Frustrating flash

[lejazzcat]

Hi , sorry but i have another question.
(seems i have more questions than answers most days )

When using the camera indoors at night in A mode, with ambient house lights on (hence mixed lighting);

I pop the onboard flash to assist in expectation of a long shutter speed, I see on the EA exposure display that the exposure will be few stops under its own CSM set shutterspeed. I have a couple of choices ,
1/ reset the min flash shutterspeed to a new slower value (CSM menu)
2/ set the camera to a higher iso or auto iso
3/ change my aperture to a wider opening if possible .

I try any/all of these BUT i dont see the exposure display changing to suggest im working towards a solution. Why not ?

If i set the camera to auto iso - it exposes at a ok setting at about 1 or 1.5 stops higher than my manual iso setting . So why then when i changed the settings more than 3-4 stops didnt the display 'centre' (....0....>) ?

i had this problem before when working with night shots where the sensor just wouldnt give me a reading to assess exposure choiceswhen setting A or S prefrences.
http://www.d70users.net/viewtopic.php?t=4202&highlight=
i posted a question to the effect and others had the same problem, but this is indoor with ambient incandescents on.


what am i doing wrong?

TIA guys ,
R

[Antsl]

When trying to mix ambient with flash at night you are better to use the flash in TTL mode but use the camera in the M for full manual mode....

Try setting you ISO at 400 or 800 ISO (I regularly work with the later); set your aperture to one of you wider settings (f 2.8 or f4) and then experiment with different shutter speeds and look at the results.

If you keep your aperture and ISO the same you will not adjust the effect of the flash... as you vary the shutter speed though you will see the background get lighter or darker, depending on whether you open the shutter for longer time or less time.

Adjusting the aperture controls the flash and the ambient... adjusting the shutter speed only will vary the ambient only (this is because the flash duration is a lot quicker than the shutted speeds we normally use!

Hope this is a help!
Antsl

[lejazzcat]

When trying to mix ambient with flash at night you are better to use the flash in TTL mode but use the camera in the M for full manual mode....

Ok trying that and i see what you mean . The meter display becomes 'interactive' again.

As you suggest ,a variable/different shutter speeds enables me to center exposure (...0...) again. Albiet a overexposure .
But I am able to balance a better flash/ambient mix, by trying out different shutter speeds. Ok with digital , but ide be pissed if it was film.

If i try Porait mode and let the camera do it all, it gives a safe OK exposure.
If i try the A mode with fixed flash shutterspeed(CSM), the ambient is darker by a couple of stops , yet the histogram tell a similar exposure because of the TTL flash creating a correct exposure.
M centered tends to overexpose.

So why does the meter say that it will be a underexposure (in A or M mode ) ? Is it because it hasnt seen the flash yet and hence recalculated the correct power output and duration of the flash (hmm how does the TTL work with flash , before or during exposure - like the Automatic settin on a SB? )?

I thought the flash was more 'intelligent ".... Mind you im not using a D lens ! (i just realised)

Well i hope i got it, seems the onboard flash is pretty weak and is really only a happy tool in M .


thanks mate.

[Onyx]

First, let's try to standardise the jargon to be sure we're on the same page. The exposure meter [---0---] display at the bottom of the viewfinder - is this what you're saying you are missing when you pop up the onboard flash?

When in Aperture Priority or Shutter Priority modes, this meter will usually not show up, as the camera controls the other parameter - you don't have to worry about balancing it for a proper exposure. When in manual mode, this exposure meter will show up and guide you towards the correct settings for the exposure (showing how much under/over you are).

When shooting in Aperture Priority mode, and you pop up the flash, the shutter speed defaults to the set minimum as defined in the menu. The flash defaults to front curtain sync. If you are wishing to balance ambient lighting with that of the onboard flash, you are wanting slow(rear) sync flash. This mode has to be manually selected (flash button + main command dial). If left at the default front sync mode, it will stay stuck at 1/60s or whatever, thereby almost guaranteeing a poor ambient exposure. At this stage, even if you alter the lens aperture from say f/8 to f/5.6 or f/2.8, you may still have the shutter reading of 1/60. You can dial up the ISO from 200 to 1600 and you may STILL have the shutter reading of 1/60!!! <--- is this the effect that is frustrating you?

Note: At a given ISO, the lens aperture and shutter speed determines scene exposure. The aperture and distance to subject determines flash exposure. ie. changes to shutter speed does NOT affect flash exposure. Therefore, the only common setting when attempting to balance flash and ambient exposure is the lens' aperture.

Capturing an image with a mix of ambient and flash lighting is IMHO one of the greatest challenges of photography.

[kipper]

I have to agree with you Onyx. I was experimenting when I was away at Easter using the 50MM F1.4. Opening the lens up, reducing shutter speed, adjusting flash compensation in the negative area. It started to produce some results I was happy with.

Also to note is that flash has greater reach with higher ISOs.

[lejazzcat]

First, let's try to standardise the jargon to be sure we're on the same page. The exposure meter [---0---] display at the bottom of the viewfinder - is this what you're saying you are missing when you pop up the onboard flash?

Its hard to describe these things, but no, the EAED(electronic analogue exposure display) is still in the viewfinder. It was that i couldnt get to respond to changes in settings .
BUT
It IS now, i dunno what ive done but its working now !
At the set ISO and fixed 'menu' shutter speed, I can adjust aperture to a point were the display disappears, although its NOT true aperture priority anymore though is it?

