Metering when using pop up flash

[ninefivepm]

Hello,

Would like to understand how to meter(adjust shutter speed/aperture) for proper exposure when using on camera pop up flash(the one that is default on most dslr) when shooting in M manual mode.

Quickly looked up online and could understand that the recomendation is to use large opened aperture and high iso. Would like to know if we need to adjust the aperture and shutter speed to get a balanced expore as we do elsewhere while shooting in manual mode.

Or is it that the exposure is automatically adjusted by the camera itself as soon as it detects that the flash is allowed to fire.

Thanks in advance.

[Colin Southern]

Hi there "person whose first name I do not yet know because you haven't filled in the real name field with (at least) your first name",

The camera will "attempt" to expose the foreground correctly; but whether or not it succeeds depends on a few things.

- If the manual settings already result in an over-exposure of ambient light then the flash can only make the over-exposure worse for any portion of the scene that it reaches.

- If the manual settings result in an under-exposure of the ambient scene then the camera will try to "make up the difference" using flash for the foreground (with "foreground" being the area that the flash can influence), but if the aperture is too small (ie "high F-Number") then the flash may very well not have enough power to get a correct exposure.

Some caveats ...

- On-camera flash is really only "suitable" for adding a little fill light; to act as a primary illuminant it's too weak - too harsh - and coming from the wrong direction to do justice to most subjects.

- High ISO may or may not help; below x-sync speed one can increase the ISO (and increase the shutter speed to compensate so the ambient exposure remains the same) (eg ISO 100 to ISO 400 and shutterspeed from 1/50th to 1/200th), but above x-sync speed the flash behaves like a constant light source, with aperture / shutterspeed / ISO affecting both flash and ambient - so changing the ISO keeps the ratio of the lighting the same.

[William W]

It might help you to think of the situation as there being TWO exposures:

The Ambient Exposure - which YOU chose in a Manual Mode - over which you have full control.

The Flash Exposure which the CAMERA chooses in an Automatic Mode – over which you have some moderate control, depending upon the camera’s make and model.


WW

[jcuknz]

It is much easier to stop trying to be clever and let the camera work it out for you in Tv mode [S] picking something like 1/100 shutter [ or P mode] ...your camera should have an "EV" adjustment for the flash and you use this to help the camera get the right exposure. If you get a burnt out exposure on your first shot then adjust to Minus one stop Flash EV and if still a bit hot try minus two stops.
This is what I do on the rare occasion I use the onboard flash despite understanding flash photography to a degree, I used to use it most days with my work way back.

That advice you found on-line is fraught with hazards becuase if you use a large aperture and high ISO and there is any ambient light around I can envisage the shutter going up high to compensate and your DSLR cannot use flash above perhaps 1/200. The flash only exposing part of the image at above 'Sync Speed'.

Better is to appreciate that the shutter has no effect on the flash exposure unless very fast and the aperture is how one controls exposure. The first thing is to establish the "Guide Number" for the flash and then one estimates the subject to flash distance and divides the GN by that and the result is the aperture to use. The GN can be metric or imperial the answer comes out the same metric GN/metres or GNImperial/feet. ie. GN56 with flash ten feet from subject use f/5.6. Five feet, 56/5= f/11

It gets a bit more complicated if your are doing 'syncro-sunlight' in daylight and here you use the shutter to get the correct daylight exposure when used with the aperture needed for the flash, calculated as in previous para.

See Wiki http://en.wikipedia.org/wiki/Guide_number

[Geoff F]

Firstly, what camera?

I always got poor results with flash until I started doing some thinking. I was originally working in the same manner as with my old film cameras which had a fixed output flash.

Modern cameras, with adjustable flash output work slightly differently.

With any of the auto settings (and to some extent I include Tv and Av settings here if you are using auto Iso etc) the camera will attempt to default with aperture wide open, shutter speed at 1/60 and the lowest possible Iso. May vary a bit on some cameras.

Things started to work better for me when I reduced the camera auto options. Set an Iso and shutter speed or aperture. But I often found even this produced incorrect results for many scenes.

So my preferred option now is; set everything manually to suit the scene. Aperture, shutter speed and Iso. But beware of your maximum shutter speed, usually around 1/200.

This forces the camera to use the auto flash output to suit your settings instead of the other way around. Some flash output compensation may be needed.

The problem with this method is that it does need a little bit of skill in working out what would be the optimum camera settings in each occasion. So a little bit of experimentation is required. And frequent checking of the review screen if the conditions change.

