Is X-Sync speed a "big deal" anymore - now that we have High-speed synch on powerful flash units?

Hi all,

I've been plowing through an online "book" on Canon EOS Flash Photography
http://photonotes.org/articles/eos-flash/ (OK - it's really just a web page,
but ran to 99 pages when I copied and pasted it into Word).

In the past I've occasionally come up against the 20D's 1/250th X-Sync
"limitation" - I knew that I could go faster if I used High Speed Sync, but
for some reason I had it in my mind that High Speed Sync (or FP Mode) was
vastly inferior, and was likely to get poorly metered results.

How wrong can a mouse be?

Having read through the article it appears that the only limitation is that
it efectively reduces the output of the unit by around 1/3 - often a
non-issue with big monsters like the 580EX (especially several of them).

To "prove the point" I setup my 20D on manual and in a room with very
subdued lighting I set it for 1/250 (and some at 1/500) - F2.8 - F5.6 -
attached my remote transmitter, and let rip with a couple of 580EX's pointed
at my victims. The result? EVERY one absolutely spot on - PERFECT exposure.

The only limitation I hit was the 580EX not being able to cycle fast enough
when I fired a burst of shots.

With this in mind, it begs me to ask the question: "Is an X-Sync speed of
"this" or "that" simply irrelivant in this day and age?

Additionally, can anyone think of a reason why Canon couldn't even give us a
custom function that says "Use FP Mode when >1/250 of a Sec"?

Would be interested to hear peoples thoughts.

 

High-speed sync works differently from normal flash mode in that the flash
actually becomes "slower" -- it fires multiple pulses instead of a single
flash, and thus is not good for stopping motion -- the exposure time is
actually controlled by the shutter speed, whereas the flash duration is
much shorter in normal mode.

Other disadvantages: the flash may use more battery power and recycle
more slowly, and will give you less total exposure; you can't calculate
flash exposure using flash power (guide number) and aperture any more;
and it will only work with a dedicated electronic flash unit.

Apart from that, there's no reason not to use it. As you discovered,
it does work as advertised. It's just not a "real" flash sync mode.

 

C J Southern skrev:

http://www.kenrockwell.com/tech/syncspeed.htm

 

Interesting article, but from what I've read previously, his "limitations"
don't appear to totally hold true in a Canon EOS Flash environment ...

eg. "On every camera I own the FP mode reverts back to totally manual
exposure calculation" - I guess he doesn't own a Canon 20D or above, because
the metering works just fine in TV, AP, and M modes.

"The flash always pops at full power on the flashes I've seen. Thus as above
you lose battery life, have long recycle times, no high frame rates and all
the other disadvantages above." - It probably does, but that doesn't mean
it's on at full power for long - or any longer than it would have been at
the X-Sync shutter speed. From what I've read it's pulsed at 50,000 times
per second.

"Since only a fraction of the light at any time is exposing the film or CCD
you lose a lot of light, again getting you back to the problems of limited
flash range" - Others have said "you lose about 1/3" (personally, I wouldn't
know) - again, with multiple, powerful units like the 580EX I wondr how much
of an issue this is?

 

Then again, if you're shooting with a shutter speed of upwards of 1/250th,
isn't that going to freeze most motion anyway?

I've only ever tried it in Av and Tv and M modes, but left the camera to
sort out the (foreground) exposure - so far it seems to be able to hit the
nail on the head everytime.

 

I found this article: http://www.photozone.de/3Technology/flashtec5.htm


B.

 

The relevance come in when you are working in the studio with strobes, and a
faster shutter speed would allow you to lessen your depth of field.

 

I take it that this is because studio strobes put out a pre-set amount of
light, whereas in an E-TTL (2) system the camera can just shut off the light
source when it's had enough light?

 

Not necessarily preset, but limited. Some sets of strobes, like my cheap
ones, have only a couple of stops of latitude in their settings others have
considerably more, but a max synch speed of 1/250, or in my 5Ds case, 1/200,
can lead you to shooting at f8 more than one would like.

 

So in that situation you can't shoot at, say F4 @ 1/125 because it won't
freeze any motion, and you can't shoot at F4 @ 1/200 because the strobes
don't have enough grunt (or if they do they wash out skin tones etc)?

 

Thanks for that - it helped to plug up a few of the gaps in my FP knowledge.

