Flash - TTL, E-TTL, FEL - some basic questions

[FlyTVR]

I've just spent 20 mins typing in a question - and lost it! Here goes again.

I currently use a Canon 400D and an entry level Jessops flash gun.

I normally shoot in manual mode (when using flash), controlling exposure via aperture and syncing to the flash (between 125/250th sec). I've picked up this technique from using my studio lights.

I stumbled upon FEL the other day, and now realise I really don't understand flash - so please be patient with me. So here are my somewhat jumbled up questions.

TTL - uses a sensor to meter and calculate the required flash power. Am I right in thinking TTL does not require pre-flash?

E-TTL - does require a pre-flash?

FEL - Not used in auto modes. Allows me to (in layman's terms) tell the camera to meter (and calculate flash power) from the 'thing' I am focusing on, and then gives me 16 seconds to re-compose my shot (locking in the settings). FEL uses a pre-flash. If TTL does not require a pre-flash, why does FEL?

When using flash are just better sticking the camera into fully auto (no shouting please!)?

So, in the following scenario, what mode would the tog set the camera.

Scenario: A church - obviously low light, pro wedding tog (allowed to use flash).

Open question - I know, but thoughts appreciated.

Cheers.

TeaVR

 

[Grendel]

Moved to Talk Lighting for you

 

[FlyTVR]

Moved to Talk Lighting for you

Thank you

 

[HoppyUK]

I've just spent 20 mins typing in a question - and lost it! Here goes again.

I currently use a Canon 400D and an entry level Jessops flash gun.

I normally shoot in manual mode (when using flash), controlling exposure via aperture and syncing to the flash (between 125/250th sec). I've picked up this technique from using my studio lights.

I stumbled upon FEL the other day, and now realise I really don't understand flash - so please be patient with me. So here are my somewhat jumbled up questions.

In can be a bit confusing

If you are using the flash with manual power output, you are not making full use of the pretty wonderful auto exposure system in the camera. Don't know what Jessops flash you've got, but the ones they are currently selling are fully E-TTL compatible, at least while they are on the camera, or hard wired to it. I don't think they do remote auto flash.

TTL - uses a sensor to meter and calculate the required flash power. Am I right in thinking TTL does not require pre-flash?

TTL just means Through The Lens. In this context it refers to auto flash exposure metering, which is done by the same sensors as the normal metering system, and indeed they measure both flash and ambient light simultaneously. Told you it was clever.

E-TTL - does require a pre-flash?

Yes, it does in all auto modes (not manual). The whole auto flash function is controlled by the pre-flash, which goes off just before the main flash while the camera's meter is still active - so quickly you normally can't distinguish it.

The pre flash is visible when using FEL (Flash Exposure Lock) and also with second curtain sync photography. You can also see it when looking through the viewfinder and actually see a flash. That's the pre flash you're seeing as of course you can't see the main flash when the mirror is up. The pre-flash also sends out morse code style commands in a multi flash set up, telling remote units what to do, measuring and moderating their output.

FEL - Not used in auto modes. Allows me to (in layman's terms) tell the camera to meter (and calculate flash power) from the 'thing' I am focusing on, and then gives me 16 seconds to re-compose my shot (locking in the settings). FEL uses a pre-flash. If TTL does not require a pre-flash, why does FEL?

As explained above. The benefit of FEL is when the subject is off centre and there is a danger of the flash metering attempting to get correct exposure on the background in the middle of the frame. This will obviously over expose the forground and usually the main subject quite badly. You see it a lot. Just frame the picture with the main subject in the centre, press the FEL to fire the pre flash which sets and holds correct exposure, then recompose the shot. Works a treat.

When using flash are just better sticking the camera into fully auto (no shouting please!)?

So, in the following scenario, what mode would the tog set the camera.

Scenario: A church - obviously low light, pro wedding tog (allowed to use flash).

Open question - I know, but thoughts appreciated.

I would use auto flash whenever possible. It works very well, and of course it changes the flash output according to subject and distance all the time without you even thinking. It does it with bounce flash too, or when using any kind of diffuser or modifier. This is a nightmare with manual flash, impossible without a flash meter or by test firing and checking the LCD/histogram endlessly.

I can't speak for others, but I know this is a common technique: shoot in Av with E-TTL and the camera will match the flash to the f/number, and will also balance the shutter speed to the ambient light. Brilliant. Sorted. (Check to make sure you have the custom function for flash sync in Av mode set to auto, which is default.)

