Some pointers with flash photography needed please

I apologize in advance if this has been already discussed.

I have recently started shooting with a flash (Canon 580 EX II) and honestly flash metering has me a bit perplexed.

For one, in ETTL mode, it almost always leads to over-exposure leading me to dial in a -1 to -1 2/3 ev flash compensation for the typical light conditions I've been shootin in.

I am not sure how flash metering works, that it decides to put out so much light that would lead to over-exposure. It has been a trial and error exercise so far with me randomly dialing in a negative flash compensation in the vicinity described above.

Question 1) Why does ETTL behave that way? And how do you folks normally figure out what compensation to use? Is there some rule of thumb I can learn to get this right without trial and error?

Question 2) An extremely strange issue. I put brand new batteries in the flash unit. It fires great. I put a flash extender (BB) and it does not fire, even after many tries. I remove the BB and it fires fine again. Any possible explanation?
The BB lens is not dirty or mucky; and even if it were, I would imagine, if anything the flash would generate even more light after metering through that muck?

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Originally Posted by Sidharth Kodikal

It has been a trial and error exercise so far with me randomly dialing in a negative flash compensation in the vicinity described above.

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From watching the videos of Joe McNally and Scott Kelby, they're also using trial and error, too, but trial-and-error based on their experiences I suppose.

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Question 1) Why does ETTL behave that way? And how do you folks normally figure out what compensation to use? Is there some rule of thumb I can learn to get this right without trial and error?

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Don't know about the Canon's ETTL, but in general TTL is not supposed to behave the way you have experienced, i.e., produce over-exposed photographs. I figure out what compensation to use by trial and error :), what's in the scene that you're photographing (dark subject vs light subject, etc). Other than that, you can use a flash-light meter or, like photographers did in the old day, use the exposure settings given on the settings chart that comes with your flash light. In other words, for a given ISO, find out how far your subject is and set the f-stop accordingly, and use the shutter speed to control the background exposure. Yes, that would be manual mode of using the flash and the basic way to use flash ;)

Sidharth- Apologies in advance if this is too simple or obvious to mention but here goes. If you do not have your flash set for high-speed synch (H-synch), then the camera will default to the synch shutter speed and your images can be over-exposed due to the available light.

As John mentioned above... if the ambient exposure is correct before you turn on the flash then you do not have the flash set to high-speed sync. The camera is defaulting back to 1/250. Easy enough to check, just watch the shutter speed drop when you turn on the flash.

As to why when using the beamer the flash will not fire???? There is no physical contact that would effect electronic connections.

Use -1.7 or -2 as default flash comp for fill in outdoors. This will typically provide fill without having the image look flashed.

Best,

Chas

Chas

Thanks for all the replies.

John, Chas, yes I do make sure to use high-speed synch, as my 50D defaults to 1/250th without it, and I almost always shoot faster than that.

But, for the sake of discussion, even if that weren't the case:
Let's say the ambient exposure was correct and I just wanted fill flash, and I forgot to put the flash in high synch, the resulting over-exposure would be because of the ambient light and not the flash, right?

What I am trying to learn and avoid is over-exposure because of the flash and to eliminate the guess work with the -ve comp involved.
It sounds like when using fill flash, dialing in a healthy -ve compensation is the norm. Not sure why the ETTL is not smart enough to not require that (it's more likely that I'm the "not smart enough" one here :)

Re. the beamer issue, I have no possible explanation. I might trash that thing because I've lost some good shots because of the flash not firing.

Don't trash your BB. As Chas said it has absolutely nothing to do with the flash firing or not. Figure out the flash problem first and then try the beamer again.

I am very aware that the BB is just a couple of flimsy pieces of plastic strapped together with a velcro strap: pretty low tech, not connected to the electronics of the flash in anyway.
And hence the confusion.

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Originally Posted by Sidharth Kodikal

But, for the sake of discussion, even if that weren't the case:
Let's say the ambient exposure was correct and I just wanted fill flash, and I forgot to put the flash in high synch, the resulting over-exposure would be because of the ambient light, right?

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Sorry to jump in between your conversation with John and Chas, Sidharth, but if you don't mind me asking, what exposure mode you are shooting in?

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It sounds like when using fill flash, dialing in a healthy -ve compensation is the norm. Not sure why the ETTL is not smart enough to not require that (it's more likely that I'm the "not smart enough" one here :)

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I think, generally speaking, the reason that one wants to reduce the power of the flash (by whatever means) is to make the final photograph looks more natural and not one that is shot with flash. And your computer aka camera and flash light do not know how natural you want your photograph to look.

Here's a site for learning the use of flash in general:

http://strobist.blogspot.com/

On-camera or off-camera, it's the same principles.

