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Thread: Flash exposure compensation

  1. #1

    Default Flash exposure compensation

    How do you calculate how much to over or under compensate the flash? I"m totally lost at the flash compensation function, no idea how to really utilise it, can anyone advise? thanx!

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    Quote Originally Posted by hoppinghippo
    How do you calculate how much to over or under compensate the flash? I"m totally lost at the flash compensation function, no idea how to really utilise it, can anyone advise? thanx!
    What camera are you using? You can underexpose the flash by changing the compensation for the flash directly. Using the meter, meter for a "correct" exposure and then set the flash value for underexposure to the value you want.

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    calculation comes with experience i guess. im sure you are not asking how to adjust it on the camera right? because that could be found on the manual. so look at your shots and guage from there... and also read up on color and tone charts to see what loosing 1 stop of light looks like... then you will have a better understanding on how to under or over compensate the flash...

    you can also balance flash compensation with exposre compensation... so play around/

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    if u using nikon then if i recall correct, nikon background exposure (shutter speed n aperture combination) and flash exposure (think of it as the amount of light output from the flash unit) are kinda "integrated". it may be more so for low light case (eg situations like 1/8 seconds, f8) . pls correct if im wrong
    if u using canon then canon background exposure and flash exposure are totally separate. think of it as 2 different paintbrushes. loosely speaking, if the flash is not programmed to act as "fill-in" flash, then dail in -1 to -1.5 stops of flash exposure compensation will make it act like "fill-in" flash. ie not too powerful output yet givr out "enough light" to light up foeground subject adequately

  5. #5

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    If you are using digital, watch the shadows.

    If you are using film, you need meter the subject and the shadows. It would be good to retain details in the shadows so keep to 1 to 1.5 EV lower than the subject. set shutter speed for flash sync, and the f-stop accordingly for a normal exposure. set the flash on manual according to the above f-stop minus 1 to 1.5 stops.

    should work... though it will be better to experiment with different film; normal film vs low contrast film like fuji NPS. With NPS, you may not even need the flash compensation..

  6. #6

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    Thanx all, sorry for not elaborating, I"m using minolta dynax 7, and unlike dynax5 which I used previously, I can now set compensation for flash and the background separately so am at a lost at how to fully use this function of flash compensation. so I take it for fill flash, I"m to meter as usual (as tho w/o flash) and dial in flash but -1 to -1.5 stops of flash compensation? what other kind of shots can the flash compensation be used for? I"m guessing here but what if you say take a normal flash shot on auto mode, let the camera do the adjustments (say on A priority), usu it would churn out a pasty white complexioned face, so is there a standard way of preventing this like setting the flash to -1 stop always for all "auto" shots like this? (assuming subject is within flash range for the chosen aperture)

    The reason why I"m confused is that for normal background exposure its easy to visualise how you can over or undercompensate to get what you want based on the metering the camera gives you (eg from spot metering). but flash is over and above all these "calculations". so how do you "merge" these 2 exposure settings? like for eg, if you have a nite scene, and if you take a reading and set background exposure at say 1/125 to prevent handshake, and you know form your reading that at this speed the background exposure will underexpose by 2 stops. so you want to bring in the flash to bump up the exposure. how do you adjust the flash? Select full power then set flash to - something stop?

    Heh hope I"m not confusing everyone further with my long winded attempt at elaborating!

