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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