Desmond, sorry I didn't reply specifically to your first post. I was still chewing on the full manual flash approach your mentioned. I have played with that a bit, but it's been trial-and-error too; no fool proof formula yet.

I generally shoot Av or manual.

Thanks a lot for the link. Much appreciated. Obviously I have quite a bit of reading to do.

Let's say the ambient exposure was correct and I just wanted fill flash, and I forgot to put the flash in high synch, the resulting over-exposure would be because of the ambient light, right?

Lets say your settings were 1/500 @ F6.3. If as mentioned above you forgot to set the flash to "High Speed Sync" the camera would default to 1/250 resulting in over-exposing the ambient by a full stop.

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Originally Posted by Sidharth Kodikal

Desmond, sorry I didn't reply specifically to your first post.

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You did thank all for the replies. I simply realized you were directing your questions at John and Chas specifically. :)

I'm pleased you posted this Sidharth, as I too, have avoided using Flash, partly not to spook the wildlife, but also, it seem appears to be a little bit of a 'dark magic' at times to me. :)

Thanks for ALL the replies, this has been very enlightening:D now to go and try it!

cheers
Steve

Agree with Chas on the BB, it has no affect on the Speedlight - thats a strange one.

Regarding ETTL flash - I started using more manuel flash about a year ago. Setting the distance with the ring on the flash and paying more attention to my subject distances; then, making adjustments. I only use the BB when the subject is over 20 feet from me, I think it adds 2.5 stops of light so be careful. ETTL is easy and manual is more precise when applicable IMO.

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Originally Posted by Sidharth Kodikal

I

Question 2) An extremely strange issue. I put brand new batteries in the flash unit. It fires great. I put a flash extender (BB) and it does not fire, even after many tries. I remove the BB and it fires fine again. Any possible explanation?
The BB lens is not dirty or mucky; and even if it were, I would imagine, if anything the flash would generate even more light after metering through that muck?

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Hi Sidharth, are you sure your Better Beamer is no firing. Sometimes I think mine is not firing, but due to the sides of the unit it is not always easy to see it fire. Try looking almost directly at it and test fire, as mentioned there is no correlation between firing or not with your BB on or off.

Sidharth, Is the flash not firing or is the beamer missing its mark. I find I must prop-up the strobe a bit under the power pack to get enough lift because the beamer pulls the strobe down. I set my beamer up with the strap tucked under to strobe so it lifts it a bit from the power pack. I’ve seen some who tape a piece cardboard under the strobe to lift it. I the flash is firing, try this to get the light on target.:o

Thanks for all the comments. Darren, Gene, I have confirmed that the flash does not fire with the BB on, and the exif info corroborates this too.
I was out hiking early today and since I didn't really need light from flash, I stuck the BB on the flash with fully charged batteries and took about 30 shots. Surprise, the flash fired on *one* of them!
Later in the day, when I did need the flash, I got rid of the BB and the flash worked reliably.

Sindarth, I agree with Gene it is very likely that the BB it is because the added weight to very front of the flash disconnects the flash from the flash shoe ... this happened with my setup in particular when the flash is mounted on the Canon Off Camera Shoe Cord2. It is worth to check whether the flash-shoe of the cable is working correctly and in case it is loose it is easy to repair have a look at http://photo.net/canon-eos-digital-camera-forum/00DriM

Geraldo

Thanks a lot Geraldo. And sorry, Gene, I hadn't completely understood your post.
I will try your proposed solutions in the evening, but I have a feeling that will do the trick. Embarrased that I didn't even think to try that diagnostic test :(
The camera is under warranty, so I wonder if this is something Canon will fix.

Sidharth, if you can't resolve the BB issue let me know. I'll be home in less than 2 weeks and could meet you and try to figure it out.

Sidharth, The issue I spoke of is different than what Geraldo is writing and given your latest post I’m inclined to think he’s got the closest answer to your problem. It makes since that the BB might be weighting your flash unit forward and causing the hot shoe to disconnect in some way. What I was saying is the weight of the BB pulls the angle of the flash down so that the beam would not light-up my target. The fix is to get something under the strobe to prop it up a bit. Good luck…

Gene, thanks for confirming that I had understood your post correctly. But there was enough information in there to have gotten me thinking. But Geraldo pretty much spoon fed me the answer!
I just confirmed that even without the BB, if I weigh the flash down ever-so-slightly by either putting a finger on it, or even simply having the camera pointing downwards, the flash will not fire.
So, it is an issue with the contact.
I've never had to use Canon warranty service/repair, but if this isn't covered, some DIY work is in order.
Thanks a lot, Geraldo for the solution, and to everyone for the help.

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Originally Posted by Jeff Parker

Sidharth, if you can't resolve the BB issue let me know. I'll be home in less than 2 weeks and could meet you and try to figure it out.

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Thanks for the offer, Jeff. The case is solved :)