Camera Lens Reference Diagram

Discussion in 'IP Cameras' started by Kenjusticejr, May 7, 2014.

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  1. Kenjusticejr

    Kenjusticejr BIT Beta Team

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    well, for anyone smart enough to do some research and get guidance form a forum such as this, here is a good explanation of lens field of views.

    basically, I wish someone would have crammed a pic like this down my throat before I ever purchased my first camera.

    In addition.... 640x480 aka 720p can really be disappointing on a cheap camera with a poor lens. Lens Explination.png
     
  2. Mike

    Mike Staff Member

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    Thanks for sharing. Made sticky for now.
     
  3. bp2008

    bp2008 Staff Member

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    640x480 is not 720p. 1280x720 is 720p

    Nice chart though. Based on that chart, it seems the maximum plate recognition distance linearly correlates with the lens size in an easy-to-remember way. i.e. 6mm is roughly good for 6 meters while 25 mm is roughly good for 25 meters and so on.

    Obviously the actual view angle and readable plate distance will vary with different sensor size and resolution, but the numbers above seem like pretty decent estimates.
     
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  4. hmjgriffon

    hmjgriffon Known around here

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    Awesome chart, I'm lazy so I've decided to pretty much use all varifocal cameras lol.
     
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  5. Kenjusticejr

    Kenjusticejr BIT Beta Team

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    Thanks for the correction on the 720p..I think I wrote that because I had it fresh in my mind from seeing a falsely advertised camera on ebay...Anyway, yes, the statement still proves true, 1280x720 can still be disappointing when formatted on a low quality camera with a less than adequate lens and 640x480 is like watching tv on an old 13 inch tube from 1980.... I'm addicted to the HD cameras now....
     
  6. hmjgriffon

    hmjgriffon Known around here

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    Yeah, even 1080p doesn't look so good to me, I'm spoiled by 3mp lol that is like the minimum my brain can handle now. Though I started with a few 640x480, then 720p, then jumped to 3mp.
     
  7. Kenjusticejr

    Kenjusticejr BIT Beta Team

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    got 4 3mp cams on the way from china.. hope to have them by next week :)
     
  8. networkcameracritic

    networkcameracritic Getting the hang of it

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    Not sure the information is valid. Taking plate capture as an example at VGA resolution, I would say that at 30m, at 12mm lens would be worthless and you would need closer to a 40-50mm lens to read a plate. I've shown a 12m lens reading a plate during the day at about 25m but that was 3MP, not VGA. Also, every lens/sensor combo is different, so a 4mm lens on one camera may not be the same as a 4mm on a different camera, even within the same brand .
     
  9. Kenjusticejr

    Kenjusticejr BIT Beta Team

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    think that was based off a 2mp camera at 1080p resolution..but yes, a 640x480 cheapy camera wouldn't provide the needed detail to view a plate.
     
  10. networkcameracritic

    networkcameracritic Getting the hang of it

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    Haha, not so cheapy. I use a camera at VGA resolution to read plates that probably cost more than you are paying for 1080P. With lens, camera and housing, it runs about $1,300 street price. That does not include the $900 IR illuminator.
     
  11. hmjgriffon

    hmjgriffon Known around here

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    Yeah I'm pretty sure if you zoom in enough on a plate with VGA you'll be able to make out the numbers. :D Which camera is that?
     
  12. networkcameracritic

    networkcameracritic Getting the hang of it

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    Ah, that is the misconception. What everyone wants is that megapixel view that includes a plate number all that is around it and I've shown that is possible during the day with a cheapy 3MP camera and a 12mm lens. The problem is at night. You have to expose for the plate to see it, when you do that, all else is very dark. People expect that if they expose for a nice picture, the plate will be fine, but then they see the plate is just a white blank rectangle and headlights blow everything out and don't realize they need to make the image much darker, but by doing so, it's worthless for anything other than capturing plates, so why have 1080P or 3MP when there are 720P or VGA cameras that have way better low light sensitivity. To give you an idea, some cameras made for this have a max exposure of 1/500th of a second. I've used general purpose cameras between 1/90th an 1/250th of second max exposure to be able to read plates. Of course you have to reduce gain way down otherwise you just get a noisy worthless image.

