canon 20D flash sync at 1/320?

When I attach a canon speedlite 550ex (high speed sync off) on a 20D, the
shutter speed automatically reduced to 1/250s if I had it faster.

Is there a way to override this?

I found by experiment, I can flash sync at 1/320s (the experiment is done
with a 3rd party flash that does not change the shutter speed). So I would
like to use this speed with the canon speedlite, but it won't let me.

Any ideas? I checked all the custom functions and none of them look like it
would help.

 

High speed synch should be turned on.

 

As I'm sure you know, flash sync speed is driven by shutter mechanics.
Faster shutters allow faster sync speeds, the best for FP shutters being
1/300 (Minolta, Nikon). Canon max sync speeds are 1/250. (Some Nikon
dslr's like the D70 also have electronic shuttering in the way they use
the sensor thereby achieving 1/500 flash sync).

It's tough doing fast shutters. Nikon have reduced the max sync in the
F6 to 1/250 from 1/300 (F5). OTOH, the added value is also questionable.

With my Maxxum 9 (flash sync=1/300) I can get 1/350 shots using the
flash sync terminal. With my Maxxum 7D (flash sync=1/160) I can get
1/200. With a Maxxum flash it of course limits it to 1/300 and 1/160
respectively (and 1/125 with anti-shake activated).

With that and your experience it's reasonable to assume that the max
shutter speed is conservative by 1/3 to 2/3 of a stop to allow for
manufacturing variance, environment (temperature) and aging.

Bret and John recommend high-speed sync but that reduces your available
power considerably, esp. when you get to 1/1000 and faster. Most of the
flash light is wasted on the shutter curtains... it remains a good way
to get shallow DOF on bright scenes where you want some action freeze
and fill in the foreground.

But then so does a ND filter with normal sync flash... and paradoxically
due to the great inefficiency of HSS, you'll actually save flash
batteries with a 2 stop ND in place once you're at 1/1000 (or so) and
faster.

Cheers,
Alan

 

It's hard to know why you would want to.

That's because 1/250s is the flash sync speed for that camera, and it
will adjust the sutter speed accordingly.

And, as a practical matter, it rarely matters much anyway sicne the
flash speed it so much faster than the shutter. If you want to reduce
non-flash light then you can also reduce the aperture or use a neutral
density filter. Or turn off the lights.

 

I don't want to, that why I turn it off.
High speed sync is less powerful than low speed sync. Cheating the sync
speed is equivalent to boosting the flash's output power when used as a fill
flash.

Don't know why canon won't allow it even in manual mode. Why is it called
manual mode if the shutter speed is changed automatically for me??

 

Thanks, you're the only reply that understands my need (almost). I do plan
to use a ND filter to reduce DOF.

If I can cheat the sync speed, I could effectively reduce the sunlight's
intensity and enable fill-in flash at greater shooting distance, or save
flash power at the same distance (battery pack last longer), and less
blinding flash into the subjects' eyes.

This auto-limiting sync speed in *manual mode* reminds me of parents who
tell their child they can do whatever they want, and then meddle in the
child's business.

 

$Don't know why canon won't allow it even in manual mode. Why is it called
$manual mode if the shutter speed is changed automatically for me??

Remember that the output of a flash is controlled not by adjusting
its intensity but by adjusting its duration. The more power you want,
the longer the flash is on. The camera's maximum X-sync speed has to
be designed such that it will not cause problems with the longest
possible flash burst, which will depend on the flash unit but is
usually more than 1 ms and perhaps as much as 2 ms. With the flash
taking that long, that means that in order to achieve a maximum X-sync
speed of 1/250, the shutter curtains must be able to make their full
motion in 2 ms (during the first 2 ms, the first curtain opens; for
the next 2 ms, the shutter is fully open; during the next 2 ms, the
second curtain closes). 2 ms isn't a lot of time to take a physical
device, accelerate it from rest to full speed and have it
traverse the opening.

Chances are that if you fire a full-power flash burst with the
shutter speed set to 1/320, the second curtain is going to start
closing before the flash has completed firing. Now, since flash
output rises rapidly and falls slowly, the part of the flash burst
that you're blocking as the second curtain starts to close is quite
dim and likely will be very hard to spot in the results - but it's
nevertheless not syncing correctly.

On the other hand, if you fire a partial-power burst, it will take
quite a bit less time, perhaps much less than 1 ms, and in this case
there *is* enough time for the flash to complete before the second
curtain starts to close, even at a shutter speed above maximum X-sync.

As for why the camera doesn't allow you to pick a higher sync speed
at least some of the time, well, the camera doesn't know how long the
flash burst will be. That's controlled by the flash. And the flash
may not know, either; among other things, it depends on whether you let
the capacitor charge fully before firing the flash. The camera and
the flash don't even know at what strength to fire the flash until
flash metering is done, which (unless you use flash exposure lock)
doesn't happen until after the ambient exposure value has already
been set.

Anyway, the bottom line is that the camera's specs clearly indicate
that 1/250 is the maximum X-sync speed. If you expected something
else, you were mistaken. If you absolutely need to use a flash along
with a shutter speed that's only a third of a stop above what the
specs say, go ahead and use a non-dedicated flash (the camera doesn't
know it's there and therefore will not impose the maximum X-sync
limit) and hope for the best.[/QUOTE]

 

High speed sync has many problems. It has a much lower GN, even at just
1/3 stop faster than the x-sync (and gets progressively worse with faster
shutter speeds). It wastes power, with the majority of light at any given
time falling on the shutter curtains instead of the sensor. It has no
action-stopping power, beyond the shutter speed, as it is basically just an
auxilliary pulsing lamp.