Sometimes the flash is a little too bright, or dark, ditto the background. I adjust the flash exposure with compensation on the gun, and adjust the background with compensation on the camera, and check the LCD until the balance is right. It only takes a few seconds.

In some situations, like when you're shooting a lot of pictures under identical conditions, eg studio, manual makes sense, but otherwise, auto flash removes a huge amount of guesswork and messing about.

Cheers.

TeaVR

HTH.

 

[FlyTVR]

In can be a bit confusing

If you are using the flash with manual power output, you are not making full use of the pretty wonderful auto exposure system in the camera. Don't know what Jessops flash you've got, but the ones they are currently selling are fully E-TTL compatible, at least while they are on the camera, or hard wired to it. I don't think they do remote auto flash.



TTL just means Through The Lens. In this context it refers to auto flash exposure metering, which is done by the same sensors as the normal metering system, and indeed they measure both flash and ambient light simultaneously. Told you it was clever.



Yes, it does in all auto modes (not manual). The whole auto flash function is controlled by the pre-flash, which goes off just before the main flash while the camera's meter is still active - so quickly you normally can't distinguish it.

The pre flash is visible when using FEL (Flash Exposure Lock) and also with second curtain sync photography. You can also see it when looking through the viewfinder and actually see a flash. That's the pre flash you're seeing as of course you can't see the main flash when the mirror is up. The pre-flash also sends out morse code style commands in a multi flash set up, telling remote units what to do, measuring and moderating their output.



As explained above. The benefit of FEL is when the subject is off centre and there is a danger of the flash metering attempting to get correct exposure on the background in the middle of the frame. This will obviously over expose the forground and usually the main subject quite badly. You see it a lot. Just frame the picture with the main subject in the centre, press the FEL to fire the pre flash which sets and holds correct exposure, then recompose the shot. Works a treat.



I would use auto flash whenever possible. It works very well, and of course it changes the flash output according to subject and distance all the time without you even thinking. It does it with bounce flash too, or when using any kind of diffuser or modifier. This is a nightmare with manual flash, impossible without a flash meter or by test firing and checking the LCD/histogram endlessly.

I can't speak for others, but I know this is a common technique: shoot in Av with E-TTL and the camera will match the flash to the f/number, and will also balance the shutter speed to the ambient light. Brilliant. Sorted. (Check to make sure you have the custom function for flash sync in Av mode set to auto, which is default.)

Sometimes the flash is a little too bright, or dark, ditto the background. I adjust the flash exposure with compensation on the gun, and adjust the background with compensation on the camera, and check the LCD until the balance is right. It only takes a few seconds.

In some situations, like when you're shooting a lot of pictures under identical conditions, eg studio, manual makes sense, but otherwise, auto flash removes a huge amount of guesswork and messing about.

HTH.

Right - I think I need to do some tests when I next have my camera with me.

So in AV mode the camera should use the aperture I specify, adjust the shutter speed (as you would expect in AV) but also adjust the power of the flash having sent out a quick (invisible) pre flash.

In the past I have tried to shoot in AV mode using flash - and the results were not good - mainly overexposed. The Jessops flash I have has no manual controls, so I guess all the hard work is done via TTL. In which case, what can I do to remedy this? I know I can adjust the shutter speed whilst in AV mode, but surely that is not going to sort things out? Maybe the metering had prioritised the background and blew the foreground?

BTW, thanks for taking the time to respond in depth

 

[HoppyUK]

Right - I think I need to do some tests when I next have my camera with me.

So in AV mode the camera should use the aperture I specify, adjust the shutter speed (as you would expect in AV) but also adjust the power of the flash having sent out a quick (invisible) pre flash.

In the past I have tried to shoot in AV mode using flash - and the results were not good - mainly overexposed. The Jessops flash I have has no manual controls, so I guess all the hard work is done via TTL. In which case, what can I do to remedy this? I know I can adjust the shutter speed whilst in AV mode, but surely that is not going to sort things out? Maybe the metering had prioritised the background and blew the foreground?

BTW, thanks for taking the time to respond in depth

I think you've got it. And no, adjusting the shutter speed will have no effect on the flash exposure.

