Flash duration of 580EX and shutter speed

[telles75]

I read on this website http://www.waynesthisandthat.com/flashdurations.html (http://www.waynesthisandthat.com/flashdurations.html)
that the estimated flash duration for each power setting of a 580EX are:

1/16 power = 1/15,000 second
1/32 power = 1/19,000 second
1/64 power = 1/31,000 second
1/128 power = 1/35,000 second

According to what I read so far, shutter speed does not affect the lighting of the subject by the flash, only the ambient light. Does this means that in a perfectly dark room (0 lux) if I shoot someone jumping using manual focus, the speed of the shutter should not matter at all to capture the action? So if I use 1/5 shutter speed should be exactly the same as using 1/250 (max sync speed of my 40D) , meaning I will not get subject blur, since it would be the equivalent of shooting at a shutter speed of 1/15,000 (if I am using 1/16 power)?

[cdifoto]

Yes. I do it all the time at weddings. While not pitch black, I can go to really slow shutter speeds to bring in some of the ambient. -2EV is usually a good rule of thumb...in other words keep the meter blinking at the left even if just barely if you're using the un-handholdable speeds.

This is at 1/15th:

http://i14.photobucket.com/albums/a304/cdifoto/2007-09-15-948-BW.jpg

[nursek]

good question, i would love to hear an experts answer on this too!

[PacAce]

good question, i would love to hear an experts answer on this too!

One already did. ;)

[telles75]

Wow..thanks for the quick answer cdifoto... Do you think using an IS lens like my 24-105 f4L IS would allow me to hand held action shots taken at let say (assuming focal range of 50mm) and 1/60 without IS or at 1/8 with IS ON???

[cdifoto]

That depends on you and the amount of ambient light and how fast the subject moves. You have to keep around -2EV because if you let in too much ambient you'll get a motion trail. Check out the corner of the lady's blouse and you can see it starting to creep in. 1/15th was borderline in that case.

[PacAce]

Wow..thanks for the quick answer cdifoto... Do you think using an IS lens like my 24-105 f4L IS would allow me to hand held action shots taken at let say (assuming focal range of 50mm) and 1/60 without IS or at 1/8 with IS ON???

Is this still in reference to your hypothetical scenario of your first post above or did you just switch gears from flash duration to lens IS? :confused:

[cdifoto]

Here's an example where I pushed it too far but fortunately is still salable. This was at 1/10th. Since IS doesn't stop subject movement, it would be of no help here other than keeping the background a little sharper and taking the light trail off the cake (due to my mashing down on the shutter carelessly, not the depth of field type of sharper).

http://i14.photobucket.com/albums/a304/cdifoto/gear/2007-09-01-418.jpg

[Wilt]

According to what I read so far, shutter speed does not affect the lighting of the subject by the flash, only the ambient light. Does this means that in a perfectly dark room (0 lux) if I shoot someone jumping using manual focus, the speed of the shutter should not matter at all to capture the action? So if I use 1/5 shutter speed should be exactly the same as using 1/250 (max sync speed of my 40D) , meaning I will not get subject blur, since it would be the equivalent of shooting at a shutter speed of 1/15,000 (if I am using 1/16 power)?

Back to the basic principle that should be burned into everyone's brain...
Every flash shot is really two shots in one
1. the portion due to ambient light (aperture + shutter speed), and
2. the portion due to flash output (flash output + aperture)

#1 is affected by shutter speed for motion stopping; #2 is not affected by shutter speed for motion stopping...unless the amount contributed by #1 is great enough to be registered on the film.

The 'shutter drag' concept is merely having #1 high enough to register a bit on the film, while #2 makes up the main portion of the content (the main subject)

The 'flash fill' concept is merely making #1 register the primary content of the scene, while #2 contributes enough light to fill in the shadows.

[telles75]

Thanks a lot guys for the input, and sorry for the IS question AcePace. I was just wondering if IS would work on flash photography but I did a couple of experiments and apparently IS does not impact shots at all (assuming flash represents more than 90% of the lighting and ambient just 5% or less), correct me if I am wrong.

To confirm my doubts I took some shots of a moving fan at different shutter speeds. All the following shots were taken with the following settings:
Canon EOS 40D, 580EX II on ETTL with EV -1, with 24-105 f4L IS
Focal length: 50mm, ISO: 400, Av: 4.0

Shutter Speed: 1/250
http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/1-250.jpg

Shutter Speed: 1/100
http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/1-100.jpg

Shutter Speed: 1/10
http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/1-10.jpg

Shutter Speed: 1/4
http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/1-4.jpg

[telles75]

Anyways the post above confirms the point that Shutter Speed does not affect the exposure of the subject and that it freezes the action (the fan was running at high speed). However we see that the different shutter speeds affect ambient light directly. I guess I just needed to confirm this fact for myself to understand the concept properly. I also took photos with IS ON and OFF at 0.3" and to be honest I could not see any difference and there is no way I can handheld at that slow speed without motion blur so I guess the flash even helped in this department.

