f2.8 vs f4...with flash

i read alot of these topics where people recommend a f2.8 lens over an f4 lens for "indoor lowlight" shooting. if you're shooting with flash, would the different fstop still comes into play? does the 2.8 still have an advantage over the f4 if pictures are taken with flash on?

Unless I was after DOF effects, I'd probably be using a smaller aperture indoors anyway, so to me the f/2.8 would not be worth it, but for others...

In the end it all comes down to money

MeNiS wrote in post #2190718
i read alot of these topics where people recommend a f2.8 lens over an f4 lens for "indoor lowlight" shooting. if you're shooting with flash, would the different fstop still comes into play? does the 2.8 still have an advantage over the f4 if pictures are taken with flash on?

There are only three advantages that f/2.8 has over f/4

1. one stop more light for low light(in this case negated by using flash)
2. more shallow DOF for more blurrier BG's used for artistic purposes(sometimes overused in my humble opinion)
3. being one stop faster, low light AF is easier to achieve since more light is being let in. (also negated by the flash if AF assist is enabled).

So, the short answer is yes... it has one advantage over the f/4. But also, if you want more ambient light to expose a lighter background, the f/2.8 would come in handy since you'd be able to use a faster shutter speed for that. So maybe 1½ advantages.

If you are shooting with flash, f/2.8 permits to you shoot FARTHER with the same flash unit. For example, a flash with Guide Number of 100 (at ISO 100) would be able to reach 25' at f/4, but reaches 36' at f/2.8. If you changed the camera to ISO400, you could reach 71' at f/2.8, and 50' at f/4. That can make a big difference in the ability to shoot in certain situations!

A lot of the benefit f/2.8 lenses bring is also to do with the speed and accuracy of autofocus - as they let more light in, the camera has more to work with. But truly, for low light photography without flash, even f/2.8 is often inadequate. Situations like this need the f/1.2 to f1/8 lenses and even these may be inadequate. there is only so much a camera can do in the dark, even with high ISO.

But 1 stop is 1 stop....

Personally I use a flash when it's dark - nicely diffused with a sto-fen, bounced sympathetically, compensated for with artistry .....you can get nice results.

One advantage of having a faster f/stop when shooting with flash is that you can let more of the background come in-- so that the subject of the flash isn't just illuminated on a black field.