Understanding Light Meters and Lighting Ratios

[RadioRocket]

Hey guys,

I'm an aspiring cinematographer and although I am confident with my camera work, my lighting definitely needs work. I've been considering getting a light meter as it seems to be a step in the direction. However I shoot primarily with digital cameras so i've heard it may not be necessary. I understand that it provides a good reference point for finding overall light and figuring out ratios but I am still relatively new to things like that. I was wondering if anyone could provide information on how to use a light meter effectively with digital cameras like DSLRs and any general information on light ratios. I know there is a standard ratio for determining the strength of a key light and fill lights.

I apologize if this is a vague and general topic but any information shared would be very useful to me and I'm sure others as well!

Thanks

 

[j1clark@ucsd.edu]

Hey guys,

I'm an aspiring cinematographer and although I am confident with my camera work, my lighting definitely needs work. I've been considering getting a light meter as it seems to be a step in the direction. However I shoot primarily with digital cameras so i've heard it may not be necessary. I understand that it provides a good reference point for finding overall light and figuring out ratios but I am still relatively knew to things like that. I was wondering if anyone could provide information on how to use a light meter effectively with digital cameras like DSLRs and any general information on light ratios. I know there is a standard ratio for determining the strength of a key light and fill lights.

I apologize if this is a vague and general topic but any information shared would be very useful to me and I'm sure others as well!

Thanks

I'd recommend getting both a spot meter and an incident meter. One can find both in the same device, such as the Sekonic L-758 Cine, but at $822 on Amazon, that may be a bit much for you. You can go to ebay and find offerings for less...

I have a Minolta Spot F, which I don't think is made anymore... and I recently bought a Sekonic L-308 dc, which gives me the FC reading of light falling on subjects.

I use the 'in camera' histogram to confirm what my meter readings are.

For determining ratios, I find the spot meter is the best, as one can check the light reflected from various areas at the camera location. However, most 'continuous' lights are rated in terms of footcandles... well if the manufacturer bothers to give the photometric data at all, and using 'wattage' is unreliable in many cases other than well known light sources, so an incident meter is good for determining and adjusting the lights to basic levels.

 

[cpc]

Start here: http://en.wikipedia.org/wiki/Light_meter
Read carefully the part on meter calibration. This will give some insight on why not all meters are created equal. And why readings can vary a bit between meters.

Here for more on meters and digital cameras:
http://www.dvxuser.com/V6/showthread.php?270957-Light-Meter-to-use-with-a-f3

I know there is a standard ratio for determining the strength of a key light and fill lights.

No, there isn't.


Digital cameras already have good through-the-lens reflective metering. An external meter is useful mostly for its incident readings.
When using an external meter with a digital camera, the single most important element is correctly matching the readings to the camera+lens combo. You will need to do some tests in order to be able to interpet these well with your specific camera.
There are 3 important variables to consider:
1) Lens f-stop is off (the t-stop is up to 1/2 stop less than f-stop usually and the difference can vary depending on specific f-number setting).
2) True camera ISO is often not equal to the nominally specified ISO (and again, these vary for specific ISO settings).
3) The camera selected gamma transfer function can tweak exposure distribution.

 

[j1clark@ucsd.edu]

Re: Standard ratios...

No, there isn't.

Sure there are 'standards', there's 1:1, 1:2, 1:3 are the 3 most popular, and in the case of most work 1:3 is probably the max ratio unless one is going for a very specific extreme high contrast look.

Digital cameras already have good through-the-lens reflective metering. An external meter is useful mostly for its incident readings

I'd differ on that as well. With a spot one can check lighting in a much narrow angle of view than the usual lens on the camera, and so get facial lighting ratios where as even in the 'centerweighted' or 'spot' mode of the camera that sort of determination is a bit awkward, especially if the camera is on a tripod.

 

[cpc]

Sure there are 'standards', there's 1:1, 1:2, 1:3 are the 3 most popular, and in the case of most work 1:3 is probably the max ratio unless one is going for a very specific extreme high contrast look.

These aren't standards. They just happen to be ratios based on whole numbers which makes them popular examples.
People light all the way from flat to extreme contrast depending on the purpose of the image.

I'd differ on that as well. With a spot one can check lighting in a much narrow angle of view than the usual lens on the camera, and so get facial lighting ratios where as even in the 'centerweighted' or 'spot' mode of the camera that sort of determination is a bit awkward, especially if the camera is on a tripod.

This makes sense. I also occasionally use my meter for reflective readings.
But for DSLRs (that the OP is asking about) sticking to the spotmeter of the camera is probably best. The instant feedback can also help learn faster when not to trust reflective readings, and consequently to not bother with them in tricky situations.