BigD Loc: The LEFT Coast

"First, take into account the fact that shutter speeds above camera's flash sync speed are achieved purely by moving the second curtain before the first one fully opens. So it seems like anything above the camera's flash sync speed (which is the highest speed at which the sensor gets completely uncovered) would not work for freezing motion. Different parts of the sensor would be exposed at different times."

The OP's explanation of how the Flash works in conjunction with the fast Shutter speed is not accurate skewing the rest of the discussion. The question is "can a fast shutter stop motion", the answer is YES. The SUPPORTING details are that in order to use the fast Shutter you must provide sufficient light. In most cases that requires HSS.

ShakyShutter Loc: Arizona

Flash duration especially the shortest duration is always stated in the flash manual. Since the strobe is a discharge device there is no way to ""sort of" turn it on to make it dimmer. The ONLY way to temper the output of a strobe is to "shorten" or lengthen the duration of the discharge in the flash tube.

The shorter the duration...the quicker the flash 1/50,000 of a second is not uncommon. A speed of about 1/20,000 of a second is typical for an low power strobe automatic strobe at close range. That is the speed it takes to stop the motion of a humming bird with an 80 beats per second wing speed.

evandr Loc: Tooele, Utah

Have you ever seen a strobe tachometer? While in the Navy on the aircraft carrier USS Kitty Hawk (CV63) years ago I have seen spinning propeller blades at full throttle look like they were standing still to the naked eye, it is quite old technology dating back to WWII and comes in quite handy when you need to see how something is working at high RPM’s.

If a flash is powerful enough and, more importantly "fast enough" to illuminate and then de-illuminate the spinning object in a square wave pattern (meaning instant on and then instant off) it can be made to look motionless without any distortion. Now, during that split second of time during illumination if you can expose the "entire" surface of a sensor equally to the light of the subject then the picture will show the subject frozen in time without any distortion. When using a flood light you simply need a shutter speed as fast or faster for an amount of time that the blade spin will be a sufficiently short distance at it extremities that the resultant blur will be imperceptible to the naked eye, something that even a “slit” of exposure will do if it is fast enough.

ShakyShutter Loc: Arizona

[quote=evandr]I think it all boils down to one simple question – "is there enough “constant” light to properly expose each pixel sensor in 1/4000 of a sec?”

This is not the question. The amount of light has never been the question.

evandr Loc: Tooele, Utah

Agreed :thumbup:

BigD Loc: The LEFT Coast

I love how we all perceive what others are saying. The use of a strobe to give the illusion "to your eye" is one thing. Your eye and your camera are not the same thing. Like I have said, and others have confirmed, to stop motion you need a fast shutter. To use a fast shutter requires proper light. To achieve proper exposure requires either very bright lights or a strobe. To use a strobe requires that you sync that strobe with the motion of the Shutter so that it is at its zenith (brightest point whatever that "output" is to achieve your proper exposure) during each "slit". I have a feeling that some people here have never actually done a HSS shoot on a fast moving object and are shooting from the hip. Guys you can stop a Hummingbirds wings dead stop if you can get the Shutter speed up there. And to do that just might require a HSS strobe. :thumbup:

evandr Loc: Tooele, Utah

Yes, but the OP suggests that at with high front and rear curtain shutter speeds you cannot effectively freez motion and that is not true. The intensity AND "duration" of the light is of paramount importance and must be included in any answer to the OP that makes any sense.

ShakyShutter Loc: Arizona

Almost every point and example you've written prove the point that 1/4000th of a second dual curtain shutter has limited motion stopping power.

Slow the prop down so it won't blur, strobe tachs use EXACTLY the same technology used in strobes today, where do you think we got the idea. Why do you suppose they didn't continue using mechanical shutter devices to check high speed mechnical devices, because physics always wins.

evandr Loc: Tooele, Utah

Yep, you are right but the principle is still the same - you need to get enough constant light onto the whole sensor equally and for a short enough time to freeze the action. I think some of us are talking procedure while some of us are talking theory. The fact that the sensor is exposed with curtains or irises and the light is a flash, a HSS strobe, a high powered flood light or a match is irrelevant, only that it works. the bottom line is that you can freeze anything with a DSLR if the setup is correct, something that the OP suggests is not possible at high speeds.

BigD Loc: The LEFT Coast

I know what was said but the "fact" that was quoted about how flash and Shutter speed are linked was incorrect. So is their understanding of front and rear Curtains I might add. So what I was trying to do was interject the correct mechanical explanation of how high speed Shutters effect motion stopping abilities and how to achieve it.

The idea of a forum is for people to share their experience and knowledge with each other to gain a broader knowledge base. When I see someone build a scenario based on incorrect data and then reach a conclusion I simply try and provide a more technically accurate version. There are people on here that are very new to this so their "filters" are more open to clogging and I like to help clear the air if I can. Just my 2 Cents worth.

BigD Loc: The LEFT Coast

Evander EXACTLY, the "rub" people are dancing around is that the Shutter is exposing in slits and not the entire sensor at the same exact time. And what I am saying is "that being true" in the REAL WORLD a 1/8000 Shutter can stop a whole bunch of motion but you have to have the correct exposure to do it.

ShakyShutter Loc: Arizona

The question has nothing to do with the "amount of light" reaching the curtain... Assume that you always have enough steady(non-strobe) light available to achieve a proper exposure.

Now, OP is correct that there is a LIMIT to the stopping ability of the mechanical shutter curtain. You always have to specify the speed of the object you are trying to stop and then specify the direction and consider these in relation to the direction AND duration or speed of the curtains.

Yes, but the OP suggests that at with high front and rear curtain shutter speeds you cannot effectively freez motion and that is not true. The intensity AND "duration" of the light is of paramount importance and must be included in any answer to the OP that makes any sense.[/quote]

evandr Loc: Tooele, Utah

If you will, try to include the post to which you are refuting as a quote in your post, it helps with continuity and provides the person who made the post to which you are referring a chance to defend his/her position, perhaps you misunderstood what you read, just a thought.

check6 Loc: Redding, CA

First: This thread is about non-strobe exposure! The OP states that clearly.

Second: That being the condition a shutter can only stop motion that is moving slower that it.

My example was a propeller blade. With a diameter of 6 and turning at 2500rpm, the tips are moving at over 800 feet per second...nearly the speed of sound. A curtain shutter at 1\4000 is only moving at maybe half that speed. It can't stop the motion the the prop tips.

Hiskid.58 Loc: Erie, PA

The leaf shutter cameras don't go up to 1/4000th of a second. I just checked and the fastest shutter speed of the newer digital Hassleblad is "only" 1/800th. The older film cameras would only go up to 1/500th. With these, you can sync the flash up to the highest speed.