[Manfred M]

Normally in one of the automated modes, both your camera and your built-in flash will be working together to “optimize” your image. Modern DSLRs, lenses and dedicated flash units (built in and external) all communicate with each other.

When you switch your camera to “manual”, you remove part of this integration as you manually set the aperture and shutter speed. The flash, left in “automatic” mode will still measure the exposure from the flash and will cut it off when the “right” exposure has been produced.

This is something I will do under certain circumstances, albeit not with the on-camera flash, but when trying to get some special lighting effects using either small flash or studio flash. An example of this is doing an architectural interior shot without blowing out the exterior view, for example:


In this case, I metered for the exterior view, set the camera to manual and used two off-camera Speedlights to light the room interior, giving a correct exposure for both inside and outside.

I’ll also go to manual when I want to create a bit of a moody look on an outdoor shot. Meter and then I’ll deliberately underexpose the background by a stop or two by going to manual and use the flash to light up the main subject correctly.

From a technique standpoint, I tend to use my camera’s light meter to set my base exposure and will bracket a bit by changing my shutter speed to give me a bit of latitude in the images. I use the camera's histogram display to judge the image, while shooting.

[Colin Southern]

It is much easier to stop trying to be clever and let the camera work it out for you in Tv mode [S]

Unfortunately, if one uses Tv mode, one then loses control of their aperture, and thus control over depth of field.

That advice you found on-line is fraught with hazards becuase if you use a large aperture and high ISO and there is any ambient light around I can envisage the shutter going up high to compensate and your DSLR cannot use flash above perhaps 1/200. The flash only exposing part of the image at above 'Sync Speed'.

If the flash isn't capable of high-speed sync, then the camera won't let the shutter speed go above X-sync speed.

Better is to appreciate that the shutter has no effect on the flash exposure unless very fast

The shutter affects the flash exposure anytime you're above X-Sync speed (typically about 1/200th to 1/250th).

The first thing is to establish the "Guide Number" for the flash and then one estimates the subject to flash distance and divides the GN by that and the result is the aperture to use.

If the flash is the primary illuminant then quite correct, but this doesn't apply if it's just only being used as a fill flash.

[William W]

^
It is also important to note that if the Camera is in P Mode then, (definitely for Canon EOS and probably all DSLRs), the Flash will act differently and that difference will be depending upon the Ambient EV - again that is less control by the Photographer.

WW

[Colin Southern]

^
It is also important to note that if the Camera is in P Mode then, (definitely for Canon EOS and probably all DSLRs), the Flash will act differently and that difference will be depending upon the Ambient EV - again that is less control by the Photographer.

WW

Yep. Off memory - in P mode - it acts as a primary illuminant below 10EV - Fill flash above 13EV, and proportionally transitions between the two between 10 and 13EV.

[William W]

Hi Colin -

Yes: It can be quite difficult to anticipate what will happen between EV10 and EV13 when using Flash, depending on the scene: Backlighting confuses it a tad. Also the cutover seems to vary a little between (Canon) Camera Models.

To the OP's question: I got the impression that it was a conscious choice to seek out HOW TO USE Manual Mode for the camera: the reason for that choice was to have as much control as possible - basically how to leverage the control of the Photographer over the camera was the premise of the question.

But then it appeared there was a little confusion over what MANUAL CAMERA MODE did, when a Flash was introduced.

If the OP lets us know the Camera make and model and the general shooting conditions - I am sure more specific information would be forthcoming.

WW

[jcuknz]

Colin ...each of your statements picking up on me is questionable if we want to nitpick, which I don't really. I was dissatisfied with my generalisations and really the subject needs a better thought out reply. On the subject of Guide Numbers which was where I started with flash there is my webpage on the subject http://www.jcuknz-photos.com/LIGHTING/GUIDENUMBERS.html since CiC doesn't seem to cover the subject. I tend to keep quiet when it comes to modern cameras and flash becuase it is a horrible mystery with unless the gear is set up correctly seems to be a can of worms. Those who have mastered it will laugh at this I'm sure .... but thank goodness for digital with costless exposures and instant review.

To advance beyond Guide Numbers there is the basic fact that aperture controls the flash and shutter speed the ambient light. This is when one doesn't have automatics interferring and trying to take charge.
I was doing syncro-sunlight this way back in the late fifties on weddings when the concept first arrived in Wellington and I saw an example in Spencer Digby's window and said to myself "That's for me" So I changed my Leica [ 1/30 sync speed] for a Japanese fixed lens camera but with compur shutter to enable me.

