Lens quality and lens adjustment are probably some of the most important factors to ensure you obtain a good quality CCTV image yet both are probably the most overlooked factors by many con-sultants, installers and end urs. So, how do you avoid poor quality images due to your lens?
新加坡留学本科Several years ago I wrote a CCTV lens article for SE&N titled “Glass, Plastic or Coke Bottles” which caud a stir with some CCTV lens manufacturers. More recently, in an article titled “Megapixels and Image Quality”, I voiced concern about the quality of some lens being ud on megapixel cameras.
It is unfortunate that some in the CCTV/curity industry forget that the first port of call for any CCTV camera image is the lens. The lens quality and lens t up can be the weakest link in a CCTV system. It does not matter if it is an analogue camera, a HD, or a megapixel camera, a low quality and badly t-up lens equals a poor quality image.
In this article I will mention some of the reasons that lens reduce the quality of a CCTV image. My comments will be made taking dome optical distortions, dirty domes, dirty lens, cobwebs, dirty camera housing face plates and high, or extreme, video com-pression out of the equation.
I will also suggest some camera test charts which will help you evaluate camera/lens “sharpness” and plea note the word “resolution” in this article will be related to camera pixel count.
CCTV camera technology and CCTV camera quality has improved over the past few years, but it appears that lens quality has dropped (notwithstanding some new megapixel lens), this loss of quality is basically due to some new players in the lens industry not understanding lens technology and a few old lens manufacturers who have allowed their quality to be reduced as they cater to the cost driven low quality ctor of the CCTV/curity market.
It has been known for some time that normal CCTV lens sharpness varies between 350 TVL and 480 TVL (there are a few variations). In basic terms the higher sharp-ness is about half the resolution you would expect from a 1.5 megapixel camera. So, you don’t have to be Einstein to reali that standard CCTV lens are not an option if you want performance
equal to the megapixels you have purchad.
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Unfortunately, many purveyors of megapixel cameras are lling “pixels”, not “image quality”. They may, or may not, be aware of lens
and camera quality issues. So buyer, beware!
The major CCTV lens manufactur-ers are now supplying megapixel lens but in some cas they are not stating how many megapixels
a particular lens is manufactured for. There would be a great differ-ence in the quality of a lens manu-factured for 1.5 megapixel cam-eras and a lens manufactured for 5 megapixel cameras. The major CCTV lens manufacturers might be a reasonable place to start, but
内地电影票房排行榜make sure you know how many megapixels the lens is actually manufactured for. Reputable
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megapixel camera brands with built in megapixel lens can also be considered a reasonable place to start.工资表格
In some cas instead of testing the camera we are actually testing the lens becau some lens are of such poor quality they mask a CCTV camera’s performance. If this is the ca you might ask why spend big dollars on high resolu-tion cameras? Well there are still good lens manufacturers out there and I suggest that when you per-form a camera shoot out you also carry out a camera/propod lens combination shoot out. You will be amazed at the difference a good quality and correctly t up lens can make when combined with a high performance CCTV camera.
When we are asked to test a cam-era for a client we ask if they wish to actually test the camera, or the camera/lens combination, as the results can be vastly different. Up until recently we ud a few trusty
glass lens from “real lens manu-facturers”, but even with the
lens we were not sure if we were
By Les Simmonds
Test Your CCTV Lens
Quality
EIA resolution chart which many 4:3 aspect ratio television test charts originated from.
testing the camera or the camera/lens combination. As it turns out we were fairly clo.
But clo isn’t good enough when you might be testing cameras for a CCTV system with camera quanti-ties in the hundreds or thousands. Suppliers and manufacturers are not known for their benevolence towards tho who recommend against their cameras or other CCTV products so you need accu-rate test results and plenty of ar-mour. Also, it is not fair to suppli-ers and manufacturers to eliminate a camera from a test if you have any doubt about the quality and/or calibration of your own test lens, or test equipment.
