Strobe issue... - DPChallenge Forums

12/21/2006 12:46:58 PM · #1

I am new to using multiple strobes and think I might have had a problem similar to what was recently posted by Jason (theSaj). The problem was that his on-camera pre-flash was setting off the slave strobe.

Here is a description of my setup:
I had a 430EX set as slave (Channel 1 B)mounted on a stand about 5 feet and 45 degrees from subject. It had a small diffuser on it. The head was pointing directly at the subject but the IR window was pointed at the master flash.
I had a 580 mounted on the camera and set to master (Channel 1 A). I used a 1:3 A:B ratio so that the on-camera flash would fill and the off-camera flash would light. I was standing about five feet from the subject (all the room I had).

I was using the canon 50mm 1.8 II

Like Jason, I couldnâ��t get a fast enough shutter speed. I was photographing a child and needed more speed to stop the constant fidgeting. I was only able to obtain very slow shutter speeds (not even close to sync max).

Both flashes were certainly firing and I had plenty of light in the room.

Is it possible that the 580 pre-flash was setting off the 430? I certainly hope not â�� I have spent a bit of money for this setupâ�¦

I did manage to get the shot belowâ�¦ but I had to add some monolights to the room. I shouldn't have needed them.

fotomann_forever

12/21/2006 01:40:43 PM · #2

I wish I knew enough about new flashes and e-ttl to give ya an answer. Consider this a bump.

12/21/2006 01:56:41 PM · #3

Were you shooting in manual mode on the camera? You should be able to dial in up to 1/250 with no problems, and even higher if you set the flashes to high speed sync.

12/21/2006 02:00:19 PM · #4

Originally posted by santaspores:

When using the IR syncing on Canon flashes, they ignore the pre-flash.

The meter in the camera will indicate the correct exposure for ONLY the ambient light. Try this: Set your camera to M, set the shutter speed to 1/200 (or your max sync speed) and then set your aperture to something like f5.6 or f8. The E-TTL should do the rest, providing you have the flash units setup right.

The only time you would need a slower shutter speed when taking flash pictures is if you need/want the ambient light to be a significant part of your exposure.

What stops motion with a flash exposure is the brief duration of the light from the flash, not the shutter speed. If there is no ambient light, it is entirely possible to freeze motion using flash while keeping the shutter open for several seconds.

12/21/2006 02:16:41 PM · #5

Sorry guys â�� I posted and then got called from my deskâ�¦

Marc â�� I was shooting in Manual mode. And I could dial in fast exposuresâ�¦ but the meter was only showing proper exposure only when I used slow shutter speeds. Am I supposed to ignore what the exposure meter is telling me and just review my histogram?

Spaz,

Thanks for that bit of info. And I am happy to hear that my slave ignores preflash â�� I was pretty sure that it wasnâ��t supposed to be a problem with this setup. It is my understanding that with flash photography, the aperture is set to expose the subject and to control dof. If I am shooting portraits and want to get a shallow depth of field shouldnâ��t I open up the aperture â�� and shouldnâ��t my E-TTL system set the proper flash strength? Do I actually have to move main (slave) flash further away or something?

I still donâ��t understand why that setup was showing under exposure on the meter when I used faster shutter speeds. And the slower shutter speeds were in fact causing blurry pictures. Everything seems to point to having not enough lightâ�¦ but of course I had plenty with those two strobesâ�¦

What am I missing hereâ�¦

12/21/2006 02:28:12 PM · #6

Originally posted by santaspores:

Am I supposed to ignore what the exposure meter is telling me and just review my histogram?

Bingo!

As I said, the meter ONLY reads the ambient light, so the fact that it tell you you're underexposing is OK.

And you can set whatever f stop you want, the E-TTL should adjust.

12/21/2006 02:28:34 PM · #7

Spaz,

The meter in the camera will indicate the correct exposure for ONLY the ambient light.

Are you saying that when I am using both of the flash units, that I should set my desired aperture and shutter speed and ignore what the meter is telling me about exposure?

12/21/2006 02:32:28 PM · #8

Originally posted by santaspores:

YES!

12/21/2006 02:44:46 PM · #9

Thanks Spaz - That information really helps - I didn't realize that the meter was only evaluating ambient - that makes perfect sense.

What do you suppose was causing the motion blur? The two flashes and the tripod should have been sufficient to stop the small bits of motion.

By the way... my last post was written before I saw your reply - sorry you answered the same question twice.

12/21/2006 02:48:12 PM · #10

Sorry I didn't respond, I was in another thread. Ya, that threw me off too when I first saw that on my camera. Good call.

Message edited by author 2006-12-21 14:48:51.

12/21/2006 02:54:15 PM · #11

Originally posted by santaspores:

What do you suppose was causing the motion blur? The two flashes and the tripod should have been sufficient to stop the small bits of motion.

If you were exposing for ambiant light and thus the slow shutter speed, you'd still get motion blur if the subject moved despite the flashes going off because the ambiant light was lighting the subject enough to show it. -bad wording, hope that makes sense.

Canon EF 70-200mm f/2.8L IS USM

12/21/2006 02:57:27 PM · #12

Perfect sense. The bottom line is... dial the shutter to whatever speed you need in order to stop motion. The camera meter may very well tell you that you are about to under-expose the image - but it is dead wrong. The Canon E-TTL II flash system will come through for you and properly expose the image.

