Hi all, any thoughts or ideas why I'm getting blur in my movement images? It's usually only the hands or the feet that are blurring and I wonder if it from the back light or something else.

Here is an example: http://www.model-kartei.de/bilder/bild/7758858/

I'm shooting at either 1/200 or 1/250 at around f8

I'm using elinchrom kit - Ranger RX AS, and Bxri, so flash duration is short enough. My main light is on the short duration plug and has an extension cable fitted to bring the duration down even more. Generally, I'm not using modeling light but there is an overhead florescent and some daylight in the studio.

Think this is just stray light or something I can change in my technique?

Appreciate you help very much.

Nicholas

I take it for a fact that the flash duration is NOT short enough. It is obvious on the picture.
I also assume you are using "Ranger RX Speed AS" (I did not find a "Ranger RX AS").

1) Do you have "Ranger A Speed-Heads" attached?
They offer flash durations of around 1/5000 s to 1/4000 s according to different sources.
The (presumably slower) "Ranger S-Heads" have no spec given...

2) The shortest flash duration is usually advertised at the lowest light output.
Now as the Ranger RX Speed AS covers 7 f-stops then even with 1/4000 s to
start with I think you are bound to hit 1/250 s already at intermediate or
higher light output levels, even though the relation is not linear. The actual
relation, rather depends on the technology used: capacitor switching will have
a quite linear relationship (but conserves color temperature well) while variable
voltage control will keep the flash duration constant (at varying color temperature).
This duration of the flash is visible as motion blur with sharp boundaries.

3) A flash is not off-on-off, but has an afterglow. Typically, two times are used
as specifications: T0.5 which is the much shorter duration when the light output
is above 50% of the maximum, and T0.1 which is the duration when the light
output is above 10% of the maximum. This latter exposure time is much longer
than the often advertised T0.5. This declining "tail" of the afterglow is quite
visible in moving subjects as a soft halo blur. The afterglow may be prolonged
when the power is ramped up, just like described above.

The best way to check this quickly is to set your flash to minimum light output
at -7 f stops, ramp up your ISO / aperture to compensate and take a picture
of a moving person. A walking person's movements at full lenght are typically
frozen at full resolution at around 1/400 s to 1/500 s. A jumping person like
in your picture might require even faster exposure times still.

Best
Hennrik

Thanks for the help.

Yes, I am using the Ranger RX Speed but with the S heads - not the short duration heads. But they should still be fast enough for people. The short duration heads (I understand) are for stopping even faster things. But perhaps my models are moving faster than I thought.

I've done the ambient light test and nothing comes through. I thought that perhaps the beginning and end of the flash cycle were causing a very small exposure - not enough to impact the whole image but just enough to show where small objects are passing by the background. But there is also blur on foreground - not just background "ghosting."

The extension cable, according to Elingchrom, reduces the flash duration by acting as additional resistance/impedance - thus effectively shortening the "curve."

I'll try a bit more testing - maybe the speed heads are in order. Or, my pack may need maintenance. If the main capacitor is starting to fail, it could cause a longer current duration than designed.

Thanks again, will keep posting.

n

Thanks, I've been using both together as well as the B channel alone. With two heads the duration is even shorter.

I think it is coming down to the fact that 1/250 is not a fast enough shutter speed to capture everything as a still moment. I am thinking of renting something without a focal-plane shutter to see if the higher flash sync changes anything. Next step could also be upgrading to the A heads, but it's an expensive investment if I still have trouble from the slow camera sync.

More investigation is in order!

n

Thanks. I will go in that direction then. Now off to find an a-head.

Ok, it's definitely down to the speed of the flash. Even at the shortest duration of the standard head, I still get blurring. So, where's that rental house and all that extra money laying around!

Here's my latest test.

Here's the pricelist for rentals

and here's the store in munich.

One thing you might want to try: get some basic continuous lighting-gear (for rent?) and shoot at a wide open apperture to reach shorter shutter-durations at the given light.

Thanks Nico. Yes, I know Calumet quite well. But last I heard they don't cary my lighting gear. Dinkle does but they do not stock - have to order - and they are terrible at communication. They really don't like Elinchrom.

I actually started out with "hot lights" as they used to be known. Tungsten and HMI would require just too much light to get into a useable range - even at f2.8 and then you have such a short depth of field that you will get blur from that. Focus tracking indoors is not a camera's best function.

I thought about flourescent but you need tubes that don't "spike" otherwise you get a lot of noise or banding with digital. They are also expensive.

Ideal is a 2 or 4 tube short duration head with what ever modifier you like - soft box or dish.

Thanks for the input.

n