Using a diffuser on flash - Exposure question

[Spodeworld]

When you use a diffuser, do you need to compensate by increasing the flash exposure for the light intensity that is reduced by the diffuser?

[scootermcq]

Originally Posted by Spodeworld

When you use a diffuser, do you need to compensate by increasing the flash exposure for the light intensity that is reduced by the diffuser?

Usually, yes...

[Spodeworld]

Is there a rule of thumb? For example, when using a diffuser, you should increase flash exposure by X....if so, is there a generally accepted number for X?

Thanks

Originally Posted by scootermcq

Usually, yes...

[zona5101]

Usually no.
too many independent variables

If you are ittl or ettl the camera should pick up the light drop off and increase the flash exposure. I know that with Nikon ittl, it likes to do its own fill flash ratio and when i add a diffuser it underexposes a bit and i crank up the flash comp by 1/3 of a stop.

If doing manual off camera flash there certainly needs to be some compensation and it will vary by the particular light modifier but you are accounting for it when you set your power and take a meter reading or test shot.

[Spodeworld]

So, are you saying that with an iTTL flash like the SB600, the flash can take the presence of a diffuser into account and adjust the exposure accordingly (although maybe not perfectly)?

Originally Posted by zona5101

Usually no.
too many independent variables

If you are ittl or ettl the camera should pick up the light drop off and increase the flash exposure. I know that with Nikon ittl, it likes to do its own fill flash ratio and when i add a diffuser it underexposes a bit and i crank up the flash comp by 1/3 of a stop.

If doing manual off camera flash there certainly needs to be some compensation and it will vary by the particular light modifier but you are accounting for it when you set your power and take a meter reading or test shot.

[zona5101]

Originally Posted by Spodeworld

So, are you saying that with an iTTL flash like the SB600, the flash can take the presence of a diffuser into account and adjust the exposure accordingly (although maybe not perfectly)?

yup. just like it figures out how much light to dump when you bounce flash...

[sk66]

In any of the automatic modes the camera reads the light coming back to it and shots the flash off when it has "enough"....But I think there's a "lead time" built in (i.e. the flash is cut off just before "enough" because more is coming) and it doesn't account for the increased dropoff due the modifier....

With Nikon I believe the SB900 actually does know there's a modifier of some sort and adjusts accordingly.

[scootermcq]

Originally Posted by sk66

With Nikon I believe the SB900 actually does know there's a modifier of some sort and adjusts accordingly.

My SB900 is better at doing proper exposure, but I do find it need to be bumped +0.7 when using a bounce card if the subject is further than 5 feet away. TTL is great, but I find I am constantly adjusting flash compensation depending on the distance to the subject.

If for some reason I was ever to do direct flash, I do find it nails it most times.

[OsmosisStudios]

Originally Posted by scootermcq

My SB900 is better at doing proper exposure, but I do find it need to be bumped +0.7 when using a bounce card if the subject is further than 5 feet away. TTL is great, but I find I am constantly adjusting flash compensation depending on the distance to the subject.

If for some reason I was ever to do direct flash, I do find it nails it most times.

Same with my SB-800 (I dont use the 600s on-camera). I tend to go for +1FEV, just enough to almost clip the highlights.

Off-camera flashes are always in manual: I adjust based on what I see the need is.

[Spodeworld]

So, I have a Nikon SB600. From what you are saying (assuming similar to SB900), it attempts to adjust flash strength for add-ons, like diffusers. Is that correct?

Originally Posted by sk66

In any of the automatic modes the camera reads the light coming back to it and shots the flash off when it has "enough"....But I think there's a "lead time" built in (i.e. the flash is cut off just before "enough" because more is coming) and it doesn't account for the increased dropoff due the modifier....

With Nikon I believe the SB900 actually does know there's a modifier of some sort and adjusts accordingly.