Off camera flash

[ozimax]

I purchased a simple shoot through umbrella and stand (from Ronny in Adelaide) and another Canon flash a little while back. I have been experimenting with the off camera flash technique. Here's a couple of first attempts. C&C appreciated. (I'm not too concerned about background clutter etc, more about actual flash/exposure technique).

Took this shot in full midday sun without the umbrella. (Sometimes it gets a tad windy up on the headland at Coffs).


Shot of my nephew in late afternoon.


Mucking around shooting into direct late afternoon sun. (Don't worry about the cluttered background - I wanted to see how the flash would operate into almost direct sunlight etc)

[Alpha_7]

These are all great, my favourite would be the first one the balance between ambient and the flash is the most compliementary. In the second, the light is very soft, but perhaps a little too flat. In the last, you've managed to balance almost direct back lighting from the sun, the light looks a little too warm.

[CraigVTR]

Agree with what Craig said, but also in #1 try shifting the pose a bit so you do not get the small patch of direct sun on your models cheek. You could also try underexposing your background by say 1 stop and dialing in an extra stop of exposure to the flash. Underexposing the background will give it a little more colour as in your posted shot it looks a little washed out.

[gstark]

I'm not too concerned about background clutter

Be that as it may, these are good images. And the first two are very bloody good, especially in terms of including a background in a photogenic manner.

In the first you have a simple but evident background, nicely OOF, well exposed, but all done in a manner that complements, very simply, the subject in the image.

For lighting in this setup, I start by working with what would be the correct exposure for the background; perhaps I'll dial it back a half to a full stop - chimping will tell me what I need. Then I'll calibrate that exposure setting back so that its shutter speed is supportive of flash, and then finally I'll set the flash power to match that of the selected aperture, again perhaps dialed down in power. Again, chimping will tell me where I am.

[ozimax]

Agree with what Craig said, but also in #1 try shifting the pose a bit so you do not get the small patch of direct sun on your models cheek. You could also try underexposing your background by say 1 stop and dialing in an extra stop of exposure to the flash. Underexposing the background will give it a little more colour as in your posted shot it looks a little washed out.

Thanks Craig (and Craig) for the C&C. (The model is in fact the missus, who hates having her photo taken, even though she is very photogenic. She is female after all and there is an anti-photo gene in most of the fairer gender. )

As for underexposing the background, I will try your comment. As for moving the subject, I didn't think of that
as we were perched on the edge of the cliff overlooking the break wall, but your comment makes sense.

[ozimax]

For lighting in this setup, I start by working with what would be the correct exposure for the background; perhaps I'll dial it back a half to a full stop - chimping will tell me what I need. Then I'll calibrate that exposure setting back so that its shutter speed is supportive of flash, and then finally I'll set the flash power to match that of the selected aperture, again perhaps dialed down in power. Again, chimping will tell me where I am.

Gary, here is the method I employed yesterday. I set up the flash/umbrella using an on camera 580EXii as a non firing master and a 430EXi on the light stand as the slave. I took a few shots to check exposure using eTTL, then simply moved the stand back or forward until the exposure seems correct. I know this seems simple. I also set the flash to Hi Speed sync.

I will make an attempt at following your suggestions here and see how I go.

Many thanks.

[gstark]

I took a few shots to check exposure using eTTL, then simply moved the stand back or forward until the exposure seems correct.

Given that eTTL measures your exposure through the lens at the time of making the exposure, I'm not sure that moving the stand would actually have all that much effect on your exposure. If you move the stand back, eTTL (by definition and design) punches out a little more light to compensate, as it's trying to achieve what it believes is the optimal exposure. Move the stand closer, it punches out a little less, for the same reason. Each time you press the shutter, it's still trying to achieve the same goal.

eTTL automatically adjusts the power to compensate for the changed distances, which is probably the exact opposite of what you want it to do.

As for moving the subject, I didn't think of that as we were perched on the edge of the cliff overlooking the break wall,

"can you just take another step backwards, dear? "

[ozimax]

I took a few shots to check exposure using eTTL, then simply moved the stand back or forward until the exposure seems correct.

