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Manage long exposure with CMOS sensors
A cost-saving solution from iDS

Capturing an image in low light conditions usually means working with high gain in order to obtain sufficient detail from the image. The trade-off is that using high gain causes more image noise (see Fig. 1) which, in turn, produces a lower quality image. CMOS sensors which offer a long exposure are a cost-saving alternative to CCD sensors
and can be used a wide range of application areas.

The solution to capturing in low light is to use long exposure which allows the taking of high-quality images with low noise even when lighting conditions are poor. (See Fig 2)

An exposure of several seconds is referred to as long exposure. Some iDS uEye models with CMOS sensors allow a long exposure, for example up to 10 seconds offering
an interesting and cost-saving alternative to CCD sensors

Fig. 1 Capture without long exposure		Fig. 2 Capture with long exposure at 1 Lux with 10 seconds and double gain

Capturing with long exposure using uEye
Rather than operating in free mode, trigger mode should be used with single shots.
A software trigger can be fired in uEye Cockpit using the button in the tool bar. As well, the timeout must be adjusted for long exposure to avoid wrong messages by setting the timeout trigger via the “Properties” dialogue in uEye Cockpit. (See Fig. 3).

Use of the rolling shutter mode is also recommended if this mode is supported by the camera. The rolling shutter mode is activated in the "Shutter" tab in uEye Cockpit.

Fig. 3 Increasing the timeout in uEye Cockpit		Fig. 4 Activating the rolling shutter mode in uEye Cockpit

The pixel clock (see Fig. 5) now needs to be set at minimum value (1) in the “Camera” tab and the “Long-term” option (2) activated the result being that the largest possible exposure time increases to the maximum long exposure time (3), in this example up to 10 seconds. This method can also be used for cameras that do not support long exposure by setting the pixel clock and frame rate to the minimum values to achieve the maximum exposure value).

		Application areas
		The long exposure is ideal for all applications where capture is conducted under low-light conditions. Due to the extended exposure time it is not necessary to increase the gain and so avoiding excessive image noise. Long exposure is of particular use in:
		• • • • • •	Microscopy Fluorescence analysis Medical technology Quality assurance Mechanical engineering Astronomy
		uEye camera models that support long exposure
		USB 2.0		USB 3.0	GigE
		UI-1250LE		UI-3250CP	UI-5250CP
		UI-1251LE		UI-3250LE	UI-5251LE
		UI-1252LE		UI-3251LE	UI-5252LE
		UI-1250ML		UI-3252LE	UI-5254LE
		UI-1250SE		UI-3250ML	UI-5250RE
					UI-5250RE PoE
					UI-5250SE
Fig. 5 Configuring long exposure in uEye Cockpit

Acknowledgement: The above is an adaptation of an article published by iDS