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05-29-2012, 11:29 PM   #1
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How Do I stop...

blowing out the background while doing fill-in flash? I think it happens when I have strong backlighting in auto mode.

05-29-2012, 11:39 PM   #2
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QuoteOriginally posted by tabl10s Quote
blowing out the background while doing fill-in flash? I think it happens when I have strong backlighting in auto mode.
Fill flash doesn't affect the background directly, however it limits your shutter speed to 1/180 which can blow out your background. The only way to avoid that is by using an external flash capable of pTTL HSS (high speed sync) which allows you to use a faster shutter speed.
05-30-2012, 01:48 AM   #3
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Or, you can shoot in M-mode. You will still be restricted to shutter speeds below 1/180s but you can stop down your lens. Also, remember to set an appropriate, fixed (low) ISO value. In certain situations, you may still discover that you would like to have an external flash with variable output in manual mode.

Under all circumstances, AUTO- and P-mode are the most unpredictable modes for uses with flash, as you leave it entirely up to the camera to "guess" what you want to achieve.
05-30-2012, 02:18 AM   #4
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Lowering the ISO to whatever works best is the easiest and simplest solution (trial and error in Manual Exposure mode) .... unless that still blows out the highlights ! You can of course also decrease/increase the power of your flash to compensate for the change in ISO if it is affecting your subject exposure too much.

06-04-2012, 10:35 PM   #5
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you need to meter the background and set exposure to suit that, then alter flash power to expose the foreground appropiately. Probably difficult to do in auto mode but would involve at least using AEL and most likely lots of (negative) FEC
06-04-2012, 10:45 PM   #6
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P-TTL flash should take care of this situation quite nicely. It's what it was designed for.
If this is all confusing for you, just set everything to green mode, including the flash (if you've got a Pentax flash) and it should just work for you...

There might otherwise be a problem of the background light being so strong that the flash cannot light the subject enough in full power. But it's hard to know without an example posted for us to see...
06-05-2012, 04:31 AM   #7
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QuoteOriginally posted by twitch Quote
Fill flash doesn't affect the background directly, however it limits your shutter speed to 1/180 which can blow out your background. The only way to avoid that is by using an external flash capable of pTTL HSS (high speed sync) which allows you to use a faster shutter speed.
From prior experience, I know if the flash output id too strong, the background looks like it's night. I would then open the lens to compensate. Can't this be done with the K-5?

06-05-2012, 08:56 AM   #8
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QuoteOriginally posted by tabl10s Quote
From prior experience, I know if the flash output id too strong, the background looks like it's night. I would then open the lens to compensate. Can't this be done with the K-5?
If the flash is too strong (ie it overexposes the subject) then opening the apeture wider will overexpose it even more!

Usually with P-TTL flashes including the built in flash it will reduce the power so the subject isnt overexposed (thats the theory anyway).
If you are very close, too close to the subject then that flash will blast them and overexpose anyway.

Obviously, if you are too far away then the flash power (particularly the built-in) wont reach the subject.
.
.
.

With backlighting or really any flash photography outdoors when there is a fair bit of ambient light you have to treat it like you are doing 2 exposures at the same time.
There is the background - which is all ambient light because the flash does reach to the distant background generally
and the foreground subject - which is mostly lit by the flash.

So for the background you can set whatever you want to get a correct exposure but you should try to keep the shutterspeed slower than 1/180s. This is because when you pop up the flash or use a normal external flash, the camera will limit the maximum speed to 1/180 if you had it higher. This will casue the background to overexpose. "Twitch" was explaining this above to answer your original question.

If the flash is P-TTL then using that mode will regulate the power to just put out enough light to light the subject properly (in theory anyway). It might still look a bit under or over when you check it. You can apply a bit of + or - flash exposure comp to alter to taste.

The idea is to balance the exposure from the flash and the exposure from the ambient light.


a bit of basic theory
If you were doing everything manual, with a manual flash at fixed power

The flash fires off all its power in about a millisecond or so - doesnt matter exactly. If you are only lighting with flash then if you have a 1/180s shot and a 1/30s shot they will both look the same as the amount of time the shutter is open doesnt matter all the flash light is deliverd to the sensor in a tiny fraction of that.

So..... if you want to alter the amount of light from a flash getting to your sensor you can adjust the apeture or you can adjust the senstivity(iso). Ajusting the shutter speed does nothing.

Now, of course ambient light for the background exposure can be altered by varying the apeture, iso and the shutter speed.

To balance the ambient lighting whilst keeping the flash exposure the same you can adjust only the shutter speed. Shutter speed has no effect on flash.
You just have to keep the shutter below 1/180 because of the camera's limitation.


In reality with a manual flash you can also adjust the power output on most of them and of course for P-TTL its all done for you.


If you're interested have a search around on youtube for "flash tutotrial" or "strobist tutorial" and theres quite a few videos showing many tecquires to use flash.
also theres this

Strobist: Lighting 101

and I found this one helpful

http://neilvn.com/tangents/flash-photography-techniques/

....and if you dont have an external flash get one. It doesnt have to be an expensive full P-TTL, capable of high speed sync but being able to go wireless is a definte plus.
then get out there and practise what you read about

happy flashing
06-05-2012, 08:58 AM   #9
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When using flash, think of it as being two photos. One photo is the background light and another is your subject being illuminated with your flash. You control ambient lighting with your shutter duration and you control the flash with power, distance and aperture.

High speed sync allows you to control your exposure the way you may be used to, with shutter duration. The flash in this case is basically acting as a continuous light source which in turn dramatically reduces the output of the flash.

High Speed Sync is typically used when you want to shoot at a low f-stop for shallow depth of field and/or to better control ambient light.
06-05-2012, 09:35 AM   #10
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This is my first experience going TTL as I've never had a unit that had such a capability(Vivitar 283, Sunpack 611 and Vivitar 5600).
06-05-2012, 09:42 AM   #11
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What are you going to be photographing? I hardly ever use TTL.
06-05-2012, 11:06 AM   #12
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QuoteOriginally posted by tabl10s Quote
This is my first experience going TTL as I've never had a unit that had such a capability(Vivitar 283, Sunpack 611 and Vivitar 5600).
Wait.... TTL is not correct on Pentax DSLR, it should be P-TTL, if you use TTL then the flash simply fires at full power all the time.

What flash and camera are you using?
06-05-2012, 11:35 AM   #13
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After all is said and done, stone G has the best answer.

Set the camera to M mode, set the green button to adjust aperture as opposed to shutter speed, set shutter speed to 1./180 and then press green button to meter off the background. This will allow you to then use the flash to illuminate the foreground to the same level as the background, as long as your foreground is sufficient area, you may want spot metering for this and center the subject in the frame.

alternatively, if you don't go the green button route, you can go to M mode and just point at the background and adjust aperture and shutter (but keeping shutter below 1/180) and read the meter off the =/- scale, and adjust as you want for the background intensity you desire. then shoot.
06-05-2012, 11:44 AM   #14
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I just have the on- board flash. Now I know I wan external .flash that can do P-TTL and that can do multiple power adjustments down to 1/128
06-05-2012, 01:06 PM   #15
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On board flash only works in P-TTL so that isn't the problem.

Like is being suggested use M mode for the camera, the amount you underexpose is the amount the flash will "fill-in" so to say, to balance the exposure to zero.
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