If that isn't right - please correct me again.

Message edited by author 2006-12-21 15:08:45.

theSaj

Canon EOS-20D

12/21/2006 03:19:50 PM · #13

However, as I learned, it's very important for everything to be synching right.

The problem I had was that flashes were out of synch. So if I did anything higher than 1/5th a second exposure I got a black image.

So raise the exposure to like 1/250th and if you get a black image then it is likely a sync issue. But with multiple flashes you will likely want to shoot in manual.

Isn't it so nice to have that viewscreen on a digital. I'd have nothing but tossed away film rolls otherwise. *lol*

Makes you understand how studios were more than mere backdrops for film but rather were environments to help keep a stable exposure.

:)

12/21/2006 03:30:53 PM · #14

The key is if you aren't doing anything creative with ambiant light (like including a sunset or something), keep your shutter speed up, usually 1/125 or more and the flashes will "freeze" the subject.

12/21/2006 03:34:39 PM · #15

Yup - I think I got it now. Thanks everyone!

DjFenzl

12/21/2006 03:49:05 PM · #16

Originally posted by santaspores:

Almost right. Your shutter speed doesn't affect stopping motion in anything but ambient light. You could stop motion with a 30+ second shutter speed if there was no ambient light.

Think of it this way, your shutter speed controls how much ambient light there will be and your aperture controls how much flash light there will be.

years ago a friend and I went to an old mining cave where it was literally pitch black and we set the camera up for a long exposure. We then would flash our selves(yea, I get the joke, har har) at various positions farther and farther away from the camera. It came out pretty cool with what appeared to be ghostly apparitions down the tunnel.

violinist123

Canon EOS-6D

12/21/2006 04:00:35 PM · #17

Originally posted by Megatherian:

Your shutter speed doesn't affect stopping motion in anything but ambient light. You could stop motion with a 30+ second shutter speed if there was no ambient light.

Maybe you're trying to say something else. This makes no sense at all and is completely inaccurate. Stopping motion is limiting the amount of distance an object travels from the instant the shutter opens till it snaps shut again so that it appears to be frozen. Good luck doing that with a 30 second exposure.

candlerain

Canon EOS-30D

12/21/2006 04:02:19 PM · #18

If it is pitch-black, even if there is motion, you won't see it!

DjFenzl

12/21/2006 04:06:02 PM · #19

Originally posted by routerguy666:

Originally posted by Megatherian:
Your shutter speed doesn't affect stopping motion in anything but ambient light. You could stop motion with a 30+ second shutter speed if there was no ambient light.

Maybe you're trying to say something else. This makes no sense at all and is completely inaccurate. Stopping motion is limiting the amount of distance an object travels from the instant the shutter opens till it snaps shut again so that it appears to be frozen. Good luck doing that with a 30 second exposure.

no,I said what I meant and it's true. Try it out. With no ambient light your exposure effectively becomes the speed of the flash - so in a completely dark room your exposure could easily be 1/25,000 of a second.

violinist123

Canon EOS-6D

12/21/2006 04:08:43 PM · #20

Originally posted by Megatherian:

Originally posted by routerguy666:

Originally posted by Megatherian:
Your shutter speed doesn't affect stopping motion in anything but ambient light. You could stop motion with a 30+ second shutter speed if there was no ambient light.

Maybe you're trying to say something else. This makes no sense at all and is completely inaccurate. Stopping motion is limiting the amount of distance an object travels from the instant the shutter opens till it snaps shut again so that it appears to be frozen. Good luck doing that with a 30 second exposure.

no,I said what I meant and it's true. Try it out. With no ambient light your exposure effectively becomes the speed of the flash - so in a completely dark room your exposure could easily be 1/25,000 of a second.

I think I get what you're saying. I guess it is a useful bit of knowledge, but for practical purposes people aren't shooting in the dark so it is good that people keep in mind 'shutter speed stops motion'.

12/21/2006 04:20:35 PM · #21

Originally posted by routerguy666:

Originally posted by Megatherian:

Originally posted by routerguy666:

Originally posted by Megatherian:
Your shutter speed doesn't affect stopping motion in anything but ambient light. You could stop motion with a 30+ second shutter speed if there was no ambient light.

Maybe you're trying to say something else. This makes no sense at all and is completely inaccurate. Stopping motion is limiting the amount of distance an object travels from the instant the shutter opens till it snaps shut again so that it appears to be frozen. Good luck doing that with a 30 second exposure.

no,I said what I meant and it's true. Try it out. With no ambient light your exposure effectively becomes the speed of the flash - so in a completely dark room your exposure could easily be 1/25,000 of a second.

I think I get what you're saying. I guess it is a useful bit of knowledge, but for practical purposes people aren't shooting in the dark so it is good that people keep in mind 'shutter speed stops motion'.

When I was doing product shots, it was not uncommon to need to shoot at f64 or even f128 to get adequate DOF after all the perspective corrections. Even with a 2400WS pack, it was frequently not possible to get enough light, so we'd black out the studio and open the shutter on "B" and simply fire the strobes multiple times to get the exposure necessary.

So yes, there are people shooting in the dark for practical purposes.

12/21/2006 04:24:22 PM · #22

f64-f128 - And I feel giddy when I hit the 20s!

violinist123

Canon EOS-6D