[Greg Jones]

Thanks Telles75 for the experiment. Looks like the last shot at 1/4 is getting close to the fire place shot you are going to do. Well maybe not close enough.
Thanks everyone for the example and expination , already new it but never hurts to refresh a bit.

[Curtis N]

apparently IS does not impact shots at all (assuming flash represents more than 90% of the lighting and ambient just 5% or less), correct me if I am wrong.Image stabilization reduces the effects of camera movement, not subject movement. Its affect, though limited, is akin to putting the camera on a tripod.

Motion blur from subject movement is affected by the shutter speed for the ambient portion of the exposure, and by the flash duration for the flash portion of the exposure.

Those shots of yours really demonstrate the motion-stopping ability of flash.

[telles75]

I did a second experiment with the fan. This time I did it on a room bright enough to be able to take the pics without a flash, I set it at EV -1 (at a low shutter speed of 1/10) so ambient light will be the main light and flash used as fill.

Even under these conditions the flash was able to freeze the movement of the fan, however a weird transparency effect was obvious as you can see in Pic 2. As I started to increase the shutter speed the ambient light started to drop and the transparency effect on the blades started to dissapear. Once ambient light reached EV - 2 the transparency is not evident and at EV -3 the blade is completely solid (almost 100% of light came from flash at this speed and on; pics 4 and 5).

http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/Fan1_01.jpg

http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/Fan1_02.jpg

http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/Fan1_03.jpg

http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/Fan1_04.jpg

http://i143.photobucket.com/albums/r123/telles75/POTN/Flash1/Fan1_05.jpg

[greygoose]

i have to admit. this thread opened up my eyes alot. thanks

[BIGTUFFGUY]

excellent thread with real life examples that are easy to follow and understand.

Imaginary rep sent :D

[ALaS]

Good work

[Sam_M]

Good read. Since I was searching for flash sync due to me being confused on a few points, this really helped me to understand it, as well as E-TTL. Thanks alot!

[MT Stringer]

Telles75, thanks for doing the experiments, especially the first one. People try to answer questions on this forum by explaining what you have captured with your experiment.

Heck, I think this should be a separate thread and maybe a sticky stuck on it. It would make it a lot easier to throw a link up for an answer rather than try to explain it.
Mike

[telles75]

I read a lot of explanations about how shutter speed only affected ambient light andnot flash light. It is a hard to grasp concept if you just read about it, so I figure it was a nice way of proving it to myself if I did some experimentation. Now I have a better and more concrete understading of this topic and I am glad others also found this thread helpful; I have learnt so much from POTN that I feel happy to contribute when I can.

One thing I thought I should note is that the fan experiment does not apply 100% to real life pictures. I did some testing with my wife and kids jumping and trying to freeze the shot and at low shutter speed (1/5 or 1/10) I was getting subject blur; not sure if this is cause by the AF or by the movement itself (for the fan the focus point is the middle of the blades, hence it's not moving). Once I used a faster shutter speed of 1/20 or 1/40 I could freeze the action properly.

[Wilt]

I read a lot of explanations about how shutter speed only affected ambient light andnot flash light. It is a hard to grasp concept if you just read about it, so I figure it was a nice way of proving it to myself if I did some experimentation. Now I have a better and more concrete understading of this topic and I am glad others also found this thread helpful; I have learnt so much from POTN that I feel happy to contribute when I can.

One thing I thought I should note is that the fan experiment does not apply 100% to real life pictures. I did some testing with my wife and kids jumping and trying to freeze the shot and at low shutter speed (1/5 or 1/10) I was getting subject blur; not sure if this is cause by the AF or by the movement itself (for the fan the focus point is the middle of the blades, hence it's not moving). Once I used a faster shutter speed of 1/20 or 1/40 I could freeze the action properly.

Think of this...



Scene 1: Think of this...in an absolutely dark room, open the shutter for 20 seconds and use the Open Flash button to trigger an electronic flash. The light is emitted for perhaps 1/500 - 1/10000 second (depending upon flash setting) and anything illuminated by that light is effectively frozen in the image recorded by that brief burst of light. The electronic flash stops outputting light, and the shutter remains open. No additional light is captured because the room is dark, so other than what was illuminated by the electronic flash, nothing else is recorded.

