Strange result using strobes. What am I doing wrong?

[Andrei Zdetovetchi]

Hi

After I recently got my new toys I started to do some test shots, to get used with the equipment.

Some come out pretty ok, but now I am puzzled by this result:

Looks like if my exposure is faster than 1/200 this problem is starting to happen. Like the flashes are too slow for the camera shutter. I know that must be something I'm doing wrong, because I don't have experience with strobes... But I need to get past this issue, so I would appreciate some suggestions.

Thanks!

 

[Clayton Lofgren]

This is completely normal. Your camera manual should give you the maximum synch speed. probably 1/250th or less. Should be no problem using slower speeds with the strobes unless you have too much ambient light.

 

[Andrei Zdetovetchi]

I will check the camera manual for this. I have a Canon 450D. The problem is that I wanted to use the largest lens aperture but in this case my photo comes out white. So there is too much light coming in, so I thought to increase the exposure speed but it seems not to be a good idea... My strobes are at the lowest power.

 

[Bart_van_der_Wolf]

Looks like if my exposure is faster than 1/200 this problem is starting to happen. Like the flashes are too slow for the camera shutter. I know that must be something I'm doing wrong, because I don't have experience with strobes... But I need to get past this issue, so I would appreciate some suggestions.

Hi Andrei,

Your shutterspeed is too fast or the synchronisation is the off (early/late discharge moment).
It is important that the shutter is wide open when the flash discharges. When the shutter speed is set too fast, then only a part of the sensor array is uncovered at any time by the 2 shutter curtains, which form a slit that's narrower than the sensor array when set faster than the sync speed. Faster speeds lead to a narrower slit. Slower speed lead to a wider slit untill it is wide enough to totally uncover the sensor array when the brief flash goes off.

Lowering your shutterspeed (1/100th or 1/125th?) will probably solve the issue. Remember, The flashes at medium to short distance are determining the exposure, ambient light wouldn't expose the frame enough at those shutterspeeds. The duration of the flash determines the effective stop motion effect, in case there is subject motion. Studio flashes in general have longer discharge durations than small flash units.

The exposure level is determined by the output power, the distance between lights and subject, and aperture. You can also use a neutral density (gray) filter (or a polarisation filter, if the subject allows it).

Bart

 

[John Angulat]

Hi Andrei,
I'm a Nikon user so I'm more familiar with their flash settings. I believe the Canon450 has what's called "first curtain" and "second curtain" flash sync.
Check your camera setting to be sure it is on first curtain (or similar) sync.

 

[Doug Kerr]

Hi, Andrei,

Some come out pretty ok, but now I am puzzled by this result:

This is a result of the use of a focal plane shutter in your camera.

For exposure speeds above a certain limit, the shutter isn't ever completely open for the entire height of the frame. We can think of it as having a narrow window that sweeps across the height of the frame, exposing all parts of it for the desired time, but just not all at once.

Then output burst of an electronic flash is very short. As a result, no matter when in the shutter cycle the flash fires, not all of the frame will be illuminated.

This is why there is a shutter speed limit for the camera for use with electronic flash (often 1/200 - 1/250 sec). It is spoken of as the "X-sync speed limit".

When an "on-board" flash is used, or a "dedicated" external flash is in place and active, the camera automatically limits the shutter speed to be within this limit. But with a general-purpose external flash, fired through the PC sync connection, the camera doesn't know it is present so it can enforce the limit. So you must!

Some flash units have a "high speed sync" mode in which the output burst is rather long - long enough to illuminate the frame while the "window" sweeps over all of it.