When in Aperture Priority or Shutter Priority modes, this meter will usually not show up, as the camera controls the other parameter - you don't have to worry about balancing it for a proper exposure. When in manual mode, this exposure meter will show up and guide you towards the correct settings for the exposure (showing how much under/over you are).

Why is it when set to A mode and auto iso doesnt the camera,when set to the CSM 21 menu shutter speed, adjust the ISO to make the camera create a correct exposure .
It stays at base iso your camera has dialed in.
Yep, i had success in M mode.

When shooting in Aperture Priority mode, and you pop up the flash, the shutter speed defaults to the set minimum as defined in the menu. The flash defaults to front curtain sync. If you are wishing to balance ambient lighting with that of the onboard flash, you are wanting slow(rear) sync flash. This mode has to be manually selected (flash button + main command dial). If left at the default front sync mode, it will stay stuck at 1/60s or whatever, thereby almost guaranteeing a poor ambient exposure. At this stage, even if you alter the lens aperture from say f/8 to f/5.6 or f/2.8, you may still have the shutter reading of 1/60. You can dial up the ISO from 200 to 1600 and you may STILL have the shutter reading of 1/60!!! <--- is this the effect that is frustrating you?

yep it did at first. Then found the csm21 menu, but i hadnt thougth about the rear curtain sync as tool for balancing the exposure. I always thought of it more as a gimic for creating a trick image.

Note: At a given ISO, the lens aperture and shutter speed determines scene exposure. The aperture and distance to subject determines flash exposure. ie. changes to shutter speed does NOT affect flash exposure. Therefore, the only common setting when attempting to balance flash and ambient exposure is the lens' aperture.

What about the flash output auto varying to adjust to the balance the scene? at the set aperture/shutterspeed.
Is the output the same amount of flash everytime ?
Doesnt it depend on the amount of ambient light?
Is the ability to do this the iTTL of ther sb800?

Capturing an image with a mix of ambient and flash lighting is IMHO one of the greatest challenges of photography.

Close 2nd to trying to explain how to do it via a text posting IMO !


THANKS ONYX i think i have it now. Now if i can just buy a digital brain...

[Antsl]

Just one thing to remember .... if you are combining flash and ambient you will need to let the flash exposure be correct and under expose the ambient or the other way about.

The reason why!? If you combine the correct flash exposure with the correct ambient exposure you will in effect have two correct exposures and you will be doubling the actual exposure the image needs ... in other words the image will be over exposed on stop.

The solution is either to underexpose the flash by at least one stop (while maintaining the correct ambient), underexpose the ambient by at least one stop (while maintaining the correct flash exposure) or underexposing both the ambient and the flash by one stop each ... the result, an balanced, correctly exposed image.

There are several ways of achieving this however the option that I mentioned in my first example is often the easiest. Learn to use the manual mode of the camera and you will have fewer headaches trying to anticipate what the camera is going to do in any given situation, particularly with flash!

[gstark]

If you are wishing to balance ambient lighting with that of the onboard flash, you are wanting slow(rear) sync flash.

I don't think this is true. It can certainly work this way, but you can also, by correctly ballancing aperture, shutter, and flash output settings, get a correctly balanced shot, with fill flash, using normal (front) curtain synch as well.

Note: At a given ISO, the lens aperture and shutter speed determines scene exposure. The aperture and distance to subject determines flash exposure. ie. changes to shutter speed does NOT affect flash exposure.

This is correct.

Therefore, the only common setting when attempting to balance flash and ambient exposure is the lens' aperture.

As is this. Note the use here of the word "common".

You know how much output your flash is capable of giving; that determines the f-stop you're going to be using.

Now, using that f-stop as your starting point, meter your ambient light and set your shutter speed accordingly, noting also Anstl's comments about building up your total accumulated exposure for the scene.

Capturing an image with a mix of ambient and flash lighting is IMHO one of the greatest challenges of photography.

Actually, I've never found it to be that difficult.

Once I was a blues concert, outdors, daylight, shooting the band from
on-stage, looking towards the audience in bright sunlight.

This was actually a relatively easy setup to manage, because I had two discreet lighting situations that I needed to balance - the audience in bright sunlight, and a mostly unlight, but heavily backlit, band, on-stage and in the foreground.

I set my shutter speed and aperture to give me a good outdoor shot of the audience, and then just dialled in flash to match that aperture. The light from the former was never going to affect the latter and vice versa; therefore there was never any risk of doubling up the exposure; each segment of the image was going to take care of itself.

Otherwise, in more typical situations, I still use a variation of this technique, metering for the ambeint light and then adding the flash as needed, matching the flash setting based upon the metered ambient light values, and dialling back a little (usually on the flash) as needed to get a correct total exposure.

[lejazzcat]

Just one thing to remember .... if you are combining flash and ambient you will need to let the flash exposure be correct and under expose the ambient or the other way about.

The reason why!? If you combine the correct flash exposure with the correct ambient exposure you will in effect have two correct exposures and you will be doubling the actual exposure the image needs ... in other words the image will be over exposed on stop.

The solution is either to underexpose the flash by at least one stop (while maintaining the correct ambient), underexpose the ambient by at least one stop (while maintaining the correct flash exposure) or underexposing both the ambient and the flash by one stop each ... the result, an balanced, correctly exposed image.

There are several ways of achieving this however the option that I mentioned in my first example is often the easiest. Learn to use the manual mode of the camera and you will have fewer headaches trying to anticipate what the camera is going to do in any given situation, particularly with flash!

THANK YOU Antsl , very well explained . I understand now why i was getting the overexposures in M mode (as well as the underexposures that originally prompted my question) .