As you say, it sounds most likely that the meter is picking up on the background because of an off-centre subject, therefore over exposing the foregound. That's what FEL is for

 

[Grendel]

Hoppy, you've provided some really useful info in this thread and have certainly answered some of my questions about the mystery of flash. Thanks

 

[incapete]

Which Jessops flash do you have? If it's not one with manual controls then it's not one of the current lineup so it might be worth checking that it works properly with eTTL.


I'd agree with everything that's been said already - except that I run into problems with very dark situations when the shutter speed given by Av mode is excessively long (even when increasing the ISO) and so I sometimes fall back to manual flash and exposure.

Does anyone have problems with FEL when they actually want Exposure Lock? I need to go through the custom settings to check if I can move it away from the * button.

 

[HoppyUK]

Hoppy, you've provided some really useful info in this thread and have certainly answered some of my questions about the mystery of flash. Thanks

Thanks Grendel, you're welcome And we haven't even started on high speed sync, second curtain sync and multi remote flash

One more thing I'll say about FEL and why it's necessary. I said it was necessary for off-centre subjects but this isn't strictly always the case; it's for occasions when the main subject occupies a relatively small area of the image.

This when the meter gets fooled into into exposing for the majority of the frame. With ambient light metering this is not a problem, but flash falls off very quicky with increased distance (double the distance, one quarter the brightness - inverse square law).

 

[Flash In The Pan]

If it's something like the Jessops 300AFD then iirc it doesn't have a manual option, the next one up the current range, the 360AFD does though...

 

[FlyTVR]

I'm still confused. I've just tried a little experiment.

Shooting in AV mode, aperture wide open, camera in ETTL mode, flash sync set to auto.

In a low light situation, I fire off a shot and the shutter speed (which is automatically adjusted in AV mode) is rather slow - maybe 1/2 sec to a second delay.

Now, I dont get this. Surely as the camera / flash are being clever using ETTL why doesn't the shutter speed just sync to the flash? ie. 125 - 250th? Is the camera exposing for the background? I realise that I can adjust the shutter speed in AV mode, but all this just seems fiddly.

I'm sure I am missing something BIG here! Confused

TeavR

 

[Merovingian]

Here's a well known, but useful, article which may help explain: http://photonotes.org/articles/eos-flash/

 

[HoppyUK]

Here's a well known, but useful, article which may help explain: http://photonotes.org/articles/eos-flash/

That is a very good link. But maybe a little long...

I'm still confused. I've just tried a little experiment.

Shooting in AV mode, aperture wide open, camera in ETTL mode, flash sync set to auto.

In a low light situation, I fire off a shot and the shutter speed (which is automatically adjusted in AV mode) is rather slow - maybe 1/2 sec to a second delay.

Now, I dont get this. Surely as the camera / flash are being clever using ETTL why doesn't the shutter speed just sync to the flash? ie. 125 - 250th? Is the camera exposing for the background? I realise that I can adjust the shutter speed in AV mode, but all this just seems fiddly.

I'm sure I am missing something BIG here! Confused

TeavR

Yes, in Av the camera is setting the ambient exposure for the background which is not illuminated by the flash. If you just want the flash exposure, then you must override this in custom functions, and then the camera will just set the x-sync speed. However, when you do this, the background will usually be very under exposed and dark.

 

[FlyTVR]

That is a very good link. But maybe a little long...



Yes, in Av the camera is setting the ambient exposure for the background which is not illuminated by the flash. If you just want the flash exposure, then you must override this in custom functions, and then the camera will just set the x-sync speed. However, when you do this, the background will usually be very under exposed and dark.

I've decided I hate flash!!

In all seriousness, I really need to practice. I was invited to Christening recently and although I did get some lovely shots, after the event it was apparent that I had been caught out by the fact that the camera was metering the ambient light and therefore some of the shots were blurred.

I tried overriding the sync and fixing the shutter speed to 1/200ths, but as already said, the background became very dark!

I also quickly figured out that flash (in my hands at least) seemed to fade over distance quite quickly. I'm guessing flash is difficult to get right when trying to take candid shots with a zoom???

Comments and advice always appreciated!!!

TeaVR

 

[incapete]

I tried overriding the sync and fixing the shutter speed to 1/200ths, but as already said, the background became very dark!

very short shutter speed = dark ambient light...
slow down the exposure as far as you can without getting a blurred background

I also quickly figured out that flash (in my hands at least) seemed to fade over distance quite quickly. I'm guessing flash is difficult to get right when trying to take candid shots with a zoom???

