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Thread: Back Fousing CCTV cameras

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    Default Back Fousing CCTV cameras

    Back focusing of cameras should be done in the office not in the field. I know, this sounds unlikely since it seems obvious that you shouldn't be able to set the focus on a camera at one place and then move it to another, but focus is one of the truly last major problems left in the field of CCTV camera setup.

    Setting the camera to a generic focal point and then doing the fine adjustments in the field saves a lot more time. I have listed below, the procedure for setting the back-focus for various types of operations:

    Zoom Lenses

    To obtain proper back focus (tracking) of a camera with a zoom lens, the following steps must be followed. If these steps are shortcut or avoided, proper tracking of the lens will never be possible.

    1. Set the lens to full wide angle (widest scene possible).
    2. Set the physical lens focus to full infinity.
    3. Insert a neutral density filter in front of the lens to force the iris into the full open position. These filters are very expensive however. To combat cost and potential loss (dropping of very expensive filters) I recommend welding glass filters (about $5.50 each). I also recommend that you purchase four different densities to combat the various lighting conditions that you may be working under (#1, #3, #5, #8). A #1 filter is very light and is like a pair of sunglasses. A #8 filter is extremely dark and is good for very bright conditions (full sunlight).

    a. Do not use such a dark filter that a usable picture is not obtainable.
    b. Use a glass filter versus a plastic filter, if possible, to insure purity of view.
    c. It is essential that the iris is opened to full position.

    4. Using a screwdriver of appropriate size, adjust the imager positioning screw of the camera for best picture while viewing an object 25 meters away for one inch cameras, and 15 meters away for two thirds inch and smaller cameras.

    a. The imager position screw may be called several things on different types of cameras: imager positioner, tube positioner, CCD positioner et cetera.
    b. The imager positioning adjustment on most quality cameras can be reached from the outside of the camera.

    5. Zoom the lens in for the closest view of the object 15 to 25 meters away.
    6. Adjust the manual focus of the lens for best picture.
    7. Zoom the lens out for widest picture. The picture should remain in focus. If it does, the camera is adjusted properly. If it does not, the camera is still out of back focus and steps #1 through 6 should be repeated.

    a. If a 2X Tele-converter lens is used in conjunction with any zoom lens, back focus will not be possible. Adjust the Imager position for best picture at either near or far view and leave it.

    8. Remove the filters and reinstall the camera to service.

    Standard Fixed Focal Length Lens

    1. Set the physical focus of the lens for full infinity.
    2. Insert a Neutral Density Filter to cause iris to open completely. (As Mentioned Above)
    3. Aiming the camera at an object that is the same distance as the primary scene to be viewed, adjust the Imager position for the best picture.
    4. Remove the filters and reinstall the camera with the lens in position to provide best possible manual focus.

    CS Lens & Camera

    Back focus, or the initial setup of the CS style camera and lens, is slightly different as well. Since the focus optics of the fixed focal length CS lens and the imager positioning mounts of the CS style cameras have been removed, a slightly different approach to back-focus is taken. The end result, however, is the same.

    1. Locate and loosen the CS lens collar lock(s).
    2. Insert a Neutral Density Filter to open the iris of the lens completely.
    3. Aim the camera at an object that is the same distance as the primary scene to be viewed.
    4. Adjust the CS collar of the lens for best picture.
    5. Re-tighten the CS collar lock(s) and remove the filter.

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    george have you got some info on the ' filters ' you are talking about? I have an issue at our workshop with some ganz cameras using ness zoom lenses and one is in the shed, so when the roller door is up the glare at the door opening is so bad it nearly washes out the whole picture. We then have 2 out side and have concrete and other zincalume sheds nearby so there is also an issue there with glare too.

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    They are called Nuetral Density Filter, sold at you local CCTV supplier. Some use tinted glass, but the problem there is tint reduces light from various wavelengths. Nuetral density filters on the other hand are designed to reduce ALL wavelengths and colors equally.

    We use ND filters to simulate night time conditions when focusing cameras, because we all know that when we focus during the day at maximum light exposure, what looks like a good image turns to shit at night time.

    However, in your case, Polarizing filters will reduce glare and reflection in bright outdoor conditions where reflection is a problem. I know Computar Lens manufactures one for like $50.

    Cameras that have Digital signal processing will also help as they have an array of analog to digital converters to balance bright and dark pixels, but the level of signal processing comes at a cost.

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    Hi have seen the Computar filters on the ganz-computar website. But where can i get them in aus, as rexel only use ness now and thats where we go them from? I was also told by ness that i should use a wide dynamic camera instead of the polarzing filter as they said polarizing filters are only good for say if there was a lake or water around and we were getting glare off of that.

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    CR Kennedy, It seems i buy them weekly at the moment due to our techs losing or dropping the dam things.

    Get atleast an 8 and a 4.

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    Quote Originally Posted by mobsta View Post
    I was also told by ness that i should use a wide dynamic camera instead of the polarzing filter as they said polarizing filters are only good for say if there was a lake or water around and we were getting glare off of that.
    Environmental factors will determine the type of camera required, ultimately the decision is yours, you can purchase a filter and see if it helps and even if it doesn't you can always replace the camera.

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    the ganz cameras are fantastic, in my opinion the best dome camera (anolouge) on the market hands down and I am open to anyone arguing this, as well!!! but bring your A game because I will take a hell of a lot of convincing!!. If your using a ganz camera do yourself a favour and don't use a rebaged ness lens, ganz and computar are the same company and computar make some of the best glass lenses available.

    wish one of the big distributors would carry ganz so prices would be competitive.

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    UMMMMM if you use a Bosch camera - you dont need to do any of this........kind of handy really ...saves time.....no need for filet, no need to adjust anyhting, just press a button and adjust the back focus ring........sooo much easier

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    You can buy Ganz or better known OS as CBC at many places, I dont know if Qvideo still sells them but Altech still do...and for a while Mainline were as well, there is a rep locally now.....yes they are good cams I should know I was one of the first to bring them into the country.....but beware not all Ganz products are made in Japan and Batch faliures have been prevelant with their Korean manufacturing plant. I agree about the lenses though...just wish they called the Cams Computar as well

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    Quote Originally Posted by cctv_down_under View Post
    You can buy Ganz or better known OS as CBC at many places, I dont know if Qvideo still sells them but Altech still do...and for a while Mainline were as well, there is a rep locally now.....yes they are good cams I should know I was one of the first to bring them into the country.....but beware not all Ganz products are made in Japan and Batch faliures have been prevelant with their Korean manufacturing plant. I agree about the lenses though...just wish they called the Cams Computar as well
    funny you mention the out sourcing, you can really tell the difference in the cameras that are outsourced to Korea. Chalk and cheese.

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    Pacom and DAS have Computar lenses but not Ganz cameras.

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    I am not trying to promote Bosch.....even though i think it is great gear...but surely that is an advantage, not having to do a back focus......if you think about your average 24 camera job 24 x $20 (min) per camera in set up time ...is a great saving, it is also a lot more accurate IMHO - why back focus if you dont need to?

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    Hi

    Is this thread applicable to ip cameras and analogue cameras as well?

    regards,

    Aus355

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    Quote Originally Posted by cctv_down_under View Post
    UMMMMM if you use a Bosch camera - you dont need to do any of this........kind of handy really ...saves time.....no need for filet, no need to adjust anyhting, just press a button and adjust the back focus ring........sooo much easier
    While I was at Rexel Video, the Panasonic cameras had auto back focus, which ensured perfect back focus that re-calibrated its self when the IR cut filter was removed for night.

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