Newbie flash user questions

[jscoles]

Hi. I have an N80, and just purchased an SB-80dx for it. I'm

confused on how the camera's exposure meter works when the flash is

attached.

 

For example, if I turn on the flash in the hot shoe, then go to

aperture-priority mode, is the camera's exposure meter still telling

me what exposure is correct without the flash? If I choose, say f/22

and 1/125 shutter speed, and the camera is telling me that will be

underexposed, the flash does all the work in getting the right

exposure, right? (I'm using the flash in TTL matrix mode).

 

One other question relates to macro photography. I bought a kirk

macro flash bracket, and want to use it and my sb-80 together with my

105d 2.8 micro lens. If I position the flash on the bracket so it is

a mere 6 inches from the subject, but with the head still in the

normal position (not rotated or angled), will the flash calculate the

wrong exposure from the distance information it gets from the d lens?

 

Thanks!

[todd peach seattle, washi]

If your camera meter is reading underexposure, that means the ambient light isn't going to register well on the film and you're relying solely on the flash to provide enough light. You need to be cognizant of the flash range. At f/22, your flash may only have a five foot range (depends on a lot of things, primarily ISO and flash zoom setting).

<p>

I have a 'basics of flash' webpage that might interest you:<br>

<a href="http://www.thepeaches.com/photography/Basic_Flash.html">http://www.thepeaches.com/photography/Basic_Flash.html</a>

<p>

I don't know the answer to your second question. I will *guess* that it won't make much difference. The distance information provided by the D function is actually very coarse, somewhere between 12 and 20 'steps'. In my mind, I consider the distances to be about 'half-stop' accuracy, so something like 2, 2.3, 2.8, 3.3, 4, etc. If you think it's faking you out, try the 'slightly depressed' bounce position on the flash. I think that disables D.

[hal_bissinger]

<i>If I choose, say f/22 and 1/125 shutter speed, and the camera is telling me that will be underexposed, the flash does all the work in getting the right exposure, right? </i><p>

Kinda. Yes, the metering is giving you exposure information the same as if there was no flash based on the light that is available (ambient lighting). The flash will do as much work as it can to properly expose the foreground or subject within it's range. You can't expect it to do that and illuminate the whole room however because it can't. You have to rely on the ambient lighting to provide that. <p>

You can think of a flash exposure as a double exposure. The flash fires and handles the exposure for the foreground. After the brief flash duration the shutter should still be open and together with the aperture determine the background or ambient exposure. <p>

This means then that if you set your shutter speed and aperture to give a proper exposure according to the meter when using flash you should have both a properly exposed foreground and background. If you don't your background will be underexposed by whatever the metering is telling you. <p>

This is not necessarily a bad thing (or maybe it could be) and is sometimes unavoidable especially when you have to handhold your camera and the location is dark like alot of reception halls. This is because you can't handhold much below 1/60s shutter speed and that is not long enough usually to properly expose the background.

[hal_bissinger]

Oh, your second question. I don't think it will make much difference either and wonder if the flash can go that low.

[lachaine]

That's basically right. When you set your exposure manually or semi-manually as with aperture priority, you are setting it for the picture without flash. The one thing many newbies don't understand is that the aperture is the key component in the equation. You can't set a shutter speed higher than the camera's max sync speed, but you can set lower ones. If you do so, it only affects how ambient light will be registered on film (lower shutter speed = more ambient light and possibly registration of movement which the flash itself would freeze). But aperture seriously affects not only the ambient light exposure, but also the useful range of the flash. An aperture of f/22 is going to dramatically lessen this range, so you wouldn't want to set it at f/22 unless it's really important for your photo (ie. depth of field, or if you don't need the flash range such as in a macro shot or close-up).

[jscoles]

ok, that's great.

 

One more question:

If I set the camera to a shutter speed that is slower than my flash sync speed, will it automatically enter into slow-sync mode, and fire the flash at the beginning of the exposure? Is there any difference in doing this and in actually setting my camera to slow-sync?

 

Thanks

[jim schwaiger]

Slow sync is just an automated mode that keeps the shutter open to expose the

background properly. If you use a slow shutter with a flash, it is doing the same type

of thing, it just isn't automated, you have to choose the exposure.

 

Most camera;s have afront curtain sync which means they fire as soon as the shutter

is fully open. Many also have rear-curtain sync where the flash fires just before the

shuter starts to close.

 

If your subject is lit and moving, these can be very different effects.