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09-17-2010, 09:24 AM   #1
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Flash retard needs help...

So I have a K7, and this past weekend around a campfire I decided to break out the ol' popup flash and see what I could get. Normally I just crank up the ISO and try to deal with 1/4 sec shutter speeds.

I was pleasantly surprised to find that I could shoot at 400 ISO and 1/100 shutter speeds in the dark of night with flash!

So I started playing around with the shutter speed, aperture, ISO etc... What happened next I don't understand... Basically if I cranked up the shutter speed, and metered, nothing happened. I would have expected it to open the aperture. Or something. Basically, no matter if I was in Manual, aperture priority, shutter superiority, etc, it seems that the camera only adjusted metering by changing the power of the flash. I think?

Anyway, I basically don't have a clue how to control flash photography or how it's working....

'elp please...

Ken

09-17-2010, 09:29 AM   #2
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I don't have the K7, but this makes sense to me... the flash does not have a manual mode that I know of, so will fire however strong it needs to... it should fire a 'test' flash, meter and then the real one... really quick... you need something like the 540 before you can 'control' your flash in M-mode... unless there is some special option in the K7 I have never heard of...


Just adding one thing... you can change the EV + or - to 'control' the flash... ie if you select EV - 1 the flash will be weaker... etc
09-17-2010, 09:45 AM   #3
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QuoteOriginally posted by Javaslinger Quote
So I have a K7, and this past weekend around a campfire I decided to break out the ol' popup flash and see what I could get. Normally I just crank up the ISO and try to deal with 1/4 sec shutter speeds.

I was pleasantly surprised to find that I could shoot at 400 ISO and 1/100 shutter speeds in the dark of night with flash!

So I started playing around with the shutter speed, aperture, ISO etc... What happened next I don't understand... Basically if I cranked up the shutter speed, and metered, nothing happened. I would have expected it to open the aperture. Or something. Basically, no matter if I was in Manual, aperture priority, shutter priority, etc, it seems that the camera only adjusted metering by changing the power of the flash. I think?

Anyway, I basically don't have a clue how to control flash photography or how it's working....

help please...

Ken
Maybe because the meter is showing you a Calculated number? That is, the lens is wide open regardless of what setting you are using, what aperture you have chosen, etc until you actually snap the photo. I Thought, the idea of P-TTL was to measure During exposure and adjust the flash output accordingly.

QuoteOriginally posted by icywarm Quote
I don't have the K7, but this makes sense to me... the flash does not have a manual mode that I know of, so will fire however strong it needs to... it should fire a 'test' flash, meter and then the real one... really quick... you need something like the 540 before you can 'control' your flash in M-mode... unless there is some special option in the K7 I have never heard of...


Just adding one thing... you can change the EV + or - to 'control' the flash... ie if you select EV - 1 the flash will be weaker... etc
The only 'controls' on the built in flash are the flash compensation. -2 to +1 I think. Otherwise, just like all the rest of the cameras, ISO, aperture, and shutter speed are used to calculate flash output strength. Evidenced by if you try to use a full manual lens (use the aperture ring instead of A), the flash will fire at full power.

09-17-2010, 10:12 AM   #4
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What I didn't understand about flash when I first started using it is that shutter speed never mattered

Aperture, ISO, and Flash EV comp (should be in the flash menu) control the distance the flash can be seen

Shutter speed controls the ambient light, to balance it with the flash or further isolate your subject, shutter speed has absolutely no affect on the power or the effectiveness of the of the flash because ambient light can be gathered over a long period of time, say 1/30th of a second, but your flash discharges all it's power in a fraction of a second, say maybe 1/10,000th, so no matter how long you open the shutter, the flash won't change

One of the basic ways to use flash is to use manual mode, 1/30th of a second, and then mess with ISO, aperture and flash EV comp until you get a good picture

In manual mode, the camera doesn't meter for the flash, it's meter just as if you were not using flash, it just meters for the ambient light, and then you adjust the flash for the specific subject you're shooting

While I've never heard of or don't understand your particular problem, maybe a basic understanding of flash might help you work through it

09-17-2010, 10:30 AM   #5
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I would also be useful to understand how light travels and how much of it is used in an exposure. This site gives a pretty good explanation that will help predict what is going to happen when you use a flash (or any other situation).

Four Flash Photography Basics we must know


Last edited by JeffJS; 09-17-2010 at 10:37 AM.
09-17-2010, 10:43 AM   #6
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QuoteOriginally posted by JeffJS Quote
I Thought, the idea of P-TTL was to measure During exposure and adjust the flash output accordingly.
Actually that is how TTL works, but not P-TTL

P-TTL measures the ambient light, with the lens wide open, and also the amount of flash it sees from a preflash, again with lens wide open, and calculates between the two, exactly how much flash it gives so that exposure is correct with the lens stopped down.
09-17-2010, 10:46 AM   #7
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QuoteOriginally posted by future_retro Quote
In manual mode, the camera doesn't meter for the flash, it's meter just as if you were not using flash, it just meters for the ambient light, and then you adjust the flash for the specific subject you're shooting
Actually in manual mode, with the in camera flash, the camera does meter for the flash. you set the shutter speed and aperture manually, yes, but then the camera looks at the flash and makes the exposure correct for the settings you have, by adding in flash based upon the metering of the system
09-17-2010, 11:35 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
Actually in manual mode, with the in camera flash, the camera does meter for the flash. you set the shutter speed and aperture manually, yes, but then the camera looks at the flash and makes the exposure correct for the settings you have, by adding in flash based upon the metering of the system
What camera do you have?

I was referring to the pop up flash and in my experience the Kx and the K7 both don't meter the flash in M, I just tried it on my desk and keeping all variables the same except the flash, the meter didn't budge.