A number of years ago we arched for test lens that would be transparent to camera perform-ance and allow us to truly say the are the performance results for a “CCTV camera”. With this in mind we purchad a Schneider Cinegon 8 mm f1.4 Manual Iris lens which is a very high quality C mount lens for u with high qual-ity analogue cameras.
Tests have shown that standard analogue cameras are impacted by the u of some low quality lens. If this concerns you, it might frighten you when you e some consultants specify, and some contractors install, the same low quality lens on a 1.5, or higher, megapixel CCTV camera, or ev
en u a supplied integrated lens on a 1.5, or higher, megapixel CCTV camera which has not been manu-factured by a recognid lens manufacturer. It is of no u at all to u a 1.5, or higher, megapixel CCTV camera and then u a lens which does not perform at least equally, or better than the camera resolution.
So where to from here? Maybe it is
time for you to take some control yourlf! Why not obtain a good quality camera test chart and sub-jectively evaluate various camera/
lens combinations yourlf? There are some very complex formulae behind optics, but the formulae are not a factor when you carry out basic subjective tests with a good quality test chart and your
eyes. You will be surprid with
IEEE resolution test chart is a relative newcomer, but with 1000 TVL.
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ISO 12233 test chart which has been made for electronic still imaging cameras and can be ud for all
electronic imaging devices.
介绍一种事物五年级作文the outcomes with an honest and commonn approach.
For many years television camera sharpness has been evaluated by the 4:3 aspect ratio EIA Resolution (Sharpness) test chart and varia-tions of it, such as the RETMA and Esr Universal test charts. It has horizontal and vertical sharpness up to 800 TVL and while there are still 4:3 aspect ratio cameras around there will be camera test charts similar to the available.
A recent newcomer is the IEEE Resolution Test Chart, it has hori-zontal and vertical sharpness up to 1000 TVL and while there are still 4:3 aspect ratio cameras around there will be camera test charts similar to this available. The ISO standard for measuring r e s o l u t i o n (s h a r p n e s s ) o f “electronic still imaging” cameras is 12233, it is available from the International Standards Organiza-tion and under copyright protec-tion, but the design of the test chart does not appear to be pro-tected; its description has been available on the web for sometime. Even though this test chart has been made for electronic still im-aging cameras it can be ud for all electronic imaging devices, in-cluding video, in the commonly ud aspect ratios of 4:3, 16:9 and 3:2. It has a horizontal and vertical sharpness up to 1000 TVL.
父母双亲The latest ViDi Labs test chart is developed specifically for the CCTV industry for both Standard Defini-tion (SD) and High Definition (HD) testing. It is suitable for SD, HD and megapixel cameras with as-pect ratios 4:3, 16:9 and 3:2. It has a SD horizontal sharpness of 960 TVL and a HD resolutio
n of up to 5000 pixels. The chart is lf explanatory, it has many other important CCTV features, is easy to u and comes with a detailed instruction manual. Available from /.
If possible try and comply with the following basic EN61146.1 stan-dards for shooting reflective cam-era test charts:
The subject illumination of a re-flective test chart shall be 2000 lux +/- 5%. The non-uniformity of the subject illumination shall be less than 5%.
The correlated colour temperature of the light source shall be 3100 K
+/- 100 K.
The camera white balance shall be t manually or automatically to 3100 K +/- 100 K.The test chart
shall be shot by the camera so that the frame limited by the ar-rows coincides exactly with the edges of the picture displayed on the video monitor in under-scan mode.
The focus control shall be in auto
or manual mode, and shall be t for optimal focus.
Have fun with your test charts.
Les Simmonds is an independent
CCTV consultant and CCTV testing authority.
Email: au
Web: au This article was originally pub-lished in Security Electronics &
Networks Australia. The latest ViDi Labs test chart is suitable for SD, HD and Megapixel CCTV camera sharpness testing and much
more.
