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Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 04:45 PM   #1 (permalink)
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I'm going to ask what to many might be a basic question, but I am stumped on this one. I have a Sekonic L-358 light meter and some cheap starter lights I bought off eBay. I put the lights in position and set them to their lowest setting. I then set the meter to "cordless flash mode" with the shutter speed set to 125. I fired the lights using the infared transmitter included with the lights and took a reading. It came back f6.3. No problem there. I put the camera in manual mode, dialed in the numbers and starting taking some pictures. The pictures look pretty good and don't need much in the way of correction.

For fun, I thought I would take some pictures at f2.8 to see if I could get a greater depth of field. I can't set the lights any lower, so I thought I would just increase the shutter speed to something like 640 on the meter and measure the f stop at that shutter speed. Problem is, the meter always says f6.3, regardless of the shutter setting.

I then call Sekonic to see if maybe it is something I am doing wrong with the meter. They tell me the shutter speed doesn't matter. Only the fstop value does. You measure the amount of light produced by the studio lights and set the camera to that value. The shutter speed has no affect. If you want greater depth of field (i.e. f2.8), you need to adjust the lights down to a lower setting, not the shutter speed.

Thinking I misunderstood, I set the camera to f6.3 as metered and took several pictures at shutter speeds ranging from 50 to 640. I looked a the pictures in Photoshop and don't really see a difference in the exposure. I thought for sure the shutter speed of 50 would cause the pictures to be totally blown out.
My questions ... Does shutter speed mater when using studio lights? If not, why? Does the camera ignore shutter speed when something is attached to the hot shoe?

Thanks in advance!

Earl
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Re: Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 04:53 PM   #2 (permalink)
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When you use strobes, your strobe *is* your shutter. Most of the time, the light from the strobes is so much more powerful than ambient that it doesn't matter what you set your shutter to: ambient won't have any impact on the exposure. That's why most cameras default to 1/60 when the flash is engaged.

Unless ambient is REALLY bright, you won't notice it "blowing out" strobe pics. Try taking a picture at the same settings with the flash disconnected. That will give you an idea of how much ambient is contributing to exposure. (Usually, not much. Under most circumstances if you're correctly set to expose for strobe light you will get a nearly black frame if the strobe doesn't fire.) f2.8 at 1/50, even at ISO100, is quite a bit of light in, say, direct sunlight, but under modeling lamps (which is all the illumination there is in my studio when I'm using strobes most of the time) it's not a lot.

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Re: Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 05:08 PM   #3 (permalink)
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You are using flash (often referred to as "strobe"). These lights emit a strong pulse of light that lasts for a VERY short time. On some high end strobes it may be less than 1/10000 second. That's the key thing you haven't grasped, I think.

You fire a shot at 1/200 second, and the pulse happens during that time, and the image is correctly exposed. You change your exposure to 1/60 second, and the pulse happens during that time, and the image is correctly exposed, and exactly the same as 1/200 second. The extra time the shutter was open makes no difference (well, the background light gets more time, but that's usually negligible by comparison to the vast amount of light from the pulse).

That's why the shutter speed is (almost) irrelevant. Does that help you understand? That's why you can only control flash exposure using aperture and ISO.

Now why did I say "almost" irrelevant? There are two reasons:

1. background light - if there's enough background light, the shutter speed will affect how much of that you see in the picture. Have a Google for "dragging the shutter" and "second curtain sync".

2. flash sync and shutter curtains - to take the picture properly, the entire sensor must be revealed when the flash pulse happens. The shutter (on lots of cameras) consists of two curtains, and the shutter speed is a measure of how far apart the two curtains are. At slowish shutter speeds, the first curtain opens, the entire sensor is revealed (flash!), then the second curtain closes, and the image is captured. At higher speeds, the curtains travel some small distance apart, and there is no time at which the entire sensor is revealed - what is revealed is a moving band across the sensor. If you try talking a flash picture with, say, 1/2000 second shutter speed, you'll find a sliver of the image properly exposed, and the rest dark - the sliver will be the portion of the sensor that was revealed when the flash pulse arrived. That's why each camera has a quoted "flash sync speed" - it is the fastest shutter speed for which the entire sensor is revealed at once - any faster and you'll start to see the "sliver" effect.

That's not the greatest explanation ever, but at least you can go Googling for sync speed, and shutter curtains, and find out the rest.

Hope that helps.
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Re: Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 05:25 PM   #4 (permalink)
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Thank you! (both of you) I understand now and it makes sense. I had taken a picture at 1/1000, but didn't mention that in the original post. I could not figure out why part of the picture was exposed and part wasn't. Didn't want to ask two dumb (basic?) questions in one post. You answered that second question without even realizing it.

