Help with strobe ghosting in studio

Hi all,

 

I need some help. I'm using the Pentax 645Z in studio for dance photography, which means that my dancers are engaging in fast movement. The only ambient light is coming from the modeling lamps. The strobes are Alien Bees, both 400s and 800s.

 

The unretouched pics below show a marked amount of what I assume is flash ghosting on the dancers' feet (which are obviously the fastest moving thing in the frame). Interestingly, other fast-moving objects, such as hands, hems of skirts, hair, and even dust are nicely frozen, but none of that matters due to the unacceptable ghosting with their feet.

 

http://www.hacklightphotography.com/ghost1.jpg

 

http://www.hacklightphotography.com/ghost2.jpg

 

The 645Z is notorious for its slow sync speed of 1/125 sec. My reading of the AB800 specs suggests that worst case I'm getting a t.1 flash duration of 1/550 seconds, and given my power settings I'm probably closer to 1/1000.

 

In an attempt to get the ghosting under control, with the dancer in red, I purchased and used a lens with a leaf shutter to get the shutter speed to 1/500, thus bypassing the 1/125 X sync of the Pentax, but her foot is still ghosting.

My questions:

 

1) Am I diagnosing this correctly? Is this ghosting or simply too slow a shutter speed?

 

2) if it is ghosting, is it being caused by the modeling lamps, or by the flash duration of the strobes?

 

If the problem is the strobes, will switching to Einsteins eliminate the problem? Based on my reading of the specs (page 13) and my anticipated lighting requirements, they would let me get me to a t.1 of around 1/4000 seconds as opposed to my current 1/1000 or so. This is a pricey solution, but I'm willing to do it if it would solve the problem (and be really bummed if i dumped that money into Einsteins and the problem persisted.

 

Any input would be welcomed. Thanks!

Your problem is not the shutter but rather your flash duration. A flash duration is at its fastest a low power settings. Higher quality pack and head flashes like Profoto and broncolor has highest flash durations. You may want to rent such a flash if this is that important.

+1 for Michael--your modeling lights can easily be set to turn off during flash exposure, so they shouldn't be a problem anyway.

Your problem is not the shutter but rather your flash duration. A flash duration is at its fastest a low power settings.

 

I concur, it's the flash duration. But the low flash power setting is not necessarily the answer - it depends on the design of the circuits. For the shortest flash duration (fastest) you want a unit that can actually cut off the flash midway through. Since you're using Paul Buff gear I concur with your thoughts on their Einstein units.

 

As I recall, you have a Canon 580 EX flash. If you want to prove to yourself what a faster flash can do, try the same photos with the 580EX set to something like 1/8 power; this ought to "freeze" far beyond what your AB800 can do.

 

As a note, I personally wouldn't worry about the amount of motion blur you're getting, unless it's an issue with the customer. If anything, I might want to increase the blur to increase the sense of motion.

 

One additional note, there used to be at least a handful of digital cameras that could shutter much faster than a normal flash (I've used em to slice off 2 or 3 full stops from studio flash that was too powerful ). As I recall, the Strobist blog once named a handful. In the unlikely (?) event that you might have such a camera, it might be worth a read.

Your modeling lights on AB's and Einsteins go off when the flash pops. Michael is correct, flash duration will freeze that motion if it is fast enough. Einsteins at low power are 1/13,500 sec. At half power, 1/2000 of a second that should stop this. The back of the einstein tells you the flash duration you are getting so you can adjust accordingly. If you found it wasn't fast enough, why not bump your iso so you can decrease the flash power til you get it sharp. Here's one with 2 Einsteins with dancer leaping from R to L. I was stuck with normal indoor ambient level that I could turn down. My camera at the time in 2012 wasn't anywhere near the high iso capability of my d500 is now. Shot it at ISO 200 at f/8 at 1/200 of a second. Now I would go to max sync speed of 1/250, close to f/11 both of which should help knock down the ambient and push the ISO from 200 to 800 or 1000 or even 1600 if needed[ATTACH=full]1201466[/ATTACH] [ATTACH=full]1201466[/ATTACH] [ATTACH=full]1201466[/ATTACH] . Should have been able to drop the power another stop or two. I am guessing this was at about half power.

[i'm getting: "

Photo.net Photography Forums - Error" when I click on those links, Bob_Bill

 

QUOTE="bob_bill, post: 5587567, member: 2401575"][ATTACH=full]1201467[/ATTACH] Your modeling lights on AB's and Einsteins go off when the flash pops. Michael is correct, flash duration will freeze that motion if it is fast enough. Einsteins at low power are 1/13,500 sec. At half power, 1/2000 of a second that should stop this. The back of the einstein tells you the flash duration you are getting so you can adjust accordingly. If you found it wasn't fast enough, why not bump your iso so you can decrease the flash power til you get it sharp. Here's one with 2 Einsteins with dancer leaping from R to L. I was stuck with normal indoor ambient level that I could turn down. My camera at the time in 2012 wasn't anywhere near the high iso capability of my d500 is now. Shot it at ISO 200 at f/8 at 1/200 of a second. Now I would go to max sync speed of 1/250, close to f/11 both of which should help knock down the ambient and push the ISO from 200 to 800 or 1000 or even 1600 if needed[ATTACH=full]1201466[/ATTACH] [ATTACH=full]1201466[/ATTACH] [ATTACH=full]1201466[/ATTACH] . Should have been able to drop the power another stop or two. I am guessing this was at about half power.