Given that eTTL measures your exposure through the lens at the time of making the exposure, I'm not sure that moving the stand would actually have all that much effect on your exposure. If you move the stand back, eTTL (by definition and design) punches out a little more light to compensate, as it's trying to achieve what it believes is the optimal exposure. Move the stand closer, it punches out a little less, for the same reason. Each time you press the shutter, it's still trying to achieve the same goal.

eTTL automatically adjusts the power to compensate for the changed distances, which is probably the exact opposite of what you want it to do.

I happily stand to be corrected here Gary (as I'm usually wrong when it comes to technical stuff!) but I thought that "through the lens" metering meant that the exposure was calculated by the lens/camera, irrespective of the flash. Of course, this info is transmitted to the flash(s) (slave(s), master etc).

Moving the flash a few inches either way does seem to make a difference to the exposure. In the yesterday's situation it was difficult as the flash stand was perched on a little tussock of grass and could not be moved.

I did think of pushing the missus over into the Pacific but then I remembered that it is I who is insured and not her.

[surenj]

I would agree with Gary.

the TTL will compensate when you move the flash. The exposure will be slightly different with each click because there will be slight movement on your part and therefore the TTL 'reading'.

If you wanted to underexpose the background, I would underexpose using the shutter speed and dial the flash up using exposure compensation.

The easiest [providing constant ambient] is to manually underexpose the background; chimp; then dial the flash up to where you want to, by chimping. [keep histogram to right, so that it's slightly overexposed] Once you got your correct flash exposure, you click away until you get the expression you want.

[gstark]

but I thought that "through the lens" metering meant that the exposure was calculated by the lens/camera, irrespective of the flash. Of course, this info is transmitted to the flash(s) (slave(s), master etc).

Yep, exactly.

The camera will read the light being reflected off the sensor (or filum) from the subject during the actual moment of exposure, and will, as you correctly point out, transmit that information do any connected flash heads that understand eTTL.

The point is though that, if you move your light source (let's say) further away from the subject, given all other elements being equal, then your flash heads' output will be weaker, and thus the camera will tell those heads to stay lit a little longer, thus increasing their effective output.

The camera is still wanting to meet a certain goal, that being what it calculates as the correct EV required for the image.

Moving the flash a few inches either way does seem to make a difference to the exposure.

Is it the exposure that's different, or the spread of the light, and how it falls upon the subject? Let's try to look at two images where you think you're seeing this, and please include the EXIF.

I can readily accept that the light spread will be different, and this can and will alter how the image appears to you. With a light source further away from your subject, the light spread will be greater, and this should be observable in the image. Similarly, moving the light source closer to the subject should also be observable when comparing the images.

In the yesterday's situation it was difficult as the flash stand was perched on a little tussock of grass and could not be moved.

And here was I thinking that you had connections in that realm.

[ozimax]

Is it the exposure that's different, or the spread of the light, and how it falls upon the subject? Let's try to look at two images where you think you're seeing this, and please include the EXIF.

Will do, many thanks.

[ozimax]

Is it the exposure that's different, or the spread of the light, and how it falls upon the subject? Let's try to look at two images where you think you're seeing this, and please include the EXIF.

Here goes Gary:

Image 1 exif:
Manual mode F5.6 1/125 ISO 100
Off camera 430EXi shot through white umbrella positioned 1.5m from subject


Image 2 exif:
Manual mode F5.6 1/125 ISO 100
Off camera 430EXi shot through white umbrella positioned 1.0m from subject


Image 3 exif:
Manual mode F5.6 1/125 ISO 100
Off camera 430EXi shot through white umbrella positioned 2.0m from subject


Image 4 exif:
Manual mode F5.6 1/125 ISO 100
Off camera 430EXi shot through white umbrella positioned 3.0m from subject


I hope this helps to unravel the mystery between my ears!

[gstark]

What mode was your flash set to for these images?

I note tht for all of these images, the camera was in M, and thus the only variable in your exposure for these was the amount of flash output - which would be a variation in the duration - that was permitted for these images.

Making the presumption that Canon eTTL still controls the flash even when in M, what I'm seeing is that the exposure across images 1, 3 and 4 seems to be pretty well constant. I'm not really seeing any variation in either the primary subject's, or the background's, illumination across these three images.

And that was pretty much what I expected to see. As you move the light further away from the subject, the power of the flash diminished, and thus the camera, through eTTL, permitted a longer flash duration to make up for the longer distance.

What do the histograms show us for these images?

Image #2 is the potentially more interesting one here - it does appear to be ever so slightly over-exposed compared with the others. I think that there are two issues of note here.

