The Importance of Megapixel Lenses

Author: John Honovich, Published on Feb 21, 2009

Selecting the right megapixel lens is as confusing as it is important. The wrong choice of lens can make an expensive megapixel camera no better than a cheap analog camera. Unfortunately, manufacturers generally do not provide sufficient information on their lenses and general educational information on lenses is scarce.

[UPDATE: October 2011: We have completed the first ever Megapixel lens shootout comparing performance of Computar, Evetar, Fujinon, Tamron and Tuss lenses.

Here are the key issues with megapixel lenses:
  • Many systems designers are not used to evaluating lens details because lens quality was generally not a significant issue with standard definition cameras.
  • Manufacturers now label their lenses "megapixel lenses" but generally do not disclose a quantitative measure of how 'megapixel' their lenses are
  • Line Pair per millimeter (LP/MM) is a widely accepted quantitative measurement of the resolving power of a lens; however it is rarely disclosed
  • Even with a given LP/MM, the performance of a megapixel camera still varies depending on the size of the camera's pixels
Background Information
In this report, I draw on a number of excellent papers. I recommend you read these papers:

Not A Traditional Concern

When you are recording video at CIF or lower (which most of the world's surveillance cameras probably do today), any stock lens is likely to be good enough. For many years, limitations in analog transmission technology and storage placed a natural constraint on the quality of lens needed.

While a designer might be concerned about the range of focus for a varifocal lens or whether or not a lens was day/night capable, the resolution of a lens was not normally a critical issue to consider.

With megapixel, you suddenly switch from a world where 320 horizontal pixels was the norm to where 2000 horizontal pixels (a 3MP camera) is not uncommon. A 200-700% increase makes lens quality suddenly much more important.

Manufacturer's Technical Information is Unhelpful

Publicly disclosed technical information on lenses generally lack a quantitative measure that designers can verify. For instance, when you buy a megapixel camera, you always know how many megapixels the camera is (1, 1.3, 2, 3, 5 MP, etc.). With lenses, there is rarely any equivalent resolution stated. Worse, many manufacturers have started to label their lenses with big 'Mp' logos. This may help in differentiating it from a standard definition lens but it does little to identify how 'megapixel' it is.

However, manufacturers certainly have this information internally. It is not simply an issue that it does not exist.

Part of the problem is that a lack of technical disclosure can help manufacturers cut corners and make their products seem better than what they are. (I am not saying that all manufacturers are doing this but it must be at least a partial factor for some manufacturers).

Get Video Surveillance News In Your Inbox
Get Video Surveillance News In Your Inbox

LP/MM is a Widely Accepted Technical Measure

Line pairs per millimeter is the widely accepted quantitative measure for the resolution of a lens. Basically, this metric describes how tiny the distance betweens lines can be for a lens to transmit. See this article for a good visual demonstration of this.

From what I can tell, standard definition cameras need about 30 lp/mm where megapixel lenses need at least 60 lp/mm (or more depending on the amount of megapixels).

Another interesting and important issue is that the resolving power of a lens (the lp/mm) decreases towards the edge of the image. In other words, a lens may have 60 lp/mm in the center but only 30 lp/mm toward the edges. Making this more confusing, the standard way of expressing lp/mm in the surveillance industry seems to be quoting the lp/mm in the center of the image. As such, someone may tell you a lens is has a lp/mm for 1.3MP but it may only be capable of that resolution in the center of the image. On the exterior, the lp/mm may only be sufficient for standard definition imaging.

Lens Performance Impacted by the Size of Pixels

To make matters more confusing, the size of pixels for various megapixel cameras differ and that size impacts the selection of lenses. LP/MM expresses resolution for a given physical width (millimeters). However, the physical width of pixels in megapixel cameras varies because of different image size formats (1/3",1/2",2/3" etc.) and the number of pixels that need to fit on the imager (1.3, 2, 3, 5 MP etc.).

The practical importance is that the lp/mm metric is only relative to the size of the pixels on the camera. For example, a lens with 120 lp/mm might be great for a 1.3MP camera using a 1/2" imager but very poor for a 2MP camera using a 1/3" imager.

