Adjusting ambient light levels when using flash

[Colin Southern]

I didn't read Colin and Bill as doubting what Arena says. Indeed he says it himself in the book (which I think is great). Without going through it (even though it's sitting beside me here on the desk), he makes the point that SAAF is not applicable in a HSS situation.

So, it's not an either/or, or good/bad, situation. I think Syl Arena is right. And Colin and Bill are right.

Exactly.

Here's a couple of screen shots from Syl's book:

[Colin Southern]

revi, try taking a image when people are moving so fast and when it's dark and keeping the bg normal. Power wise yes it uses a lot of power but it is only a short duration. When you use your flash with the camera it is usually in first curtain mode and if you took a image when they where moving the flash fires at the opening of the first shutter and if the subject is still moving you get the subjects features still getting taken and if you use second curtain with a slow shutter speed you get the trail behind them.

It comes down to the flash to ambient ratio; once you can get a couple of stops between them then the trails become far less of an issue (although if there was movement then dragging the shutter may well have produced a less "static" photo).

In the example photo you gave (assuming that the dancers were the subjects) then personally, I'd probably have had my camera in manual mode, set a couple of stops below ambient and then zoomed the flash head so that it targeted the dancers and didn't over-expose both the back of the gents head and the backs of the chairs; freezing the dangers and giving a natural vignette. With regards to shutterspeed, not sure what I would have used to be honest.

[William W]

For all of you who doubt Syl Arena and his SAAF read his book 'Speedliter's Handbook' and also Neil van Niekerk three books on 'On-Camera Flash, Off-Camera Flash and Direction & Quality of Light', they are worth reading if you want to understand using Flash better.

+

I didn't read Colin and Bill as doubting what Arena says. Indeed he says it himself in the book . . . he makes the point that SAAF is not applicable in a HSS situation.
So, it's not an either/or, or good/bad, situation. I think Syl Arena is right. And Colin and Bill are right.

I concur with 100% of what Donald and Colin have just written.

I wish to add:

Sly's book is a good book.
I have it.
I use it as a teaching tool.

But I am critical of that ‘SAAF’ acronym and for the reasons I outlined.
There is nothing wrong with having a difference of opinion about how to explain a fact or the method of the presentation of facts to students or an audience.

On the page in Sly’s book where he introduces the ‘SAAF’ acronym the section is headed:
“Why Shutter does not control Flash Exposure”
The first sentence then states:
“I know it’s hard to believe, but it’s true. As long as you are shooting at or slower than the sync speed of your camera, then the shutter speed has no control over the amount of speedlite flash hitting your digital sensor.”

Now what I have found happens is:
Students whom I tutor and also Pros who attend Master Classes remember the acronym and the Section Heading and maybe the first sentence . . . and none of the detail about the exception.

***

Neil's knowledge is extensive and his practical approach is fantastic so are his practical exercises –
But by the same token, and I have worked with Neil, (Competition Judging Panels), we have disagreed on various points of presentation (not facts) - and there is nothing wrong with that: it is healthy so to do.

***

If anyone wants another quality reference (Canon Specific) then I recommend:
Mastering Canon EOS Photography, NK Guy, RockyNook Publishing.
Advice for this book and also the proof-reading was by Nadine Ohara: who as well as being a close colleague and friend of mine, was one of the quickest and most accurate Wedding Photographers in executing Flash in Situ - under the pressure of time, I have ever known.

***

Just an additional comment on High Sped Sync (HSS):
This is an area (probably the main area) of Flash Photography, where the adage oft quoted about: ‘Flash Freezes Motion’, can come unstuck, also.


WW

[jcuknz]

I started syncro sunlight using the SAAF method back in the 1950's but have been told it doesn't exactly work with modern TTL cameras and flash so all I will say is that it is probable that your camera has two controls Exposure Compensation for the picture and on another menu setting the strength of the flash.

SAAF works well if the flash doesn't have a brain to confuse things [ to my old fashioned way of thinking] and simply works at either full power or a reduced strength which you can relate to and use a 'Guide Number'* to determine the aperture to use ie GN 56 = f/5.6 with the flash ten feet from the subject f/11 with flash five feet from subject [ assuming it is an average coloured subject ... the result is that the aperture controls the effect of the flash. 56/10=56 or f/5.6 56/5=11.2 or f/11

Having worked out the aperture you then for syncro sunlight need a shutter speed which with that aperture gives the correct exposure for the ambient light of subjects not reached and lit by the flash .. the backgound?.

