Technical questions about Shutter and Aperture


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tokrot

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Jun 2, 2003
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#1
Hi Guys,

Got a question. I just took a pic with 3"s with Aperture F11 with an external flash using handheld. Surprisingly, the pic turn out to be very sharp.

I did a test again with a serious handshake and amazingly the shot taken was again sharp.

My question is

1) Is the shutter opened for 3sec to absorb the light to balance the exposure?

If 1) holds truth, how do you guys explain the sharp pic with handshake/handheld ? :think:
 

nickmak

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Apr 16, 2004
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#2
tokrot said:
Hi Guys,

Got a question. I just took a pic with 3"s with Aperture F11 with an external flash using handheld. Surprisingly, the pic turn out to be very sharp.

I did a test again with a serious handshake and amazingly the shot taken was again sharp.

My question is

1) Is the shutter opened for 3sec to absorb the light to balance the exposure?

If 1) holds truth, how do you guys explain the sharp pic with handshake/handheld ? :think:
Did you take the picture in an extremely dark place? If its that, then the flash is the only available light that the sensor can capture and it won't capture anymore light because there's just not enough... Try this then: With the same settings, press the shutter but right after the flash has burst, move the camera away from the subject and see what happens... If its really really dark then it should still be sharp...
 

AReality

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Jun 9, 2003
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#3
The larger the aperature number (in this case is f/11), the larger the DOF, thus pics will be sharper.

The flash help to freeze the moment when it fired. Thus U don't see any handshake. Assume u took the pics in a dark environment. In bright environment, U'll be able to notice the handshake.
 

scott

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Oct 14, 2004
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#4
tokrot said:
Hi Guys,

Got a question. I just took a pic with 3"s with Aperture F11 with an external flash using handheld. Surprisingly, the pic turn out to be very sharp.

I did a test again with a serious handshake and amazingly the shot taken was again sharp.

My question is

1) Is the shutter opened for 3sec to absorb the light to balance the exposure?

If 1) holds truth, how do you guys explain the sharp pic with handshake/handheld ? :think:
the shutter speed of camera only determines the ambient (background), not the object that's exposed with the flash.
 

AReality

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#5
Usually in a dark environment, your subject will be darker than the surroundings.
Thus, u need to use flash to brighten your subject. However, the flash is not strong enough to brighten the whole background. Thus, by using a slow shutter speed, the background can be properly exposed. Your subject remains sharp coz the moment is frozen by the flash. (Then your subject becomes dark again for the rest of the 3 secs, & no light is recorded from your subject.)
 

tokrot

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Jun 2, 2003
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#6
nickmak said:
Did you take the picture in an extremely dark place? If its that, then the flash is the only available light that the sensor can capture and it won't capture anymore light because there's just not enough... Try this then: With the same settings, press the shutter but right after the flash has burst, move the camera away from the subject and see what happens... If its really really dark then it should still be sharp...
No, I still had the room lights on. After the flash, I moved my camera away and the output pic was still very sharp but there's a tiny blue strip of light around the object which I supposed simulated my movement of the camera. Thanks for replying..
 

tokrot

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Jun 2, 2003
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#7
AReality said:
The larger the aperature number (in this case is f/11), the larger the DOF, thus pics will be sharper.

The flash help to freeze the moment when it fired. Thus U don't see any handshake. Assume u took the pics in a dark environment. In bright environment, U'll be able to notice the handshake.
So am I right to say that since my external flash has no control over the aperture/shutter function on my camera regardless of what my shutter speed setting, the photos were taken at the mininal setting of flash? eg 1/125ms?
I am going to try that in the morning again. Thanks..
 

tokrot

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Jun 2, 2003
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#8
scott said:
the shutter speed of camera only determines the ambient (background), not the object that's exposed with the flash.
errr... dun get it.. sorry... :dunno: But thanks anyway...
 

tokrot

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Jun 2, 2003
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#9
AReality said:
Usually in a dark environment, your subject will be darker than the surroundings.
Thus, u need to use flash to brighten your subject. However, the flash is not strong enough to brighten the whole background. Thus, by using a slow shutter speed, the background can be properly exposed. Your subject remains sharp coz the moment is frozen by the flash. (Then your subject becomes dark again for the rest of the 3 secs, & no light is recorded from your subject.)

Understood what u trying to say.. I have taken the object without flash (3 sec shutter and F11 aperture too) it turned out blur too. But in this case with ext flash, the image should be blurred too since it still absorbed light for next 3 secs. :dunno:
 

Feb 3, 2002
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#10
Your effective shutter speed becomes that of the flash duration when ambient light levels are low. i.e. if ur flash fires for 1/500s, that is effectively the shutter speed that ur subject (in this case) was exposed at. Understand?
 

tokrot

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Jun 2, 2003
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#11
imaginary_number said:
Your effective shutter speed becomes that of the flash duration when ambient light levels are low. i.e. if ur flash fires for 1/500s, that is effectively the shutter speed that ur subject (in this case) was exposed at. Understand?
so how do you explain the light trails? Isn't the shutter still open during the 3 secs exposure? Thanks.
 

Feb 3, 2002
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#12
tokrot said:
so how do you explain the light trails? Isn't the shutter still open during the 3 secs exposure? Thanks.
Yes, the shutter is still open during the 3s - this explains the light trails. But for the object/areas which appeared sharp, they were illuminated during the flash duration (e.g. 1/500s) and that was the effective exposure for these areas.
 

tokrot

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Jun 2, 2003
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#13
imaginary_number said:
Yes, the shutter is still open during the 3s - this explains the light trails. But for the object/areas which appeared sharp, they were illuminated during the flash duration (e.g. 1/500s) and that was the effective exposure for these areas.
So go by your explaination, am I right to say that most of the image were taken (freezed) during the flashing duration, however the next 3 secs exposure does not warrant enough light to make it blur enough? That probably explains why there are only slight light trails. If this object is taken during daylight, the object would be blurred like what nickmak/AReality described? Thanks...
 

Feb 3, 2002
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#14
tokrot said:
So go by your explaination, am I right to say that most of the image were taken (freezed) during the flashing duration, however the next 3 secs exposure does not warrant enough light to make it blur enough? That probably explains why there are only slight light trails. If this object is taken during daylight, the object would be blurred like what nickmak described? Thanks...
Yes, you could put it that way.

If u want to, u could experiment taking a shot in complete darkness (switch off ur lights, close your windows, etc.) with your shutter speed set to 3s or something. Then you'll see that your flash effectively "freezes" the subject (even if the subject is moving).
 

AReality

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Jun 9, 2003
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#15
Example will be better...


1sec, f/4, ISO800

Look at the above shot.
In the ambient lighting, the subjects will be very dark (not illuminated by any light).
Flash is used to light up the subjects.
In that instant the flash brightens the subject, the light from the subject is recorded.
However, the flash is not bright enough to reach the buildings.
Thus, for the rest of the 1 second, the sensor takes in the ambient light from the building. (Remember that the subject is dark, so no light coming from subject.)
But if U look at the buildings, U can see some serious handshake.

This type of technique is called Slow-sync flash. The shutter speed is slow, & flash is used to freeze the moment, while the long shutter speed accounts for the capturing of the background.
 

reachme2003

Senior Member
Oct 6, 2003
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#16
it will help if you post your pics and provide your equipment used and technical info, including lens, autofocus settings and other pertinent details. otherwise, we are trying to determine your problem when details are scanty. much like a doctor trying to diagnose a patient's illness when the patient is unable or not clear about his symptons. so, the doctor started ordering many tests to narrow down his diagnoses.
 

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