Thanks!!!!!!!

Earl
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Re: Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 06:54 PM   #5 (permalink)
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Two things came to my mind in reading this post.
First, the guys that responded to you are completely correct and it would seem they have solved your issues in regards to shutter speed and flash-synch.
This may, or may not, help you to understand what they've already pointed out;
If you were in a completely dark room...no ambient light whatsoever....you could take a photo with flash and your shutter speed could be set to 1/125th of a second or it could be set to 5 hours and it wouldn't make a bit of difference in the exposure.
Second, and something that hasn't been addressed yet, you mention that you started out shooting at an aperture of 6.3 and you took some photos. Then you say that you set the aperture to 2.8 becuase you wanted more depth of field.
I'm not sure but maybe you meant to say "less" depth of field?
A larger aperture (and 2.8 is much larger then 6.3...the lower the number the larger the opening) will give you LESS depth of field.
Dean
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Re: Cordless Flash Mode and Shutter Speed
Old 06-02-2006, 07:54 PM   #6 (permalink)
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Dean,
Thanks to you as well! Before reading the three replies, I had no idea that "you could take a photo with flash and your shutter speed could be set to 1/125th of a second or it could be set to 5 hours and it wouldn't make a bit of difference in the exposure." I assumed that it would be the same as taking a picture outside with no flash. Play with shutter speed and aperture to increase the amount of light thereby making the picture "lighter" or "darker". The explanations provided in this post certainly make it clearer.

As far as depth of field goes ... yea .. .that's what I meant. Like most newbies, I understand in my head what I was trying to accomplish, but getting the right terminology for things like greater/less depth of field, open/close the aperture, increase/decrease the f stop is not always easy to keep straight. Thanks for taking the time to explain it better!!!!!! Maybe if I read it 20 more times I will finally get it right.
Earl
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Re: Cordless Flash Mode and Shutter Speed
Old 06-03-2006, 06:01 AM   #7 (permalink)
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Glad to be able to help.

We all start knowing exactly the same amount about photography - absolutely nothing

Some of us try to learn: by asking questions, by Googling and reading, by taking photos and working what went wrong. Never be ashamed of asking a question - it's sometimes the only way to work out what you don't understand.

Some people don't try to learn. I think they are the ones who get labelled GWC
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Re: Cordless Flash Mode and Shutter Speed
Old 06-03-2006, 08:12 AM   #8 (permalink)
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Quote:
Originally Posted by Earl_B
Dean,
Thanks to you as well! Before reading the three replies, I had no idea that "you could take a photo with flash and your shutter speed could be set to 1/125th of a second or it could be set to 5 hours and it wouldn't make a bit of difference in the exposure." I assumed that it would be the same as taking a picture outside with no flash. Play with shutter speed and aperture to increase the amount of light thereby making the picture "lighter" or "darker". The explanations provided in this post certainly make it clearer.
As far as depth of field goes ... yea .. .that's what I meant. Like most newbies, I understand in my head what I was trying to accomplish, but getting the right terminology for things like greater/less depth of field, open/close the aperture, increase/decrease the f stop is not always easy to keep straight. Thanks for taking the time to explain it better!!!!!! Maybe if I read it 20 more times I will finally get it right.
Earl
You're very welcome. Forums like this can be very helpful..keep asking questions...evenually things will fall into place.
Dean
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Re: Cordless Flash Mode and Shutter Speed
Old 06-03-2006, 03:11 PM   #9 (permalink)
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While not a pro with the studio lighting thingie , the shutter speed won't change the 'subject' but SHOULD have an affect on the background if far enough away from the subject ( assuming there is room lights on- not totally in the dark untill strobes go off )

Also you mentioned depth of field issue , if you can lot lower lights any more , there are 3 options to try

#1 - Diffuse the lights behind some netting/ white sheet/ gels
#2 - Move the lights back farther from the model
#3 - try just using the modeling lights ( might have to move the lights closer ) also might not work at all , depends on how bright the modeling lights ( do the E-bay lights even have modeling lights )
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Re: Cordless Flash Mode and Shutter Speed
Old 06-03-2006, 04:00 PM   #10 (permalink)
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StanTom,

Good suggestions. I do have a 5 in 1 reflector that has a white diffuser as the base. I will move the lights back and try the diffuser to see what affect that has.

And Yes ... the eBay lights I bought do have modeling lights, but they are not very bright.

Thanks again!

Earl
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