First, you've moved the flash closer to the subject. This (obviously) is the reverse of what's happened in #s 3 and 4. As you move the light closer to the subject, the power of the flash increased, and thus the camera, through eTTL, permitted a shorter flash duration to make up for the reduced distance.

Now, one meter is actually fairly close to the subject, and it may be that this about the edge of the close operating distance of eTTL and your flash. Basically, there's a point where the light source gets too close to the subject, and there's simply not enough time for the camera's metering systems to read, react, tell the flash head to shut down, and then have the flash head react and shut itself down. Remember that we're talking about doing a lot of stuff in less than a poofteenth of a millisecond ... and I suspect that your one meter distance here may be at the bleeding edge.

Second, your one meter distance is, er, quite close. To the extent that we're seeing the brolly in this image. Think about what's illuminating that brolly at the time of the exposure, and then consider that it may be just a little bit hot, exposure wise.

This has some potential to affect your metering, depending upon what section of the camera's metering system was in use. In this instance you're way off to the left edge, probably beyond the metering area. I don't think that this is an issue - I don't think that your exposure has been affected by this (why?) - but it's certainly a point to keep in mind.


Finally, and this is not relevant to this post, but handy to be aware of nonetheless, we may need to consider from where the metering is being done. In this case, you're TTL, so Robert's your mother's brother.

But what if you were reading from the flash head, with the brolly in place? Consider the placement of the flash head's sensor in relation to your subject, and the possibility that the brolly's location may interfere with that line of sight. That one's a trap for young players.

[ozimax]

What mode was your flash set to for these images?

The 580EX on camera was set to master, and did not fire. (It does does fire a pre-flash however to communicate data to the 430ex slave flash on the umbrella - evidently Canon flashes fire 3 times in a "poofteenth" of a second ).

I note tht for all of these images, the camera was in M, and thus the only variable in your exposure for these was the amount of flash output - which would be a variation in the duration - that was permitted for these images. Making the presumption that Canon eTTL still controls the flash even when in M, what I'm seeing is that the exposure across images 1, 3 and 4 seems to be pretty well constant. I'm not really seeing any variation in either the primary subject's, or the background's, illumination across these three images.

Yes, the exposure from 1,3,4 does seem fairly consistent, as you say.

And that was pretty much what I expected to see. As you move the light further away from the subject, the power of the flash diminished, and thus the camera, through eTTL, permitted a longer flash duration to make up for the longer distance.

Your comment here makes sense.

What do the histograms show us for these images? Image #2 is the potentially more interesting one here - it does appear to be ever so slightly over-exposed compared with the others.

It is definitely hot. I purposely placed the flash quite close to Robyn. Usually I have have moved the flash only a few inches at a time, but I wanted to make sure that it was moved a reasonable enough distance to give every chance for change in exposure to be evident.

First, you've moved the flash closer to the subject. This (obviously) is the reverse of what's happened in #s 3 and 4. As you move the light closer to the subject, the power of the flash increased, and thus the camera, through eTTL, permitted a shorter flash duration to make up for the reduced distance.

So what you're saying here is that, if the eTTL processing by the camera had not reduced the flash time, it would have even brighter than it was. (I'm not sure if that makes sense).

Now, one meter is actually fairly close to the subject, and it may be that this about the edge of the close operating distance of eTTL and your flash. Basically, there's a point where the light source gets too close to the subject, and there's simply not enough time for the camera's metering systems to read, react, tell the flash head to shut down, and then have the flash head react and shut itself down. Remember that we're talking about doing a lot of stuff in less than a poofteenth of a millisecond ... and I suspect that your one meter distance here may be at the bleeding edge.

I have no idea of the operating parameters of this setup, but your point is taken.

But what if you were reading from the flash head, with the brolly in place? Consider the placement of the flash head's sensor in relation to your subject, and the possibility that the brolly's location may interfere with that line of sight. That one's a trap for young players.

I swivel the sensor on the slave unit and on the master unit so that both are facing each other, but again, point taken.

Thanks for taking the time to respond here Gary. Your input is much appreciated. I read through another post similar to this (on another forum) and this question was discussed. The OP (a very good photographer) stated that he always just moved the flash/stand instead of adjusting the on-flash' settings. Others disagreed with his point of view. I thought it was interesting to try and find out how these things work. I suppose the bottom line is to get the results wanted. Small flash setups can seem complicated, especially to someone like me who has little experience with them. I expect trial and error is the best (and only) means of gaining proficiency in this photographic endeavour.