Best regards,

Doug

 

[Andrei Zdetovetchi]

Guys, you are all right and I feel a little ashamed by my noob question. Looking in the camera manual and also searching the google for Canon 450D x-sync, revealed to me that my observation is right, the 450D cannot sync an external flash at more than 1/200s.
So I must use slower exposure and to find other ways to decrease the light on my subject... so, back to school

 

[Bart_van_der_Wolf]

Guys, you are all right and I feel a little ashamed by my noob question. Looking in the camera manual and also searching the google for Canon 450D x-sync, revealed to me that my observation is right, the 450D cannot sync an external flash at more than 1/200s.
So I must use slower exposure and to find other ways to decrease the light on my subject... so, back to school

Hi Andrei,

Do note that, while 1/200s may be fine for on camera or other small flash units, for Studio strobes it may still be too fast! Whether that appies to your specific combination, I don't know. But it won't hurt to try it on a uniformly lit surface at 1/200s, and one or two notches slower.

As for the correct exposure, try getting there with smaller apertures, and buy a neutral density filter to allow shooting with a wider aperture with the required number of stops difference.

Bart

 

[Asher Kelman]

Hi Andrei,

Do note that, while 1/200s may be fine for on camera or other small flash units, for Studio strobes it may still be too fast! Whether that appies to your specific combination, I don't know. But it won't hurt to try it on a uniformly lit surface at 1/200s, and one or two notches slower.

As for the correct exposure, try getting there with smaller apertures, and buy a neutral density filter to allow shooting with a wider aperture with the required number of stops difference.

Bart

Bart and Anrei,

These are both such good points. I keep promising to buy myself Neutral Density filters. I MUST get them for my larger format camera! Otherwise I can't use the camera wide open to get the soft blur I want. Having ND filters of different power is really a must!

The other point of the need to go even slower than the synch speed may be surprising but is real. This is because some flashes, as one increases the power, say from 50 WS (Watt Seconds, I don't know what they use in Europe, is it Ergs/sec?) to 1000WS the time duration of the flash can really stretch out. worse the color of the light might be different as it builds up in intensity and then dies down from that level to zero again. Don't believe the flash duration specifications given without looking at what they really describe. Sometimes it's only the 50% of the light in the center of the peak that is referenced. This variation applies to Lumedyne. so to keep the time constant, increase the number of lights that power goes to and then the discharge tome will remain constant.

To escape and avoid and abolish color changes use a more sophisticated modern system such a Profoto, Eleinchom or Balcor, Porty and so forth. Same with flash duration.

So depending on you make of flash gear, the duration of the flash will easily fit in 1/200 sec or else it may not and that will give you these leaf/curtain problems too.

Asher

 

[Doug Kerr]

Hi, Asher,

Watt Seconds, I don't know what they use in Europe, is it Ergs/sec?

Joules.

It is of course the international, not just European, unit.

And of course neither watt-seconds nor Joules is a measure of luminous output.

Best regards,

Doug

 

[Andrei Zdetovetchi]

These are both such good points. I keep promising to buy myself Neutral Density filters. I MUST get them for my larger format camera! Otherwise I can't use the camera wide open to get the soft blur I want. Having ND filters of different power is really a must!

To escape and avoid and abolish color changes use a more sophisticated modern system such a Profoto, Eleinchom or Balcor, Porty and so forth. Same with flash duration.

So depending on you make of flash gear, the duration of the flash will easily fit in 1/200 sec or else it may not and that will give you these leaf/curtain problems too.

Bart and Asher, thank you for the tip about ND filters. I completely forgot about this, and I do have a filter like that for one of my lenses. It's a nice solution if I want to keep the lens wide open in order to have the soft blur in my conditions.

Although my studio strobes are Elinchrom, I don't know how sophisticated they are... I mean on their website are listed as entry-level. Anyway, in time as my experience and skill improves (and also my budget) I guess I'll switch to more advanced strobes.

So, looking at my photos, even 1/200s is not ok, I can see a slight darker gradient on a side. I guess I can fix it with a software ND filter in Lightroom, but I prefer to shoot right, with less adjustments after...

I've been shooting all day with 1/160s at f/8 and now my pics are looking ok. Well... ok for me, if I show you some I'm sure you'll find lots of issues