    We use an Axis Q1604 + 5-50mm Fujinon lens and an Axis housing. It is 720p, but sort of waste to use 720P because to get the best capture, I have to limit the view to about the width of the car and VGA is plenty for that field of view. In it of itself, it does not do too bad with lighting just from the license plate lights. But with a Raytec RM100 illuminator, we can actually see the car and not just the plate. I set it to 4fps and we get about 2-4 plates captures as the car drives by, That would be good up to 30-40mph, faster would require a higher frame rate.
     
  13. hmjgriffon

    hmjgriffon Known around here

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    That is pretty freaking awesome, are you capturing these for fun or is this for some purpose?
     
  14. networkcameracritic

    networkcameracritic Getting the hang of it

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    Everything in life I do is for fun. But this is used to open the gates to our community based on a plate match.
     
  15. hmjgriffon

    hmjgriffon Known around here

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    fancy pants.
     
  16. icerabbit

    icerabbit Getting the hang of it

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    Fancy!

    Does that by chance scale down to do pet recognition and open/close a cat flap ;)

    I've had a raccoon and a stray cat wander in the house. Not fun & safe for the creatures who's home it is. It causes big fights, sends fur flying, stuff gets broken, ...
     
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  17. bp2008

    bp2008 Staff Member

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  18. icerabbit

    icerabbit Getting the hang of it

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    Not a bad draft for a chart. It could be improved some (like field of view width at distance shown), but then in the end there are too many factors to keep it simple.

    I plotted some angles and fields of view last week, in an attempt to dial in better what I need to order, and trying to circumvent visual obstacles I can't move.
     
  19. icerabbit

    icerabbit Getting the hang of it

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    I've looked at those or similar product in the past. Almost bought it. The issue is cats need a break a way collar and if they lose the collar they can't get back in, plus then replacement tags were either $$$ or non-existent (just buy a new kit). I've had a cat lose a collar before and one cat get stuck with a collar; plus one incident where the cats were chased by a pit bull and ran like a cheetah for cover into the house. Not a time to have a collar issue or door issue. But, I guess the same RFID issue would go for face recognition. Way back when I read about a guy who did it via a webcam where the cat entered a tunnel and was checked whether it was carrying in wildlife, and would not open the door if it did.

    Anyway. It was just a brainstorm thought regarding recognizing stuff on camera and activating/operating something.
     
  20. digger11

    digger11 Pulling my weight

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    If our cats weren't indoor only cats I'd get one of these: http://www.amazon.com/SureFlap-DualScan-Microchip-Cat-Door/dp/B00GAZZIMY
    It would read the chip the cats already have implanted.
     
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  21. hmjgriffon

    hmjgriffon Known around here

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    I'm kind of against letting my animals run around outside willy nilly, too many douchebags who like to hurt animals, not to mention the danger of other animals.
     
  22. digger11

    digger11 Pulling my weight

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    We've got hawks, owls, foxes and coyotes in the neighborhood, which is why our cats never get let out of the house.
     
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  23. icerabbit

    icerabbit Getting the hang of it

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    Thank you, digger.

    That is neat! Didn't know they existed. I will have to have a closer look at that!
    Actually, this one or similar which includes a timer so you can lock them in: http://www.amazon.com/Cat-Mate-Elite-Microchip-Control/dp/B009GODTTK/

    Gotta love friendly online folks who share a solution to a brainstorm idea!
     
  24. icerabbit

    icerabbit Getting the hang of it

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    I understand the risk and totally respect that we probably should keep them inside at all times for their safety.

    We have less wildlife than digger and actually don't let our cats out all that much, any more. Certainly less than prior years, where they had some free roaming time every day. We lost one cat a few years back, which must have had pure bred hunting dna. Could not keep her inside, used to hunt all the time and came in to sleep (was kept inside with the rest to stay warm in the winter). We think a fisher may have snatched her. We still feel bad about that. Since that time, combined with free roaming dogs & "bully cat" it is pretty much a supervised affair now. We always keep them in at night, when the weather will turn or when we're away from home, unless maybe just running to the grocery store.

    It depends on the space too. We have a lot more space now than at our previous in-town property which had just a small fenced in patio. We're away from the road and other properties. The cats like to roam around the house in circles, lounge on the deck, follow their humans in the garden, check for mice, moles & voles. Maybe chase after a squirrel. After 6 months of winter, the cats deserve a little break too. They seem much happier when they've been able to go on patrol a little ... and far less intent on gunning for the door to get out, tripping humans or getting stepped on in the process.

