Flash compensation vs. exposure compensation

Started Sep 4, 2005 | Discussions
JensR Forum Pro • Posts: 17,971
Flash compensation vs. exposure compensation

Hi forum!

Maybe this is old news to the veterans here, but if the *ist DS is used with flash (internal/external TTL) in Av mode, the exposure time is changed to 1/125 upon fully flash charge and exposure compensation dialed in via the command wheel will now serve as flash exposure compensation. IMO, this makes adjusting flash exposure simpler than in M mode, where you have to go through the menu. So, if I do not need to adjust exposure time for my flash shots, I will now use Av mode.

I found that if you have dialed in -1EV via the menu and +1EV via the command wheel, the exposure will be identical - obviously the two compensations get combined (as long as the flash can provide enough light).

IIRC, the *ist D, which does not offer flash expoisure compensation via a menu works similarly (exactly?) like the DS in Av mode.

Sorry, if this is old news to some DS users, it surely was an "aah!" experience for me
Jens

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racehorse in the desert Veteran Member • Posts: 4,103
Re: Flash compensation vs. exposure compensation

Using exposure compensation will change the exposure on the entire image. Using flash compensation is useful with fill flash when you want the reading of the ambient light, or background, to remain the same, and only want to change the fill flash. But I know that you knew that; you are just saying that it is easier to use the dial than the menu, and that certainly is correct, right?
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OP JensR Forum Pro • Posts: 17,971
Re: Flash compensation vs. exposure compensation

Hi John!

Using exposure compensation will change the exposure on the entire
image. Using flash compensation is useful with fill flash when you
want the reading of the ambient light, or background, to remain the
same, and only want to change the fill flash. But I know that you
knew that;

Thanks, and yes.

you are just saying that it is easier to use the dial
than the menu, and that certainly is correct, right?

Yes and no. Sorry if I did not make myself clear. I did not expect to have two access paths to flash exposure compensation in the first place.

What surprised me was that the exposure compensation dialed-in in Av mode does a) have no influence on shutter speed at all and b) works as flash-exposure compensation instead.

I found it surprising but useful that the exposure compensation dial changes its meaning in this situation. I would have either expected that exp. comp. adjusts shutter speed to give more or less importance to ambient light OR that exp. comp. is simply ignored for this use (Av + flash) .

Don't know whether this made it any clearer, though
Jens

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RoscoT Senior Member • Posts: 2,943
Re: Flash compensation vs. exposure compensation

Jens, What flash are you using? I would think this would only work with a P-TTL unit.
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OP JensR Forum Pro • Posts: 17,971
Re: Flash compensation vs. exposure compensation

Hi Rosco!

It works both with the internal P-TTL flash as with my external SCA 300 TTL flash.

Cheers
Jens

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Dave Lewis Forum Pro • Posts: 10,425
That's only with the built in flash, though.
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Dave Lewis

Dave Lewis Forum Pro • Posts: 10,425
Re: Flash compensation vs. exposure compensation

JensR wrote:

Hi Rosco!

It works both with the internal P-TTL flash as with my external SCA
300 TTL flash.

Cheers
Jens

My D will not control flash output without the flash up, thus won't control flash output of an external flash. The Ds will control flash output with its flash exposure compensation.
--
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OP JensR Forum Pro • Posts: 17,971
Re: Flash compensation vs. exposure compensation

Hi Dave!

My D will not control flash output without the flash up, thus won't
control flash output of an external flash.

Ok, I just did a search and indeed only the internal flash is mentioned:
http://forums.dpreview.com/forums/read.asp?forum=1036&message=12445217
http://forums.dpreview.com/forums/read.asp?forum=1036&message=8978123
http://forums.dpreview.com/forums/read.asp?forum=1036&message=12409506

The Ds will control
flash output with its flash exposure compensation.

OR with the exp. comp. dial, when in Av mode, as I (?) have found. AND it works for both internal and external flash - obviously different from the D.

Cheers
Jens

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RoscoT Senior Member • Posts: 2,943
Re: Flash compensation vs. exposure compensation

JensR wrote:

Hi Rosco!

It works both with the internal P-TTL flash as with my external SCA
300 TTL flash.

Thanks, Jens. I'm going to have to do some experimenting with this.
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OP JensR Forum Pro • Posts: 17,971
Samples

Ok, here are some samples.
For all three shots:
Exposure time: 1/125
F-stop: 2.8
ISO speed: 200
Focal length: 100.0000
Flash: fired (external TTL, not P-TTL)

EC and FEC at 0

EC at +1EV, FEC at 0

EC at +1EV, FEC at -1EV

the resulting exposure is identical tp +1-1=0EV (first shot)

Now, who said that brickwalls are boring?

Cheers
Jens

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John Bean (UK) Forum Pro • Posts: 18,035
Re: Samples

JensR wrote:

Now, who said that brickwalls are boring?

Bricks? What bricks?

This is interesting though, I've ignored "A" mode with TTL flash because the fixed 1/125 seemed too restrictive but now I see why they've made it that way. This is very, very handy if flash is the primary light source.