[gstark]

First, you've moved the flash closer to the subject. This (obviously) is the reverse of what's happened in #s 3 and 4. As you move the light closer to the subject, the power of the flash increased, and thus the camera, through eTTL, permitted a shorter flash duration to make up for the reduced distance.

So what you're saying here is that, if the eTTL processing by the camera had not reduced the flash time, it would have even brighter than it was. (I'm not sure if that makes sense).

Correct. Think of this as being a just-in-time process, with the camera normally telling the flash to stop .... ready ... steady ... now.

When your flash is closer to the subject, you have less distance (and therefore less time) within which to perform that task, so the camera tells the flash to stop ... ready ...stea ... damn! too bloody late. Stop already!

Now, one meter is actually fairly close to the subject, and it may be that this about the edge of the close operating distance of eTTL and your flash. Basically, there's a point where the light source gets too close to the subject, and there's simply not enough time for the camera's metering systems to read, react, tell the flash head to shut down, and then have the flash head react and shut itself down. Remember that we're talking about doing a lot of stuff in less than a poofteenth of a millisecond ... and I suspect that your one meter distance here may be at the bleeding edge.

I have no idea of the operating parameters of this setup, but your point is taken.

Precisely. Try shooting something fairly close (half a meter?) with the off camera flash held at your arm's length, but very close to the subject. Use exactly the same settings on the camera. Let's see how hot that image is. Don't bother with the brolly.

Thanks for taking the time to respond here Gary. Your input is much appreciated.

Always a pleasure.

I read through another post similar to this (on another forum) and this question was discussed. The OP (a very good photographer) stated that he always just moved the flash/stand instead of adjusting the on-flash' settings. Others disagreed with his point of view.

But what sort of flash, and in what mode, was he working?

In our workshops, I have done exactly this using my strobes. The difference here is that with what you are doing, the flash heads will give you variable light output, based upon the readings being taken by the camera through eTTL. When using the studio strobes, they (typically) have a constant output, controlled by a power setting on the head.

In my setup, I may dial the power down at the head, but once that's done, the power output remains constant from the light source.

With a constant output from the head now being provided, as I move the light source closer to or further from the subject, I will see more or less light on the subject as a result of the change in distance.

The really important factor to remember here is that with what I'm describing, the light output remains constant regardless of the distance. As the distance to the subject increases, the amount of light falling on the subject decreases. With eTTL, the camera always calculates (and varies) the light output so that regardless of the light to subject distance, the subject still receives the same amount of light.

Is that making sense?

Getting back to this other photographer, what sort of flash, and in what mode, was he working? Was he using eTTL, or perhaps a studio strobe setup?

I suppose the bottom line is to get the results wanted. Small flash setups can seem complicated, especially to someone like me who has little experience with them. I expect trial and error is the best (and only) means of gaining proficiency in this photographic endeavour.

Basically, yes, although I happen to think that the basics of lighting setups are pretty simple, and systems like CLS over complicate what is essentially a very simple process.

[ozimax]

Getting back to this other photographer, what sort of flash, and in what mode, was he working? Was he using eTTL, or perhaps a studio strobe setup?

Similar to mine from memory, except it was bare flash. I'll try and see if I can locate his post and refresh my memory.

I can understand why many photographers use manual mode with their flashes and not eTTL. Once you have the exposure right, it seems simple to just move the light source, instead of bringing complicated in-camera algorithms etc into play.

[chrisk]

systems like CLS over complicate what is essentially a very simple process.

i agree with you in the most part but i dont think cls or ittl/ ettl is overcomplex at all. they are only as complex as they need to be as long as people realise what the limitations are and how best to use it. if your subject is moving around and/ or you dont have the opportunity/ time to manually adjust output then ittl is invaluable...i'd go so far as to say its actually a necessity.

a couple of micro adjustments to flash comp and your essentially in a type of manual flash mode anyway.

[ozimax]

Getting back to this other photographer, what sort of flash, and in what mode, was he working? Was he using eTTL, or perhaps a studio strobe setup?

This is the original quote from the bloke concerned. (Should I give the URL address?)

