F80 & sb-50dx combined guide number - what is it?

[birdy]

I have the f80 and sb-50dx flash. I did a search here, and a quick

review of the camera/flash documentation but couldn't find the answer

I wanted. I read somewhere that using the internal pop-up flash in

combination with the sb-50dx results in an increased guide number.

If so, does anyone know the GN for this combination? Is is something

a mathematically challenged person can calculate? Please be gentle

with your answers, I am new to this and what I don't know would fill

volumes!

[jason michael]

Page 33 of the SB-50DX Manual:

 

combined GN = the square root of ((GN of the main flash) squared + (GN of the built

in flash) squared)

 

Cheers,

[birdy]

Thanks, Jason, that's exactly what I wanted to know.

[spencer_hahn]

I don't think that's exactly true, though, because doesn't the white diffuser panel of the SB-50dx cover the built-in flash? As I understand it, just as if you were using a stofen, it would significantly decrease the GN component of the built-in flash (from like 13 feet to 4, har har).

[birdy]

I don't believe the diffuser must cover the built in flash. There could be some good reasons for doing so, though. Perhaps someone could explain.

[payyakkil]

"I don't think that's exactly true, though, because doesn't the white diffuser panel of the SB-50dx cover the built-in flash? "

 

You can use the SB-50DX and the built-in speedlight together without the diffuser covering the built-in speedlight. But as you said when used with the diffuser, the guide number will be different.

[psul_aul]

The diffuser is meant to be used over the built in flash when you are bouncing the sb-50dx off the ceiling. This way, both light sources are diffused and you get uniform lighting. You do not have to put the diffuser down when using the flash normally.

 

The Sb-50's manual goes through a series of guide number calculations for different situations. I am sure the diffuser reduces the guide number, but so does bounce flash. If you are using TTL and trusting the system to get the exposure right, does it really matter what the guide number gets reduced to?