Also a reminder that Ninefivepm is talking about their pop-up flash unit which if it is a modern camera are not nearly as useless as they were even five years ago and have quite respectable and useful GNs for closer subjects.

[William W]

It is important to note the fact that the OP is discussing the Pop Up Flash (and NOT Hot-shoe Flash Units).

This point is relevant to the discussion of GUIDE NUMBERS: because as we are discussing POP UP FLASH, that fact makes the Guide Number mostly irrelevant: save for that of knowing what the MAXIMUM Flash Power might be for any given circumstance.

This statement is made, because:

The Pop Up Flash CANNOT be used in a MANUAL FLASH MODE.
(Maybe there are some camera(s) in which the PuF can be used in a Manual Flash Mode - but I know not of it – anyone?)

There is FLASH EXPOSURE COMPENSATION, but that functionality is an AUTOMATED function, in so far as it is dependent upon EACH SINGLE EXPOSURE.

That is to say the flash exposure is read for each individual exposure and then the compensation is applied to that specific reading.

WW

[Colin Southern]

To advance beyond Guide Numbers there is the basic fact that aperture controls the flash and shutter speed the ambient light.

This is often said, but unfortunately, it's just not true. Aperture affects ("controls") both ambient and flash (both light sources pass through the same hole). And when using high-speed sync, the shutter speed affects ("controls") both ambient and flash also (in HSS mode the flash is modulated for the full duration of the passage of both shutter curtains, and thus behaves like a constant light source) (so altering shutter speed and/or aperture or ISO has no effect on the RELATIVE exposures because the ratio of flash light to ambient light remains the same); all one can do is to change the effective output of the flash somehow.

What the old addage MEANS of course is to use shutter speed to control the ambient light; aperture really shouldn't enter into it. So as a "fact", I'm afraid that - on it's own merits - it's wrong - and if gets even more wrong when folks start using HSS (which is a lot of the time).

Also a reminder that Ninefivepm is talking about their pop-up flash unit which if it is a modern camera are not nearly as useless as they were even five years ago and have quite respectable and useful GNs for closer subjects.

Debateable in my opinion - yes, they may be powerful enough for closer subjects, but (a) it's still a VERY harsh light (and thus not flattering), and (b) since it's on the same axis as the shot, it's going to produce a very flat light (which is also not flattering). So good for a little fill light - or point & shoot work - but not a lot else in my opinion.

[jcuknz]

Colin .... Syncro-sunlight
How the aperture controls the flash and the shutter the ambient light.
Working manually it is probably best to establish the ambient light exposure first bearing in mind that one is going to fill in shadow detail with the flash. One then considers the flash to subject distance and the degree of fill light one requires for asthetic reasons. If one wants less than 'full' exposure such as one would give at night time et.al. then one increases the Guide Number accordingly.
Having detirmined that, one then picks a shutter speed which in conjunction with the choosen aperture gives a correct exposure for the ambient light.

So instead of saying I am wrong it would be more helpful if you had added the extra information which for brevity I omitted to include, in establishing the basic facts of the matter.

This is probably not how you work with your sophisticated modern automatic gear but it is the tried and true way of working manually which I established without the benefit of blogs or other help some five decades ago when readilly portable flash units became available.

As to if the pop-up is a harsh light is debatable. Normally being so close to the lens it is actually quite a soft even light unlike the harsher light that a flash unit some distance from the lens produces and which is usually only acceptable as a means to get a shot rather than a good way to go, even if one hand holds or uses a bracket to hold the flash some way away from the camera.

WW It was worth your mentioning that some focal plane shuttered cameras will not permit one to fire the flash with the shutter above sync speed which I discovered to my annoyance with my latest M4/3 camera. It is a modern wrinkle which caught me out awhile back. "Big Daddy" knows best damm him. Again maybe I should have checked if the OP was familiar with the way focal plane shutters work.

[William W]

. . . It was worth your mentioning that some focal plane shuttered cameras will not permit one to fire the flash with the shutter above sync speed

I believe Colin, not I, mentioned that point. And it is important and very good 'safety feature' in my opinion. I believe this is a safety feature with most DSLR cameras.

***

ASIDE for those interested:

Although if one is persistent enough to seek to understand how the guts of these safety features work; there is usually a way to make DSLRs with this safety feature ‘limitation’ - actually do it – i.e. to allow the flash to fire when the Tv is set above the Flash Sync Speed, that is . . .