    My apologies for taking this thread off topic!!
    But happy to learn about RFID cat flaps :)
     
  25. leepoffaith

    leepoffaith n3wb

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    I just joined this forum and this particular post really helps me to understand the lens size vs. view angle. I do have a few questions about this. 1. I currently have D1 cameras (704x480) that have a 5mm lens and say they have a 60 degree viewing angle. I'm going to upgrade my system to 3mp 1080p PoE and would like to keep my viewing angle about the same. From what I can tell I should be good with 6mm lens, correct? 2. With a 6mm lens I should be able to read a license plate from roughly 15 feet based on this chart. I guess I thought that with a 3mp 1080p camera you should be able to zoom in from even a farther distance. My house is about 20 feet from the curb of the street. Does this mean that I should really be going with a 8-12mm lens if I wanted the ability to read license plates from cars on the street? 3. Does viewing distance change a lot if you go from 2mp - 3mp and 3mp - 5mp?

    Thanks in advance!
    ~Lee
     
  26. digger11

    digger11 Pulling my weight

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    Last edited by a moderator: May 14, 2014
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  27. leepoffaith

    leepoffaith n3wb

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    Thank you very much for this information!! The two spec sheets are great!! I skimmed through the part about px/cm and I'm going to have to sit down and really read that to understand it properly. At least I have the information needed to make an informed decision now.
     
  28. icerabbit

    icerabbit Getting the hang of it

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    There are some websites too that offer an online Field Of View calculator you can play around with to better determine the needs. Some are okay. The following site & tool may be the best out there, though maybe the software isn't exactly the easiest to use, due to its specialist nature.

    Online tool I used:
    http://www.jvsg.com/online/#

    Offline tool I used:
    http://www.jvsg.com/software/ip-video-system-design-tool/

    I played around with that as well as a bit of property layout.

    But, without enough time to draw up a site plan or one to import; I went old school. Traced a property outline, blew it up to draft plan size and cut some FOV wedges to match the cameras I was interested in at their resolution (3mp set to 1920x1080 for a bit of extra width). Which worked a treat. I felt I needed a) higher resolution cameras than just analog tvl or standard big box kit; and b) a mix of cameras (not just all the same standard 2.8 or 4mm) due to a bit of topography, some medium and longer distances (compared to a city property), landscaping, curved driveway, ... and I particularly want to capture vehicles & registration. Anyway, we all have similar needs. And it really didn't 't take much time to cut some wedges out and move them around to verify my easily accessible mounting points and see what angles and resolutions I'd be looking at.

    Then after playing around with it on paper I actually went out on the ladder to get my head up to the lower floor soffit areas to see first hand. (close one eye, hold wedge close to the other eye - helps I wear glasses! - check FOV) Sure enough some results were confirmed. And one was eliminated, because while I can trim the adjacent tree shorter, I can't shoot through nor trim a decorative Japanese maple. From the driveway it looks doable, but once you look from the other way, I'd be recording more tree than driveway. Then factoring in tree growth, wind, ... (other harder location, less concealed, loads more install work required)

    Anyway. Just a couple tools & thoughts.

    And, PS. I did settle on couple 3 axis domes with varifocal based networkcameracritic's general recommendations and me wanting to dial things in a bit more or less if need be, adjusting the focus & WAF. Was going to just go with smaller & cheaper fixed bullets of varying mm; but then out of the blue the spouse wanted domes! Who knew? Which made it easier to spend the extra dollars for a couple adjustable domes. Will probably get a couple more if these work great. I'm trying to phase it a little as to not put all eggs in one basket and jump in too quick. Test some software, test with a couple cameras, see what works for recording and review. Etc. I may for the one camera need more telephoto, like a 16mm, but I want to build a case for that first before spending the extra $$$ and finding out it is too much and I can't use it at all. A wider or adjustable camera can always move to another spot. Etc. :)
     
    Last edited by a moderator: Jun 26, 2014
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  29. lojix

    lojix Getting the hang of it

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    Excellent reference, and a good read through the comments. Thanks guys.
     
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  30. vsmax

    vsmax n3wb

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    Thanks for your detailed post and for recommendation of JVSG video surveillance design software.
    I wonder can you please share the camera layouting you made?