  7. #7

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    how to merge the 2 settigns? the flash can give out enough light only to light up the foreground subject. it is unable to light up the whole background scene. so, to visualise how the flash output will look like, u got to visualise upon the foreground subject (imagine it being somewhat brighter)and anticipate where the shadow will be cast upon.

    your "auto mode" is it belongs to the property of the flash? or camera body? if u very unsure then a very loosely generalised method is just switch on the camera body and flash as usual and for flash exposure compensation, dail in -1 stop and leave it like that all the way; given that its a guess that it will unlikely give u overexposed subjects. if u have the time u can do a series of test shots using your existing cam body+ flash +the film u normally use and gather your own specific conclusions

    worked example: say u have a model posing along the boat quay river bank at 6:30pm at evening. and the meter readign gives you f4, 1/30 but u mentioned (for eg) u dare not handhold at 1/30 for fear of handshake and that u can only manage at 1/125. since the flash is only able to light up the model and it cant light up the entire boat quay scenery, the recommendation is u use a tripod/some other form of support and go ahead with 1/30

  8. #8

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    Thanx clive, that's a very good point about flash lighting up foreground subjects only. So in a way all I should do is meter the background, estimate how much the foreground subjects are underexposed if I shoot at the background exposure and adjust my flash accordingly? but exactly how do you translate this difference in exposure to the flash compensation? eg. if my background is such that my foreground subject is 1 stop under the background metering and I wish to bump up the foreground subject, I need to provide enuff flash of +1 stop. so how do I adjust my flash? set it as full power then adjust -ve stops compensation? (if so by how much?) or set the flash as auto fill in (on camera body) and assuming flash will overexpose the foreground, dial in -ve stops on flash (if so how much?)?

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    Quote Originally Posted by hoppinghippo
    Thanx clive, that's a very good point about flash lighting up foreground subjects only. So in a way all I should do is meter the background, estimate how much the foreground subjects are underexposed if I shoot at the background exposure and adjust my flash accordingly? but exactly how do you translate this difference in exposure to the flash compensation? eg. if my background is such that my foreground subject is 1 stop under the background metering and I wish to bump up the foreground subject, I need to provide enuff flash of +1 stop. so how do I adjust my flash? set it as full power then adjust -ve stops compensation? (if so by how much?) or set the flash as auto fill in (on camera body) and assuming flash will overexpose the foreground, dial in -ve stops on flash (if so how much?)?
    Hi Hippo,

    I'm using the same camera as u and I still have yet to get a consistent hang of it. But I'll try to help with the little I know. There is a very long thread on this in the Minolta forum and I'm just rehashing what was discussed there as succinctly as I can. FYI, the starter of that thread was ME!

    But first I must make clear that I'm using a Minolta 5600 Program Flash with the useful LCD panel which tells me flash coverage distance. If u du have this it might be a bit hard to see the effects I mention. THe 5400 also has the same data panel.

    Anyway from what I know, the camera behaves differently (based on its auto exposure modes -P, A and S) when u shoot under different lighting conditions.

    If u shoot under bright light with flash, both flash and exposure compensation behaves normally as u would expect it to. For example, if u shoot on A mode and u get 1/250 at f/5.6 on ISO100. If u dial in exposure compensation, then the shutter speed will alter according to the number of stops u dial in. So if u dial in +1 stop exposure compensation, the shutter speed will drop to 1/125 to expose the background by 1 stop. And when u dial in flash compensation, the flash pulse will fire for a longer or shorter duration depending on how much compensation u dial in. So if u dial in +1 stop flash compensation, the flash will overexpose the subject by 1 stop. So as far as I know, under bright shooting condition, the exposure compensation dial compensates for the background (it does not affect the subject exposure cos u have a TTL flash which will fire to expose the subject properly within the limits of the flash range and power). And on the other hand, the flash compensation affects the subject exposure almost exclusively. Well, this is the easy part.

    However, if u are shooting under low light conditions, again if on A mode, u get 1/60 at f/5.6 on ISO400. Now the camera limits the shutter speed to 1/60 regardless of how much exposure or flash compensation u dial in.

