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10-26-2008, 12:05 PM   #1
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Flash & Shutter Speeds .. I don't get it!

I've had my k10 for one year, and am just now starting to learn to use the flash!

I've learned about Flash Compensation (fn menu, arrow down, spin rear dial), and have also learned that closing/opening aperture influences the effective range for the flash.

I've also learned that slow-speed sync (fn menu, arrown down, select it, only in AV/P/SV modes) slows the shutter speed, thereby allowing in more ambient light, and eliminating the risk of dark corners/backgrounds.

What I am trying to understand is if/how metering comes into play .. and if so, what considerations I need to remember regarding shutter speed??

I was practicing in AV mode, and noticed that with the flash on, no matter what changes I made to aperture, the SS remained constant at 1/45sec. However if I switched to slow-speed sync, the SS adjusted according to my aperture setting. Not sure what that tells me about things, but it was just an observation.

Anyone have any advice/instruction on using in-camera flash & shutter speed? There's something missing in my understanding of this, I just dont know it well enough to articulate a specific question!!

..Thanks ...

10-26-2008, 12:53 PM   #2
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Is not all that difficult to understand.

If camera is set to regular flash, it measures light considering that a flash will be used, so shutter speed will not go below 1/45 just to keep picture "steady".

If camera is set to slow sync flash, then it measures to ambient light NOT CONSIDERING that a flash will be used. This way, the camera may drop shutter speed to very long exposures (if ambien light is low enough). When photo is taken, the flash will burst but only as a fill flash.


Example: Scene is of a portrait with a dimly lit background. With regular flash, your picture will come out with a black background and properly exposed subject (in foreground). With slow sync, the photo will show background (possible blurred due to camera shake) and a properly exposed foreground.

Do some experiments and you will soon master this technique.

One last thing, in slow sync mode, it is always handy to use a tripod.

Robert B.
10-27-2008, 06:02 AM   #3
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My little P-TTL "recipe"

Basically, with flash, the FLASH exposure is solely determined by flash power (actually duration, how long the bulb is actually firing for), aperture and ISO. Ambient exposure is determined by ISO, shutter speed, and aperture (just like without any flash), so the trick is balancing the two. If I'm indoors in a smallish room (such as in someone's house), I usually just forget about ambient since the flash is powerful enough to light up the entire room (hence the 1/180s below, if the flash didn't fire, I'd have a more or less black picture) Now although you're shooting MANUAL Mode, that's only for the ambient exposure (the exposure needle in the viewfinder will blink warning you about underexposure, but ignore that). The camera's P-TTL metering will determine the needed flash output for a proper exposure.

Here's something I wrote on another forum -
"Easy" recipe for great P-TTL flash shots -
1)Point flash at ceiling
2)Put camera in MANUAL mode on the mode dial
3)Set FEC to +1 on the flash head


4)Shoot RAW (this allows you to recover some highlights that might get blown as a result of #3 above)

5)Set ISO to 200 (to start)
6)Set shutter speed to 1/180s
7)Set f-stop to whatever DOF you want



Now if the flash runs out of "power" because of high ceilings, you can raise the ISO or open up the f-stop to compensate. Or you can slow down the shutter to bring more ambient light into the exposure (in addition to adjusting ISO/f-stop) If the ceiling is REALLY high (like in a church), you may need a reflector to throw some of the light forward (I use the Joe Demb Flip-it).

Quick and dirty outdoor fill flash tutorial -

Basically, if your subject is in shade and the background is bright (ie under a tree) or majorly backlit, fill flash is your friend. Think of those times when you got a properly exposed background, but the subject was almost pitch black.

Put camera into Av mode, metering will set the shutter speed to expose the overall shot (which in the situations that call for fill-flash will generally be the background) based on your selected aperture/ISO.

Make sure flash is set to HSS (in case your shutter speed go faster than 1/180s) and P-TTL. Fire away! The shutter speed/f-stop/ISO will expose the background, and the flash should output enough power to light up the foreground.