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martym Regular Member • Posts: 464
Re: Flash compensation vs. exposure compensation

Dave Lewis wrote:

My D will not control flash output without the flash up, thus won't
control flash output of an external flash. The Ds will control
flash output with its flash exposure compensation.
--
Dave Lewis

Hi Dave

It does work with the AF240FT, I think you mentioned you had one of these in a previous post. Just put it on the hotshoe, turn the camera on, then the flash (set to TTL) go to TV or AV on the camera (make sure the flash is ready), set the EV comp up two or down two. You should notice that the aperture and shutter speed do not change and the flash output varies. Won't work with P mode or Green. If it doesn't you may have a bad contact or something. Don't know if it works with other flashes other than Pentax though.
Marty

Dave Lewis Forum Pro • Posts: 10,425
Re: Flash compensation vs. exposure compensation

Yes it was a disappointment when I found I just couldn't use my older Sigma flash with the D because that flash over exposes badly without flash exposure compensation to calm it down. On my Ds it works perfectly once I dial in about a stop and a half of flash exposure compensation. Both are just wonderful with an older genuine Pentax 330 flash though.
--
Dave Lewis

Dave Lewis Forum Pro • Posts: 10,425
Re: Flash compensation vs. exposure compensation

martym wrote:

Dave Lewis wrote:

My D will not control flash output without the flash up, thus won't
control flash output of an external flash. The Ds will control
flash output with its flash exposure compensation.
--
Dave Lewis

Hi Dave
It does work with the AF240FT, I think you mentioned you had one of
these in a previous post. Just put it on the hotshoe, turn the
camera on, then the flash (set to TTL) go to TV or AV on the camera
(make sure the flash is ready), set the EV comp up two or down two.
You should notice that the aperture and shutter speed do not change
and the flash output varies. Won't work with P mode or Green. If
it doesn't you may have a bad contact or something. Don't know if
it works with other flashes other than Pentax though.
Marty

Yes, I think I remember that thread. I was wrong, though. My Pentax flash is the 330 model and it works perfectly on both the D and the Ds. Honestly, though, in retrospect, I think I used the Sigma on the D with P. I should try it with TV or AV. I use flash so seldom in the summer that I foget more than I remember about it.
--
Dave Lewis

OP JensR Forum Pro • Posts: 17,971
Re: Samples

Hi John!

Now, who said that brickwalls are boring?

Bricks? What bricks?

I meant, in comparison with shooting a white wall, shooting brick walls doesn't seem so boring suddenly

This is interesting though, I've ignored "A" mode with TTL flash
because the fixed 1/125 seemed too restrictive but now I see why
they've made it that way. This is very, very handy if flash is the
primary light source.

I agree. I wonder where in the manual this is hidden?!

Nice!! Does the WA converter come with a protective cap/lens hood?

Cheers
Jens

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John Bean (UK) Forum Pro • Posts: 18,035
Re: Samples

JensR wrote:

I meant, in comparison with shooting a white wall, shooting brick
walls doesn't seem so boring suddenly

Ah, now it makes sense. Maybe for your next project you can shoot an action sequence of drying paint

Nice!! Does the WA converter come with a protective cap/lens hood?

Cap: yes, push-on. Hood: no, and no threads either. The adaptor tube has a rectangular hood to use with the camera's normal lens. It's nice quality stuff for such a low price.

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OP JensR Forum Pro • Posts: 17,971
Re: Samples

Hi John!

Ah, now it makes sense. Maybe for your next project you can shoot
an action sequence of drying paint

LoL! Exellent!

Cap: yes, push-on. Hood: no, and no threads either. The adaptor
tube has a rectangular hood to use with the camera's normal lens.
It's nice quality stuff for such a low price.

Thanks very much for the info!

Jens

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Ishpuini Veteran Member • Posts: 6,259
Re: Samples

Hi Jens,

I haven't tried this myself, and I'm at work now (no I don't take my DS to work ), but should a correct comparison not have a foreground and a background object.

Perhaps I've got it all wrong but I assumed that:

  • EV compensation plays on exposure thus influencing overall exposure

  • Flash compensation determines the amount of light the flash sends out. I.e. the foreground will be influenced, but the background may not.

So dialing a EV of +1 and a FEV of -1 would compensate the underexposure of the background you would normally have with flash at full power, but make no difference to foreground exposure.

Please correct me promptly if I understood wrong...

thanks!

Wim

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OP JensR Forum Pro • Posts: 17,971
Re: Samples

Hi Wim!

I haven't tried this myself, and I'm at work now (no I don't take
my DS to work ), but should a correct comparison not have a
foreground and a background object.

Not necessarily. The shutter speed and aperture are held constant for my white wall tests.

Perhaps I've got it all wrong but I assumed that:

  • EV compensation plays on exposure thus influencing overall exposure

  • Flash compensation determines the amount of light the flash sends

out. I.e. the foreground will be influenced, but the background may
not.

Yes, but this is what is interesting when using flash in Av mode: Exposure compensation does not change the shutter speed! But the exposure is different, so, the exposure compensation dial must act as flash exposure compensation in this circumstance!

Cheers
Jens

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Ishpuini Veteran Member • Posts: 6,259
Re: Samples

JensR wrote:

Yes, but this is what is interesting when using flash in Av mode:
Exposure compensation does not change the shutter speed! But the
exposure is different, so, the exposure compensation dial must act
as flash exposure compensation in this circumstance!

Cheers
Jens

Ok, I see now what you mean... I'll have a look this evening.

Wim

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