CCTV Test: Megapixel Lenses
Given the advances made in higher resolution video in recent years, it is astonishing that in many cases little attention is paid to the selection of lenses. Any camera’s performance will be affected by the choice of lens. When end users specify HD and 4K cameras, they are making an investment to achieve higher image quality. Therefore, the lens performance is as – if not more – important than the camera’s capabilities. Benchmark took a look at some megapixel lenses to see what they offer.
[dropcap]T[/dropcap]he lens is effectively the eye of the video surveillance system. It focuses light onto the sensing area of the camera: the CCD or CMOS sensor. The sensor then converts the level of light into a video image – the process differs dependent upon the chipset, but the job of the lens remains the same. This very basic explanation serves to underline one fact; focusing the light as best possible onto the sensor is a vital part of creating good quality video images.
Megapixel lenses are essential to allow higher resolution cameras to deliver their full levels of performance. There is a very simple reason for this – lenses used in video surveillance are not perfect. They are only as good as they need to be!
It stands to reason that if a lens is intended for use on a 4CIF camera, there is no point in grinding the lens to a higher tolerance than the camera can actually resolve. Therefore, the glass is ground to a degree that eradicates only the aberrations that the sensor will display. The situation changes when looking at high and ultra-high definition video.
Most lenses will be given a rating in megapixels dependent upon how precise they are. It must be remembered that these ratings will be given for a 4:3 image, so an adjustment to the figure will need to be considered if the image is 16:9, such as with HD and 4K video.
For the purpose of this test, the lenses were compared using HD1080p and 4K cameras (dependent upon the lens specification) with a 16:9 output, and fine detail across the entire picture area was examined.
Tests were carried out around the clock, with night images being assessed over two sessions, one using white light and the other infrared illuminators.
The DV2.2×4.1SR4A-SA2L is a varifocal DC-iris lens with a focal length of 4.1-9mm and an aperture of F1.6. It is rated for 6 megapixel video, making it suitable for HD1080P cameras; the manufacturer also states that it is suitable for 4K (8 megapixel) applications. The lens is a 1/1.8 inch format unit, catering for the larger image sensors which are now common in higher end HD and 4K cameras. It is rated for day/night use and features an IR compatible coating to address focus shift under artifical illumination. The lens is the largest in the test, measuring approximately 62 (L) x 65 (W) x 68 (H) millimetres. It weighs in at 130g.
The DV2.2×4.1SR4A-SA2L is the largest lens in the test, but it certainly isn’t bulky or heavy. It also weighs the most, but at 130g that isn’t going to represent a problem. There are certainly no concerns about build-quality, and the lens is well finished.
Focus and zoom adjustments are smooth, and the securing knobs are easy to access. The focus securing knob is not used to make the adjustment – a focus ring performs this task – so tightening can be performed without accidentally changing the focus, which is a benefit.
On a typical British winter day, in a shaded area with ambient illumination levels of around 500 lux, the Fujinon lens shows its capability. All of the test lenses were initially compared against an unbranded budget 4K lens (claimed) obtained from a popular auction-type website. The difference between this and the Fujinon lens was visibly significant, with the DV2.2×4.1SR4A-SA2L delivering much higher levels of detail and crispness. Colours were also more accurate and iris response was superior. While the lens is rated as 6 megapixel, it showed clean and sharp detail up to the edge of the image area with a 4K stream.
In low light applications, the DV2.2×4.1SR4A-SA2L delivered clean and detailed images with minimal noise at light levels which were approximately 2 lux lower than those required when using the unbranded control lens, which is a significant difference. Under artifical illumination, the lens performs well, and there was no visible focus shift during day/night switching.
Samsung Techwin: SLA-M2890PN
The SLA-M2890PN is a varifocal P-iris lens with a focal length of 2.8-9mm and an aperture of F1.2. It is rated for 3 megapixel video, making it suitable for HD1080P cameras. The lens is a 1/2.8 inch format unit, catering for traditional sensors along with the slightly larger image chips found in many mainstream HD cameras. Designed for use with day/night cameras, it features an IR compatible coating to ensure that the use of IR illumination does not initiate focus shift. The lens measures approximately 54 (L) x 45 (W) x 52 (H) millimetres and weighs 82g.
The SLA-M2890PN has a decent level of build-quality, and the lens is well finished. It gives no concerns about longevity in the field.
There is a good smooth motion with the focus and zoom adjustments. The securing knobs are easy to access. The focus ring is large; it is made up of the entire front case of the lens. Motion is easy but there’s enough resistance to allow tightening without any unwanted changes!