Now to control the background exposure, you use exposure compensation on the camera body (which would adjust the shutter speed), to adjust how much fill for the flash exposure, you use Flash exposure compensation. The trick is balancing the two (as it is with indoor work), and that comes with experience/experimentation.
10-27-2008, 11:15 AM   #4
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QuoteOriginally posted by deludel Quote
I was practicing in AV mode, and noticed that with the flash on, no matter what changes I made to aperture, the SS remained constant at 1/45sec.
perform the same experiment using longer focal length (let say, 100mm).
will the shutter speed still set to 1/45 sec?

afaik,
the shutter speed will (more or less) follow (1/the focal length)
so, when the shutter speed is set to 1/45sec, you are probably using focal length of 50mm.

I'm not really sure about this so I'll check it later.

10-28-2008, 11:03 AM   #5
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Flash photography adds another element of exposure to your pictures.

When you use the flash, you actually have 2 exposures to manage, not 1. These two are ambient lighting, and flash lighting.

Ambient Lighting exposure is effected by these 3 things:
Aperture, Shutterspeed, ISO

Flash Lighting exposure is effect by these 3 things
Aperture, ISO, FLASH POWER

Notice that Aperture and ISO affects BOTH exposures, however, your shutterspeed DOES NOT.

What does this mean?

It means you adjust your Aperature for depth of field, you adjust ISO for light sensitivity (as usual), but you adjust shutterspeed for the amount of ambient lighting to show up in the picture, and you adjust the flash power for the amount of flash lighting to show up in the picture.


-------------------------------------
Because you are using sync flash in low light, the camera is programmed to believe the flash is now the primary lighting. As a result, the camera is picking the slowest shutterspeed that will safely not cause camera shake. In your case, 1/45. This figure is based on the focal length (zoom on the lens) you're at.
10-28-2008, 04:19 PM   #6
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So if taking candids at a perty, say, what settings would be recommended?

My guess - f4ish, maybe f8 for groups with depth (a compromise between DOF and flash reach)
1/60th
400-800ISO to let the flash "go further"
flash power of 1 if front on, more power if bouncing.

This is ignoring any ambient lighting you may want.
Please comment.
10-28-2008, 04:58 PM   #7
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QuoteOriginally posted by AVANT Quote

Flash Lighting exposure is effect by these 3 things
Aperture, ISO, FLASH POWER

-------------------------------------
Because you are using sync flash in low light, the camera is programmed to believe the flash is now the primary lighting. As a result, the camera is picking the slowest shutterspeed that will safely not cause camera shake. In your case, 1/45. This figure is based on the focal length (zoom on the lens) you're at.
PTTL determines flash power based on distance between flash and the subject (focus point). So, if you use Av mode with PTTL flash, it is better to turn off "link AF point to AE" and use center weigh or multipoint metering, otherwise, you may get different results depending on what the subject (person) wears; I am assumig you are taking a picture of person or group of people.

If you are not setting to slow sync - the flash is assuming that you are using the MTF setting of the lens which could be 1/45 if you are using a 50mm lens. Also, you probably don't need to use a tripod as long as you are not shooting at too low shutter speed than the recommended threshold which is 1/focal length. This is one big advantage of in-camera SR.

QuoteOriginally posted by Arpe Quote
So if taking candids at a perty, say, what settings would be recommended?

My guess - f4ish, maybe f8 for groups with depth (a compromise between DOF and flash reach)
1/60th
400-800ISO to let the flash "go further"
flash power of 1 if front on, more power if bouncing.

This is ignoring any ambient lighting you may want.
Please comment.
It depends on what focal length, background light, distant from subject, DOF and how big is the group. If you are using 18mm wide, and a group of two rows, you can go with f3.5 or f4 and ISO 400. This is direct flash, for bounce flash, you may need to either do EV adjustment if using Av mode or bump ISO a tad to compensate for flash power loss or spread if I am using manual mode.

I am no expert here, but in general it works for me.
10-29-2008, 10:06 AM   #8
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Arpe - Read my "recipe", it should answer all your questions. Only thing to do now is to go to as many indoor "functions" as possible and experiment so you'll quickly get a feel for how flash works.

10-30-2008, 01:10 PM   #9
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Original Poster
Just wanted to say "Thanks" to all, I'll try these methods over the weekend and post a report with how it goes/what I learn!
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