External flash : what should be the Aperture, Shutter speed and ISO in Manual mode?

radhak · April 22, 2012

Where can I go to read up on using an external flash (SB600) with my D90? (I am thinking the technique should be independent of the equipment, right)?

I am trying to figure out how I am supposed to meter when a flash is used. When I try the pre-sets (Portrait / etc), the output is not to my liking, and I'd like more control on it.

Of course, I could keep shooting in 'Portrait', then tweak the settings in Manual; but then, that's not learning, is it!

I searched and found this thread that puts words to more of my doubts, but the Strobist is a bit of an ocean - am not sure how to find what I'm looking for. Unless you can help me narrow down my search.

ziggy53 · April 22, 2012

An external flash may be used for either key or fill. Additionally, The D90 can be used as a Commander and the SB-600 can be Slaved, allowing off-camera use of the SB-600.

While Manual mode of the camera allows more complete control of ambient light contribution, in changing light it may be relatively slow to use.

Your best bet is to approach each job or project with a vision and a goal for the light. The direction and the light ratios desired will determine the relationships between ambient, D90 on-board flash and the SB-600, either as external (hot-shoe mounted) or off-camera light.

There is no simple formula or default configuration, but for social situations and events I prefer to use the external flash on the hot-shoe, with a suitable flash modifier, and then either aperture priority mode or manual mode.

If you should use manual mode, check the meter first for accurate exposure for ambient light, and then figure out how much ambient you want to allow compared to the flash contribution. If the flash is to be the key light, then I recommend adjusting the manual exposure for ambient to be 1-2 stops under the flash contribution.

If the flash is to be used as fill light, adjust the manual exposure for ambient exposure first, and then add flash with a -1 or -2 Flash Exposure Compensation (FEC) value.

Remember that using a flash will normally limit the shortest shutter duration to 1/250th, so aperture and ISO may be more of a determinant for the ambient component. (FP/HSS flash mode can help for close subjects, allowing very short shutter speeds to help control ambient light.)

lifeinfocus · April 27, 2012

ziggy53 wrote: »

1. If you should use manual mode, check the meter first for accurate exposure for ambient light, and then figure out how much ambient you want to allow compared to the flash contribution. If the flash is to be the key light, then I recommend adjusting the manual exposure for ambient to be 1-2 stops under the flash contribution.

2. If the flash is to be used as fill light, adjust the manual exposure for ambient exposure first, and then add flash with a -1 or -2 Flash Exposure Compensation (FEC) value.

Ziggy, could you give some examples for number 1 above.

And the same for number 2.

I am using an SB700 and I used a trial and error method as noted in the http://dgrin.com/showthread.php?t=219193 posting where I justed loaded one of the photos.

BTW, the max sync speed for the D90 is 1/200th. That is what I am using now and looking forward to upgrading in the next six months.

Thanks again,
Phil

ziggy53 · April 27, 2012

lifeinfocus wrote: »

Ziggy, could you give some examples for number 1 above.

And the same for number 2.

I am using an SB700 and I used a trial and error method as noted in the http://dgrin.com/showthread.php?t=219193 posting where I justed loaded one of the photos.

BTW, the max sync speed for the D90 is 1/200th. That is what I am using now and looking forward to upgrading in the next six months.

Thanks again,
Phil

For the first scenario, where the flash is to be the primary and key light, let's say you measure ambient at f5.6 and 1/60th. In order to push that down one stop you just increase the shutter speed to 1/125th, leaving the aperture at f5.6. In order to drop the ambient 2 stops under just use a shutter speed of 1/250th or 1/200th (generally the highest flash sync speed without resorting to FP/HSS mode).

(In practice this may also slightly overexpose the scene, so review the histogram and adjust the settings accordingly.)

Going the other direction, where you want ambient to be the primary and key light, you just use the measured exposure of f5.6 and 1/60th, and then add an FEC correction of -1 or -2.

