Calibrate shutter open lag

This dialog is used to determine the DSLR's shutter open lag. It works by photographing the LEDs on the relay switch.

Camera Settings:
  • Use RAW with no jpg (less in camera processing)
  • Use Mirror Lock (if camera supports it)
  • Use Manual Exposure mode.
  • Set the shutter speed to 1/1000th second or faster
  • If possible, use the aperture you will use in the field (fully open is recommended for satellite trails)
  • Set the ISO so that the power LEDs on the relay switch are easily visible.
  • Use a tripod. Focus on the relay switch. Then set the camera to Manual Focus.
DSLR Trigger - Calibrate shutter open delay dialog:


  • Tick the 'Mirror Lock' check box if the camera is using mirror lock.
  • Set an initial 'Shutter open delay'. 100 - 300 ms are good starting values.
  • Press the 'Test' button.
Analysing the results:

If both the power and switch LEDs are visible, decrease the 'Shutter open delay' and repeat the process.
If only the power LED is visible, increase the 'Shutter open delay' and repeat the process.
Once the transition between these two conditions is found, press the 'Apply' button to apply this shutter open delay value to DSLR Trigger.

USB Relay Switch showing both the power and the switch LEDs illuminated.

How does this test work?

When the user presses 'Test', DSLR Trigger closes the relay switch for the specified number of milliseconds. The switch's second LED will be illuminated for the whole of this time.

As soon as the switch is closed, the camera starts the processes required to take the shot. This takes time, so the shutter opens after the shutter open delay.

If the shutter delay is longer than the specified number of milliseconds, the switch LED will have gone out before the shutter opens. Only the power LED will be visible.
If the shutter delay is shorter than the specified number of milliseconds, the switch LED will still be on when the shutter opens. Both LED's will be visible.
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