| Article #: | 17 |
Dear Charlie,
Do you know of a high resolution hand-held monitor for focusing the cameras
at installation. The best we could find was 480 lines and compared to the
computer screen it is a bit course and hard to get detail. It is difficult to
drag a 9" or larger monitor up to the roof tops. Anything that you have
will be of a great help.
Have a merry holiday and great new year!
Looking Small in White Plains, NY
Dear looking,
To answer your question quickly; No, unfortunately, I do not know of a single
hand held monitor that should be used for focusing.... That is there are several
hand held monitors out there (used to be anyway until Sony quite making them a
couple of months ago), but you cannot use them to focus the cameras. These
monitors are great for use as a quick reference to verify the video image or to
aim the camera at the scene that you want. However they should not be used for
focusing the camera in the field!
The problem is that the hand held screen is too small to gather detail....
The smallest screen that I recommend for focusing a camera (regardless of
resolution) is 9"... Personally, if I thought that it was practical to drag
anything bigger than a 9" into the field, I would recommend a 14" or
bigger.... This is due to the amount of "Focus Fuzzy" information that
is needed to do the job well.... Basically speaking, the smaller screen, of the
hand held units, compresses the image too much and things look in focus that are
not... You will end up making several trips to the field to correct the
problem....I am really sorry to pass this type of bad news on so close to the
Holiday seasons, but If I lie now, even my good Irish, Catholic wife won't be
able to save my soul...
To help you out however, you can, and should be doing your master focusing
back at your office. 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. To accomplish what I am speaking about, you need to
back-focus your camera and lens.... This is a form of setting the camera to a
generic focal point and then doing the fine adjustments in the field. I have
listed below, the procedure for setting the back-focus for various types of
operations:
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 gel, welding lens, or other type of filter in front of the lens
to force the iris into the full open position. If you contact a manufacturer,
they will tell you to use an "ND" (neutral density) filter. 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 75 feet away for
one inch cameras and 50 feet away for two thirds inch and smaller cameras.
a. The imager position screw may be called several things on different types
of cameras: Vidicon positioner, imager positioner, tube 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 50 to 75 feet 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.
1. Set the physical focus of the lens for full infinity.
2. Insert a gel or filter to cause iris to open completely. (See Paragraph
#3, #3a, #3b, #3c under Zoom Lenses 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.
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 gel or filter to open the iris of the lens completely. (See
Paragraph #3, #3a, #3b, #3c under Zoom Lenses above).
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.
I sincerely hope that this information is of some use to you... Take care of
yourself, stay in touch, and let me know if there is every anything that I can
do for you... I am in your service.