Trev.

That was exactly the explanation I needed – totally makes sense (so much so that i can’t believe I didn’t realize it in the first place). Thank you very much for taking the time to post that.

Dave

The metering of f4 to f5.6 so the ambient light is one stop under-exposed is no problem, that’s how he wanted to have the ambient, so far that’s easy.

Now, the explanation of why you then meter the flash to f5.6 is because that’s his current f-stop, 5.6, therefore he must have the flash metered to f5.6 to match the camera, so the subject is at the correct exposure, but not the ambient fall-off since the flash will only light a part of the scene, making the subject stand out.

If he was to meter the flash at f4, which is the original ‘correct’ exposure for the overall scene, you would end up with, in theory, the exact same light as the ambient, therefore the image would almost be identical as shot without flash, -1 stop.

Remember, f4 lets more light in then f5.6, and flash works with aperture, so by saying the flash needs to be set to have an f4 rating is telling the flash that there is already enough light to only need f4 where in fact you need that extra stop of light to match f5.6

You forget the actual *camera* setting is aperture of f5.6, so the flash will not then put out enough power to compensate the difference between f4 and f5.6. Ergo, flash metering needs to read f5.6 [more light] to match camera’s f-stop, so that ‘more’ light then correctly exposes the subject.

Flash is only light, and if you just pretend for a moment that it’s ‘ambient’ if that flash is then used like ‘ambient’ and you only meter it for f4, with the camera at f5.6 it will simply be underexposed, no different if there had been no flash in the first place.

Hope this explains it.

Trev.

I’m not sure if you’re still answering questions posted on this page, but hopefully so…

I’m baffled by your suggestion that, after metering for ambient and dropping exposure by 1 stop (from f/4 to f/5.6 in this case), you’d then go attempt to get a manual flash reading of f/5.6. Why not f/4?

To my way of thinking, this would be tantamount to dialing in -1 FEC if you’re going the ETTL route, which I don’t think you’d do unless there was a specific reason to do so. When I’m shooting with ETTL flash, I’ll manually determine ambient exposure, drop exposure by 1 stop or so, and then default to +/- 0 FEC unless scene reflectivity is an issue one way or another.

So my gut tells me than when using manual flash, you should meter for ambient, drop exposure by 1, then adjust flash power/distance until your flash meter gives you the aperture that was originally suggested as correct in the original ambient metering step. What am I missing here?

BTW, I bought your book on off-camera flash, and I love it.

Good day!

Dave

Ross, that would be a typical problem with TTL flash – the change in exposure as you change your composition. Manual flash is the best option when you’re working in a static set-up, especially in the studio. Metering is then best done with a flashmeter. So that’s the good news .. you’re going shopping!

Neil vN

Hi Neil, As usual great site great info. Quick question on the above comment. I am trying do some amateur studio work and I am using two SB-800′s, one bounced into a Westcott Softbox (the umbrella style that requires no speed ring) and the other into an umbrella. I’m getting inconsistent exposures with TTL everytime I recompose or change from landscape to portrait format so I am trying to switch to manual flash to increase the consistency of my exposures. Here’s my question. When I’m using the 800′s in wireless mode triggered by the my camera (no Pocketwizard) I then have no aperture reading from the flash only the ratios as the appear on my D200′s menu. So in that case how do I determine my aperture setting? Can’t really uses the GN method because the flashes are both being bounced in to their respective light modifiers. Don’t have a flash meter either.

Sorry for the long winded question and thanks again for a great website.

Ross

When you say there is no transmitter involved, are you using the camera and speedlight in wireless mode?

My confusion, or clarification, is once the exposure is set without flash for the ambient (-1 stop) light, do I then set the flash power to 1/4, or 1/8 to begin and adjust as necessary to match the light meter’s suggested F-stop.

ok .. let’s take it a step back.
You have your ambient exposure, and it tells you .. for example:
f5.6 @ 100 ISO (at whatever shutter speed, no higher than max sync speed)

Then you take it to f8
It seems that is what you’re trying to do there with the (-1 stop) comment?

ok .. so you now want f8 at100 ISO from your manual flash.
You have a few ways of getting there.
1. You can use your flashmeter, and dial your flash’s power (1/2 or 1/4 or 1/8) until you get f8.
2. You use your histogram in the same manner.
3. You can guess, take a shot, and look at your LCD preview. Repeat until you like what you see. It’s a clumsy method, but will get you there, but not with as much accuracy as the other two methods.

It’s that simple. : )

Neil vN

I am lost it would seem! I am aware that the flash and camera in E-ttl mode are communicating – it must have been the long night! :)

I am practicing shooting portraits with some loaned equipment and was trying to learn setting up an off-camera flash with my Canon 40D. There’s no transmitter involved, so camera and flash would be set manually.

My confusion, or clarification, is once the exposure is set without flash for the ambient (-1 stop)light, do I then set the flash power to 1/4, or 1/8 to begin and adjust as necessary to match the lightmeter’s suggested F-stop.

If it’s that simple, then I obviously had been over-engineering it :)

Your posts are great, and I appreciate the feedback!

best,

JH

Hi there Julian .. you seem a little lost. :)

With E-TTL, your camera and flash will follow your settings. In other words, as you change your aperture and ISO, your camera and flash will work together to give you correct flash exposure (Within reason of course.) You then change your FEC to have more or less flash than the camera thought you need.

So it isn’t quite as you have it there: “do I set my flash settings to match my camera settings”. That is how manual flash would work. Not TTL.

Back to the first part of your question. Your 550EX should be dedicated to your camera if it is a Canon D-SLR. What camera do you have?

And with manual flash, this is exactly what you would do … you would set your ISO and aperture on your camera. You would set the ISO and aperture, based on your ambient light, and what you want to do with your manual flash.

Neil vN

Can I ask about setting the manual flash. I have a 550EX speedlite. It wouldn’t be dedicated to my camera, so I would set the flash manually. You mentioned setting the flash to a power output that would register 5.6 when read with a meter. If I had to set this are you just dialing in say 1/2 power and taking a meter reading to see where you’re at. I can’t set my ISO and F.stop in this mode.

If I shot in ETTL, do I set my flash settings to match my camera settings and then dial in FEC?

Thanks