    So let's say u are on TTL flash mode and A mode on the camera and u meter a scene and get 1/60 at f/5.6. On the 5600 flash, u get a flash coverage range of 1.5m to 10.0 m. If u dial in +1 exposure compensation, by right, one would expect the shutter speed to drop. But on the Dynax & (and I think all Minolta SLRs), it does not. What the exposure compensation does is to shorten the flash range. I'll find that your flash coverage range drops to 1.5 to 7.0m. The same occurs if u try the same with flash exposure compensation. Dialling in +1 EV for the flash also drops the flash coverage range to 1.5 to 7.0m. The reason is that the camera is programmed (according to what I learnt from other Minolta users here) to keep the minimum shutter speed to 1/60 to prevent camera shake.

    Okay, that settles the way flash and exposure compensation works on the Dynax 7.

    For the part about overexposed (white-out) faces in a low light shot, I also get that problem in the beginning. It's begin to go away now but still can be a problem when I forget some of the pointers from the bros in this forum.

    The flashes we use (Minolta program flashes) are all TTL, so they should expose properly the faces. The TTL system works by metering the scene and determining which is the subject and deciding how long to fire the flash to properly expose the subject. This is read from the reflected flash pulse off the subject's face. Sometimes this system cocks up due to a variety of reasons but on the whole it works pretty well for me so far bearing in mind some pointers.

    1) The flash pulse has a certain minimum timing. If u are too close to the subject (as when u use wideangle and move in close), the distance between the subject and lens is too short for the flash to cut off the flash pulse in time so u get an overexposed subject.

    2) Make sure your subject is inside the flash coverage range. It seems that being somewhere in the middle of that range reduces the white-out look significantly. This prevents underexposure of the subject as well cos if u are outside the flash range, the subject will not be lit up properly.

    3) Try to make sure that the subject fills up at least 1/3 of the frame. Cos if that is not the case, the camera will think that the dark background is the subject and then fire the flash at full power and try to expose the dark background properly and in the process severely overexpose the subject which is much brighter (and more reflective) than the background. I usually ensure that one of the focus sensors are placed on the subject's face as the TTL metering system seems to be tied in with the focus sensors. (Apparently this helps the camera to decide where the subject is in the frame).

    4) U can use a bounce card, or bounce the flash off a ceiling or wall to reduce the hotspots on your subject's face. It diffuses the light so that it creates a softer, more natural look. Bouncing is tricky and I prefer a bounce card. But these two methods eat up a lot of battery juice cos the flash will probably be firing at full power all the time to expose the subject properly.

    5) Shoot on M mode. From the old birds here - set aperture to what u want (shallow preferably f/5.6) and then set shutter speed at 1/30. Set the flash to TTL mode. Make sure u hold the camera steady and fire away. The 1/30 shutter setting will take care of the background details (most of it anyway) while the TTL flash will take care of the subject's exposure. Anything slower, u need a tripod.

    6) If all else fails, use the P mode. Full auto or semi-auto P. It works wonderfully.

    To Hippo, if u've seen all these before, sorry for the crap but if not, I hope this helps.

    To the rest, please feel free to correct any misconceptions in my post. I still got a heck lot to learn about flash photography. Thanks and cheers!

  10. #10

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    Quote Originally Posted by hoppinghippo
    So in a way all I should do is meter the background, estimate how much the foreground subjects are underexposed if I shoot at the background exposure and
    ohoho..usually the background n foreground subject are the entire scene as one ..so it really boils down to how much extra light u want the flash to throw upon the foreground subject

    Quote Originally Posted by hoppinghippo
    set it as full power then adjust -ve stops compensation? (if so by how much?) or set the flash as auto fill in (on camera body) and assuming flash will overexpose the foreground, dial in -ve stops on flash (if so how much?)?
    full power then minus about 2 stops is an ok method. ie it works ok.

    "auto-fill-in" is very very unlikely to overexpose foreground subject. can sefaly leave it at +0 or if u like to play safe, leave flash at "auto-fill-in" with -0.5 to -1

  11. #11

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    Thanx Clive and TME!!! Really appreciate all your time, really learnt quite a bit! seems like flash is really a whole big area for learning in itself!!