This will be especially difficult to measure because you need to know both the size of a pixel for a given camera and the lp/mm for the lens - neither of which are generally provided.

Conclusion

Megapixel lens selection matters greatly yet megapixel technical disclosures are lacking for this element. I am looking forward to a discussion to help improve the level of eduction on this.


Related Reports

Avigilon Pro 4K Camera Tested on Jan 03, 2017
Avigilon is best known for their large sensor, high megapixel cameras. But with new offerings from Sony and soon Axis, the questions is how well...
Surveillance Cameras 2017 Review on Jan 02, 2017
This report concisely explains the developments and most common options for surveillance cameras offered in 2017, including resolution, H.265, HD...
Lux Rating / Minimum Illumination Guide 2017 on Dec 23, 2016
Lux ratings are one of the poorest specifications to use in selecting cameras. Now, with the rise of integrated IR, they are increasingly...
The PPF / PPM Video Surveillance Guide on Dec 23, 2016
Pixels per foot / Pixels per meter is the most fundamental and valuable, though imperfect, metric for specifying video surveillance image...
Surveillance Camera Imager Tutorial on Dec 23, 2016
Imagers - CCD, CMOS, 1/2", 1/4", big pixels, small pixels, etc. In this tutorial, we explain the fundamental issues and drivers in surveillance...
IR Video Surveillance Tutorial 2017 on Dec 21, 2016
Almost all surveillance cameras perform worse in low light than they do in the day time. One of the most common techniques to overcome this is to...
ONVIF Tutorial 2017 on Dec 19, 2016
ONVIF is well known within the surveillance industry as an interface to connect IP cameras and VMS systems but: Is ONVIF a 'Standard'? Why...
Lens Iris Tutorial on Dec 19, 2016
Cameras, like humans, have irises. However, cameras have five types of iris options - fixed, manual, auto, P iris. In this tutorial, we explain the...
API / SDK Tutorial on Dec 18, 2016
While Application Programming Interfaces (APIs) are key to 'open' platforms, they are frequently misunderstood and over-hyped in physical security....
F-Stop Tutorial on Dec 16, 2016
To understand low light surveillance, appreciating the importance and role of the f-stop metric is critical. In this tutorial, we explain: Why...

Most Recent Industry Reports

Free VMS Software Directory on Jan 13, 2017
Many Video Management Software (VMS) providers offer free versions, either open source, for a limited number of cameras or for a limited amount of...
Milestone Essential Subscription Removed on Jan 12, 2017
Subscriptions may be the future for Milestone and VMSes but not right now. Responding to negative feedback, Milestone has removed subscriptions...
Alarm Reporting Formats Overview on Jan 12, 2017
Alarm reporting formats are methods for communicating complicated information quickly, using plain old telephone service. It is still the main...
Amazon Sales of Hikvision China Cameras on Jan 12, 2017
Hikvision has become widely available in the US, including on popular retail outlets like Amazon, with over 2,600 results: 4MP Hikvision outdoor...
Last Day IP Networking Course January 2017 on Jan 12, 2017
This is the only networking course designed specifically for video surveillance professionals plus it includes live training, personal help and...
ONVIF Favorability Results on Jan 11, 2017
ONVIF has been one of the most debated aspects of the video surveillance industry. On the one hand, its aim to increase interoperability has been...
Honeywell Ademco Vista Intrusion System Tested on Jan 11, 2017
One of the biggest brands in security holds one of the most common intrusion lines. We bought and tested a Honeywell Vista 15P intrusion...
ADI Battles Manufacturer Partners on Jan 11, 2017
ADI is battling their manufacturer partners, building up their own competitive house brand W-Box, while manufacturers still fund ADI's business...
10 Key Comparison Metrics For Intrusion Panels on Jan 10, 2017
In this note, IPVM reviews fundamental features and attributes for evaluating and comparing intrusion alarm panels.  These criteria are: Number...

The world's leading video surveillance information source, IPVM provides the best reporting, testing and training for 10,000+ members globally. Dedicated to independent and objective information, we uniquely refuse any and all advertisements, sponsorship and consulting from manufacturers.

About | FAQ | Contact