In P and all the priority modes though the meter takes the pop up flash into the account but for M mode I have to rely on GN and and trial and error

.....I just did a small test and took two pictures in M, one with the pop up flash and one without, the meter didn't change and upon checking the EXIF, the exposure didn't change either

09-17-2010, 11:50 AM   #9
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QuoteOriginally posted by future_retro Quote
What camera do you have?

I was referring to the pop up flash and in my experience the Kx and the K7 both don't meter the flash in M, I just tried it on my desk and keeping all variables the same except the flash, the meter didn't budge.

In P and all the priority modes though the meter takes the pop up flash into the account but for M mode I have to rely on GN and and trial and error

.....I just did a small test and took two pictures in M, one with the pop up flash and one without, the meter didn't change and upon checking the EXIF, the exposure didn't change either
I have *istD, K10D and K7D, and to me when using a lens with an A on it, the P-TTL flash performs the same way in all cases, where it correctly esposes. No the meter does nto change but the flash works as it should, and uses the known exposure in the flash calculation,

Now if you are takling real M mode, with manual aperture lenses, no the flash does nothing at all but go at full power, except on m,y *istD, where the *istD has both TTL and P-TTL metering. This is a great little camera because you can do correctly metered TTL flash shots with manual aperture lenses.
09-17-2010, 11:55 AM   #10
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QuoteQuote:
What I didn't understand about flash when I first started using it is that shutter speed never mattered
As long as it is within the flash-sync speed of 1/180 or slower, in Pentax's case.
09-17-2010, 12:58 PM   #11
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In M mode and with manual lenses on the K-x and on- board flash, does flash comp work?

In other words, can I adjust the power level?

I know--I should read the manual.
09-17-2010, 01:30 PM   #12
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wait did you mean the flash is compensated automatically?
09-17-2010, 04:35 PM   #13
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QuoteOriginally posted by future_retro Quote
wait did you mean the flash is compensated automatically?

Perhaps I'm not understanding your question, but my answer would be yes.

There's a flash technique that's called "Dragging the shutter".

You meter the scene for the background, set your aperture and shutter speed to expose this correctly, then you set up the flash to meter for the flash only for a subject in the scene. P-TTL makes this technique very easy, but remember P-TTL requires using either "A" series or AF lenses to work correctly.

Try this -- go to a room that's lit by a single lamp in a far corner, meter the scene so the room is reasonably exposed and take a shot in M mode. Have someone stand in the middle of the room and take a shot with the same settings. The person will be underexposed, somewhat silhouetted by the rear lighting. Now pop up the flash, keeping the same settings, and take another shot. The room (now the background) should still be exposed pretty much the same, but the person should now be reasonably exposed because of the flash. If the person is still underexposed, it should be by less, and you could probably correct this by switching to center weighted or spot metering. Don't worry about blur, IQ, composition, or any other quality but exposure in this test.

What just happened is that you set up the camera (aperture and shutter speed) to expose the background, then P-TTL metered the flash with the preflash to give you a reasonable exposure for the previously underexposed person you added. You've also discovered how to prevent one of the most common objections to flash photography -- a well lit subject but a blacked out background.

If you extrapolate from this, you can use select focus points and the camera's ability to lock AE to AF, so you can select where the flash will be metering and focusing other than just in the center. External flash with flash modifiers gives you even more versatility and control of the light. You can also vary the flash's contribution to the lighting with Flash Ev compensation.

There are, of course limitations -- if the shutter speed is too slow, you might get a blurred background -- but that can be corrected by using higher ISO to keep shutter speeds up (up to the 1/180 max synch speed) -- and with the flash giving you a properly exposed subject, noise is usually much less than you would expect for a given ISO.

You can, of course, use a manual flash, and GN calculations or experimentation, to get to the same place -- but P-TTL makes it pretty brainless, and I personally like that. . .

Scott

Last edited by snostorm; 09-17-2010 at 04:50 PM.
09-22-2010, 08:54 AM   #14
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QuoteOriginally posted by future_retro Quote
What camera do you have?

I was referring to the pop up flash and in my experience the Kx and the K7 both don't meter the flash in M, I just tried it on my desk and keeping all variables the same except the flash, the meter didn't budge.

In P and all the priority modes though the meter takes the pop up flash into the account but for M mode I have to rely on GN and and trial and error

.....I just did a small test and took two pictures in M, one with the pop up flash and one without, the meter didn't change and upon checking the EXIF, the exposure didn't change either
The METER (in the viewfinder) only reads the ambient light, so of course it doesn't change if the ambient light remains constant.

When you say "the exposure didn't change", what do you mean?

Go inside. Go into Manual mode, ISO100, f/8, and a 1/180s. Keep the flash off. Take a picture. It should be black.

Now pop the flash up and take a picture. The picture should be exposed pretty well, even though you were still at ISO100, f/8, and 1/180s. What happens is the flash sends out a brief pre-flash, of which the meter reads the light reflected back form the pre-flash, and determines WHAT power to fire the main flash at, based on (1)The ISO, (2), the aperture, and (3)The "distance" the light needs to travel to the subject and back.
09-22-2010, 08:56 AM   #15
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QuoteOriginally posted by Ira Quote
In M mode and with manual lenses on the K-x and on- board flash, does flash comp work?

In other words, can I adjust the power level?

I know--I should read the manual.
If the body can't determine the aperture (which is the case with M lenses), the pop-up flash will always fire at full power. Your only way to properly expose is to adjust the ISO and f/stop until it looks "good"

If you have an external flash, you can manually set the flash power level so you have a lot more control.

Like my previous post mentioned, PTTL needs to know the ISO and the f/stop to properly set the required power level (after reading back the pre-flash)
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