"I wanted to share my OCF process with you guys..... others may do the same or even have something totally different that they do:

When shooting wireless, which is most of the time, we either shoot via the built-in IR of the Canon Flash or we have just started using Radio Poppers. We like both of these because they both allow for us to shoot using eTTL. This takes a lot of the guess work out of the equation for me. Also allows for the ability to shoot with High Speed Sync enabled.... meaning I can shoot in full sun.... at f2.8 and get great blue skies and soft backgrounds which I prefer.

Camera settings are pretty normal: Av mode most of the time...... if light is getting low I will switch to Manual to prevent the camera from dropping to slow shutter speeds. Evaluative metering..... I do not worry about ratios when dealing with the flash..... set flash to eTTL.... take shot.... review pic on lcd.... if it looks hot or not light enough..... have my assistant move forward or backward..... to me much faster than fooling with the controls..... although I can control with the controls.... if my assistant plays sick for the day....

I shoot with a 580 mounted on either a monopod or stand.... have been using LumiQuest Softbox..... but just started using the Apollo box..... really like it.... its bigger. I have a 550 mounted on camera to serve as the master flash. I never shoot in manual mode for the flash always eTTL."

[gstark]

Thanx for this ...

Getting back to this other photographer, what sort of flash, and in what mode, was he working? Was he using eTTL, or perhaps a studio strobe setup?

This is the original quote from the bloke concerned. (Should I give the URL address?)

If you wish. You said there was some discussion about the veracity of is methodology; that might be worthwhile if others wish to peruse and/or pursue this further.

When shooting wireless, which is most of the time, we either shoot via the built-in IR of the Canon Flash or we have just started using Radio Poppers. We like both of these because they both allow for us to shoot using eTTL. This takes a lot of the guess work out of the equation for me. Also allows for the ability to shoot with High Speed Sync enabled.... meaning I can shoot in full sun.... at f2.8 and get great blue skies and soft backgrounds which I prefer.

Ok ... eTTL, possible high speed sync.

Camera settings are pretty normal: Av mode most of the time...... if light is getting low I will switch to Manual to prevent the camera from dropping to slow shutter speeds. Evaluative metering..... I do not worry about ratios when dealing with the flash..... set flash to eTTL.... take shot.... review pic on lcd.... if it looks hot or not light enough..... have my assistant move forward or backward..... to me much faster than fooling with the controls..... although I can control with the controls.... if my assistant plays sick for the day....

I hope that he's using the histogram when he reviews the image on the lcd. Trying to assess exposure directly from the LCD alone is not a good idea; it's not a calibrated screen, and (for instance) the screen brightness is directly adjustable by the user, thus making any potential assessment null and void.

But apart from that, in moving the light source if the image looks hot or dark ... I suspect that he's dreaming. Even if he's also dialed in some exposure compensation to cope with the available ambient light, eTTL would alter the flash's output to compensate for the changes distances so as to achieve the target EV, as you've seen for yourself.

I shoot with a 580 mounted on either a monopod or stand.... have been using LumiQuest Softbox..... but just started using the Apollo box..... really like it.... its bigger. I have a 550 mounted on camera to serve as the master flash. I never shoot in manual mode for the flash always eTTL."

I'm just trying to understand how and whether having the 550 on-camera as a master flash might affect things. I'm also trying to understand why ... surely the goal of using off-camera flash is exactly that: why would you then use a 550 on-camera as the "master flash". Controller? Sure. But flash ???

[ozimax]

This is the original quote from the bloke concerned. (Should I give the URL address?)

If you wish. You said there was some discussion about the veracity of is methodology; that might be worthwhile if others wish to peruse and/or pursue this further. [/quote]

It is a loooong post, there's quite some reading involved but it is interesting.

http://photography-on-the.net/forum/showthread.php?t=653964

I'm just trying to understand how and whether having the 550 on-camera as a master flash might affect things. I'm also trying to understand why ... surely the goal of using off-camera flash is exactly that: why would you then use a 550 on-camera as the "master flash". Controller? Sure. But flash ???

I pretty sure he means using the 550ex as a master trigger, without firing the flash itself.

