Calibrating LIght meter and Camcorder

[photograpix75]

I find lightmeter to be useful to check exposure and more importantly lux in the scene being shot.   

To get best results, the light meter and camera need to be calibrated.  Easier to have a software to do it for us by shooting test shots in the camera and plug and play the light meter.  Well if we do not have the luxury of the software then manual calibration can be done.

Spot meter the gray card and adjust aperture till you get 50% reflectance .. note the aperture.

In the light meter, set the frame rate, shutter speed (shutter angle).  Now spot the reading off the grey card.    Now dial in the ISO to get the Fstop that corresponds to the reading from the camera...  now you will have the light meter and the camera reading the same f/stop. 

well, if you do not have a 18% grey, do not worry.  Use the black lens cap of the camera or the white of the reflector...  well both are at the extremes of the grey scale, so do remember to calibrate accordingly.

Hope this helps...

[Alvin Ang]

thanks! 

[rogersoh]

thanks for sharing the tips. 

How about if the light meter does not have the spot meter function, is there other alternative?

[photograpix75]

Hi Roger,
yes, there is an alternative. 

since it is not spot, using this method, you will be close by about 1/3 to 1/2 of a f/stop. 

You need to expose a gray card to the camera and spot it, set it to 50% bightness.  Set gain to zero all along.  Now note the fstop and the shutter speed.  If you can get the shutter angle, get that as well.

Now take exposure at the grey card using the light meter.  instead of poinging the white dome to the camer, point it to the gray card and be as close as possible to the card and take the reading with same shutter speed as the camera.  Then adjust iso to get the same fstop from the camera.  Now your light meter and the camera are calibrated at the same gian level.

You may notice that at zero gain, ISO 100 to 120 may be given.  but as gain increases/ decreases, there will be geometric increase in the ISO - meaning that if you move from gain 0 to gain 3, you expect ISO to be around 300, but you will not that the ISO may be about 450 instead.  it is due to the fact that you are retaining the shutter speed and fstop ratios and hence the ISO compensation is higher in the gain on videocamera...

Anyway, now that your light meter and camera are claibrated, you need to maintain the gain level to use the light meter to guide exposures...  if you change the shutter speed, you need to change it on the camera as well and no gain on camera / iso on lightmeter should be changed.

[rogersoh]

Thanks for the useful tip. I will try it out this week.