I really need some help with flash

maman · Mar 5, 2010

I'd like some advice on setting up my (non-canon) wireless slave flash, using my pop-up flash as the trigger, on my Canon 40D.

I'm using diffusers on both the pop up and the slave, and what I'm looking for is soft fill-in flash, in ambient light (such as a person at sunset) as opposed to flash being my main light source.

Am fairly new to flash, and have avoided it mostly... however, with the diffusers I'm actually quite pleased with the softer results and am now looking to use it more.

I'm trying to get my head around output / ratio calculations...

But i think I'm overthinking it...

So, bearing in mind that I lose about a stop on each diffuser. And that the internal light meter is reading for the pop-up flash only. How do I factor in the wireless slave and compensate for a good exposure?

I'm also thinking I want to lower the power output on my slave to the lowest setting because none of my subjects are gonna be more than few feet away and I'm really looking for a soft fill-in. Not knowing what the hell all the numbers on the back on my flash mean, can anyone explain how to do that simply too.

Thanks.

Big Mike · Mar 5, 2010

Do you want the camera's flash to be part of the fill, or it only for triggering the remote flash? I'm guessing that since you are using a diffuser, you want that light as well. So then you have three light sources, the sun and the two flashes.

Taking a step back, are you using the camera's flash in E-TTL (auto metering) mode? If so, it will be firing a preflash, which is how it meters. This preflash may cause a remote slave flash to be triggered early if it has an optical trigger. So how are you triggering the slave flash? (some optical slaves can be set to ignore a preflash).

Either way, the camera's metering won't know anything about the slave flash, so the best thing to do, is to put the camera into manual mode and input the settings you need for the ambient light. Then adjust your flash output to the level you want.

Jeremy Z · Mar 5, 2010

For fill flash, in situations like you mention, I would just skip the slave.

If it is too much, dial down the flash exposure compensation a bit rather than diffuse it.

maman · Mar 5, 2010

Thanks for your comments guys! I appreciate it.

Jeremy Z, I thought I'd play about with a wireless slave, to try and get my head around using a different light source other than just the one on camera. I want to start getting a bit more creative and I know full frontal flash can be very unflattering and harsh.

Big Mike, yes, 3 light sources.

I hear what you say about the camera's metering not knowing anything about the slave flash, which is what I need help on... I'm not that technically oriented, so am finding it a bit difficult to get my head around...

When I put my camera into manual mode and input the settings for the ambient light, how do I compensate for the extra light coming from the slave? Can I compensate in stops, as I would in any overexposure situation? In that case, how do I work out how many stops I need to adjust for...? My flash is a digi-slave deluxe 3000 (if that helps).

iskoos · Mar 6, 2010

I guess what Big Mike is trying to say is that you just use the manual mode and adjust for the exposure by taking several pictures. If they are over exposed for example, dial negative exposure compensation till you get it right.
I do not think there is a formula that will tell you exactly how many stops you need to dial...

AnthonyS · Mar 7, 2010

Congratulations on trying some new lighting. I would suggest getting used to manual mode, its not as bad as you may think. With digital you have the screen on the back, and a histogram. The center of your histogram is your neutral exposure and its divided into f-stops so you adjust from there.
When I was giving a workshop I noticed that new photographers didn't realize when shooting flash you shutter speed is really only able to control ambient light. Aperture controls the flash exposure. In general you flash will fire under 1/1000 so most of the time the shutter isn't involved. Pick a shutter speed that you can handhold (for example) and adjust your f-stop until you have a fairly even histogram without any clipping (spikes to the top).

I hope that makes sense.

Jeremy Z · Mar 8, 2010

Anthony, you're right about aperture controlling the exposure with flash shots. Flash duration is also a factor, but it is usually much, much shorter duration than the shutter speeds we use. 1/10,000 sec. is not uncommon. Flash duration is controlled either by metering Modern SLRs meter through the lens or TTL, older flashes either measure the light with a thyristor built into the flash or just give full duration flash and force us to adjust aperture appropriately.

One question Anthony, what did you mean when you said: "In general you flash will fire under 1/1000 so most of the time the shutter isn't involved." Did you mean "longer than 1/1000 sec."?

maman · Mar 9, 2010

AnthonyS said:
Congratulations on trying some new lighting. I would suggest getting used to manual mode, its not as bad as you may think. With digital you have the screen on the back, and a histogram. The center of your histogram is your neutral exposure and its divided into f-stops so you adjust from there.
When I was giving a workshop I noticed that new photographers didn't realize when shooting flash you shutter speed is really only able to control ambient light. Aperture controls the flash exposure. In general you flash will fire under 1/1000 so most of the time the shutter isn't involved. Pick a shutter speed that you can handhold (for example) and adjust your f-stop until you have a fairly even histogram without any clipping (spikes to the top).

I hope that makes sense.

That does make sense AnthonyS. I never use my histogram while I'm shooting - I guess I'm missing using a valuable resource! I will look into that more.

Thanks for all the other comments too, I really apprecaite your ideas, guys! Just a quick question though...

Is anyone familiar with the digi slave 3000 deluxe flash? And if so, can anyone tell me if I can use if off camera, as my main light source, using a wireless trigger,thereby doing away altogether with my pop-up flash?

Thanks.