Your camera I expect has a focal plane shutter so there are restrictions on the shutter speed you can use maximum called 'Sync Speed'. possibly around 1/200 which limits the range of shutter speed you can use ... why originally I dumped my Leica for a Japanese fixed lens camera in the fifties. This had a compur type shutter working like the shutter found in P&S and bridge cameras today and synced at any speed I needed. These days you can get a flash which pulses its light for the duration of the sync speed permitting you to use faster shutter speed at reduced power. Canon calls it HSS or high speed sync I believe.

So working this way the aperture controls the brightness of the flash and is determined by the flash to subject distance ... camera can be anywhere. So to organise the flash as a fill light at about half strength in sunlight I change that GN from 56 to 80 [ not 112 as you might think ] so at ten feet I would be using f/8 which might tailor nicely with bright sunlight and a shutter speed of 1/200 [ in bright New Zealand anyway, perhaps 1/100 in the UK]

Now when you come in for a close shot from five feet the aperture required is f/16 [ 80/5=16] which means you need a shutter speed of 1/50 [or 1/25 in the UK maybe]

These days with TTL as far as I am concerned it gets horribly complicated with flash thinking for themselves.

So my solution is to adjust the strength of my on-board flash to minus one stop and leave it up to the camera which usually does AOK, sometimes a little bright as here.

This means I don't have to get my old brain around the new ways of working

*The guide number can be in imperial or metric and works the same if you do not mix the measures.
The Guide Number comes from the aperture you use to get a good exposure of an average subject ten feet from the flash when shooting with 100 ISO Camera position is immaterial to the calculations

Note the GN doesn't double as you double the ISO but I think of it in terms of aperture stops where f/8 is half of f/5.6 so the original GN of 56 becomes 80 when the ISO changes from 100 to 200
It is complicated these days with flash units which beam the light for the longer lens and often the stated GN for a flash is the tight beam GN and not the weaker wide angle light.

It used to be quite simple which is why I was able to teach myself to do syncro sunlight SAAF way back when it was relatively new. Truely portable flashes had only recently come on the market to facilitate the method back then.

[jcuknz]

Most of us know this but for the newbie the concept of sync speed may be puzzling.
There are two basic types of shutters. The first is the 'compur' which opens and closes the whole sensor to light at the same time and is commonly found these days in P&S and Bridge cameras .. it can be mechanical or electronic.

The second type of shutter uses two blinds, the first uncovering and the second covering the sensor. these travel across the sensor and what we call 'sync speed' is when the first blind has fully uncovered the sensor and the second blind has not started to cover it. It is this moment that the elctronic flash is arranged to fire and its light exposes the whole of the sensor.

However this is usually at a quite a slow 'shutter speed' of around 1/200 and to get faster 'shutter speed' the second blind starts to cover the sensor before the first blind has fully uncovered the sensor. The result is that at a faster shutter speed the flash only exposes part of the sensor.
Hence the need for HSS flash units if you want to combine flash with high shutter speed.

2nd shutter or 'dragging the shutter' {?} is when instead of flash sync being when the first blind reaches 'full open' but when the second blind is about to start covering the sensor. This means that with a long exposure to capture ambient light the subject reaches the end of its tmovement when the flash goes off. If you use front sync for such a shot the subject it flash lit aat the start of its movement and this seems to be normally not favoured. I have never needed to use other than front sync so it is academic to me though I know my camera has 2nd..

[arith]

I can't read all that stuff, no time, so I'll just say what I do. I always use manual and spot exposure. Suppose I want a dark background that is underexposed by say 2 stops, I would take a background reading at the aperture that gives me the required dof and either have the needle on -2 or bang in the middle and adjusting the speed 4 times faster.

Then use a speedlight on the subject, or use the guide number and power level remembering that halving the power multiplies the guide number by 1/(2)^0.5 about 0.71. You might be restricted by a maximum speed but that means you can't have everything.

It is a hard trick to do, say your using a 70mm lens on your crop camera and you shooting a model wanting about a foot of dof. You find at 3 metres you get the required head shot and your flash has GN 32 at 35mm 100iso. Setting on manual fixes the GN at 100% power to 32 but your at f4 to achieve the dof.

Reading the exposure on a bright spot in the background gives 1/60 say at f4 and 100iso, so at least that's working and choosing 1/8 power on the flash with a hanky over the head or diffuser might just do the trick.