--

 

You should know the answer to that quite well. A larger aperture
produces a smaller DOF. Depending on conditions (lack of tripod,
slow shutter speed required for shot, already using lowest ISO,
excessively bright day) it may be difficult or impossible to
increase the aperture unless an ND filter is available.

Technically, and rather obviously, an ND filter by itself has no
effect on the DOF. Cameras have many interrelated attributes (think
ISO/noise), but in the process of trying to show your mastery of all
things photographic by winning an easy debating point, you show that
once again a clear response that actually helps people probably
isn't the primary goal. The flash complicates matters, and if you
think that it would somehow prevent an ND filter from helping the OP
to get a shallower DOF, it would have been nice to explain why,
rather than baiting the OP with your question. You have better
things to do, and as I've said elsewhere, Floyd is currently on a
roll. Why not help him out. He needs you, desperately.

 

And of course you saw my reply as an "attack", just as I predicted
you would.

And as usual, your knee-jerk reaction is not to open the dialog
that you profess to prefer, but to turn an imaginary attack into a
real one.

 

THE VARIOUS GROUPS I OCCASIONALLY VISIT ARE HEREBY PUT ON NOTICE
THAT THEIR PREVIOUS RANTS, LIES, DEFAMATORY COMMENTS, DISPARAGING
REMARKS AND NICKNAMES, AND ALL OTHER FORMS OF DEFAMING ME, MY
GOOD NAME, MY REPUTATION, AND MY ABILITY TO EARN A LIVING WILL
HEREBY STOP - IMMEDIATELY. COMBINING WITH OTHERS TO DEMEAN ME
WILL BE CONSIDERED TO BE PRIMA FACE EVIDENCE OF A CONSPIRACY OF
TWO OR MORE PEOPLE TO COMMIT LIBEL, SLANDER, PERJURY, OR OTHER
FORMS OF DEFAMATION OF CHARACTER. ALL OF WHAT YOU HAVE SAID TO
DATE HAS BEEN CAPTURED INTO SAFE TEXT REPOSITORIES COMPLETE WITH
YOUR HEADERS SHOWING YOU ISP AND NSP, IP ADDRESS, AND OTHER
MEANS OF IDENTIFYING YOUR IDENTITY.

The various games played by so many people under the guise of
simple humor, flame wars, making sport, inventing lies, and other
forms of believed light-hearted fun will stop immediately wrt to
me.

I will no longer tolerate any aspersions cast at me, my family,
my career at work or in the military, or . . . or . . . oops.

Whew! Please excuse. I don't know what came over me. Maybe it's
the resemblence. Very slight. Very slight. No indication yet that
meds are called for.

 

Interestingly, he made similar accusations a couple of months ago
several hours after I praised him for posting the kind of helpful
reply I was trying to nudge him towards, and which I knew he was
knew he was capable of making. He sees things differently of
course, but what I see is that he has a really hard time accepting
criticism, seeing most positive criticism as negative, going so far
as to equate it with "attacks". Contrast that with a number of
others, especially from the much more mature Wayne J. Cosshall, who
finds ways to recognize useful suggestions even from those that go
out of their way to reply with insulting comments.

 

On 21 May 2007 15:23:00 -0700, acl wrote:

OP :
::: If I can cheat the sync speed, I could effectively reduce the sunlight's
::: intensity and enable fill-in flash at greater shooting distance, or save
::: flash power at the same distance (battery pack last longer), and less
::: blinding flash into the subjects' eyes.

You didn't miss anything and the OP gave every indication that he
fully understands the tradeoffs of using an ND filter. Proving my
contention that if Roger had any useful, helpful, unobvious
information to provide, he should have simply posted it, and it
would have been to everyone's benefit. He later claimed that his
reply was simply an "honest question", but his final, 'obvious'
explanation shows otherwise, the condescending "How does an ND
filter reduce depth of field?" was more likely asked for the reason
I gave than Roger's face saving after-the-fact explanation.

I showed how the ND filter could reduce DOF, said that Roger
should also know the answer "quite well" and I'd be amazed if the OP
hasn't also known that for many years, as well as most people that
have purchased ND filters. As you've shown, owning and using an ND
filter (or flash) is no great obstacle to understanding such a
simple concept.

 

The problem is that you find it extremely difficult to admit the
obvious. If a complete newbie asked "How does an ND filter reduce
depth of field?" I'd have no problem believing that it was a simple,
honest question. That you'd ask such a question and feign ignorance
given your history of knowing and writing papers delving into the
most minute, esoteric camera and photography details, such as
(remember this?) trying to prove or demonstrate that DSLRs have as
much DOF as point & shoot cameras, and then expect us to believe
that you're asking someone to explain to you how a ND filter can
reduce DOF? Give us a break! Whether we get along or rub each
other the wrong way is of no matter in this instance. I readily
admit that you know more about photographic minutia than most people
here, and most ng regulars that have read your messages probably
agree. But that doesn't mean that you can get away with pretending
to not understand such a basic concept as to how an ND filter can be
used to reduce the DOF. That's so simple one might almost expect it
to be rejected from a "Dummies" manual. And all this to avoid
having to admit the real motive for your question. Sheesh.

 

English translation: I remain no less resolute than Señor Bush
when it comes to admitting no error or deception, despite
overwhelming evidence sufficient to embarrass a Wolfowitz.

 

I simply never came back to this NG since that posting, but the use of
an ND to reduce DOF (by forcing a larger aperture) should be quite
evident to most, whether or not flash is used. Yes, more flash power
will be required, but it's still less than wasteful HSS.

Cheers,
Alan

 

My 580EX has a high speed sync mode and I can pick
any shutter speed I want. Don't know about your
flash. I have found that using a slower shutter
speed helps use more ambient light.