Image sensor technology is outpacing lens designs, which is leading us into a strange world.
You can now buy 5 megapixel surveillance cameras from a number of vendors. However, there are no 5 megapixel lenses!
Sound strange? Unfortunately, it seems to be true. If anyone knows of a real 5 MP lens for surveillance, I’d love to hear about it.
We’ve talked to all the major lens manufacturers. They all advertise megapixel lenses, but they don’t say how many megapixels their lenses are designed for. When you push them for an answer, you find out that none have 5 MP lenses.
We even asked the lens manufacturers who make the lenses that the megapixel camera vendors recommend for their 5 MP cameras. They told us that their lenses were good for 1 MP or sometimes up to 2 MP. We haven’t found a 5 MP lens yet, except for the fisheye lens from Theia.
This means that you aren’t going to get the full value of all those extra megapixels. You might still be able to cover a much wider area than a single lower resolution camera, but it won’t have all the detail you think it will.
Our camera expert at VideoIQ, Steve Lefkowitz, who has been working with lens vendors for over 20 years, asked them a good question: If they can design lenses for the 8 MP and 10 MP point and shoot consumer digital cameras, why can’t they make one for surveillance?
Apparently, the situation is no better for consumer cameras: The imagers may be capable of 8 MP or 10 MP, but the lenses fall far short. They don’t even come close.
This is bizarre.
Here’s a little extra info on lenses. When evaluating the quality of a lens, there are three main specs to look at:
- Resolving power or resolution: This means how many horizontal lines the lens can accurately distinguish. But you need to be careful that you find out the resolution not just in the middle of the lens, but check the edges and corners as well, since they generally have much better resolution in the center. A good lens is sharp to the edges.
- Geometry or distortion, which means how round a circle will look anywhere in the scene. A circle will often look perfect in the middle, but looks like an oval in the corners. This kind of distortion is common. A smart digital camera can actually correct distortion like this, but as far as I know the only MP company doing this today is Mobotix.
- Flatness of field, which means that when the lens is in focus at its center, it is also in focus in the corners. Often this isn’t true. No, it isn’t your eyes, it’s the lens.
Another little know fact that our expert Steve told me: Everyone looks at the F-Stop spec, but this only shows the amount of light coming through the iris. The real spec to know is the T-Stop, which tells you the amount of light coming through the iris and all of the lens elements. A good 1.4 F-Stop lens might have a T-Stop of 1.5, which means that the lens elements aren’t blocking much of the light. But a poor 1.4 F-Stop lens might have a T-Stop of 1.8.
If you want more info on megapixel lenses, check out John Honovich’s recent column:
http://ipvideomarket.info/report/the_importance_of_megapixel_cameras
I think it would be a big help if the lens manufacturers started being more up front about their full lens specs. I can’t imagine why the good lens manufacturers wouldn’t lead this change, since the specs will show how much better their lenses are. Why not show why it is worth paying more for good quality?
Unforunately, dealers are left to figuring this out by trial and error. Dealers come to learn the hard way that some lenses are a lot better than others, but why put the burden on them to figure this out? Hiding the specs doesn’t help anyone.
We’ve seen the IP camera manufacturers coming together to establish standards. Why not the lens manufacturers?
February 27, 2009 at 11:15 pm
Hi Doug,
My understanding is that if you want to do 5MP, you should use a fixed focal machine lens, not a cctv lens.
Does that make sense?
Best,
John
February 27, 2009 at 11:23 pm
John,
We had the same thought.
We’ve been talking to the machine vision lens manufacturers as well. Some make lenses for both machine vision and surveillance.
The problem is that machine vision lenses generally don’t have the ability to focus far away. They can’t see far enough out to be usable for surveillance.
They do have real 5 MP machine vision lenses however. They only only work in short distances and are also expensive.
That’s what we’ve seen so far. Still researching.
Thanks.
Doug.
March 3, 2009 at 3:50 pm
Hello,
and what do You think about Avigilon’s idea: using photo lenses (with Canon mount EF in this case)? No problem with focusing, wide range of focal lengths available etc.. I know: prices are high…
Regards.
March 3, 2009 at 6:16 pm
Marian,
Good question.
When you are using large format imagers designed for APS or 35mm cameras, then you can use those lenses. They definitely have good optics and good resolution. As you mentioned, both the lenses and the imagers are a lot more expensive.
The APS format imagers have a diagonal of just over 1″. The 35mm imagers are about 1.4″ diagonal. The imagers used in most surveillance cameras are about 1/3″, and the megapixel imagers used by most surveillance cameras run from 1/3″ to about 1/2″.
The resolving power of a lens, however, comes down to how small the pixels are. For example, a 35mm or APS imager might have pixels of 6 microns square, or sometimes even larger. The pixels in the low cost megapixel imagers, however, are from 1.4 microns to about 2.5 microns. So, the lenses have to be at least 3X better in resolving power.
Thanks.
Doug.
