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

Burglar Alarm Strobes Guide on Mar 31, 2017
Strobes provide visual notification of alarm incidents, as sirens are used to give audible notification. Using a strobe gives alarm users and alarm...
Burglar Alarm Sirens Guide on Mar 27, 2017
Sirens are used to alert users to an alarm condition. In this note, we examine how to choose, locate, and install alarm sirens, including Siren...
Glass Break Sensor Tutorial on Mar 21, 2017
Burglars often break glass windows to get into a house. Using glass break detectors in conjunction with alarm contacts is a good way to protect the...
Alarm Panic Switches Tutorial on Mar 16, 2017
Panic switches allow silently triggering an alarm system when it is otherwise disarmed. In this tutorial we explain and contrast the 7 most common...
Environmental Sensors For Burglar Alarm Tutorials on Mar 15, 2017
Intrusion detection systems can be used to alert users to environmental issues. By connecting sensors that monitor the heat, humidity, and...
Alarm Contacts Tutorial on Mar 07, 2017
Contacts are the devices that tell an alarm panel when an entryway is open or closed. The act of opening or closing an entryway, such as a door or...
Alarm Motion Detector Tutorial on Mar 06, 2017
Sensors designed to detect movement are a good way to protect large, open areas. In this tutorial, we examine motion detectors,...
Glass Doors and Access Control Tutorial on Feb 22, 2017
The biggest challenge for many access control systems are glass doors. Here's what happens when a maglock is improperly installed to an existing...
Hikvision PanoVu Multi Imager Tested on Feb 08, 2017
Hikvision has entered the multi-imager market with their 180° PanoVu DS-2CD6986F-H, an 8MP, 4-imager model equipped with ~1/1.8" imagers and...
Alarm Panels - Canned vs Integrated on Feb 07, 2017
Alarm control panels generally come in one of two types: Integrated alarm controllers, with controls and the keypad in the same...

Most Recent Industry Reports

IP Networking Course May 2017 on Apr 26, 2017
NOTE: Registration ends tomorrow, Thursday the 27th. This is the only networking course designed specifically for video surveillance professionals...
Tri-Ed Favorability Results on Apr 25, 2017
Tri-Ed, owned by Anixter, far outranked Anixter, the lowest ranked company in our distributor favorability series. Still, Anixter's ownership did...
Chinese 'Attacking Us From Every Direction', Says US FBI on Apr 25, 2017
"Chinese eating our lunch. Attacking us from every direction" said the US FBI's Deputy Director Andrew McCabe at the ASIS 2017 CSO Summit. .@FBI...
Eagle Eye Exec On Mountain Of Servers - VSaaS Growth Analysis on Apr 25, 2017
Eagle Eye VP of Operations, Hans Kahler, posted a picture of himself sitting on top of a shipment of new servers, as a testament to the companies...
Axis Posts Strong Q1 2017 Financial Results on Apr 24, 2017
Axis posted strong numbers for Q1 2017, after having some challenges in 2016 (Q1 2016, Q3 2016). Inventory levels and overall spending show...
Axis Lowest Cost Outdoor IR Camera M2025-LE Tested on Apr 24, 2017
Axis has lagged offering low cost IR cameras while their Asian competitors have made IR standard even in their most entry level cameras. Recently,...
IPVM First Dean's List W2017 - Thomas Atkinson, Matt Hurly and Fredrik Lundqvist on Apr 24, 2017
IPVM is happy to congratulate and celebrate our first "Dean's List", the top students in our courses. For the Winter 2017 IP Networking course...
Splicing Alarm Circuits Guide on Apr 24, 2017
Alarm installers commonly connect multiple sensors to a single zone. They do this by splicing the wires together. In this report, we will explain...
PureTech Video Analytics Examined on Apr 21, 2017
PureTech's analytics were chosen for a US border protection system (see related post), which the company claims no other analytics vendor was able...
US Border RVSS / Video Analytics System Examined on Apr 21, 2017
US Customs and Border Protection has been rolling out a video analytics-based detection system along the US/Mexico border, with detection ranges...

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