The light from your flash obeys the inverse square law - essentially this means that if you double the subject's distance from you, the light reaching the subject is reduced to a quarter.
Alternatively think the other way that if you double the distance you need four times the amount of flash power to give an equivalent exposure - or open up the aperture by an extra two stops.

Candid shots with a long zoom are pretty much out unless you've got fast glass, a powerful flash and low-noise high ISO handling woudn't hurt either!

 

[FlyTVR]

very short shutter speed = dark ambient light...
slow down the exposure as far as you can without getting a blurred background

I hate compromises!

Starting to realise that using flash is far from an automatic process. In fact, I can't really see the advantage of using AV mode in conjunction with flash if I'm having to deal with exposure. Surely I might as well shoot in fully manual? Remind me - will ETTL work in fully manual mode?


The light from your flash obeys the inverse square law - essentially this means that if you double the subject's distance from you, the light reaching the subject is reduced to a quarter.
Alternatively think the other way that if you double the distance you need four times the amount of flash power to give an equivalent exposure - or open up the aperture by an extra two stops.

Candid shots with a long zoom are pretty much out unless you've got fast glass, a powerful flash and low-noise high ISO handling woudn't hurt either!

70-200 F2.8. However, I don't think my 400D likes high ISO settings

When I get time, I'll upload some shots!

AND another thing. Am I right in thinking diffusers sap flash power?

Any more tips chaps / ladies?

TeaVR

 

[incapete]

I hate compromises!

Starting to realise that using flash is far from an automatic process. In fact, I can't really see the advantage of using AV mode in conjunction with flash if I'm having to deal with exposure. Surely I might as well shoot in fully manual? Remind me - will ETTL work in fully manual mode?

Av mode with flash is good when there is a reasonable amount of ambient light - I agree with you that once the ambient drops too much then Av just forces extremely long exposures that blur the backgrounds.

I think that eTTL works just the same in manual mode and this is what I've been playing with recently - set aperture to be as wide as possible (whilst still allowing focus on all the subject, especially an issue with groups) and set shutter speed to be 1/30 (or 1/60 if I'm feeling tired). This allows me to get some ambient light but the flash eTTL is still going to expose the subject.
I've got my eye on an IS lens to help with the longer shutter speeds.

70-200 F2.8. However, I don't think my 400D likes high ISO settings

I try not to go over 400 ISO on my 400D - the noise above that starts to be an issue in my shots.

AND another thing. Am I right in thinking diffusers sap flash power?

Anything that sits in front of the flash will sap power - diffuser, umbrella, softbox etc although don't discount bare flashes since you can still bounce them off the ceiling and they're good for long-throw flash like your candid zooms.

 

[HoppyUK]

I've decided I hate flash!!

In all seriousness, I really need to practice. I was invited to Christening recently and although I did get some lovely shots, after the event it was apparent that I had been caught out by the fact that the camera was metering the ambient light and therefore some of the shots were blurred.

In adition to the good advice from Incapete...

If it's camera shake, then Image Stabilisation will probably fix that. If it's subject movement, either in the background (usually not such a problem) or causing ghosting of the main subject, then you need to raise the shutter speed by a) increasing ISO, b) using a lower f/number, c) increasing the shutter speed a bit and putting up with a slighly darker background. If you're on Av, dialling in minus exposure compensation is the easiest way to get two stops, which is probably enough. Or if you shoot on P, I think the camera will track the ambient exposure level until it gets down to 1/60sec and then stops, precisely to avoid the blurring you've had (check handbook for details on this).

I tried overriding the sync and fixing the shutter speed to 1/200ths, but as already said, the background became very dark!

Yes. See above.

I also quickly figured out that flash (in my hands at least) seemed to fade over distance quite quickly. I'm guessing flash is difficult to get right when trying to take candid shots with a zoom???

Bounce flash is good for this as it spreads the light more evenly over a large area. You need a good dose of power though.

Comments and advice always appreciated!!!

TeaVR

If you can raise the ISO it solves a lot of flash problems at a stroke

 

[FlyTVR]

In adition to the good advice from Incapete...

If it's camera shake, then Image Stabilisation will probably fix that. If it's subject movement, either in the background (usually not such a problem) or causing ghosting of the main subject, then you need to raise the shutter speed by a) increasing ISO, b) using a lower f/number, c) increasing the shutter speed a bit and putting up with a slighly darker background. If you're on Av, dialling in minus exposure compensation is the easiest way to get two stops, which is probably enough. Or if you shoot on P, I think the camera will track the ambient exposure level until it gets down to 1/60sec and then stops, precisely to avoid the blurring you've had (check handbook for details on this).