September 16, 2009 at 4:57 am
Hi
I have some problems with security cameras witch are more than 5 MP resolution.
I do not know what kind of lenses should i use for this cameras.
For example, if I have 5 MP camera and I use 3 MP lens for it, what is the actual resolution ?
that is, can I use all the 5 MP resolution for my searching in playback or in live viewing.or the resolution will be less than 3 MP(the lens resolution)
hope you could help me
September 18, 2009 at 7:19 pm
Ali,
I agree that it isn’t easy finding good lenses for cameras with 5 megapixels. However, if you ask your camera manufacturer, they should be able to offer a solution.
To answer your question: If you use a 3MP lens on a 5MP camera, you will still get a resolution of 5MP. The lens won’t change the resolution. But it does change the quality of the image significantly.
The end result might be slightly better than a 3MP camera, but it won’t be nearly as good as if you used a true 5MP lens. The image won’t be as sharp and you will lose the fine details, which is why you are buying a megapixel in the first place.
Some people would probably advise you to just buy a 3MP camera if you were going to use a 3MP lens.
Another thing to keep in mind is that there are a number of 1080p cameras coming out now that have 2.1 megapixels. This might sound like a lot less than 3 MP, but in fact they often cover about the same area because they are much wider than tall. The number of pixels in the width of a 1080p camera is 1920 pixels, which is almost the same as 3 MP cameras that have 2048 pixels width. Since most security scenes don’t need the extra height, it is often a better choice.
Doug.
September 20, 2009 at 12:19 pm
Hello Doug,
“The lens won’t change the resolution. But it does change the quality of the image significantly.”
In my opinion, to be 100% correct – it DOES change the resolution. Not the sensor’s resolution (it is obvious), but the overall optical resolution of the imaging system, which takes effect in loosing the fine details.
Best,
Marian
September 23, 2009 at 12:36 am
Good point, Marian.
As you said, the optical resolution is limited by the resolving power of the lens, and your way of stating it is more accurate. It’s a good thing to bring up, to help others who want to understand.
I believe what Ali was asking, when he used the term, resolution, was the digital pixel resolution output of the camera. I’ve heard this question come up before. It sounds as if you know camera design, so you realize the digital pixel resolution output isn’t changed by the lens, but this isn’t obvious to many people who don’t know how cameras are designed.
Most camera resolution specs only list the pixel resolution. The optical lens characteristics are only usually stated as 1/3″ optics or 1/2″ optics, and of course the focal length and F-stop.
The resolving power of the lenses, which define the optical resolution, are rarely described to the final users, and is not always easy to get even from the lens manufacturers. That’s part of the reason this can be confusing to camera users.
Thanks.
Doug.
February 22, 2011 at 4:57 am
Hi Doug,
You spoke about the difference between the focus center quality and the side quality. Does exist any solution to this issue? Actually I’m working with a megapixel camera and a megapixel lens.According to the datasheet, the lens resolution is supposed to fit with the camera resolution and I have the same problem concerning the focus quality in the sides…
Thanks,
Raphael
February 23, 2011 at 9:38 pm
Raphael,
There are a few good quality lenses, that provide clear focus in the corners as well as in the center of the lens, for megapixel cameras.
We had to hunt to find one, but we are quite happy with what we found. That’s why we ship the lens with our camera, to assure there is no quality lost in the lens.
We saw a lot of incredibly poor lenses. So, you have to pick carefully.
The good news is megapixel lens designs are getting better.
February 24, 2011 at 2:23 am
Hello,
first of all you should give an exact model of lens and camera – it would by very informative. Secondly: maybe you should try a lens designed for a bigger sensor (when you use 1/3” camera, use 2/3” lens – only central part of lens coverage will be used and thus quality should be better. Remember about focal length). But, as Doug said, there are no many good lenses for MP cameras in the market.
Regards.
February 24, 2011 at 2:44 pm
Good suggestions, Marian.
Unfortunately, we can’t list model numbers on the lenses we use, because the vendor sells them only directly to camera manufacturers. So, they aren’t available on the open market.
You can use lenses for larger formats, but these are generally a lot more expensive, and bigger. Size is a problem in dome cameras. Fortunately, there are now better choices available today, than even a year ago.
February 25, 2011 at 4:56 am
My fault, my fault. Raphael should give models of lens and camera to better understand the problem, not you Doug
.
February 25, 2011 at 3:05 pm
Ah, now I understand what you meant.
Thanks for the clarification.
Doug.
March 8, 2011 at 7:34 am
Doug and Marian,
Thank you for your answers.
I’m working with severals megapixel cameras (0.4MP – 1.2 MP – 2 MP and 1/3″ – 1/2″ – 2/3″) and lenses.
Actually with fixed focal lens, I have less problem.
But my focus quality issue appears essentially with Varifocal megapixel lenses.
It’s very difficult to find out a good megapixel lens company that propose varifocal lenses.
Raphael
November 8, 2011 at 2:20 am
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