I'm guessing you may be getting a sort of double image effect from the modelling lights because they are too close in power to the actual strobe?

Chazfenn, had a problem with a double post then getting rid of it. I haven't a clue where the links came from.

there used to be at least a handful of digital cameras that could shutter much faster than a normal flash

 

Chazfenn, fyi I think that your little Fuji S7000 MIGHT be one of those ultra-high-speed sync-capable cameras when using an external flash (via a hot shoe pc sync adapter?). Definitely the S20 Pro was, and they are fundamentally very similar. If so, studio flash sync at full shutter speed, 1/10,000 second(?); not widely known, but sometimes useful.

IIRC its good up to some high speeds (800th or so) but not all the way to the max.

I have upgraded to a 9100 now & It is definitely good "way up there", they actually warn you that it may drop flash exposure on some (slow burning, relatively) studio units.

Since you have two strobes already just place them next to each other and think of them as a single light. Lower the power to 1/4 on each head and you will have a total of 1/2 power combined. This will get your flash duration up and double the power. To get more power from there or double that power at the same fast duration you would have to have 4 strobes each set to 1/4 power. Where there's a will there's a way and of course the help of physics.

Update: I just completed a shoot with the rented Einsteins, shooting around 3 or four stops down from maximum. Result:

 

http://www.hacklightphotography.com/frozen.jpg

 

Hard to tell from this crop, but this girl was completely in the air flying across the studio.

 

Ghosting problem solved. Now to save up for Einsteins. :)

Glad it worked out. What exactly were your setting? ISO? F-stop and shutter? 3 or four stops down means 1/8 or 1/16 power?

This looks like it's South Asian Katak dancing where exact hand and foot position is important?

 

Which dance company - if you're allowed to say?

 

My daughter is a dance graduate and would be interested. Thanks!

BF not only will the einsteins give you 1/2000 sec, that's T1, not T5, at half power, they will pop max 10 times per second although I have shot about 6-8 because that was all my d700 would do. Haven't tried it with a new 10 fps body, finally have a body that will keep up with my lights, but need to test that tomorrow. That is on the battery pack as well since it can fire without the capacitor being completely filled.. That speed is in action mode. If you want flat line color, change to color mode. They have been a wonderful light for the price. It took some time to adapt to the cybercommander, but I can change power, turn/off lights, adjust the power of the 250 watt modeling lights to get the size pupil I want, all from the camera. I fell off a ladder hanging paper a few years ago, so staying off the ladder is nice and faster especially in a dark studio. It even has a built in meter if you are just getting lights and don't have a meter yet.. If you shoot wide aperture, they dial down to 2.5 watt seconds from the 640. Michael, Einsteins have 9 stops of adjustment over the range so down 3 -4 stops has him near or slightly above mid power. I'm guessing he was at about 1/1600 sec flash duration. BF, did you happen to look at the back of the flash to see what flash duration you were getting? It's in the upper r blue area on the readout at the back of the unit. They adjust down to 2.5 ws so with a double diffusion soft box, I can get down of 2.0 or even 1.4. When struggling, I just pull off the front diffuser from a 7'octa or 6' scrim and clamp it to my other octa. and 1.4 is achievable with the box in tight.

This looks like it's South Asian Katak dancing where exact hand and foot position is important?

 

Which dance company - if you're allowed to say?

 

My daughter is a dance graduate and would be interested. Thanks!

 

Not a dance company, actually; just an individual in my studio doing standard classical ballet.

Glad it worked out. What exactly were your setting? ISO? F-stop and shutter? 3 or four stops down means 1/8 or 1/16 power?

 

ISO 200, 1/125, 8.0, @1/8 or 1/16 (power settings changed a bit during the shoot, but in that neighborhood).

Just fired up an Einstein. That is 80 ws when 3 stops down from full power, 640, and 1/6,050 of a second flash duration t1 That should stop dancers. Michael, please excuse my math on the reference to half power above, as I mentioned on a post today to Dieter, I am not a math guy. I try not to allow the math to get in the way of my art, but it rears it's ugly head often. Einsteins don't list power in fractions and on my on camera speed light, I am only in ttl and looking at compensation stops and zoom only. I can't remember the last time I did a shoot with off camera speed lights and looked at power fractions. Interesting, I may want to pull those out or sell them.