Yes. See above.



Bounce flash is good for this as it spreads the light more evenly over a large area. You need a good dose of power though.



If you can raise the ISO it solves a lot of flash problems at a stroke

Event was in a domed building - so bouncing was not really an option

Right - I'll try P mode. To be honest I'm still swaying towards just shooting in fully manual mode!

One thinks - practice practice practice and........... hmmmm...... Canon 5D looks tempting

 

[HoppyUK]

Event was in a domed building - so bouncing was not really an option

Right - I'll try P mode. To be honest I'm still swaying towards just shooting in fully manual mode!

One thinks - practice practice practice and........... hmmmm...... Canon 5D looks tempting

Just thinking about what I imagine you're shooting, I think P might be worth a try, if only because it takes the thinking out of worrying about manual (though that works too!). It will track the ambient exposure as long as it dares before movement becomes an issue, then it gives you a darker background instead of movement blur. Sounds like a decent trade off.

5D won't change the laws of physics, which is what you're battling with. What you need is better high ISO performance for this kind of thing. So that'll be... 5D!

 

[cowasaki]

As explained above. The benefit of FEL is when the subject is off centre and there is a danger of the flash metering attempting to get correct exposure on the background in the middle of the frame. This will obviously over expose the forground and usually the main subject quite badly. You see it a lot. Just frame the picture with the main subject in the centre, press the FEL to fire the pre flash which sets and holds correct exposure, then recompose the shot. Works a treat.

oo didn't realise that, just set the D200's (nearest camera) function button to FV lock and it works a treat NICE

 

[kluen]

Just wanted to pop a note on here to thank everyone for the very useful info in this thread.

I previously owned a 480EXII and sold it on due to lack of use / frustration at results. Having another crack this time i've bought a 580EXII, at that cost i'll make my self persevere with it! From this thread alone I am already getting better results.

I have a few things to chuck into the mix...

If I have my flash on, but tell the camera not to fire it, will the AF beam aid the camera in gaining focus or will it be shooting around for no reason?

I'm assuming that shooting in Tv will work the same way as Av but trading the aperture control for time control? I haven't experimented in "the field" with flash yet.

My normal setup / location ties me to f1.4 and shutter speeds around 1/80 - 1/125 anything slower and I lose sharpness in the image due to motion. I've lost opportunities before due to performers moving out of the stage area, joining the crowd etc where there are no lights.

I think the next thing for me to do will be scour flickr for people in similar venues and get an idea of their settings.

I've also got some cactus v4's coming in the post, looking forward to stashing a strobe somewhere on stage with some of the friendly bands I shoot, should give some interesting results.

In summary I think incorrect use of flash in my line of shooting will be detrimental to others at the gig/show therefore I need to be confident I'm not going to be firing off more than I need to be.

Hmm this ended up being more of a ramble than I intended!

 

[FlyTVR]

Just wanted to pop a note on here to thank everyone for the very useful info in this thread.

I previously owned a 480EXII and sold it on due to lack of use / frustration at results. Having another crack this time i've bought a 580EXII, at that cost i'll make my self persevere with it! From this thread alone I am already getting better results.

I have a few things to chuck into the mix...

If I have my flash on, but tell the camera not to fire it, will the AF beam aid the camera in gaining focus or will it be shooting around for no reason?

I'm assuming that shooting in Tv will work the same way as Av but trading the aperture control for time control? I haven't experimented in "the field" with flash yet.

My normal setup / location ties me to f1.4 and shutter speeds around 1/80 - 1/125 anything slower and I lose sharpness in the image due to motion. I've lost opportunities before due to performers moving out of the stage area, joining the crowd etc where there are no lights.

I think the next thing for me to do will be scour flickr for people in similar venues and get an idea of their settings.

I've also got some cactus v4's coming in the post, looking forward to stashing a strobe somewhere on stage with some of the friendly bands I shoot, should give some interesting results.

In summary I think incorrect use of flash in my line of shooting will be detrimental to others at the gig/show therefore I need to be confident I'm not going to be firing off more than I need to be.

Hmm this ended up being more of a ramble than I intended!

I'm just pleased I've started a useful thread!!

For those interested, here are the results of my efforts - http://picasaweb.google.co.uk/DavHughes/LeoSBaptism#