Nikon SB800/900 real GN value ...

Started Apr 2, 2014 | Discussions thread
gear1box Senior Member • Posts: 1,515
Re: Nikon SB800/900 real GN value ...

michaeladawson wrote:

There should be no increase in GN due to putting in an extra battery. The power to the flash is provided by the capacitor. A 5th battery should only serve to recharge the capacitor faster and to provide more total flashes off a set of batteries.

Mike --

Ummm.  Now we descend into the practical matters of the electrical engineering in the sb800 units.  If the circuits are perfectly voltage regulated to the capacitors, you are correct.  But five cells gives 25 percent more voltage bias headroom to the capacitor charging electronics (in addition to reduced internal resistance from the battery pack, which is what drops the recycle times that we all notice).

And i am sure that you have noticed in a shoot that shots lose energy as you get to the limit of the capacitor's capacity.  That is a somewhat different, but related, effect:  the designers let you shoot when the capacitor is not completely full.  That margin is there for the obvious reason that not every shot takes full power.  So if four cells fill them less than five, the flash still works fine, but with less total energy.

So, as a practical matter, the capacitors may have more energy into them with five cells.  It just depends on tolerances, design, blah, blah.

I'm too lazy to get out my Sekonic and test it though.  But my sense is that it is likely.  On the other hand, those self-same charging circuits are one of the best reasons to upgrade to the sb9x0 in my opinion.

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gary ray
Semi-professional in early 1970s; just a putzer since then. interests: historical sites, virginia, motorcycle racing. A nikon user more by habit than choice; still, nikon seems to work well for me.

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