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    Quote Originally Posted by hoppinghippo
    Thanx Clive and TME!!! Really appreciate all your time, really learnt quite a bit! seems like flash is really a whole big area for learning in itself!!

    Trust me it's DIFFICULT!!! Very often u shoot the same way as before but the results are a little different.... and u dun know why!

    The data logging on the Dynax 7 is the perfect tool for this manz..... can always look back at your detailed settings and then take it from there!!

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    yar man, last time when I used dynax 5 when it came to using flash I"ll always simply press the "P" button. cuz I was and still am damn sotong about flash. now can wayang with flash compensation dial, memory checking, etc! but then its damn hard to rem all the functions and how to use them, donno press what button and what button together, etc. more custom functions then underwear I possess.

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    Quote Originally Posted by hoppinghippo
    yar man, last time when I used dynax 5 when it came to using flash I"ll always simply press the "P" button. cuz I was and still am damn sotong about flash. now can wayang with flash compensation dial, memory checking, etc! but then its damn hard to rem all the functions and how to use them, donno press what button and what button together, etc. more custom functions then underwear I possess.

    Actually the Custom Settings in Dynax 7 very friendly leh! The large LCD screen enables the camera to tell u what the Customs Function does lar! It's a heck lot better than Dynax 505si where u have to know which Custom Function No. did what otherwise u can't get at that setting. Like when u want to remove the date imprint, u just need to scroll through the Custom Functions until u find it and then just just the dial to switch intensity of switch it off. Simple, fuss-free and very user-friendly.

    But actually I hardly use more than 10% of the custom functions. Mainly just the date imprint on/off and sometimes the shutter release priority only. Kekeke.... the rest of the Custom Functions, once u set u forget about it liaoz!

  15. #15

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    yeah that's true its a lot more user friendly now, last time my D5 had the customs set to default after battery went flat, I didn't realise and had my roll of film rewound with the tip zipping all the way in... arrgghhh.

    one thing bad about D7 tho, I don't see why they can't have a mirror lock up function since the self timer already has it enabled, can't they just put a button or some option to activate mirror lock up?

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    Quote Originally Posted by hoppinghippo
    yeah that's true its a lot more user friendly now, last time my D5 had the customs set to default after battery went flat, I didn't realise and had my roll of film rewound with the tip zipping all the way in... arrgghhh.

    one thing bad about D7 tho, I don't see why they can't have a mirror lock up function since the self timer already has it enabled, can't they just put a button or some option to activate mirror lock up?

    Just use the self-timer function lor.... the Dynax 9 has the lock up feature.

    BTW, dun know if u are using the 5600HS or not but here's a lobang for it ata very good price.

    http://forums.clubsnap.org/showthread.php?t=59912

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    I already have 3600 and sigma 500EF (not the latest one) so no need, but thanx for the lobang! actually I still blur about the sigma flash, damn a lot of functions.

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    Quote Originally Posted by hoppinghippo
    I already have 3600 and sigma 500EF (not the latest one) so no need, but thanx for the lobang! actually I still blur about the sigma flash, damn a lot of functions.
    I find that the TTL is not so accurate on the Sigma lens. I dun know if it applies to the Minolta mounts cos I used the EF-500 on a D30 and found that going on TTL mode blew out my subjects under low light! I had to compensate by using a lower power. On the other hand the 5600HS doesn't seem to that if I leave the flash on auto to its business.

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    hhhmmm agreed, it does overexpose the subjects, but most of the time I use it with my DIY bounce card or DIY omnibounce, so not so bad.

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    Quote Originally Posted by hoppinghippo
    hhhmmm agreed, it does overexpose the subjects, but most of the time I use it with my DIY bounce card or DIY omnibounce, so not so bad.

    Well I dun know about using bounce cards with it.... I just didn't like the hotspots on my subjects' faces as well as the obvious lighted circle in the middle of the frame at about 50mm.... some communication break down between the flash and the D30 it seems.... go get the 5600HS. U'll never regret it!

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