Scene 2:
Think of this...in room lit by a 7 watt bulb, open the shutter for 20 seconds and use the Open Flash button to trigger an electronic flash. The light is emitted for 1/500 - 1/10000 second (depending upon flash setting) and anything illuminated by that light is effectively frozen in the image recorded by that brief burst of light. The electronic flash stops outputting light, and the shutter remains open and still gathering light from the 7 watt bulb. Additional light is captured because the room is illuminated; increasing the time from 20 seconds to 40 seconds will double the light gathered from the 7 watt bulb, or decreasing the time from 20 seconds to 10 seconds will halve the light gathered from the 7 watt bulb -- But the flash portion of the exposure will not be changed significantly, yet any motion will be frozen in the brightly lit segment of the motion, but motion will be captured as motion blur in the dimly lit segment of the motion.

[telles75]

I agree with you Wilt but how do you explain the flash being able to stop motion of the fan blades even when the ambient light was strong enough to illuminate the fan for 1/10?

My only guess is that is could be something related with the reflectivity of the blade once the flash light hits it , producing a highlighted area that is more evident than the trail left by the ambient light blade motion. The transparency effect demonstrates that there was enough exposure of the background to make the blade seem transparent.

Am I completely off in my reasoning?

[Wilt]

I agree with you Wilt but how do you explain the flash being able to stop motion of the fan blades even when the ambient light was strong enough to illuminate the fan for 1/10?

My only guess is that is could be something related with the reflectivity of the blade once the flash light hits it , producing a highlighted area that is more evident than the trail left by the ambient light blade motion. The transparency effect demonstrates that there was enough exposure of the background to make the blade seem transparent.

Am I completely off in my reasoning?

Fan rotates based upon the cyclic rate of the AC power source...60 Hz in USA, for example. So at 30 Hz rotation rate, if flash fires at slow 1/500, the fan is rotating 30/500 turns, or 0.06 revolutions while the shutter is open and the flash is emitting light. That is good enough to capture a fairly sharp outline of the fan blade. If the shutter speed is at 1/250, the fan captured by ambient light has moved 0.12 revolutions, so you might see slight evidence -- and you CAN see faint effect at the trailing edge of the fan blades in the shot at 1/250!

When the shutter is open longer, it captures the fan blades just enough to leave a semi transparent haze over the areas traversed by the fan blades, and to a larger extent than what is visible in the 1/250 shot, because multiple blades are traversing the same area during the shutter open time.

[Dr. Flynn]

this is really an amazing thread! I am going to play with freezing water in the dark!

Rian

[Wilt]

this is really an amazing thread! I am going to play with freezing water in the dark!

Rian


Water freezes in the dark just as well as it freezes in the light, assuming it can first chill below 32 degrees F for a moment before it crystalizes! ;)

[telles75]

Fan rotates based upon the cyclic rate of the AC power source...60 Hz in USA, for example. So at 30 Hz rotation rate, if flash fires at slow 1/500, the fan is rotating 30/500 turns, or 0.06 revolutions while the shutter is open and the flash is emitting light. That is good enough to capture a fairly sharp outline of the fan blade. If the shutter speed is at 1/250, the fan captured by ambient light has moved 0.12 revolutions, so you might see slight evidence -- and you CAN see faint effect at the trailing edge of the fan blades in the shot at 1/250!

When the shutter is open longer, it captures the fan blades just enough to leave a semi transparent haze over the areas traversed by the fan blades, and to a larger extent than what is visible in the 1/250 shot, because multiple blades are traversing the same area during the shutter open time.

So assuming my fan goes at a rotational speed of 30Hz (1800RPM which is pretty common for household fans), when I used a shutter speed of 1/10 the fan rotated 30/10 or 3 revolutions while the shutter was open, so that created the transparent haze?

Anyways, enough with the physics lesson and coming back to the flash freezing capabilities at low shutter speed it is amazing how at 1/15 or 1/20 even with ambient ligth above -2 can we quite surprisingly.

[Wilt]

So assuming my fan goes at a rotational speed of 30Hz (1800RPM which is pretty common for household fans), when I used a shutter speed of 1/10 the fan rotated 30/10 or 3 revolutions while the shutter was open, so that created the transparent haze?

Yes, correct.


Anyways, enough with the physics lesson and coming back to the flash freezing capabilities at low shutter speed it is amazing how at 1/15 or 1/20 even with ambient ligth above -2 can we quite surprisingly.

If the ambient light is, relative to the flash, below -3EV the items receiving that faint level of illumination will register as black (or not visible). As the accumulated exposure of multiple passes increases, first to -2EV then to -1EV and so on, the 'fog' of the rapidly moving object increases in intensity, even if the item itself which is responsible for the 'fog' is not sharply visible.