hexar af GN question..

[yeah!]

Hi,

i've been reading a bit trying to learn more about flash photography, but i'm a bit confused about guide numbers..

I've read that the hexar flash (hx-14) is rated as GN 14, but then i've read else where that at 100iso its 43??
" The guide number is 43 at ISO 100, which translates to 21 feet at f/2.0 (or 43 feet with ISO 400 film)."

the main thing i'm confused about is the meters/feet, when programming in manual guide numbers in the hexar, does it measure in meters of feet?

i'm using a nikon sb15, bit bulky but it will do for now...

 

[Dante_Stella]

The AF takes the guide number of the flash at 100 in meters (the SB-15 is 25 in meters)

25 meters = 82.5 feet

To get shooting distance at a given ISO, divide the GN by the aperture.

Or to get shooting aperture at a given ISO, divide the GN by the distance.

GN of 82.5 divided by f/2 = 41.25 feet range

GN of 82.5 feet divided by 41.25 feet shooting distance = f/2

GN of 82.5 feet divided by f/2.8 = 29.5 feet range

The guide number does not move up mathematically with the ISO; doubling the ISO, multiply the GN by 1.41; you have to quadruple the ISO to double the guide number. Likewise, opening the aperture by 1 stop increases distance by 1.41. Basically, everything revolves around the square root of 2.

The Hexar does all these calculations for you.

Note that for most Matsu shi ta-made flashes (Nikon, Canon, any any OEM), the GNs are slightly exaggerated. Measure the flash yourself for absolutely critical use (as daylight fill on the Hexar, the mismatch is not a problem at all).

Dante

 

[foto_mike]

The Hexar AF uses Guide Numbers in meters. The HX-14 has a Guide Number (at ISO 100) of 14 meters or about 43 feet.

The Hexar AF can use the Nikon SB-15 in two ways. It can use it like a more powerful HX-14 in Programmed mode. To do that, enter the Guide Number of the SB-15 in meters by holding down the SELECT button while you switch the camera on to Program mode. While continuing to hold the SELECT, press the UP/DOWN buttons to override the default Guide Number to P25 (25 meters). When you let go of SELECT, the display will show PFL, indicating you're in Programmed Flash Mode and you've overridden the default Guide Number.

When you switch the camera off and back on with a flash attached, it will show FL (not PFL) indicating it's in Flash Mode but you haven't overridden the Guide Number. It remembers the override value you previously used, but it doesn't use it unless you hold down the SELECT while you switch the camera on to Program mode again.

Assuming you've successfully overridden the default Guide Number and the camera is showing PFL in the LCD window, you're ready for Programmed Flash Mode. Make sure your flash is set for MANUAL (full power). When you take a picture, the Hexar will first do it's best to take an available light photo using the Program Mode parameters already in place (minimum camera shake speed, measured ambient light, etc.). At the end of the exposure, just before shutter closes, the Hexar uses the distance to the subject and the Guide Number of the flash to calculate the appropriate f-stop for a flash exposure, moves the aperture to the calculated value, and fires the flash. Impressive. The effect is like a rear-curtain sync fill in flash using the Program Mode exposure.

The other way is to use the SB-15 Automatic mode utilizing the auto thyristor of the flash to shut it off after an appropriate exposure is reached. In this mode, set the flash to one of the Auto modes (depending on the which f-stop you want to use) and turn the Hexar on to Manual mode. There is no need to override any Guide Number setting in this mode. Set the aperture to the value that corresponds to your flash auto mode and set the shutter speed to whatever value you want. A speed of 1/60 sec would be common, but you can use a longer or shorter exposure desired. The flash will sync with the shutter opening and the exposure will be completely calculated by the flash.

Edit to add:
Of course, a 3rd way to use the SB-15 flash is in complete manual mode as Dante described above.

 

[jaimiepeeters]

how can you use a Fuji EF20 on the Hexar?

 

[yeah!]

thank you both for 2 very in depth reply's, makes a bit more sense about setting the GN! Will try both P and M modes out and hopefully get a bit more comfortable with it.
Have also ordered a off shoe flash cable so hopefully that works too..

and jamiepeters; to my knowledge the Hexar hot shoe dosn't sync with all flashes i've only heard of people using either the konica flashes or nikon.

 

[foto_mike]

how can you use a Fuji EF20 on the Hexar?

Any flash that can operate in full manual mode or has an automatic thyristor function can operate with the Hexar.

The Fuji EF-20 appears to a dedicated flash compatible with a small number of Fuji cameras. I couldn't find a manual, but I didn't see any way to switch it to Manual or Automatic mode.