[Mr Darcy]

The camera will read the light being reflected off the sensor (or filum) from the subject during the actual moment of exposure,

Are you sure of this Gary? It is not true for Nikon Digital. I don't know about Canon. Nikon used to read the exposure off the film, but when they went to digital, they switched to reading the exposure immediately prior to opening the shutter. This is part of what the preflashes are about. It seems a retrograde step to me, but I'm sure Nikon had their reasons (sadly more likely to do with "State of the Bank Balance" than "State of the Art")

[gstark]

I pretty sure he means using the 550ex as a master trigger, without firing the flash itself.

I would hope so.

That is a long thread, with 120 pages ... and lots of great images to sift through.

The meat of the discussion, relevant to this thread, starts on page 9, although Tony does outline his basic procedure on the first page. On page 9, the poster Choomps seems to be fully conversant with the issues at hand, and I think is more correct in his assessment than Tony.

Look at the last two images on page 9, and the explanation of the differences in how they were shot. There are evident differences in the background's illumination, but the lighting differences on the subject are due not to exposure or power of the light, but in how the light has been spread, due to the differences in the light's apparent size when viewed from the subject's PoV.

Also, please look at the first post on page 10. This is a Canon feature (and there's a Nikon equivalent, but I'm not sure how it manifests itself in terms of iTTL) and I suspect it's modifing the base concepts of how eTTL may work.

And Tony's page 11 post from which I'm taking this excerpt is also very interesting ...

Remember my OCF (580ex) is a slave flash...... TTL is through the lens flash metering and gets the preflash for the measurement from the flash (550ex)mounted on the camera (set to master) not the OCF (slave). (If TTL was measured from the slave flash.... what would it do if I used two slaves? Try it out.... there is no preflash from the slaves.) So by not moving the camera while moving my ocf closer/further from the subject.... I'm controlling the amount of light that will be increased or decreased. As long as I don't move the camera, distance to the subject. TTL will calculate the same amount of light to fire. The key is to remember the flash mounted on the camera is the master.... TTL is being measured from its preflash..... the slave will not fire a preflash.... its simply waiting on orders from the master flash.

*note: I do not always have my on camera flash set to fire flash but simple serve as the master, communicate and trigger the slave..... the preflash will still fire (believe me, I almost blinded myself testing )....

I think I need to reread what he's saying here and see if I can better comprehend his technique.

[gstark]

The camera will read the light being reflected off the sensor (or filum) from the subject during the actual moment of exposure,

Are you sure of this Gary? It is not true for Nikon Digital. I don't know about Canon. Nikon used to read the exposure off the film, but when they went to digital, they switched to reading the exposure immediately prior to opening the shutter. This is part of what the preflashes are about. It seems a retrograde step to me, but I'm sure Nikon had their reasons (sadly more likely to do with "State of the Bank Balance" than "State of the Art")

Both methods are still in use. My recollection is that iTTL was introduced with the D70 - the SB800 was introduced concurrently, and it was the first Nikon flash unit to support this (metering from pre-flash) feature.

Certainly, the original TTL flash (pre-digital) was taking a reflected reading from the focal plane media during the exposure, and certainly the preflash is used to calculate the expected exposure. Here's what the D300 manual says on this ...

i-TTL balanced fill-flash for digital SLR: Speedlight emits series of nearly invisible preflashes (monitor preflashes) immediately before main flash. Preflashes reflected from objects in all areas of frame are picked up by 1,005-segment RGB sensor and are analyzed in combination with range information from matrix metering system to adjust flash output for natural balance between main subject and ambient background lighting. If type G or D lens is used, distance information is included when calculating flash output. Precision of calculation can be increased
for non-CPU lenses by providing lens data (focal length and maximum aperture; see pg. 198). Not available when spot metering is used.

Standard i-TTL flash for digital SLR: Flash output adjusted to bring lighting in frame to standard level; brightness of background is not taken into account. Recommended for shots in which main subject is emphasized
at expense of background details, or when exposure compensation is used. Standard i-TTL flash for digital SLR is activated automatically when spot metering is selected.

The devil is in the details: Note that for Standard iTTL, there is no mention of the use of pre-flash. Also of interest here is that if you're using spot metering (my preference) then I'm also using Standard iTTL, and that the iTTL balanced flash mode is exactly that: for balancing flash with ambient light.

Of course, all of this is off-topic, but still relevant to Oz: are there similar restrictions with the 5D/30D and 550/580 combos?

This is starting to sound like it's a workshop in need of doing.

[gstark]

My recollection is that iTTL was introduced with the D70 - the SB800 was introduced concurrently,

I recline corrected. The SB800 was introduced about six months earlier, with the D2H.

