Bit of advice on settings for flashguns

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Right, my Cactus V4 triggers turned up last night (much better that the older versions by the looks of it).

I want to have a play around with them when I get home but wanted to understand something first.

The flashguns will be in Manual.
If the camera is at f8 or f2.8 or anything else, then the flashguns need to be at the same right?
Will shooting at f8 1/4power be the same on the photo as shooting at f2.8 1/4power (if the camera & flashguns are both on the same aperture?)

Is there a chart thats a quick reference so I can judge the distance of the flash to work out if I need to shoot at full power, 1/4 power, 1/16 power etc (or is it trial and error)?

I don't have any manuals with me at the moment so I apologise if it's covered in them.

Last question.

I have an SB800 & SB25, if both are on the same settings then am I right in thinking the flash output will be identical?

Thanks :thumbs:
 
firstly, you cant change the aperture on the flashguns. soo lets break it down a bit

if you set the flash to 1/4 power and shoot the cam at f8 then change the cam to f2.8, the shot will be 8 times brighter. because you are only changing the aperture.
if you change the aperture by 3 stops, then you could lower the power of the flash by 3 stops to get the same result.
i doubt the sb800 and sb25 are the same power output, so noo they wont have identical output.
its not trial and error, but a light meter may be a helpful bit of kit to get.
 
idigitize said:
firstly, you cant change the aperture on the flashguns. soo lets break it down a bit

if you set the flash to 1/4 power and shoot the cam at f8 then change the cam to f2.8, the shot will be 8 times brighter. because you are only changing the aperture.
if you change the aperture by 3 stops, then you could lower the power of the flash by 3 stops to get the same result.
i doubt the sb800 and sb25 are the same power output, so noo they wont have identical output.
its not trial and error, but a light meter may be a helpful bit of kit to get.
Click to expand...

Ok, now I’m confused, on both my flashguns I can select the aperture, does it not matter then if that aperture doesn’t match the aperture on the camera?

Should I just focus on the power output of the flash?
 
Hi Dal, i just started playing with off camera flash myself.
(i'm also based in essex by the way, maybe an essex strobist meet sometime?)

I took my first strobist shot the other day of my son.
Linky as this isn't a photo sharing thread.
Not had time to play more but this is what i did after a lot of reading around.

I set my camera to full manual, set the shutter speed to the fastest sync speed, 250 in my case.
set the camera to f8
Set the flash to manual and then 1/16 power, underexposed.
Then set the camera to 1/4 power, still under, but better
Changed aperture to f5.6, bam, nicely exposed pic.

So i think you can safely ignore the aperture settings on the flash and just experiment until you get a decent exposure.

Once i get some time i'll set the whole lot up again and play some more, but my son doesn't like to sit still, so i think i may be shooting teddy bears for a while until i get the hang of it.
 
What’s all this set aperture on the flash? I am guess it has a chart with a read out for F-stops.
With digital it’s much easier if you not got a hand held meter as you can view test shots Just get and play with it you soon learn more then reading on here
 
Forget about the f-stop settings on the flash, just set your gear up choose a setting, say 125/S, F/8, Iso200, take a picture, see how it looks, adjust the aperture up or down and take another shot, rinse and repeat...

Next leave the aperture alone and adjust the shutter speed, note the results. Finally, leave both the aperture and shutter alone and adjust the iso....
 
it would possibly help/confuse to search google for a sb800 gn (guide number) table

then you can decide what power to set the flash at depending on the other factors.

GN = distance * aperture (when at iso 100)
ie GN = 4m * f8 = 32, look up 32 in the table, depending on what focal length you are at, say 50mm, then you need the flash on 1/2 power.

you need a table for both of your flashes. like said above, dont worry about the f/number on the gun.
 
Thanks for that everyone.

I didn't want to just play around with the flashes without some understanding and the aperture on the flash was confusing me.

I'll ignore the aperture for the moment then and just play around with the power settings, and camera settings.

Thanks everyone.
 
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