How important is lens selection in CCTV Camera deployment ?

PoE based Digital l IP CCTV Camera OEMs provide a choice of lenses for many fixed focus camera models starting from  2.8mm ang going all the way up to 12mm. One must consider before ordering that what is the right lens for each camera deployment, otherwise you will have blind spots, poor focus and insufficient detail when zooming, spoiling the overall experience. Here is an illustration:

generally f2.8mm, f3.6/4/4.4mm, f6mm, f8mm, f12/16mm could be typical focal lengths . Please also note that a field of view of one camera with given focal length may not be the same as that from another even if the focal length is same due to difference in sensor sizes. Larger sensors will yield larger viewing angles. Anyways once you have zeroed in on a brand and model, the lens is your only customization choice (along with maybe nighttime IR LED ranges like 30/60/80m available on select models). Please note these things:

(a) A lens always has a blind spot in-front of it, where it cannot see. The wider the lens (shorter focal length ), the less is the blind spot in front and more is the field of view.

(b) The wider the lens, the better is the low light performance 

(c) the shorter the lens (larger focal length), the longer the lens can see with clarity and loss of focus on zooming

This is very similar to Digital SLR camera lens. 

Based on this and our deployment case we can make some observations/recommendations:

(1) 3.6/4/4/3mm is the general purpose jack of all trade lens suitable for mid size rooms/shops/etc. It is ideal for a lobby and maybe good enough even in some staircase deployments

(2) For small areas like elevator cars, use a 2.8mm lens AFAP as possible as range required is least, width required (mounted in top corner) is maximum and a camera with bigger sensor size

(3) For walkways/driveways/staircases 6mm or 8mm lens is ideal . And can be coupled with both 50m and 80m IR for effective night time coverage, 

(4) 12mm/16mm lens are very narrow, but will see far way objects well and should be used to cover far away areas only. They could be used to cover long narrow walkways/driveways but must be used with high IR range like 50m or 80mm to be of any use at night

Generally an IR range of 50m or 80mm makes little sense with a 2.8mm and 4mm lens and OEMs may not provide that option even if their documentation seems to suggest availability of that option. Similarly they may offer only 30m & 50m IR with a 3.6/4/4.3 mm lens. And 6/8/12/16mm lens will likely come only with 50 or 80m IR capability, not 30m.

We also noticed that supply chains have problems readily supplying anything other than a 4m lens with 30 and 50m IR. If you want longer IR, or 28/6/8/12/16 mm lens, you may have to place an order and wait 4-6 weeks for delivery (at-least in India). So camera should be procured in project planning not after all cabling is done but midway or at the beginning, depending on how long the work will take.

Their are also some special lens like fish eye which can cover 180 degree and suitable for monitoring large warehouse/store/office or other area with a single camera. But they see/record extremely high barrel distorted lens images. We have to use the NVR or PC software to digitally manipulate the recorded footage and show undistorted (de-warped) and comfortable to view images.  Howeverr the de-warping usually takes up multiple channels on the NVR and therefore limits the channel capacity on NVRs. This type of lens could be applied for example to cover a large community/party/banquet hall/restaurant, a large number of car parking bays, supermarket, etc. with a single camera rather than multiple ones, if the idea is to only keep a cursory view of the situation. 

- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee

What is the use of Camera IR range ?

CCTV cameras may specify their night time IR range as 10 or 15 m (wireless cameras), 20m or 30mm (small dome or bullet camera), 30m or 80m or more (large bullet camera, PTZ, etc.). In daylight or sufficient ambient lighting,  almost all cameras will work well, but the more powerful the IR the better is the nighttime or low light range of the camera. Indoors generally 20-30m is good enough for most cases, but outdoors we may need 50m, 80m or even longer range. Therefore this has to be considered during the procurement stage only along with focal length tunings. 

Please also note that while deploying such cameras with IR LEDs, ensure that no object/wall is very near  in the field of view of camera otherwise it will scatter the IR, reflect it back into sensor and completely ruin the night time view making the camera unusable at night, till its mounting position is changed to get a clearance from that object. Some trouble some situations:

(1) If you have the camera looking through a window, the IR will bounce of the window.
(2) For cameras with a glass dome cover, you need to make sure the LED lights on the IR board are not being obstructed by the camera body. .
(3) Dirty Glass dome. Clean it with a damp microfiber cloth or windshield cleaner only.
(4) You have mounted the camera to close to a wall, ceiling, or in between two walls. In this case the camera's IR LEDs will be obstructed and cause IR reflection.

(5) When you have an object too close to a security camera with infrared, it will cause that object to be over exposed because of the IR light shining off of it.

(6) IR LEDs attract spiders and insects, especially if camera is doing continuous recording (even though NVR will store only motion triggered recording) and is mounted near garden area. Spiders will create a web at night over the camera housing enclosing the lens. This will not bother you at daytime, but will show clouded view at night. It has to be cleaned periodically with a soft brush

Also worth noting is that higher the IR range, the more is power consumption. For eg.

A 30m IR  camera may use 6W at daytime, 7-8W at night

A 50m IR camera may use 8W at daytime, 9-10W at night 

A 80mm IR camera may use 8W at daytime, but use 11-12W at night which is very close to max powel levels of 802.3af

It maybe useful for deciding how many cameras to connect to any PoE switch, whose PoE capacity is often less than ports multiplied by  maximum PoE (12.3 watts at PD, 15.5W at PSE) that can be supplied per port.

- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee