Freezing movement: fastest sync speed of RZ67?

Holly · May 15, 2012

Hey all
I'm having problems with getting the sharpness I want from a moving subject. I'll have my model in the studio, simple two-light set-up, she's not doing anything particularly action packed, but still if she moves her arm I get blur. This was using Velvia 50, with a normal 90mm lens, mirror lockup...stars aligned..am I not using a fast enough shutter speed? At what point does the RZ not sync anymore?
On this thread we get 1/400 max sync speed: (there was a url link here which no longer exists)
Will that freeze arms and things tossed into the air properly (which may be a feature of the shots)? Sorry if this is an elementary question, I just haven't
used a moving human subject in a while, I need it to be blur-free for what I'm doing and if there's a better way to get that result I'd love to know about it.

many thanks

Larry H-L · May 15, 2012

I assume you are using strobes? If you are still getting blur, you could try turning the strobes down, which might shorten flash duration. Adjust f-stop accordingly.

Leaf shutter lenses generally synch at any speed, 1/400th should work fine.

Holly · May 15, 2012

Yes, using strobes, couple of Style 600rx Elinchroms. How much of a difference would it make to shorten the flash duration? Are we talking
minute fractions of a second?

OzJohn · May 15, 2012

Holly said:
Yes, using strobes, couple of Style 600rx Elinchroms. How much of a difference would it make to shorten the flash duration? Are we talking
minute fractions of a second?

The Style 600Rx is claimed to have a flash duration of 1/2050 sec on full power and this would be even faster as the power is reduced. In a studio environment using strobes the shutter speed normally plays no part in the exposure because the flash should overpower any ambient light and its duration effectively becomes the exposure time. If you are getting subject blur I would suggest that either your studio has high ambient light levels eg a large window or skylight or your modelling lights are too bright. Your blur is possibly the result of a secondary available light exposure at the shutter speed set on the camera. OzJohn

polyglot · May 15, 2012

1/400 is the max speed of the camera - are you set at that speed or something slower? How much ambient light do you have? If there's a lot, you might get visible blur from the ambient contribution regardless of the flash duration. Keep in mind also that the 1/400 setting is 1/400 worth of light, taking into account the non-instant opening and closing motion of the shutter. The total duration for which there is any exposure is closer to 1/250.

Assuming you're at 1/400 and your ambient is very low (i.e. requiring at least 1/15 exposure at your chosen aperture therefore 4+ stops underexposed), the limiting factor to the exposure is your flash. Cheaper flashes (higher-impedance capacitors that have a longer discharge) can have an exposure as long as 1/500 so not really much improvement over the shutter speed. Better ones will be about 1/2000 to 1/10000 depending on power settings. You should be able to look up the flash duration for your strobes but be careful: it can be quoted as a t.1 (10% extinction) or t.5 (50% extinction) time and clearly the lower extinction value takes more time. A flash rated at 1/1000 t.1 is much faster than a flash rated at 1/1000 t.5.

Turning down the flash power will almost always shorten the flash duration, approximately according to power. Take two stops off, the flash should go about 4x shorter in duration, but there are some funny lumps in the speed/power graph where capacitors are switched in/out to control power instead of adjusting voltage. It all depends on the flash model and at some point, you will reach a minimum duration, which may or may not be at minimum power.

Tossing an apple lightly in the air means an arm speed of about 2m/s, which is 5mm in 1/400s, 10mm in 1/200s. If you have any ambient contribution, you can expect to see plenty of blur! Say your flash is a moderately decent one with 1/2000 duration, you're still looking at 1mm of motion blur in the exposure. If you want to halt extreme speeds, the common approach is to use a large hotshoe speedlight set at its minimum power setting (1/32 or so), which will give you exposures down around the 1/16000 mark for 0.1mm of blur. You obviously don't get much light like that though.

Beyond that, you're talking about building a custom high-voltage, low-capacitance flash circuit. Very dangerous stuff but you can probably hit 1/50,000s, at which point you can run into short-exposure reciprocity failure on some films.

Edit: these are the flashes you were asking about transformers for, right? I take it you have them all hooked up and working nicely (other than motion blur) now then?

polyglot · May 15, 2012

Oops, it's worse. Tossing an apple 1m in the air requires a launch velocity of 4.4m/s, so it's 2x as bad. 1/2000 will leave you with >2mm of blur.

By kinetic/potential energy exchange:
E = mgh = 0.5 mV^2
V = sqrt(2gh); g=9.8m/s^2, h=1m, V=4.4m/s

David A. Goldfarb · May 15, 2012

Reduce flash power and keep the ambient light at least 4 stops under the strobes, and that should address the problem. The sync speed isn't important, unless you have a lot of ambient light relative to the strobes. If you need a lot of strobe power at short duration, then the solution is to divide the power among more strobe heads or use dual-tube heads, so you might have two heads at half power and about half the duration of one head at full power.

polyglot · May 15, 2012

Another thought... if motion blur is the only problem, try to time the shot when things are obviously in-flight but actually stationary, i.e. at the top of their path.

Say someone tosses an apple; by the time the apple reaches its highest point, their arm will be pretty much stationary and the apple will too. Press the shutter at that point and you will get practically no blur. The tradeoff is that you lose the muscular tension in the actor and the pose is relaxed/spent instead of tense/powerful. The flying apple and extended arm will imply the motion but it won't (IMHO) be as visceral as capturing the model in the middle of throwing.

Holly · May 15, 2012

polyglot said:
Oops, it's worse. Tossing an apple 1m in the air requires a launch velocity of 4.4m/s, so it's 2x as bad. 1/2000 will leave you with >2mm of blur.

By kinetic/potential energy exchange:
E = mgh = 0.5 mV^2
V = sqrt(2gh); g=9.8m/s^2, h=1m, V=4.4m/s

Oh dear god, I knew this would prompt horrible mathematical things! lol
So yes, it's the same lights I got the trannies for (as they are now affectionately known). They work fine!! Really happy with them! They're bloody heavy but they were the best investment, I've had no worries at all.

I'm working in a studio with one big window but whenever I've shot there, it's either been after dark so no daylight
coming in, or I've had a pretty thick UV-blocking-backed curtain drawn. Only other ambient light is the crappy fluorescent
strip lighting to the room itself.
I think for the arm-blur session I was shooting on 1/60. I've just done a mini test of 1/400 with a moving target (a glove
spinning around at a medium speed hanging from a string - don't ask) and can see when that's dev'd how it worked.
Left the manual at the studio, but as OzJohn said, the Style 600rx should be around 1/2050, so that's a decent flash.
I've noticed this blurring thing happening in a totally different studio with no windows whatsoever and even crappier
dimmer fluoro lighting - and the strobes were Elinchrom 1200s in there.
If I lower the flash output, how can I keep my big depth of field though? I'm aiming to have every single hair and molecule
of detail in focus so I've been aiming for f16 + (going on the idea that the smaller the aperture, the bigger the DOF). Although
isn't it true that for every lens, the sharpest aperture is going to be about half the maximum aperture number? i.e. an f32 lens
will be sharpest at f16.

Someone like Harold Edgerton would have had a specialised flash then yeah?

polyglot · May 15, 2012

I always bring the horrible mathematical!

Shooting at 1/60 could well be a problem as the lighting from the fluorescents might show up. Unlikely at ISO50 f/16, but possible. I guess you'll know when you get the 1/400 test back.

To reduce power but maintain exposure & DOF, you can move the light closer to the subject (can cause issues with uneven light but twice as close gives you about +2 stops) and/or use a faster film. I'd suggest (separately from your love-affair-with-Velvia question) trying some Portra 400. Especially if you're doing a hybrid (scanned) process, you can add in plenty of saturation later. It's not as fine as RVP but it's still very good in 6x7. You can also try Provia 400X - a bit pricey but it has the saturated contrasty chrome look.

Sharpest aperture on most RZ lenses will be about f/11 or f/16. f/11 might give you more resolution but obviously slightly less DOF. Something else you can explore is lower magnifications, i.e. including more in your frame and making the subject smaller by stepping the camera further back and/or using a shorter lens. That will increase your DOF without needing more light intensity.

If you want stationary-looking bullet photos, you need very custom flash hardware, big apertures and fast film.

ic-racer · May 15, 2012

Cut all the ambient light. Increase the strobe power if possible or bring the lights in closer.

markbarendt · May 15, 2012

ic-racer said:
Cut all the ambient light. Increase the strobe power if possible or bring the lights in closer.

Yep.

E. von Hoegh · May 15, 2012

ic-racer said:
Cut all the ambient light. Increase the strobe power if possible or bring the lights in closer.

Increasing the strobe power will increase the duration of the strobe. Not what the OP wants.
Moving the strobes closer and using the same aperture but a lower power setting will result in the same light intensity on the subject and a shorter flash duration.

markbarendt · May 15, 2012

E. von Hoegh said:
Increasing the strobe power will increase the duration of the strobe. Not what the OP wants.
Moving the strobes closer and using the same aperture but a lower power setting will result in the same light intensity on the subject and a shorter flash duration.

My B800 alien bees lamps at full power have a maximum duration of 1/1100th, they typically run at less than half power, so run even shorter, in my setups when I'm trying to lose the ambient light.

Even at 1/1100th subjects really have to move darn quick to cause a blur.

Edit - I do believe in getting the lights closer, not just for power but for shaping.

ic-racer · May 15, 2012

E. von Hoegh said:
Increasing the strobe power will increase the duration of the strobe. Not what the OP wants.
Moving the strobes closer and using the same aperture but a lower power setting will result in the same light intensity on the subject and a shorter flash duration.

It is a woman's arm not a bullet.

David A. Goldfarb · May 15, 2012

The sync speed should be irrelevant to stopping motion with strobes. You should be able to stop motion with a sync speed of 1/40 sec. (just imagine what you would get on film at, say, 1/60 sec, f:16, ISO 100 in average indoor lighting--not much of anything), if you set the strobes to a short duration/low power and reduce the ambient light so that it doesn't make a difference, but that doesn't mean it has to be totally dark. If you want more light with a short flash duration, then the way to do it is to use more strobe heads at the same power. The model to follow is more Lois Greenfield than Edgerton:

Dead Link Removed

If you look at this video, you can see there's enough light from the modeling lights to shoot video, without it getting too close to the level of the strobes for shooting stills:

http://vimeo.com/11541771

E. von Hoegh · May 15, 2012

ic-racer said:
It is a woman's arm not a bullet.

Pardon me. The OP didn't state precisely what the model was doing, or what power level/duration she was using.

The thread title is "Freezing movement" right?

Holly · May 17, 2012

David A. Goldfarb said:
The sync speed should be irrelevant to stopping motion with strobes. You should be able to stop motion with a sync speed of 1/40 sec. (just imagine what you would get on film at, say, 1/60 sec, f:16, ISO 100 in average indoor lighting--not much of anything), if you set the strobes to a short duration/low power and reduce the ambient light so that it doesn't make a difference, but that doesn't mean it has to be totally dark. If you want more light with a short flash duration, then the way to do it is to use more strobe heads at the same power. The model to follow is more Lois Greenfield than Edgerton:

Dead Link Removed

If you look at this video, you can see there's enough light from the modeling lights to shoot video, without it getting too close to the level of the strobes for shooting stills:

http://vimeo.com/11541771

Bummer is I only have 2 lights at this stage. Another one could be obtained if I go without food and rent
However!! This video is amazing! I watched it 4 times and could only discern 2 main lights going, so WHYYYY is her
model not blurrrriiiing. Is it because they have a Blad with a kickass digital back?? The principles would be the same, right?
And looking at the size of their studio compared to mine in terms of the distance of light to model, it is relatively about the
same in my studio except on a much smaller scale. Mine is about a third that size, so if I was to bring the light in closer and
lower the power, the light would be like sitting on the model's cheek.
I must go back to the drawing board.
Thanks for the link - the work she's doing would've been soooooo useful to me about 2 years ago, I was doing a
very similar action/choreographed motion thing, damnit!

Holly · May 17, 2012

E. von Hoegh said:
Pardon me. The OP didn't state precisely what the model was doing, or what power level/duration she was using.

The thread title is "Freezing movement" right?

I should clarify: I'm not after frozen bullets through water balloons (although that would be fun) but just
have a model simply moving from position to position on the spot, and she's mostly motionless as I'm shooting
but on the occasions when she's still turning around or what have you, there's blur in the hands and arms.
So it's not as if I'm trying to capture insane micro miliseconds of action but more trying to solve the reason
why a really slow moving model still has blur.

MattKing · May 17, 2012

I see you are using two strobes.

Is there any chance they aren't synching together - i.e. there is a slight lag between them?

Try an experiment with just a single strobe to see if the blur disappears.

Holly · May 17, 2012

polyglot said:
I always bring the horrible mathematical!

You really do, what are you, a physics teacher lol

Shooting at 1/60 could well be a problem as the lighting from the fluorescents might show up. Unlikely at ISO50 f/16, but possible. I guess you'll know when you get the 1/400 test back.

Indeed.

To reduce power but maintain exposure & DOF, you can move the light closer to the subject (can cause issues with uneven light but twice as close gives you about +2 stops) and/or use a faster film. I'd suggest (separately from your love-affair-with-Velvia question) trying some Portra 400. Especially if you're doing a hybrid (scanned) process, you can add in plenty of saturation later. It's not as fine as RVP but it's still very good in 6x7. You can also try Provia 400X - a bit pricey but it has the saturated contrasty chrome look.

I'll check it out on my next B&H run. The thing with moving in closer with the lights is just space - if you picture a 1930s dormitory room/cell, you're
pretty much seeing the size of my studio. But I can at least try the lower output/closer in theory on a small scale to see if it does totally
stop motion.

Steve Smith · May 17, 2012

MattKing said:
Is there any chance they aren't synching together - i.e. there is a slight lag between them?

That's a good point. Something else to consider is the method of triggering the second flash. If it's using an optical slave, it should be o.k. but if you are using radio receivers the delay involved might differ between the two.

Steve.

Holly · May 17, 2012

MattKing said:
I see you are using two strobes.

Is there any chance they aren't synching together - i.e. there is a slight lag between them?

Try an experiment with just a single strobe to see if the blur disappears.

Don't know, I'm pretty certain they go off together fine? I may have to dig through my files of previous shots where this
blur thing is happening to show a visual for people, it might help to show the exact problem. Hmm. But in a different
studio the same thing was happening, and that was using just the optical slave on the flash head with possibly a Skyport
if I recall correctly. So for it to be happening to me again in a totally different studio, it must be something else.
I'll certainly try the one strobe on its own though. It just puzzles me because I can freeze a piece of fabric thrown
in the air with my little Canon digital point and shoot, but my lovely proper camera and lights can't handle it.

Or rather, it handles it, but with edges of fuzziness on the very edges of objects that are moving.

polyglot · May 17, 2012

Holly said:
You really do, what are you, a physics teacher lol

worse, an engineer with PhD...

Holly said:
I'll check it out on my next B&H run. The thing with moving in closer with the lights is just space - if you picture a 1930s dormitory room/cell, you're
pretty much seeing the size of my studio. But I can at least try the lower output/closer in theory on a small scale to see if it does totally
stop motion.

To be clear, bringing things closer won't shorten the exposure; it's merely a way of making up for the loss of brightness caused by reducing the flash power. Another similar option (if it's compatible with the photo you're trying to achieve) is to reduce/remove anything that soaks up light, like softboxes or flags/gobos. Direct flash can look nasty, but it is very power-efficient and I bet you could run at minimum power and some decent DOF that way - if testing at min power gives you the short exposures you need.

Steve Smith said:
That's a good point. Something else to consider is the method of triggering the second flash. If it's using an optical slave, it should be o.k. but if you are using radio receivers the delay involved might differ between the two.

Steve.

I would have thought the opposite. If one is slaved from the other, there must by definition be lag between them of the same order as the exposure duration because the photocell in the second won't trigger until it sees the rising edge of the first, by which time the first is kind of half-over. With a pair of quality radio remotes from a SINGLE transmitter on camera (no craziness like hanging an RF transmitter off a Wein cell), the timing difference due to radio should be in the order of 10 microseconds. I would expect the total exposure duration to be approximately halved if you can avoid using an optical slave on the second flash.

Doing a one-light test is a good thing to try, especially if (as you say) you have a digital back to play with such tests. In fact, such a thing makes all this testing much faster/easier.

Holly said:
Don't know, I'm pretty certain they go off together fine? I may have to dig through my files of previous shots where this
blur thing is happening to show a visual for people, it might help to show the exact problem. Hmm. But in a different
studio the same thing was happening, and that was using just the optical slave on the flash head with possibly a Skyport
if I recall correctly. So for it to be happening to me again in a totally different studio, it must be something else.
I'll certainly try the one strobe on its own though. It just puzzles me because I can freeze a piece of fabric thrown
in the air with my little Canon digital point and shoot, but my lovely proper camera and lights can't handle it.

Or rather, it handles it, but with edges of fuzziness on the very edges of objects that are moving.

Shutter and exposure in a P&S is quite different. The P&S may be running with very short shutter times to exclude ambient or (more likely) has a much-shorter flash duration because it needs a lot less light. The P&S probably shoots with flash at ISO800, f/4 or so but you're trying to get ISO50, f/16, which is 8 stops or 256x as much light, so it's not really surprising that the flash duration from the P&S is shorter.

In that vein, you should still try to borrow a speedlight (hotshoe flash) and test with that because they often have shorter durations than studio strobes. And definitely test with the strobes at lower powers.

David A. Goldfarb · May 17, 2012

Lois Greenfield has been photographing dancers like this for 30-odd years, so it ain't the digital back, but the digital back might be letting her use a higher ISO, and thus less light. She may also be using dual-tube heads, which let you shoot at half the duration at the same power as a single-tube head.

Freezing movement: fastest sync speed of RZ67?

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