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stefuel
Joined: 07 Mar 2006
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Location: Green Harbor MA USA
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 Link Posted: Wed Jun 24, 2009 1:10 am Post subject: OK camera buffs, lens question |
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How does one select the correct zoom lens for a application. I am going to ad PTZ to one of my CCD cameras and the area that needs zoom (end of driveway) is about 150 feet from the camera location. If you wanted to read a licence plate from 150 feet away, how would you calculate the MM lens you need. I've been looking at fleabay and there seems to be a wide range of CCD lenses to choose from.
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greg_mitch
Joined: 03 May 2006
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| Link Posted: Wed Jun 24, 2009 1:40 am Post subject: |
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What is the resolution? I would think that is just as if not more important than the lens.
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Clarence
Joined: 08 Mar 2006
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Location: Northern Virginia
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| Link Posted: Wed Jun 24, 2009 2:11 am Post subject: |
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What is the mm on the current lens on your camera and what is the current width of the field of view at 150'?
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stefuel
Joined: 07 Mar 2006
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Location: Green Harbor MA USA
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| Link Posted: Wed Jun 24, 2009 4:12 pm Post subject: |
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| Clarence wrote: | | What is the mm on the current lens on your camera and what is the current width of the field of view at 150'? |
The current lens is fixed at 3.6 MM.
I'm guessing the field of view with the current lens at about 150 feet is about 125 feet.
The resolution of the camera is 420 tv lines and the DVR scales the output to 1024X768 for PC monitor display or I can take composite out and scale it to whatever I wish.
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ecrabb
Joined: 13 Mar 2006
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| Link Posted: Wed Jun 24, 2009 4:38 pm Post subject: |
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Knowing the current lens' field of view and focal length makes it easy. If you want about a 2' field of view at that distance, then you need about 60x more focal length than you have, or about 200mm. Of course, you probably don't need to go quite that far just to read the plate. A 3-4' field of view would probably be adequate and would require a lens in the 110-150mm ballpark.
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Clarence
Joined: 08 Mar 2006
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Location: Northern Virginia
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| Link Posted: Wed Jun 24, 2009 4:42 pm Post subject: |
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| stefuel wrote: | | Clarence wrote: | | What is the mm on the current lens on your camera and what is the current width of the field of view at 150'? |
The current lens is fixed at 3.6 MM.
I'm guessing the field of view with the current lens at about 150 feet is about 125 feet.
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What are the common replacement lenses available?
If you zoom 10x (optical), then that should give you a field of view at 150' of about 12'... full frame about the size of a car, so you should be able to read a license plate with 420 lines.
Looks like there are a lot of varifocal lenses that could do this zoom range, but I'm not sure if it would fit in your PTZ housing.
If you really want to do the math:
http://en.wikipedia.org/wiki/Angle_of_view
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jvanderwalker
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stefuel
Joined: 07 Mar 2006
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Location: Green Harbor MA USA
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| Link Posted: Wed Jun 24, 2009 5:27 pm Post subject: |
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| Clarence wrote: | | stefuel wrote: | | Clarence wrote: | | What is the mm on the current lens on your camera and what is the current width of the field of view at 150'? |
The current lens is fixed at 3.6 MM.
I'm guessing the field of view with the current lens at about 150 feet is about 125 feet.
|
What are the common replacement lenses available?
If you zoom 10x (optical), then that should give you a field of view at 150' of about 12'... full frame about the size of a car, so you should be able to read a license plate with 420 lines.
Looks like there are a lot of varifocal lenses that could do this zoom range, but I'm not sure if it would fit in your PTZ housing.
If you really want to do the math:
http://en.wikipedia.org/wiki/Angle_of_view |
The PTZ device is Crestron and it's universal to most camera/lens applications that use 2.5-12 VDC for zoom and focus. The Crestron device provides the pan and tilt then supplies the signal to the lens for zoom and focus. I think it can handle a lens/camera combination weight of about ten pounds. Is 10X the same as 10MM? I have seen lenses on the bay at 120MM. I think that would be extreme zoom. I don't care if it has the capacity to do extreme zoom as long as it can at least do what I want. From the location I wish to mount it in, I would be able to sweep 270 degrees which would cover my whole back yard and the other half of the driveway which is 150 feet long. If I had it to do all over again I would have bought a DVR with more than just four channels.
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Clarence
Joined: 08 Mar 2006
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Location: Northern Virginia
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| Link Posted: Wed Jun 24, 2009 5:34 pm Post subject: |
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| stefuel wrote: | | Is 10X the same as 10MM? |
No, by 10x, I meant 10x the zoom of the standard lens... 3.6mm x10 = 36mm
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