What is an Aperture/Iris and why is it important for Long Range PTZ Surveillance Cameras and Night Vision ?
A cameras or lens's Aperture also know as ƒ number or f-stop refers the size of opening of the the lens (aperture) vs the power of the lens which is called focal length (measured in mm). The smaller the F number the bigger the aperture which results in a higher light or infrared collecting ability while a high ƒ stop results in lower amount light or infrared collecting ability. The lower the f‑number (Larger Aperture) the better the lens is and the better the camera will operate in visible, NIR imaging and SWIR and especially thermal infrared imaging. In Visible, NIR and SWIR cameras a lower f stop results in in a camera system with increased light (or Lux) sensitivity which allows the camera to capture more accurate images in lower light levels and respond better to IR or white light illumination. For Infrared thermal cameras it increases the heat gathering capability which is measured mk (millikelvins .001°C). A "FLIR" (Forward Looking Infrared Cameras) thermal camera equipped with a lower F stop GE lens improves the range and performance for both LWIR uncooled cameras as well as MWIR cooled thermal cameras. Infiniti optics custom builds all types of EO/IR solutions and can offer them as open frame modules (lens and sensor attached) or as complete integrated PTZ cameras with Visible and SWIR sensors for ultra long range imaging required by a host of military and defense applications.
For Visible, SWIR and NIR A motorized iris is a lens that uses mechanism that can adaptively adjust the amount of light coming through the lens as well as the cameras depth-of-field. It is measured by an f-number (ƒ/#) or f-stop, which refers to the ratio of the lens’s focal length to its aperture’s diameter in visible cameras an motorized IRIS allows the camera to adjust the amount light coming in, for Cooled MWIR thermal cameras due to NUC calibrations the F stop is often fixed and constant even as you zoom in and out. The greater the focal length the harder it is to obtain a low f stop as an example our 135x 15.5~2075mm at max zoom is an F32 lens which reduces sensitivity of a camera to about 1/700th compared to a F1.2 lens which is often the assume lens specs which allows manufactures to claim a lower light performance than will be achieved in the real word This is why despite manufactures claimed lux ratings there is no such thing as long range low light camera meaning that for long distances at night for visible/NIR cameras you requite IR/White light LED illumination for about 100-500m or for 5-6km of active illumination ZLID (Zoom Laser IR Dioide) are required.
For thermal infrared cameras, having a lower f‑stop number increases the image contrast and clarity, which results in higher detection distances. This is particularly true for uncooled LWIR cameras where lower f‑number lenses like ƒ/1.0 to ƒ/1.6 are required. An ƒ/1.0 Ge lens allows for 2.5x more infrared thermal energy to be transferred to the infrared sensor than an ƒ/1.6 lens. Thermal cameras do not require illumination and can operate in 0 lux (complete darkness).
When looking at thermal imaging it is very important to look at the lens’s f‑number, as this is often as important the thermal sensor in determining the actual performance of the system. Infiniti uses mostly ƒ/1.0 and ƒ/1.3 lenses in our LWIR thermal cameras to ensure high contrast, long-range performance for detection, recognition, and identification with the exception of our biggest LWIR lens which is 15-400mm and is F1.5.
Infiniti optics is provides a wide variety of EO/IR camera solutions all the way from a component level, open frame modules (lens and sensor attached) or as complete integrated PTZ cameras with Visible, SWIR and Thermal sensors for ultra long range imaging optimized for a host of military and defense applications.
For more information about thermal infrared imaging for night vision and surveillance see our Thermal Imaging Explained page.
Image source: https://www.photographer.org/aperture-f-stop/