On our typically overcast test day, the Samsung lens did a good job of upstaging the unbranded budget control lens, despite the latter’s claim of being a higher specification model. While the difference between the Samsung lens and the control unit wasn’t as great as with the Fujinon and Theia lenses, there was still a visibly noticeable improvement on the camera using the Samsung optics in a side-by-side comparison. Detail was sharper, colour fidelity was more accurate and the overall scene rendition was more faithful.
In low light applications, clean and relatively noise-free images were obtained at light levels which were around 1 lux lower than those required when using the unbranded control lens. Under artifical illumination, the Samsung lens showed no signs of focus shift, and it performed well with both infrared and white light sources.
The M13VG2812IR is a varifocal DC-iris lens with a focal length of 2.8-12mm and an aperture of F1.4. The lens is suitable for use with HD1080p cameras as is rated for 3 megapixel video. The lens is a 1/2.7 inch format unit. This makes it ideal for use with cameras which deploy traditional image sensors along with the slightly larger image chips found in many mainstream HD cameras. It features an IR compatible coating to eliminate focus shift, making it ideal for day/night applications. The lens measures approximately 56 (L) x 43 (W) x 55 (H) millimetres and weighs 70g.
The M13VG2812IR has a decent level of build quality, and is finished to a fairly good degree.
The zoom adjustments are smooth, but the focus adjustment was pretty loose and this made fine adjustment something of a slow and tricky task, especially on a cold day! To get around this we had to tighten the securing screw to add some friction. It’s not the best approach but it did the job. Interestingly, we haven’t experienced this with other Tamron lenses.
When pitted against the control unbranded lens, the Tamron unit did well and showed that the optics have been made to a high standard. There was a visible difference between the Tamron unit and the control lens, and this was significant when it came to colour accuracy. Detail was also enhanced, and the image was sharper.
In low light applications, the M13VG2812IR performed well and offered a significant increase over the control lens.
The Tamron-equipped camera delivered detailed colour images with minimal noise at light levels which were approximately 1.5 lux lower than those required when using the camera equipped with the unbranded control lens. There was no visible focus shift during day/night switching using both infrared and white light illumination.
The SL410P is a varifocal P-iris lens with a focal length of 4-10mm and an aperture of F1.4. The lens is rated for up to 12.4 megapixels, making it suitable for use with HD1080p and 4K cameras. The lens is a 1/1.8 inch format unit. This makes it suitable for use with many of the higher end cameras using the larger chip for HD and 4K video delivery. Billed as a day/night unit, it features an IR compatible coating to eliminate focus shift. The lens measures approximately 53 (L) x 43 (W) x 50 (H) millimetres and weighs 108g.
Theia Technologies will be a new name in optics for many in the security market. The company was founded in 2006 to develop ultra wide angle lenses. The US-based business concentrates on the delivery of optics, and is also active in other sectors such as machine vision and medical imaging.
The SL410P is billed as a true 4K lens, and has a stated resolution of 12 megapixels. As ratings are based upon 4:3 ratios, the required 8 megapixels for 4K is achieved.
The launch of the 4K lens range is imminent, and as such we received a pre-production sample for testing. This makes it difficult to comment on final build quality. Whilst the sample was well constructed and gave no reason to think that there might be issues, it did include one piece of the casing which was not properly finished. This will obviously not be the case with production models.
Focus and zoom adjustments are very smooth, with easy-to-access securing knobs. The focus adjustment is via a ring which also holds the securing screw, but this has enough friction to eliminate issues with accidentally changing the focus when tightening.
The Theia lens was in a different class when compared against the unbranded budget control lens. The SL410P showed an easily discernable improvement with regard to image detail, and colour fidelity was very good too. The image was strong and vibrant, even as the gloom closed in during a typically English rain storm. Detail was sharp and clean, right up to the edge of the image area with a 4K video stream.
In low light applications, the SL410P continued to deliver sharp, detailed and colour-accurate images with minimal noise at light levels which were just shy of 2 lux lower than those required when using the unbranded control lens.
Under artifical illumination, there was no discernable focus shift during day/night switching, and the lens performed well around-the-clock.
All of the test lenses were unconditionally better than the control unbranded lens, which had specifications that would not have been out of place in this test! Its price was around 40 per cent less than a professional quality lens, but the difference in camera performance was more than worth the additional cost of the test optics.
Both the Fujinon DV2.2×4.1SR4A-SA2L and the Theia SL410P perform very well. The main difference is that the Fujinon lens is ‘4K compatible’ as its 6 megapixel rating falls short of UHD resolution. The Theia lens delivers true 4K optics. Both offer high levels of performance, and ultimately the decision will come down to the needs of any given site.
The Tamron M13VG2812IR and the Samsung SLA-M2890PN represent high quality choices for HD applications.
All the lenses in the test are recommended (aside from the control unit), and the results prove the most cost-effective way to boost video performance is with a quality lens!