 

Something like that. Full power on my strobes results in a meter reading of
f16 and 1/250. So, two stops either gets me f11 and 1/125, f8 and 1/250 or
f22 and 1/60th. A shutter of 1/500 would get me to f5.6, large enough to
get the backdrop nice and soft...

 

Not nearly as well as a flash that's at least an order of magnitude faster.

It should work fine, you just need to understand its limits.

 

direct flash is not the most pleasant light, and with high shutter speeds
you get the equivalent of a coal miner's point of view, whatever is directly
infront of you is brightly lit, everything else is black.

somehow I don't think that HP sync works with slaved flash so you won't get
any key fill light.

I've always worked the other way around, slow shutter speeds, nearly wide
open lens, minimal flash power, camera on a tripod, so the background gets
to build up, I have a properly exposed subject with enough background to
give the image some detail and depth.

this reply is echoed to the z-prophoto mailing list at yahoogroups.com

 

As far as I can tell, High Speed sync shrinks the guide number
exponentially as shutter speed exceeds X sync.

I have found it useful only when the subject is close to the camera. On
wide angle shots in the sun, you could wind up with very little fill flash,
not as much as you could have achieved with regular flash.


What I would love to see is a leaf shutter as rugged and fast as a focal
plane shutter. Now we could get some serious bokeh with our fill flash.
Wouldn't that be nice?

Patrick

 

Outdoors or anywhere where ambient levels compete with flash, what you say
is true.

However, if you are shooting manual flash ( a studio strobe) in a studio,
and keeping the ambient light real low (not dark, just tungsten lit room),
you can use any shutter speed as long as the shutter speed and aperture
combination do not allow ambient light in the exposure, or very little. And
so flash is dominating and thus controlling the exposure, so shutter speed
is much less relevant. This is why a flash meter only registers aperture
when I pop the flash to meter it. So, shutter speed is irrelevant in a
studio, and most certainly won't affect DOF, only the aperture on the lens
will affect DOF in this environment.

Patrick

 

?? On my flash meter, I set the shutter speed required, the meter matches
that with the appropriate aperture, since all it can measure is the amount
of light, not the speed of the shutter. There is an interconnection between
the shutter speed and the aperture, and, while shutter speed is less
important in the studio than in the field, because of the ease of
controlling the light, you still need to be able to change the shutter speed
to compensate for the aperture. If the fastest available shutter speed is
1/200, it is hard to get to f2.8 with strobes that only have a range of 2
stops.

 

High Speed synch is useful in somewhat limited situations, and because
only part of the film/sensor plane is exposed any one time, highly
inefficient, draining the flash batteries very quickly while affording
only short flash to subject range, and at that with the widest apertures.

That last bit is okay, as the typical use of HSS is when there is a lot
of ambient light and a wide aperture is desired for creative purposes.
This could over expose at synch limited speeds, so HSS allows shooting
at high shutter speeds and not over exposing the ambient, while getting
fill and/or "freeze" from the HSS.

I've used HSS from time over the past 8 years or so, but rarely has it
really been needed or produced wonderful results. A set of ND filters
can get a wide aperture shot down to sycn speed (may present a
vignetting problem unless your sensor is "cropped")

The Nikon D70's sensor based 1/500 synch speed is a wonderful solution,
and much better than HSS, IMO.

Cheers,
Alan

 

Studio strobes don't have HSS. You charge them to the energy level
required and they dump completely (opposite of TTL/E-TTL flashes that
are fully charged and dump down to a point cut off by the thyristor
under command of the camera exposure system).

You can dial your strobes down and/or put covers over them to lessen the
light output and/or add ND's to the lens to get those fat aperture shots.

Cheers,
Alan

 

Skip M wrote:

I'm sure this is not news to you Skip:

In flash work, aperture controls both flash and ambient light, but
shutter speed contols _only_ ambient light.

This is why, for most flash photography where ambiient is not desired,
that the max sync speed is used. (And the beauty of leaf shutters with
studio strobes).

If your studio strobes have limited control (like mine) then you sew
extra softbox difusers, bounce the light off of white cardboard, use
ND's or slower film to get those fat apertures...

My flash meters (Minolta VF and Sekonic 508 and 558) have a "ratio"
reading for flash v. ambient. For most studio work, the ratio is 100%
flash, but if you reduce the shutter speed enough, then the flash
content drops (of course).

Cheers,
Alan.