In an earlier post I spoke about the new Long Exposure module from David Milligan (http://photography.grayheron.net/2014/08/another-great-magic-lantern-feature.html ). David has now tweaked the module and it is now accessible under its own menu (under the ML Shoot menu) and has some new functionality: namely a way to calibrate your ND or ND stacks.
To calibrate your NDs, which you only need to do once, simply take a normal photo of constant exposure scene, ie one that is not going to change over the calibration and follow the instructions under the “Measure ND” sub-menu, ie dial in your manufacture’s ND Strength field, press Measure ND and follow the instructions (be sure to have the Canon Info screen on or be in LV).
For me I found the following:
- ND1000 = 10Ev drop, calibrated at 10Ev;
- ND 16 = 4Ev drop, calibrated at 3.5Ev;
- ND 1000+16 = 14Ev drop, calibrated at 13.5Ev.
Knowing the calibrated figures, I can confidently capture LE exposures, which I do with the following workflow:
- Take off any filters, ie including any (UV) ‘sacrificial’ ones;
- Compose and focus without any ND filters on;
- Select aperture and ISO, ie for LE you will usually be using the base ISO of 100;
- Consider the need to select exposure lock in the ML Expo menu (this allows coupled adjustment of exposure settings);
- In the ML Bulb ND menu set your ND value (ie 3.5 or 10 or 13.5 for me).;
- Ensure ML Bulb ND is on and you are in M mode, ie not Bulb;
- Select ETTR and ‘grab’ an auto-ETTR exposure, or choose your own exposure setting;
- Assuming you have the info screen on your camera’s LCD turned on (or be in LV), you will see the ‘ND exposure time’ in the top left hand corner of the camera’s LCD;
- Adjust the aperture and/or exposure time to ‘tune’ the ND time to achieve your artistic vision;
- Carefully attach the ND filter (mine screw on);
- Press the SET button and hold until you see the ND bulb timer count down start.