off camera confusion

[bulldog413]

Hey gang,
I have a little question that I don't seem to fully understand how to handle. I usually get what I want (in re: to this question), but that's after ignoring what seems to be the most important part... okay... here it is...

Here's the scenario: I'm setting up an off camera flash. But I decide to meter first. I set my camera to let's say, F5.6 in Aperture mode. Let's say the reading says that the shutter speed would need to be 1/15. I set up my flash. Now I have several options for output.... if I only wanted to dial down the ambient by a stop or two, do I only bump up the speed (in Manual) to 1/30? I feel like I'm usually wrong when figuring out how to dial down a stop or two and like I said, I usually find it, but it's never what I think it should be. Or worse, what do I do if the speed is even slower? I get that speed affects ambiant, but like I said, when it drops below 1/50, I'm at a loss.

Can someone school me on how to master this without wasting time dialing til I get it right?
Thanks.

[zona5101]

you essentially have it. You have metered at 1/15@5.6 and have set your flash to some setting that works with the 5.6. You want to darken the ambient light you would increase the shutter speed to 1/30. the ambient would be one stop darker. You can continue on that path all the way up to your max flash sync speed and each increase in shutter will darken the ambient. You will effect the flash lit part too but it will not be as dramatic a change as what you will see in the non flash lit areas...

[bulldog413]

Thanks Zona... so here would be my next question: wouldn't 1/15 and even 1/30 (actually 1/30 with the 7D works pretty well) still too risky considering shake? I guess I'm just afraid of that speed and lower, so I shut it out...

[zona5101]

Originally Posted by bulldog413

Thanks Zona... so here would be my next question: wouldn't 1/15 and even 1/30 (actually 1/30 with the 7D works pretty well) still too risky considering shake? I guess I'm just afraid of that speed and lower, so I shut it out...

camera shake - ya sure you need to consider that-a function of your ability, your focal length chosen.
Some people can hand hold 1/15 with short focal lengths...i'd opt for a tripod or push the iso up...

[Dajuan]

It sounds like you're using your camera to measure the ambient light, with camera set to aperture priority mode? Is your lens a variable aperture lens with f/5.6 its widest aperture at the focal length you desire? If so, bumping your ISO would bring your shutter speeds in more desirable level if you want to eliminate camera shake while hand holding.

If you don't need the depth of field f/5.6 provides and have a faster lens, you could widen your aperture which would also increase your shutter speed w/o raising your ISO.

Many ways to solve exposure challenges. Good thing is that we get to choose the one which best works for us individually.

[JFSanders]

The flash will freeze the subject. As the flash exposure is a very small slice (typically 1/1000 to 1/200) of the 1/30 shutter speed. If your camera has a rear curtain flash mode, use it and I think you will be pretty happy.

[bulldog413]

I usually use Aperture Priority just to get a reading, then back to manual. I do have use a 50 1.4, but that's not always the best lens for the situation. Until recently (I just got your reply), I would forget to bump up the ISO, and since I'm now using the 7D, I have little fear about noise. So in such a situation, would you try to bump up the ISO to get to a reading that would register the speed in a more manageable speed (say around the 1/60-80 range) ? Or would I still be safe if, let's say I continued to keep the speed around 1/30, if that's what the reading gave me?

As far as rear curtain, I recently fell upon a tip for using it especially for night time w/flash. Would I have more success using rear curtain all the time?
Thanks

[JFSanders]

I generally stick with rear curtain flash as it gives me less headaches. I shoot a lot of moving things and as such I need the blur if I get one to be in the correct direction. By doing so the blur always follows the subject. I try to use the lowest ISO I can get away with but in such a situation as yours and with the 7D it really isn't a problem to bump it up. So go for it if doing so makes for less headaches for you. In my experience less headaches is a priority.