I use a Yongnuo flash (YN-460) in manual mode. I use it mostly indoors, so I bounce the flash off the ceiling. What is a good approach to read the camera metering and make adjustments to flash intensity?
My flash does not support TTL/ETTL, so cannot communicate with my camera.
I have four manual flashes. I love them. I just make a test shot and look at the histogram on the back of my camera: adjust to suit.
Works great.
Check out the Strobist, he loves manual flashes.
The question was how to meter, not how to eyeball the histogram or guesstimate from guide numbers. I mean no offense to those who answered this way. Just that the original question had specifically to do with metering.
As far as I know, the most reliable way to meter a flash is to trigger it from an incident flash meter. You can then know exactly how much light is falling on your subject. Period. It takes diffraction/absorption of bounce surfaces and distance into account because all it is doing is measuring what falls on the subject.
I use a Sekonic, and I think it's probably overkill for what you're doing -- if you wanted to add an expensive flash meter you would probably be better off getting some ETTL flashes instead.
Getting back to my first comments, it is probably way more productive to do as @pat_farrell suggested -- shoot some test shots until you're happy with the result as it is reflected in the histogram. Then you have a good setup until some factor in your scene changes, such as subject position.
The important thing to remember about metering with digital cameras is that you can use the meter as a guide and tune to suit. You don't have to constantly take new readings. The same for test shots. Unless you alter things drastically, you can just move your exposure setting around -- just be aware of the histogram with each shot.
If you're using guide numbers to calculate, then bouncing is going to increase the distance by 50-100%, and less of the light is going to reach your subject as it's scattered by the ceiling. So if the guide number is 80, I'd start by cutting it in half to 40. So at 10 feet that's f/4 (40 divided by 10 at base ISO).
But as you're likely using it as fill, it's going to be trial and error to just add in a pop of flash. Say the camera meter tells you 1/30th at f/4, you might try 1/125th at f/4 assuming the flash can add a few stops worth of light.
From there, if the flash is too bright you would have to adjust the aperture to f/5.6 or f/8 (because shutter speed won't affect the flash exposure).
If the flash exposure looks ok, but the subject's shadows, or background, or anything not illuminated by the flash looks too dark, then you'll want to lower the shutter speed. This will let in more ambient light,making the image brighter overall, but it won't affect the flash exposure (the flash is so quick, all the light will reach the sensor no matter what the shutter speed - up to the synch speed at least)
I'm not aware of a good formula you can use because the object you're bouncing off of can change -- both height and color. For example, when bouncing off of the white ceiling in my house, I know I want to use +0.7-1.0 EV. But in my parents house, with a lower white ceiling, often shooting at +0.3 EV is good. When bouncing off the wall behind me, I often use +2 EV, or even more.
It's safe to say you'll need a little more oomph when bouncing, but exactly how much is probably best answered either with a few quick snaps, or with an incident light meter.
Estimate the sum of the two sides of the angle you-ceiling-subject and set the distance manually in flash (distance can be set in flash (speedlite 430 ex) when head is in front pointing position)