Greg, you may find this page to be of some interest.

[ATJ]

The devil is in the details: Note that for Standard iTTL, there is no mention of the use of pre-flash. Also of interest here is that if you're using spot metering (my preference) then I'm also using Standard iTTL, and that the iTTL balanced flash mode is exactly that: for balancing flash with ambient light.

I'm with Greg here. And while there is no mention of pre-flashes with standard iTTL, it most certainly happens. (I know because I can't take photos of a certain species of goatfish if I use iTTL as they are spooked by the pre-flash.) As it says in that linked article, the anti-aliasing filter on the front of the sensor changes the way the light is reflected and with digital it is no longer possible to do the reading as the exposure is happening.

The end result should be the same but it has the potential for being less accurate.

[biggerry]

This is starting to sound like it's a workshop in need of doing.

I would be up for that, this has been a good read so far

[chrisk]

(I know because I can't take photos of a certain species of goatfish if I use iTTL as they are spooked by the pre-flash.

yepp, and the smaller fly species are the same. i wont tell you how long or how many wasted frames i took before my dumb ass worked that out either.

[gstark]

And while there is no mention of pre-flashes with standard iTTL, it most certainly happens.

I know this too, and this has me slightly puzzled.

What also has piqued my curiousity is the impact of extra flashes upon the exposure. Let's bring this back on topic and discuss this a little more.

Consider the statement made in the other forum: that the pre-flashes only occur from the main flash, which that poster states he uses, mounted on the camera. His assertion is that the pre-flash only comes from that camera (which I have no reason to doubt or question) and it is those pre-flashes that determine the exposure.

Let's also not forget that he sets his camera exposure to -1 or -2 EV ... and that he claims that he never sees a variation in apparent flash power from the slave(s), for which he compensates by moving those slaves closer to or further away from the subject.

So ... we have exposure based upon pre-flash coming solely from the main ...

We have slaves that need to be balanced (output power) by relocating them ....

And we have a camera set to (say) -1.3 EV ...

And he's using evaluative metering!

There's the key! I think.

By using evaluative, he's potentially getting a somewhat unbalanced image, when looking at foreground and background illumination. Consider the impact of the camera mounted flash, and the EV compensation.

I think that's giving him a skewed reading with darker backgrounds, and that is potentially forcing the slaves to push out more light - perhaps even full power - regardless of what is required.

I would be very interested to hear everyone else's PsoV on this.

[ATJ]

My guess is the slaves are putting out the same amount of light regardless of what the main flash/camera determine is required. This will add to the total amount of light in the exposure which is why a) he needs to use negative compensation and b) moving the slaves changes the exposure.

[gstark]

My guess is the slaves are putting out the same amount of light regardless of what the main flash/camera determine is required.

The problem with that is that if he's shooting with high speed sync - which he says he may do - that is unlikely to be a possibility.

[Mr Darcy]

Consider the statement made in the other forum: that the pre-flashes only occur from the main flash, which that poster states he uses, mounted on the camera. His assertion is that the pre-flash only comes from that camera (which I have no reason to doubt or question) and it is those pre-flashes that determine the exposure.

I do have reason to doubt it. For Nikon anyways. I HAVE noticed preflashes from remotes with my system (1xSB900 2xSB800) I suspect there are more from the master. Makes sense. It needs to tell the other flashes what to do. Then all the flashes do a measuring pulse just before the the shutter opens. Then the camera works out what needs to happen. Sends a set of fine tuning commands as required, Fires the shutter, then the flashes for their main power strobe. BTW The reason I looked into the way iTTL works in the first place was that I had an anomalous result in a bracket. One of the middle shots was badly underexposed. After reading the manual, I realised that the ambient changed dramatically between the preflashes and the shutter opening (I was using TTL-BL) and that was what threw it off.

[ozimax]

This is starting to sound like it's a workshop in need of doing.

I would be up for that, this has been a good read so far

If a Saturday workshop was in the pipeline, I would try my best to find time to drive down from Coffs to attend.

[biggerry]

I would try my best to find time to drive down from Coffs to attend.

and that would put Sydney members to shame in terms of commitment.

[ozimax]

I would actually attend more mini-meets if I could, but distance is the problem, plus the fact that I travel away from home 6+ months of every year.