Remember that ISO may also be adjusted to keep shutter speeds and/or aperture values within the range that satisfies your photographic intentions for the situation and scene.

lifeinfocus · April 27, 2012

ziggy53 wrote: »

For the first scenario, where the flash is to be the primary and key light, let's say you measure ambient at f5.6 and 1/60th. In order to push that down one stop you just increase the shutter speed to 1/125th, leaving the aperture at f5.6. In order to drop the ambient 2 stops under just use a shutter speed of 1/250th or 1/200th (generally the highest flash sync speed without resorting to FP/HSS mode).

(In practice this may also slightly overexpose the scene, so review the histogram and adjust the settings accordingly.)

Going the other direction, where you want ambient to be the primary and key light, you just use the measured exposure of f5.6 and 1/60th, and then add an FEC correction of -1 or -2.

Remember that ISO may also be adjusted to keep shutter speeds and/or aperture values within the range that satisfies your photographic intentions for the situation and scene.

OK, I should have understood that.

What about it if you have two flashes setup with triggers and both are set to manual.

What I did recently was set my camera to the aperture I wanted for depth of field, manual, shutter to 1/200th, and the lowest ISO available on the camera, in this case 200.

Then I set my key light (with an umbrella) to its brightest manual output setting and for fill light (with an octodome softbox) I set it to 2 stops less say to 1/4.

I took a few shots, checking histogram on camera and dialed down the settings on the flashes.

Took a few more shots, check histogram and then loaded the resultant photo onto my laptop to check the resutls. This is what I meant by trial and error.

So is there a way I can get to the flash output settings more accurately and quickly without a flash meter or use of distance/guide numbers?

Thanks again,
Phil

ziggy53 · April 27, 2012

lifeinfocus wrote: »

...

So is there a way I can get to the flash output settings more accurately and quickly without a flash meter or use of distance/guide numbers?

...

In short, a hand-held meter that is capable of both ambient and flash, properly calibrated to your system, is the fastest and most accurate possible method.

I do recommend testing all of your flashes and all of your flash modifiers so that you understand what the flashes output at the different settings and different distances, and so that you understand the relative efficiency of your flash modifiers. (Don't assume that a manual flash output directly correlates to the setting. Full power and 1/2 power are often a different ratio than 1/2 power and 1/4 power, for instance. You have to test to know for sure.)

Once you know that flash "A" produces such-and-such output at such-and-such power setting and such-and-such distance, you have part of the solution. Knowing that flash modifier "X" absorbs 1 stop of light, while flash modifier "Y" absorbs 2 stops, is another part of the solution.

Unfortunately, the room/site itself also plays a part, as does the spill from the flash modifiers, so it's not always easy to guess even with the recommended testing. Experience will often give you sound starting points as you develop a routine and a methodology.

For instance, I'll often start with a set of flashes and flash modifiers that I am pretty familiar with (and my standard set of camera settings), and then tweak the camera settings based on a few test shots and my observations of the room/site.

lifeinfocus · April 27, 2012

ziggy53 wrote: »

In short, a hand-held meter that is capable of both ambient and flash, properly calibrated to your system, is the fastest and most accurate possible method.

I do recommend testing all of your flashes and all of your flash modifiers so that you understand what the flashes output at the different settings and different distances, and so that you understand the relative efficiency of your flash modifiers. (Don't assume that a manual flash output directly correlates to the setting. Full power and 1/2 power are often a different ratio than 1/2 power and 1/4 power, for instance. You have to test to know for sure.)

Once you know that flash "A" produces such-and-such output at such-and-such power setting and such-and-such distance, you have part of the solution. Knowing that flash modifier "X" absorbs 1 stop of light, while flash modifier "Y" absorbs 2 stops, is another part of the solution.

Unfortunately, the room/site itself also plays a part, as does the spill from the flash modifiers, so it's not always easy to guess even with the recommended testing. Experience will often give you sound starting points as you develop a routine and a methodology.

For instance, I'll often start with a set of flashes and flash modifiers that I am pretty familiar with (and my standard set of camera settings), and then tweak the camera settings based on a few test shots and my observations of the room/site.

Very good. Thanks much.

External flash : what should be the Aperture, Shutter speed and ISO in Manual mode?

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