Desert Star Knowledge Base

Search the Knowledgebase	Browse by Category
[Advanced Search]

How does FrogEye's EMCCD based night vision performance compare to image intensifier tubes?

Would you like to...

Print this page

Image intensifier tube based night vision systems provide a fairly constant performance throughout a range of night conditions from starlight to reasonably well illuminated urban conditions. As compared to day imagery, both the resolution and contrast of image intensifiers is low.

The EMCCD technology used in FrogEye yields an image quality that depends on the level of illumination abd the particular sensor being used in the camera. The model TC-253 EMCCD currently available for FrogEye will perform worse than a GEN3 OMNI4 (i.e. high performance) intensifier tube at very low light levels, but also yield much better resolution and contrast at higher light levels such as full moon or many urban conditions.

The following images provide some examples. The EMCCD images were shot with FrogEye, and the image intensifier tube images used an Electrophysics 9350 intensifier assembly with GEN3 OMNI4 tube mounted on a Canon film camera. Both cameras used the same lens, a Canon 28mm-105mm F/3.5-4.5 zoom lens.

This first image shows a full image taken with the intensifier. It gives you a general idea of the image quality. Note the particular field of view (i.e. the house and trees around it) covered by this image. The light conditions are 3/4 moon, and the house is about 230m distant.

The following two images are the view of the same house taken with the EMCCD (top) and the portion of the above intensifier image cropped to show the same field of view as the EMCCD (bottom).

What is apparent here already is that while the image intensifier offers a much larger field of view with a given lens, the EMCCD provides better target detail and contrast under the 3/4 moon conditions in this picture.

Before we continue, a couple of sentences about field of view, target resolution and how it relates to your work. The EMCCD generates a more narrow field of view than the intensifier tube, simply because the device is much smaller than the photo sensitive area of the intensifier tube. In our tests, both cameras used the same lens, but the smaller EMCCD 'captures' a smaller portion of the image projected by the lens as compared to the intensifier because it is physically smaller. Specifically, the TC-253 EMCCD measures about 4.9mm x 3.7mm, while the photo sensitive area of the intensifier tube is a circle 18mm in diameter. The wider field of view available with the intensifier is an advantage of that technology, and in particular at short-range work. However, in long-standoff work you are normally looking at a distant target that appears quite small even with the longest lens that you can realistically carry. So, target detail becomes more important than field of view - and target detail and contrast is where the EMCCD excels.

The next set of picture shows what happens when more light is available. Here, we are looking at a street sign in Monterey along a reasonably access road. The EMCCD (top) makes use of that additional light to produce a very crisp image, while the inetnsifeier image quality remains about the same as in lower light conditions.

Another difference between intensifiers and EMCCD is performance at night in the presence of bright light sources. Such bright lights interfere with both technologies. Intensifiers experience a halo around the light source and a general reduction in contrast, while EMCCD will show blooming. Yet, the impact of the bright lights tends to be more localized in the EMCCD, allowing it to produce better images under such conditions.

The following picture shows a portion of Monterey harbor at night as seen by the intensifier. Note the bright lights on the dock. The glare was such that the fishing boat in the darker water was hard to make out with the naked eye.

The next two pictures compare the EMCCD to the intensifier. Once more, we cropped the intensifier picture (bottom) to match the field of view of the EMCCD picture (top). We also contrast enhanced the intensifier picture in Photoshop, to get the best possible representation of the boat.

Yet, despite that enhancement, the higher contrast of the EMCCD allows it to resolve the name of the boat: it is the Anthony Boy. The intensifier shows the boat, but details such as the name are lost.

Now we move to some very dark conditions. Here, the better sensitivity of the intensifier as compared to the TC-253 EMCCD becomes apparent. The following shots show a test target at 15 microLux illumination on the sensor. That would be about the same as a camouflaged person at clear starlight conditions as seen with a light sensitive F/1.4 lens. The intensifier advantage is obvious.

Once the light level is increased to 125 microlux on the sensor plane (approx. white truck image with F/1.4 lens at somewhat brighter than starlight conditions), both technologies perform about the same...

In summary, our tests showed that intensifier technology is preferred in the under very dark conditions and for wide-field work. The better target detail of the EMCCD makes it the preferred choice for long-standoff imaging as long as higher light levels are available, and for night vision in the presence of glare.