But I would do what Colin says if I read it

[jcuknz]

However my question is this....If I'm in aperture priority mode (and I shoot a lot in this mode) can I simply reduce the EV reading in the viewfinder to reduce ambient light as I assume that, for any given aperture, the shutter speed will increase?Cheers Adrian

I agree with WW that really you should experiment with your camera and read the EXIF of each shot you take to discover what the camera has done.

My experience with a modern focal plane shutter camera is that the damm thing would not use a faster speed than sync speed when I wanted it to. So with that governing condition even if in A mode I suspect it will open the aperture. But the proof of the pudding is in EXIF Let us know though I suppose we could do the trial for ourselves Though that would only tell us what our camera does.

My first reaction to your question was that it will make the whole picture darker as EC I believe controls the total result of flash and ambient .. but I could well be wrong. Again I suggest insted of asking us you ask the camera itself what it will do. Since the camera is dealing with an electric signal I think it quite possible that EC may work after the exposure is made and doesn't alter aperture or shutter .... just a horrible thought ... you know what HAL did? [Space Odessy Kubrick for young folk ]

[jcuknz]

Most definitely SAAF is not just for automatic modes becuase that is what I worked out in the fifties when I worked out how to do syncro-sunlight ... I didn't have any automatics back in those days apart from maybe a Movie camera with AE and everything else manual. I don't really see how it can work in an automatic mode. though Colin loves his limited Auto ISO which I don't think I want to know about ... once you get the hang of it ... it is easy enough work, particularly if you have moved to a Rolleiflex T with shutter and aperture linked to maintain an EV ... 15ft full length horizontals f/5.6 .... 10ft vertical full lengths f/8 ... 5ft Head and shoulder single f/16 That is all with a 50mm lens on full frame .... even with non coupled cameras and having to manually focus to boot ... frankly you don't know what living was .... I jest Colin you know more about working today

Those apertures were working with my original Mecablitz and GN56 with 100 ISO.

[Colin Southern]

If anyone wants another quality reference (Canon Specific) then I recommend:
Mastering Canon EOS Photography, NK Guy, RockyNook Publishing.

+1 for this book. NK was kind enough to send me a free & personally autographed copy of the book when he released it, which was much appreciated.

NK wrote the "online bible" of EOS flash photography ... http://photonotes.org/articles/eos-flash/

[Dusty]

If anyone wants another quality reference (Canon Specific) then I recommend:
Mastering Canon EOS Photography, NK Guy, RockyNook Publishing.
Advice for this book and also the proof-reading was by Nadine Ohara: who as well as being a close colleague and friend of mine, was one of the quickest and most accurate Wedding Photographers in executing Flash in Situ - under the pressure of time, I have ever known.

***



WW

I have got this book and it is also a good book to learn from. There is quite a lot to learn about flash in photography.
Dave.

[darekk]

The flash should not increase the shutter speed more then by 1 F stop if the flash light alone is weaker then ambient light alone. So maybe for example if the sync speed is 1/125 and you use aperture priority mode (Av) with F8 preselected and camera shows 1/125, switch aperture by 1F stop to F11. The camera would show 1/60 (without flash) and probably should not exceed 1/125 (1/60 + 1F stop) when you fire flash (?).
If you use Shutter priority mode (Tv) everything should be OK if aperture camera shows (without flash) is lower then maximum allowed aperture - 1 F stop.

Aperture rather should not be higher more then by 1 F stop in comparison to stronger light source alone.

If aperture for ambient light alone is 8 and for flash light alone is 5.6, for both light sources together is
square root from (8^2 + 5.6(7)^2) = 9.8 (less then 8 + 1 F stop).
Obviously photographed object is not uniform surface and contains shadowed fields, so probably it would not be exactly 9.8 for optimal exposure.

If aperture for ambient light alone is 8 and for flash light alone is 8, for both light sources together is
square root from (8^2 + 8^2) = 11 (+ 1 F stop if initial apertures are equal).
This is obvious, because f stop difference equal to 1 corresponds to double difference in "light amount".





Is supplementary flash light weaker or stronger than sunlight or depends ? I think that at least in most of cases weaker.
But this is not important, because cameras probably show final exposure parameters (sunlight + flash together) ...

What is SAAF ? Is this South African Air Force ?

[arith]

Is manual mode now the easiest mode? I thought programmers worked out all the other modes, I've got a camera to avoid that with manual controls and it looks like I was right. It is definitely more complicated to use a program mode, where the programmer has dominant control. That is somebody else.

I'm just not interested and can't do program modes, I did a couple and found out it is not easy and you end up with a programmers picture, not too clever.

Try manual, it is easier than trying to get a good shot with automatic.