Scruit 0 Posted November 26, 2007 I have a BW camera (520TVL Sony) that has a 60mm lens and 850nm IR Pass filter attached to it. When I try to focus on an object in the middle of the picture I can get a good clear image, but there is a 20% wide strip across the top and sides (not the bottom) that is blurry. The camera is mounted abut 10' above the ground and reads license plates from passing cars (no OCR or anything). When a car first comes into shot the license plate appears in the top right and travels to the bottom left. It's not until the plate is in the middle of the screen that it's clear enough to read. I believe the focus issue is because objects at the top and sides of the screen are 10-20' behind the focal point. Is this a product of the zoom lens? ie Is it normal for an object that is in focus at 80' to be out of focus at 100'? I have removed and cleaned the lens and IRPass filter and they are perfectly clean. The ccd sensor appears to be clean but I haven't tried to clean it for fear of causing damage. The biggest issue that I have is that the during a motion event the bulk of the framerate of the DVR is allocated to channels with motion and and the rest drop to 1fps. This means that a car leaving my house will trigger the motion sensing on the front cameras and the license plate camera will drop to 1fps. When the car passes under the license plate camera it's a 50/50 chance that the 1fps just happens to catch the plate when it's in focus. Once the car reaches 100' from the house the plate is no longer in focus (even though it's still large enough to read if it was). If the whoel image was in focus then the lower framerate wouldn't be so bad becuase I'd still capture at least one good image. There now follows lots of nonsensical rambling. Read at your own risk: As a temporary measure I'm going to reinstall my old 4ch DVR that does 30 frames per second and use the loop output from the primary DVR to feed the license plate images to the secondary DVR. The secondary DVR will always record at 30fps so it will always get a shot of the plate while it's in the range of focus. heck, I can feed the 3 door cameras to the secondary DVR too - they'll all record at 7.5fps but that's still good enough and will provide a backup DVR for the most important cameras (the ones that provide evidence that can lead to a suspect, rather than just fuzzy pictures on an untraceable bad guy ripping me off) in cae of failure of the primary DVR (has happened once this year due to failed HD - system was down 3 days before I realized it) The licence plate camera is useful for about 10'. At 1 fps a car has to be travelling under 10 feet per second to be assured of a good image (assuming the plate is otherwise readable). That's about 6.5mph. A car leaving at 13mph will be missed 50% of the time. However with the DVR running at 7.5 frames per second the bad guy would have to travel at 75 feet per second to clear that 10 feet between frames. That's over 50mph, and he only had about 60' of acceleration space, on gravel. Share this post Link to post Share on other sites
CollinR 0 Posted November 26, 2007 Completely refocus it at night with IR on. You may need an IR corrected lens for 24 hours use. Most of mine do not use 60mm lenses and I think that has/will become a large factor in this. Share this post Link to post Share on other sites
survtech 0 Posted November 26, 2007 Is this camera inside a dome? The longer the lens, the more likely a dome will affect the focus. You may have to focus it with the dome held in front of the lens. Also, it may be a bad lens or one that is not correctly back-focused to the camera or is made for a different size imager. Share this post Link to post Share on other sites
Scruit 0 Posted November 26, 2007 I initially focused it during that day, then went back and tweaked the focus at night with the IR on. The camera is not in a dome. I'm going to try putting something in that blurry area and see for sure that I can focus on it - that would rule in / out focal length as the problem versus issues with the lens or imager being damaged or dirty. Share this post Link to post Share on other sites
zmxtech 0 Posted November 26, 2007 If its and old lens or normal one it might not be good for IR ? I have two really great 75 and 100m zoom lens's that are no good for IR ! not on purpose -they just dont have all the new fancy IR stuff etc... You really need to get a IR lens for sure otherwise the filter will be just dropping the light level. I think most No plate cams work at 950nM not 850 there is a big difference in performance. tho you should get something ok with what you have. z Share this post Link to post Share on other sites
CollinR 0 Posted November 26, 2007 You may have to focus it with the dome held in front of the lens. That would really stink. Share this post Link to post Share on other sites
survtech 0 Posted November 26, 2007 Not really, It's just a problem with long focal length lenses. For some reason the dome acts as part of the lens element and throws the focus off. I found that out years ago when I installed a camera with a 5-50 lens on the ceiling approximately 50 ft. up. Everything looked good, so I installed the bubble, cleaned up and drove the scissors lift outside. When I looked at the picture on a monitor, it was out of focus . I went back, removed the bubble and refocused the lens, reinstalled the bubble, and it was out of focus again. Then I tried focusing with the bubble in front of the lens. It works like a charm. Now some manufacturers actually recommend the same procedure with long focal length lenses. Share this post Link to post Share on other sites
CCTV_Suppliers 0 Posted November 27, 2007 I initially focused it during that day, then went back and tweaked the focus at night with the IR on. The camera is not in a dome. I'm going to try putting something in that blurry area and see for sure that I can focus on it - that would rule in / out focal length as the problem versus issues with the lens or imager being damaged or dirty. You really need Infrared Lenses... Here is a url for CBC Infrared Lenses available at this time... http://www.cbcamerica.com/cctvprod/computar/vari/index.html Similar lenses are available from other manufacturers, but Computar by far is the most popular. The closest lens configuration available to your 60mm is range of 8.5-40mm and the part numbers are located here: http://www.cbcamerica.com/cctvprod/computar/vari/8513.html Good luck... Share this post Link to post Share on other sites
