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?
