things and then set it back to the LPR settings and hope the focus works LOL.

But you can see in @bigredfish example, that isn't going to be of much use to see people as he set it up for LPR at the bare minimum he could get away with.

@Parley what PTZs are you using? Dahua PTZ doesn't have the ability to set a focus number like the fixed cams, so without enough light, focus will be all over the place.

 

[Parley]

Yes, but you are moving your PTZ with a spotter. I do not think that is what he is talking about. I think he wants to leave it stationary.

 

[bigredfish]

Right same effect. Daytime easy, nighttime, in a fixed position, like you, IF it can maintain a focus then yeah. But I found it wandered when i set it in on capture spot already focused at night as soon as I moved it to go to the other capture point and it returned. So if you can leave it set in one spot, it can work.

 

[wittaj]

His question is can he use it for plates but then also move it around for punks at night.

At the shutter speed needed to capture plates, the image will probably be too dark like in @bigredfish example to reliably do that.

So he would have to then go into the settings and slow down the shutter to be able to make out people and stuff and then return the settings to the settings for LPR and hope it gets something to focus on.

 

[bigredfish]

Now if you have enough light, AND a spotter to get it to the capture point in time, AND get them to Stop, then you might be able to capture in color and maintain use for other stuff


View attachment HOA Ent_ch1_20230526214115_20230526214130.mp4

 

[Cold-Lemonade]

Thank you. I understand the issue now. If I am going to get a PTZ and try it, which PTZ should I buy? The one I linked to earlier a relatively less expensive one and would be easier for me to install because I would be putting it on the side of my brick house about 25 feet above the ground, or 33 feet about the street (because I'm set back a little up a slope).