built-in lightmeters on flashes..

Hi

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<p>Almost all old flashes has built-in lightmeter "eye", and I guess

that most of the modern flashes too has.

<p>At least Nikon SB-serie flashes have lightmeter. That leads to my

question - Does the metering field of internal light meter change

while using flashead's zoom (SB-24, SB-25, SB-26, SB-28, ..).

 

<p>If it won't, then how big should I assume the built-in meter's

reading area? That information would help a lot when shooting against

dark/light background.

 

 

<p>Regards, Juke

I'm no expert but various manufacturers have used different technologies to assist in making accurate flash exposures.

 

The basic sensor you're thinking of on older flash units was part of an auto thyristor technology that worked independently of the camera. The flash usually had one or more auto settings (besides full manual output), which would quench the flash when the sensor detected a certain amount of reflected flash. It was pretty reliable in most situations and still works well. However it can be fooled by tricky reflective surfaces - white dresses, black tuxedos - at night or with backlighting.

 

Some camera/flash systems added a primitive but effective technology based on guide numbers and focus distance. Some older consumer grade fixed lens rangefinders, like the Canonets, used this system. It was also an option for some early Canon SLRs, lenses and hotshoe flashes. I had a Canon FTbn, 50mm normal lens and AB-something or other flash unit that used this system.

 

Later some Olympus autoexposure/autofocus cameras added a more sophisticated guide number/focus distance based flash technology that added some TTL technology. If I'm recalling correctly the iS-series "ZLRs" used this.

 

Okay, back to your original question...

 

As far as I've been able to learn, the sensor on the Nikon flash units you mentioned (and later models) isn't a "light meter" in the sense of a handheld flashmeter or incident meter. While the auto thyristor function operates the same way on or off the camera - or on any non-TTL camera - it can't function independently of the TTL flash compatible camera in TTL mode.

 

So it's probably safe to say that what you see through the viewfinder affects TTL flash metering pretty much the same way it affects non-flash TTL reflected light metering.

 

At least, that's been my experience with my D2H and SB-800. When I throw in variables, such as turning off automatic flash head zooming or using one of Nikon's flash modifiers, such as the pop-on diffusion head, things change - sometimes significantly. For example, when the pop-on diffusion dome is used, or the pull-out/flip-down diffusion screen is used, the SB-800 defaults to wide angle mode only regardless of the lens focal length. This can occasionally result in flash errors.

Sorry to disagree, but the photocell in an SB-28 (and other models) used for AUTO exposure mode is completely independent of TTL and the camera, with one exception. When on the hot shoe of a suitable camera, information relating to the ISO, focal length and current f/stop can be relayed to the flash. You can, however, put the flash on a pole and trigger it remotely (CU-4 in manual mode, PC cable or Pocket Wizard) and still get effective use of the AUTO mode. You have to manually set the ISO, focal length and which f/stop to use, and transfer that f/stop to the camera.

 

The SB-800 has an AA mode which makes some use of TTL, in addition to the A mode which operates as above. I never use it, so I can't say how well it works.

 

The photocell does not "zoom" with the flash - its field of view is constant. Nikon does not specify the FOV, nor is it critical as long as it is 30 degrees or larger (i.e., averaging or center-weighted). As the flash is zoomed in or out, the amount of light on a given area of the subject changes. The photocell simply registers the intensity (not total) of the light reflected from the subject, including ambient light.

 

The AUTO mode can be used effectively with any camera, including the newer Nikon DSLR's or even a manual camera (like my Hasselblad). If you want better response to subjects against a light or dark background, you need MATRIX TTL metering, and a newer flash for compatibility. Even then, good results often require judgement and compensation.

I'd guess it to be about 35mm's view on film. It will be very critical if you try to shoot someone with a 200mm and don't care about a bright window beside that person.

<p> 30� or about field of view of 35mm lens.. Thats good starting point.

<p> I think that I should rely on flash meter (or guide numbers) when using longer lenses.

<br>Thanks for your answers :)