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06-17-2010, 06:43 AM   #1
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Why would the flash change the speed?

Ok, maybe I didn't phrase that right. I was practicing taking pictures yesterday. I sat out on the back porch and took pictures of the ceiling fan to see abut stopping motion, capturing motion, etc.. In one shot, the fan blades are just a blur-which is what I wanted. The second shot is shot exactly the same, only I used the flash-the pop up button on the camera. Why does the 2nd shot look still while the first one is moving? Here are the specifics:
kit lens=15-55mm focal length-35.0mm-exp. 1/20-aper.f/4.5-ISO200. First one no flash, 2nd one flash.

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06-17-2010, 07:01 AM   #2
Ira
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What mode were you in?

You see, once the camera "knew" that the flash was on, it adjusted its other parameters--shutter speed and aperture--to properly expose the scene. So your aperture gets small, and the scene is captured by the high speed burst of the flash.

In other words, the ambient light was no longer the major player in proper exposure, it was the FLASH, and since the flash burst is so lightning quick, it froze the action.

There are flash techniques where you can have your cake and eat it too, but it's a little hard to explain here. Also, I don't know how to correctly explain them.

For example, if you were in shutter priority mode, you could have selected a slower shutter speed, allowing the ambient light to be more of a factor, and you would get more blur.
06-17-2010, 07:05 AM   #3
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that's what the flash does, it freezes the shot.
slower shutter speed means more time the film/sensor is exposed to incoming light, that's why when a movement happens in that period of time it appears on the photo. when flash is used it will freeze the moment that the flash fires and most of the time the rest of incoming light will have very little effect on the picture taken because the flash light is much more dominant.

I hope it makes sense to you, english is not my first language
06-17-2010, 07:10 AM   #4
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So are you turning into a total geek yet like the rest of us? It's FUN!

And kudos for what you're doing:

You'll learn an awful lot quickly the way you're testing like this.

06-17-2010, 08:00 AM   #5
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The flash on your camera (K-x?), has a duration of, at most, about 1/1000 second. That is fast enough to stop the motion of the fan blades.

However, the flash duration is variable. That's how the camera controls exposure when using flash. When the primary subject is close to the camera (along with some other factors, such as ISO), the flash duration may be as fast as 1/30,000 second or even faster. I'm not sure of the exact speeds for the K-x.

In the simplest case, ambient light has little or no effect on exposure when the flash is used. Exposure is controlled only by the light from the flash. As someone else posted, there are techniques that allow you to combine ambient light with flash, but when you simply pop the builtin flash up and shoot, that is probably not the case.

One other fact that you should be aware of when using any flash on your camera. On Pentax dslrs, the fastest shutter speed you can use when using flash, is 1/180 second. The reason for this has to do with the way a focal plane shutter works. The shutter is actually two shutters, a leading and a trailing shutter. When the shutter opens, the leading shutter opens, while the trailing shutter remains behind. When it is time to cut off the exposure, the trailing shutter closes. At speeds of 1/180 or slower, there is a period of time during which the entire frame is exposed. At faster shutter speeds, the trailing shutter begins closing before the leading shutter is completely open, resulting in a moving slit that travels across the frame (vertically in a Pentax dslr, some older film cameras travelled horizontally). Since the flash duration is so fast, it must be triggered while the entire frame is open and that, on a Pentax dslr, is only at 1/180 second or slower. This is referred to as the maximum sync speed, or simply the sync speed.

With some (usually expensive) external flash units, you can use a technique called High-Speed Sync (HSS), which allows you to use faster shutter speeds. In this mode, the flash fires several times, as the shutter slit travels across the frame. Interestingly, this mode is less able to stop very fast motion than normal flash mode is. This is because, in HSS mode, the camera's shutter controls the motion stopping ability. A shutter speed of 1/250 or 1/500 may not be fast enough to stop very fast motion. The builtin flash does NOT support HSS.

As you are perhaps beginning to realize, flash photography can be a very complex subject by itself.

Last edited by noblepa; 06-18-2010 at 06:54 AM.
06-17-2010, 09:14 AM   #6
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QuoteOriginally posted by noblepa Quote

As you are perhaps beginning to realize, flash photography can be a very complex subject by itself.
You said a mouthful, but your explanation was really good. I don't understand 90% of this stuff.

Flash frightens me.
06-17-2010, 12:17 PM   #7
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I was using shutter priority mode. I understand now what the deal is. Pablom, your English is fine-I understand what you are saying. Paul, flash photography does seem complicated, but I honestly don't plan on using the flash that much. I have the flash off on the menu, and just decided to use the pop up on a whim yesterday.
Ira, I've always been kind of a camera geek. I could almost shoot my K-1000 in my sleep and knew how many clicks it took on the dial to get to the setting I wanted. This digital stuff has a steeper learning curve. LOL! I learn by practicing, so I may be asking more "what did I do" questions. My husband's comment when I showed him the pictures-"that fan really doesn't look that dirty just standing under it". LOL!
Thanks for the help, everybody.
06-17-2010, 12:18 PM   #8
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QuoteOriginally posted by Ira Quote
You said a mouthful, but your explanation was really good. I don't understand 90% of this stuff.

Flash frightens me.
The duration of a camera flash even at full power is about 1/1000 of a second and can be much shorter. It will freeze almost any motion. It does not change shutter speed but because the flash dominates in the exposure(usually) it freezes the image. If you set flash to only be fill and the natural exposure ( combination of shutter speed and aperture is only about 1/2 a a stop under exposed, and you have a slow shutter speed you cam get a combination of motion blurr and frozen image

06-17-2010, 12:23 PM   #9
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QuoteOriginally posted by subeeds Quote
.
Ira, I've always been kind of a camera geek. I could almost shoot my K-1000 in my sleep and knew how many clicks it took on the dial to get to the setting I wanted.
This digital stuff has a steeper learning curve.
There's a lot more stuff you *can* control, but no one ever said you have to mess with it. Put the camera in M mode and it's essentially the same as your K1000, except you set the aperture using a dial rather than the aperture ring.
06-17-2010, 12:35 PM   #10
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Messing with the new stuff is half the fun, Marc. The purpose of my getting this camera was two-fold. One, I make and sell jewelry online and wanted to have better pictures.2 I have really, really missed having a 35mm camera. Living in the woods like we do, we have a lot of endangered species around (gopher tortise, bobcats, birds and the occaisional Fl. panther) and I want to be able to get shots of them. That's not something my little HP p&s does well.
06-17-2010, 04:00 PM   #11
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QuoteOriginally posted by subeeds Quote
Living in the woods like we do, we have a lot of endangered species around (gopher tortise, bobcats, birds and the occaisional Fl. panther) and I want to be able to get shots of them. That's not something my little HP p&s does well.
If you can get a good shot of a Florida Panther, that will make the purchase of your camera worthwhile. I've lived in Florida since 1969 and have only seen one back in the early 70's. But then that's one more than most people ever see in the wild.

CW
06-17-2010, 04:17 PM   #12
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Well, hey there "almost neighbor" straightshooter. We've had two panthers in the last 8 years. The first one I saw in the yard twice and saw her tracks in the driveway numerous times. She was around several weeks before DNR got her and took her back to the Ocala Nat'. Forest-she was part of that release program. She was such a gorgeous golden color. The second one, we just saw the tracks around-out by the pen where we used to have pheasants. Apparently it decided to move on since we didn't have any take out handy. LOL!
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