Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

[Phil Perry]

Help desperately needed. I have just returned from a once-in-a-lifetime trip to Brazil’s Pantanal. While there I experienced some flash problems. I am sure that I have done something really stupid and will kick myself. But for the moment I cannot work out what the problem is.

I have not deliberately changed anything to the way I normally use my telephoto flash for night-time photography. But somehow things have gone wrong.

I am using a Canon EOS 7D with a 580 EX flashgun and a Better Beamer – for night-time photography using a spotlight to focus. As far as I can tell from the manuals the 7D and 580 EX are supposed to be compatible for ETTL shooting.

For as long as I can remember the flash synchronization speed has always been 1/250th second. However on this trip I have been getting shutter speeds of anywhere between 1/10th second and 2 seconds. I have had to use much higher ISO ratings than I have ever used before – up to 6400 – despite modest subject distances. As a result a lot of my pictures have blur due to two images being recorded – one from the flashgun and one from the spotlight. Also the extreme ISOs mean that pictures have high 'grain'.

My settings were :
Canon EOS 7D Settings : e.g. Tv (or C1, C2, C3); 1/250th ; Flash Control Enabled ; 1st Curtain sync
580 EX Settings : ETTL ; Manual Zoom at 50mm ; Better Beamer

If I do a test using manual metering – then lo and behold I get 1/250th shutter speed. But any of the TTL systems give me a weird range of shutter speeds.

I did not even realize you could change the default 1/250th setting – and no I did not accidentally set 2nd curtain sync.

I have now learnt that there is a setting for Av (Aperture Priority) that should be set to 1/250th sync speed as the default in Custom Function I is 'Auto'. I will set that for future use. But I am certain that for most of my photos I was using Tv (Shutter Priority) and the 1/250th should be the default sync speed for that as far as I am aware.

Any ideas anyone ?

[Trevoreast]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

the flash synchronization speed has always been 1/250th second

You mean max sync speed ?
Trev

[Trevoreast]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Can you clarify this question please.
From what you've written it almost looks like you expect a shutterspeed if 1/250 just by putting a 580ex on your camera.

At 1/10 or slower you may have had more joy switching to 2nd curtain.

If I do a test using manual metering – then lo and behold I get 1/250th shutter speed. But any of the TTL systems give me a weird range of shutter speeds.

Meter in low light and tell me if you get shutter speed of 1/250 - metering a bright scene will give the 1/250 max sync unless you used HSS

Trev

[DrJon]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Here's a quote from the (excellent) photonotes article (http://photonotes.org/articles/eos-flash/index.html) on EOS flash (which is the third time I've mentioned it here, but it is good):

"In Av, night and Tv (shutter speed priority) modes the camera meters for ambient (existing) light and fills in the foreground subject using the flash. It does not assume that the primary light source is the flash, and therefore the shutter speed it sets is the same as it would set if you weren’t using flash at all.

Alternatively you can switch to full auto (green rectangle) or Program (P) mode, which automatically expose for the flash-illuminated subject and not the background. These modes try to ensure that the shutter speed is high enough to let you handhold the camera without a tripod. The drawback of P and basic modes is that photos taken in dimly lit areas usually end up with black or poorly lit backgrounds."

The flash won't change the shutter speed you have selected in Tv mode (well, unless it was set to over 1/250th).

P.S. (After a quick hunt through my old sent e-mails) Best explanation of 1st/2nd curtain flash sync I have seen...

http://forums.dpreview.com/forums/read.asp?forum=1041&message=33391497

John

[Trevoreast]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Here's a quote from the (excellent) photonotes article (http://photonotes.org/articles/eos-flash/index.html) on EOS flash (which is the third time I've mentioned it here, but it is good):

Dr John that is a good article and they seem to keep it up to date as new flashguns are released. Please don't feel bad about quoting it 3 times, as you say it is good.
What many people might find very useful is if you quote a paragraph, then give a simple example of how it applies to every day shooting situations. WDYT ?

Trev

[DrJon]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

BTW just call me John, I'm not a Dr as such, it's just a nick-name I got on a (I imagine) long-dead forum a fair while back (IIRC because I spent a long time diagnosing what someone's issue really was and coming up with a fix, and it amused me - hey, if it's good enough for Rossi...), and I use it just so people know who I am between forums (plus I can remember my logins more easily). The only person here who might recognise me by it (Stalker) really doesn't need a nick-name to know who I am as he aimed me at the forum. (Oh, and the Jon is a Dr Who reference...)

In this context I don't think the paragraph needs much more explanation, it talks about fill flash and dark backgrounds so the most I could add would be something about back/side-lit subjects, but the OPs issue was not to do with that. (Plus I've done some long posts lately and thought concise might be worth a go.)

John

[Trevoreast]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

BTW just call me John

Will do John !

Trev

[colin C]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Go into menu, Custom Functions and see what you have set for the flash. If you have it on Auto, it will be looking to use the flash as fill-in. If you have it on 1/250sec Fixed, it will be using the flash as the main light source when you choose Av.

I suspect you have had the CF set on Fixed in this, or another body, which is why you were surprised when you saw long exposures and over-exposed shots.

Colin

[DrJon]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

(Since I'm creeping up on 100 posts I'll add another link - I'm pretty sure there is no need to be in CPS for this to work... I tried it in a second browser which shouldn't have any CPS cookies, apologies if I'm wrong.)

If you are thinking of playing with the 7D custom functions this article is worth a read:

http://cpn.canon-europe.com/content/education/technical/eos_7D_custom_functions_explained.do

Although personally I prefer this one:

http://cpn.canon-europe.com/content/education/technical/eos_5d_custom_functions_explained.do

(Despite the link name it's for the 5DmkII. Edit - ah, but the forum hides that bit anyway.)

John

[Trevoreast]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

John as I said it's all good stuff, some people sign up to multiple forums specifically to paste in an urgent question, and why not ?
Maybe he will return and answer a couple of basic questions that will help us solve this simple problem, you never know

Trev

[Phil Perry]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Thanks for all the comments guys. Most useful. I will check out the references. I just cannot believe that Canon change something so basic without telling everyone. I never had any problems at all on the 50D, 40D, 30D, 20D, 10D and prior film cameras.

[MX5]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

For anyone who gets stuck or can't fathom CF's ... but still wants an increased probability of a decent snap ... set to Full Auto (Green rectangle). I know it'll only be a JPEG ...

It's like scrambling up a mountain ... no points lost for using hands and bottom to get over a bag step.

[Phil Perry]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

Mystery solved.

I had two CF functions wrongly set : CF I-7 - Flash needs to be set for 1/250th (not Auto) and CF I-6 needs to be set to disabled (safety shift).

Now I will always get a 1/250th flash sync speed which I need for my night-time telephoto flash with spotlight (for focussing) photography.

Thanks everyone.

[djguk47]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

I have a 430EX II and 50D, and have read and re-read about CF I-6 which tells me that if enabled and I am shooting in either Tv or Ae modes and the light suddenly changes then the camera automatically shifts the aperture or shutter speed.
I enabled this function as I figured if I was shooting say outdoors and the light changes then the camera would automatically make the necessary adjustments for the change in light.

Am I correct, am I setting something that is unnecessary, am I restricting myself when using flash????

David

[Phil Perry]

Re: Help Needed: Flash Sync Problem : Canon EOS 7D & 580 EX

David

The problem I had with using CF 1-6 was that the camera chose a long shutter speed and so the spotlight (used for focussing) made an image as well as the flash. I needed a short shutter speed (1/250th) so that only the flash registered.