How do I calculate lens requirements?

[C7 in CA 0]

Hi all. I am a low voltage contractor in California but new to cctv. For fun and education I am going to play with a couple of cameras around the house. I think I can figure out the voltage drop,cabling techniques and all that. But how do I calculate depth of field and all those other measurements?

 

What I am trying to cover is a T shaped intersection. The center of attention is from 135 feet out to 160 feet. At 160 ft the width to cover is about 50 ft. The camera would be mounted about 15-17 ft. high in a big'ol oak tree.

 

Street lighting is decent with what I think are sodium vapor bulbs? (yellow light) The sun will always be behind the camera. Resolution: the better the better. I would like to at least distinguish vehicle type. Color would be cool, but I think I am more interested in night time usability.

 

Any tips and industry terminology you could pass along on the subject would be appreciated.

 

Thanks.

[AVCONSULTING 0]

Try out this link. They don't specify the imager size but I'm pretty sure it would be for a 1/3" camera which is the most common these days.

 

http://www.silentwitness.com/support/lens/lenses.php

[Cooperman 0]

AVCONSULTING,

 

The figures certainly look like they correspond to 1/3" format.

 

C7 in CA

 

The depth of field (DoF) will vary according to the focal length of the lens, the iris setting, and the distance to target.

 

With the example you've provided you would have to use a 16mm lens on a 1/3" camera (or 25mm on a 1/2" camera).

 

At any given distance, the 16mm will provide a greater depth of field than the 25mm, and as with all lenses, the DoF will increase as you close the iris.

If you want to cover from 135' up to 160', you will need to set the focus at roughly 144' (DoF works on the principle of 1/3rd in front of focus point, 2/3rds behind).

 

In practice, you will probably have sufficient DoF for what you want, even at maximum aperture (typically f1.4 for a C mount lens).

 

Have you bought any cameras yet, or do you need some advice from others experienced in the North American market? Maybe if you haven't, you could give an indication of how much you want to spend, and then others will be able to advise.

 

Hope the lens stuff makes sense.

[C7 in CA 0]

AVCONSULTING, thanks for the link. That is a great resource.

 

 

Have you bought any cameras yet, or do you need some advice from others experienced in the North American market? Maybe if you haven't, you could give an indication of how much you want to spend, and then others will be able to advise.

 

Hope the lens stuff makes sense.

 

Yes. Thanks! I think it will come back to me. I kinda knew this stuff back in highschool. Well, as it pertains to 35mm SLR's. Thanks for the refresher. One thing I gotta say, focal length will take some getting use to. 50mm lens on 35mm film is incredibly different then 50mm on a 1/3" CCD.

 

Yes, I am looking for advice. I don't know how much I want to spend. I have to consider the camera probably will not be in that tree forever. So I may want to look at a camera I could put on a pan/tilt motor in the near future.

[AVCONSULTING 0]

Best bet is to get an auto iris varifocal lens. Here is a link to show you a typical type to consider.

 

http://www.vitekcctv.com/ProductDetails.asp?ProductID=61

 

Here is another link to a very good resource to find information.

 

http://www.vsscctv.com/dealtools.asp

[C7 in CA 0]

Best bet is to get an auto iris varifocal lens. Here is a link to show you a typical type to consider.

 

http://www.vitekcctv.com/ProductDetails.asp?ProductID=61

 

Here is another link to a very good resource to find information.

 

http://www.vsscctv.com/dealtools.asp

 

Thanks for the additional resources! looks good. What camera would you suggest for that lens? Again considering this setup would probably be mounted to a Pan/Tilt unit in the near future.

 

Thanks.

[Cooperman 0]

C7 in CA,

 

A photographer .... yippeeeee.

 

Sorry about that, the stiff upper lip slipped a bit then!

 

Your 50mm lens on 35mm is equivalent to an 8mm on 1/3", and 12mm on 1/2".

 

50mm on 1/3" is roughly equivalent to approx. 300mm on an SLR.

Varifocals are very popular for ease of use, but they generally do not perform quite as well as top notch fixed focal length lenses; (exactly the same principle as for photographic lenses).

 

Good luck with choosing your cameras.

[C7 in CA 0]

C7 in CA,

 

A photographer .... yippeeeee.

 

Sorry about that, the stiff upper lip slipped a bit then!

 

 

Well I could hardly be called a photographer. I just learned alittle bit about it.

[AVCONSULTING 0]

Look for a B/W camera with about 570 lines resolution and a low light ability. Toshiba and GE are good ones to try out. We had a thread going in this section on lowlight cameras so you might want to look it up and see some of the links. I think the header was IR Sensitive Cameras or something like that.