how do I adjust the 'exposure' time for an NI-1428

[oso]

Is it possible to adjust the amount of time devoted to capturing an image? (I have seen this calle dthe integration time, I believe.) Similar to extending the exposure of a camera. I have an app that we are using a 50x objective (fully zoomed) and wish to get a brighter picture than we are currently. If this is possible, what is the best method to do so.
Thanks in advance,
Chuck Bear

[BruceAmmons]

Chuck,

All of the options I have ever seen for changing the exposure time and using integration all depend on the camera. Once the camera has digitized the image and sent it to the computer, there is no way to do the integration.

One possibility is to acquire multiple images in a sequence, then add them together to get a single brighter image. Essentially, you are integrating the images.

Another possibility is to use binning to trade resolution for brightness. If you combine 2x2 blocks of pixels into single pixels, the resulting pixels will be 4x as bright. Unfortunately, this method reduces your resolution in half.

Perhaps another solution would be to use a brighter light for illuminating your target. There are some very high intensity lights fo
r small areas available.

Bruce

[Brent_R]

Chuck Bear,

Which camera are you using? Since you are connecting via Camera Link then you most likely have a mid to high-end camera, and there is a very good chance that it supports variable exposure times. Some of the exposure modes typically available in machine vision cameras include:

1) Free Run, No Shutter - Camera runs at a fixed frame rate and exposure time is ~(frame period).

2) Free Run, Fixed Shutter - Camera runs at a fixed frame rate and the exposure time is controlled by the camera to be some value less than or equal to the frame period. This exposure time is typically set using serial commands or sometimes DIP switches on the camera.

3) Triggered, Fixed Shutter - Camera returns a frame when it receives a trigger pulse. The exposure time is con
trolled by the camera as in option 2. This is sometimes referred to as edge triggered, edge preselect, frame on demand, or something like that. Depending on your configuration, the trigger pulse could come from the IMAQ board or through a separate connector on the camera.

4) Triggered, Pulse Width - Camera returns a frame when it recieves a trigger pulse and the exposure time is equal (approximately equal in some cases) to the duration of the trigger pulse. Like option 3, the pulse could come from the IMAQ card or from an external device. The term "shuttered" is often used when the exposure time is less than one standard frame period, while the term "integration" is used for exposure times longer than one period. There is little practical difference for the end user as long as the camera supports the correct mode.

5) Triggered, Two Pulse - Camera starts integration when it recieves a trigger pulse, then stops integration and returns the frame when it receives a second pulse.
This mode is not very common.

Take a look at the camera properties in MAX to see what modes are supported by the camera file for your camera.

Regards,

Brent R.
Applications Engineer
National Instruments