Cost-saving capture in low-light
Long exposure with CMOS sensors

Take advantage of lower costs
For the first time, long exposures of up to 10 seconds with a CMOS sensor is now possible while offering a cost-saving alternative to CCD sensors.

Capturing an image in low-light conditions means working with a high gain in order to obtain sufficient detail from the image. The trade-off in using a high gain is that it produces more noise leading to a loss in image quality. (see fig. 1)
However, long exposure provides the capturing of high-quality images with low noise even in low light conditions. (see fig. 2)

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

Why is long exposure useful?
Long exposure is ideal for all applications where capture is required in low light conditions. Gain does not need to be increased when exposure time is extended and therefore avoiding an increase in image noise. This ability is of particular interest, for example, to microscopy applications which must be conducted in low light in order not to destroy the light-sensitive sample. Another application
where long exposure is useful is in the field of fluorescence analysis. Applications in medical technology, quality assurance, mechanical engineering and astronomy all benefit from this technology.

Using Long exposure: How to
If a long exposure time is required, the camera cannot be used in freerun mode. Instead, trigger mode with single shots should be adopted and if using iDS' uEye Cockpit software, clicking will produce the required result.

Also, the timeout must be adjusted to "trigger timeout" for long exposure to avoid wrong timeout messages. The trigger timeout is adjusted in the "Trigger" tab of the "Properties" dialogue box in uEye Cockpit (see fig. 3). If rolling shutter mode is supported by the camera, this facility should also be chosen.

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

The pixel clock must also be set to minimum value and a "Long-term" option selected. In this way, the largest possible exposure time increases to the maximum long exposure time. Note this method can also be used for cameras that do not support long exposure. Setting the pixel clock and frame rate to the minimum values will result in achieving the maximum exposure value (Fig 5)

Adept Turnkey Pty Ltd - Smarter Imaging for Better Lives - are distributors for iDS imaging products in Australia and New Zealand. To find out more about iDS, CMOS cameras or any other machine vision product, please call us at Perth (08) 9242 5411 / Sydney (02) 9905 5551 / Melbourne (03) 9384 1775 or contact us online.