Tuesday, October 14, 2008

Let's focus on focus.

Many installers don't realize how important it is to properly focus a camera. A high resolution Pelco 540TVL camera can instantly become a Costco 380TVL camera by barely bumping the focus ring out of place when closing the housing. Here are a few tips to help you properly focus your surveillance camera:

1) Only adjust focus when using a "local" monitor, meaning have a small LCD plugged directly into the camera. Buy a 5$ BNC Male-to-RCA Female adapter at Radio Shack and turn your kids portable DVD player into a local monitor by plugging the aux TV jack into the back of the camera, using the adapter.
2) Don't rely on someone else telling you that a camera is in focus from the console. No shouting or radios. It just won't work out well, and becomes rather frustrating.
3) Steer clear of using a computer and IP connection as a monitor, as the focus adjustments will be delayed and you risk losing resolution by being slightly out of focus.
4) Focus your cameras at night. If you buy a "true" day/night camera (meaning one that has a mechanical IR cut filter), then the night image will be slightly out of focus if you previously dialed in the focus during the day. This is called "focus shift". The effects of focus shift can be reduced by purchasing a lens made specifically for IR. Aspherical "IR" lenses are worth the extra money. Check out Tamron and Ikegami lenses for some good examples. Also, focusing at night allows you to avoid the glare of the sun on your monitor, if you don't have one of those nifty viewfinders that cup around your eye. I remember being up on a 30ft lift along the runway fence of a large international airport. The sun was beating down so bright that the poor LCD was barely viewable. We ended up having to go back and re-focus a few of the cameras at night simply because we lost some resolution due to the sun.
5)Adjust your BACK FOCUS ring first. Think of it as a course focus adjustment. Start by setting the ring to the middle position. Next adjust your zoom lens (If you're using an adjustable zoom lens), to about where it will be to capture the scene you want. Lock down the zoom ring. Now adjust the focus ring of the lens. Here is the tricky part: If you can focus your scene without turning the focus ring to the maximum one way or another, then the back focus is about right. If you have to turn the focus ring to one side all the way, just to focus the scene, then return to the backfocus and adjust slightly to compensate. The whole point it to adjust the back focus so it allows the lens focus to be near the middle position. All the lenses on your camera were designed to work best in their middle position. An extreme one way or another will cost you resolution. Believe me, after testing camera after camera on a waveform analyzer, I can tell you that you will lose resolution if your focus ring is maxed out one way or another. When you're done, the back focus should be slightly to one side or another, and the focus ring should also be adjusted slightly one side or another from center. As long as neither ring is extended to its max in either direction, you will be properly focused.
6) Don't over tighten your ring screws. This is especially a problem on dome lenses. If you tighten them down too much, it warps the lens housing ever so slightly and, again, you lose focus and resolution. Keep an eye on the monitor as you tighten the focus ring screws down. Make sure you don't see any focus shift.
7) Finally, and most importantly, pick a good focus target. Look for something in your scene that has as much detail as possible. If you're pointed at a brick wall, concentrate on the lines between the bricks. If you're looking at a field, concentrate on the small blades of grass, or small twigs. Don't pick large objects with little detail, like clouds or water. Don't forget to keep the monitor plugged in until you absolutely have to close the housing and unplug it. This allows you to make sure the camera stays in focus while it is being mounted back in the housing, or while the outer dome is being screwed back on.

Well I hope this helps you next time you're installing a cam. If anyone thinks of any more focus tips, feel free to comment below.