WW

[Colin Southern]

Colin .... Syncro-sunlight
How the aperture controls the flash and the shutter the ambient light.
Working manually it is probably best to establish the ambient light exposure first bearing in mind that one is going to fill in shadow detail with the flash. One then considers the flash to subject distance and the degree of fill light one requires for asthetic reasons. If one wants less than 'full' exposure such as one would give at night time et.al. then one increases the Guide Number accordingly.
Having detirmined that, one then picks a shutter speed which in conjunction with the choosen aperture gives a correct exposure for the ambient light.

So instead of saying I am wrong it would be more helpful if you had added the extra information which for brevity I omitted to include, in establishing the basic facts of the matter.

You understand the relationships between ambient/flash aperture/shutter speed - as do I - as does any experienced photographer. Unfortunately though, the berevity of statements like "shutter speed controls ambient / aperture controls flash" gives the false impression to those who don't understand these relationships that (a) changing the aperture won't have any affect on the ambient exposure, and (b) changing the shutter speed won't have any effect on the flash exposure; and of course neither of those statements are correct - which is why I feel obligated to point it out. I apologise if that offends, but I would rather offend than have mis-information lead someone astray.

This is probably not how you work with your sophisticated modern automatic gear but it is the tried and true way of working manually which I established without the benefit of blogs or other help some five decades ago when readilly portable flash units became available.

I think you'll find that most working professionals (myself included) use the automation where it benefits us -- and work around it when it doesn't benefit. Personally, I'm completely comfortable working up to 7 zones of light full manual without a light meter - full manual with a light meter - manual ambient / ETTL flash (multi-zone) - ETTL ambient / manual flash - ETTL ambient / flash (with appropriate EC/FEC) - standard mode - HSS mode - with up to 5 speedlites and/or 1200WS studio heads (either in-studio or on location with 3 generators). The automation is my assistant, but not my master.

As to if the pop-up is a harsh light is debatable. Normally being so close to the lens it is actually quite a soft even light

Umm, no. The softness of light is a function of the RELATIVE size of the light source, so assuming a "non-macro" flash to subject distance, there is nothing "quite soft" a 1/2" x 1" light source. Period.

[Colin Southern]

ASIDE for those interested:

Although if one is persistent enough to seek to understand how the guts of these safety features work; there is usually a way to make DSLRs with this safety feature ‘limitation’ - actually do it – i.e. to allow the flash to fire when the Tv is set above the Flash Sync Speed, that is . . .

It's a trick I've seen used for outdoor portraiture, where a bright sky/background above the subject needs to be toned down - but there may be restrictions on the minimum aperture that can be used. If the shutterspeed is in the 1/400th region, the camera can be turned upside down for the shot, resulting in the top 2/3 of the frame (where the subject now is) getting the flash, whereas the bottom 1/3 (where the sky/background now is) just gets the reduced ambient.

Biggest problem with the technique is convincing the subject "It's OK - I'm a professional - I know what I'm doing"!

[William W]

It's a trick I've seen used for outdoor portraiture, where a bright sky/background above the subject needs to be toned down - but there may be restrictions on the minimum aperture that can be used. If the shutterspeed is in the 1/400th region, the camera can be turned upside down for the shot, resulting in the top 2/3 of the frame (where the subject now is) getting the flash, whereas the bottom 1/3 (where the sky/background now is) just gets the reduced ambient.

Biggest problem with the technique is convincing the subject "It's OK - I'm a professional - I know what I'm doing"!

ASIDE -

HAHAHAHAHAHAHAHA!

I love your work!

BTW – family over for dinner - a fantastic Coonawarra 2001 Shiraz this evening, smooth as silk – Pork spare ribs, steamed rice and mushrooms and snow peas . . . I might even have a Cognac – and diet tomorrow

All the very best,

Bill

[Manfred M]

ItThe Pop Up Flash CANNOT be used in a MANUAL FLASH MODE.
(Maybe there are some camera(s) in which the PuF can be used in a Manual Flash Mode - but I know not of it – anyone?)

Bill - It looks like some cameras do have a manual setting on the built in flash.

Just checking my camera manual; the built in flash on the Nikon D800/D800E can be set to manual via a menu item and can be powererd from 1/128 power right through to full power, Guide number is 12m / 39ft at ISO 100. It's not something I would normally use, but it's nice to know that it is there

[William W]

It looks like some cameras do have a manual setting on the built in flash.

Thank you for checking that and also answering my query.
I concur - a very nice function to have, but maybe not used that often: but that information is relevant to this thread and I have filed that info away for future use.
Thanks again for taking the time to respond – I appreciate the learning.
Regards,
Bill