DSLRUsers.com

Hi all,

This is probably a trivial question. I was going through SB800 manual and on p. 31 there is a table with effective distances of flash versus aperture setting/ ISO setting. If I use my D70 for which the lowest sensitivity is ISO200 and then I chose f1.4 on my 50 mm lens, then according to the table there is no setting. Does this mean that I need to use a smaller aperture of f2 as the largest to not over-expose my shots?

Thanks

Alex

You are correct but you could reduce the flash power to 50% or less as required. That would allow you to use f1.4 etc.

Matt - so does this mean that the SB800 wouldn't automatically set itself to a lesser power in the scenario above ?

I would have thought that it'd note the 1.4 aperture and dial it's power down accordingly.

Unfortunatey, I don't own a 1.4 lens to test the theory....

I assume the SB800 only recognises apertures to 2 or 2.8 (past that, you need to use manual flash mode) ??

I believe that when the SB800 is on auto it will use whatever aperture you have set. Ie, it won't overexpose just because you have set the apperture to 1.4.

ajo43 wrote:I believe that when the SB800 is on auto it will use whatever aperture you have set. Ie, it won't overexpose just because you have set the apperture to 1.4.

that's what I thought. Perhaps I'm reading Matt.K's response the wrong way

Thanks, Matt and everyone else who have commented.

Alex

Sorry guys, but having read the post and understanding that the manual tables show f1.4 @ ISO 200 to be outside the flashguns setting I simply made the most obvious reply. The answer was not from experiance. A more considered response would be I am not sure if the gun would manage correct output or you would have to "force" correct output by manually setting some flash compensation. I will give it a try tomorrow and see.

The SB800 does need a textbook to operate.

The SB800/camera does manage correct output (TTL) at F1.4 providing that the minimum flash output does not exceed the required flash output. I have run into this problem when shooting fairly close (ie within ~ 2 or 3 metres) with a shutterspeed/aperture combination close to ambient, say 0.3-0.7 stops below ambient. Sometimes the flash output needs to be reduced 2 stops or more below minimum power to get correct exposure. The quick fix is to reduce the effective flash output by using the diffuser dome with the head up one click - output is effectively reduced by something more than 2 stops bringing the flash back into a useable range. It also pays to be attentive to ISO, because, while shutter speed has a relatively small effect on a flash exposure, ISO has the same effect as aperture.

I have no idea why the manual is the way it is but the above comments may have something to do with it.

Cheers

MattC wrote:The SB800/camera does manage correct output (TTL) at F1.4 providing that the minimum flash output does not exceed the required flash output. I have run into this problem when shooting fairly close (ie within ~ 2 or 3 metres) with a shutterspeed/aperture combination close to ambient, say 0.3-0.7 stops below ambient. Sometimes the flash output needs to be reduced 2 stops or more below minimum power to get correct exposure. The quick fix is to reduce the effective flash output by using the diffuser dome with the head up one click - output is effectively reduced by something more than 2 stops bringing the flash back into a useable range. It also pays to be attentive to ISO, because, while shutter speed has a relatively small effect on a flash exposure, ISO has the same effect as aperture.

I have no idea why the manual is the way it is but the above comments may have something to do with it.

Cheers

Thanks very much for this, Matt. I did notice a lot of overexposure when I used 50mm f1.4 at or near wide open with sb800.

Regards
Alex

My question is this - why would you want to use flash at an aperture of f/1.4?

How would SB800 adjust flash output when the ambient exposure edging at over exposure? If the Flash could detect it, it should not fire at all to give you the correct exposure - right? It should be so but the SB800 always fire away.

And yes, at f1.4 why would you use flash? Best if you don't need to - afterall that why you buy a fast lens. However, if you are using flash to light the shadows under the model's eyes, won't it be better to move the model so that ambient light can adequate remove the shadows? Reflectors will do a better job than flash and can make a big difference in the final results.

Alternatively, use the SB800 on remotely at an angle, bounce it, reduce the output to avoid harsh lighting from the flash.

regards,

Arthur

Arthur and Chris,

Thank you for asking this question and brining it up. Very good point, but I was just trying to understand the table in the manual and did tests with my lens.

Alex

I guess the other point is.....on a clear sunny day at ISO 200 the exposure will be 1/500th of a second at F8. Because you have the SB800 fitted the camera will lock the shutter at 1/500th because it is the highest synch speed. So at F1.4 the camera will over expose by about 4 stops. F1.4 will only be possible in low light.

sirhc55 wrote:My question is this - why would you want to use flash at an aperture of f/1.4?

Good question. I dont. Normally I am working at f2.8 through to F8 with flash... but I have played with the 50/1.4 wide open and with flash.

Cheers

Matt. K wrote:I guess the other point is.....on a clear sunny day at ISO 200 the exposure will be 1/500th of a second at F8. Because you have the SB800 fitted the camera will lock the shutter at 1/500th because it is the highest synch speed. So at F1.4 the camera will over expose by about 4 stops. F1.4 will only be possible in low light.

Matt,

That is when you slip an appropriate ND filter onto the lens.

Cheers

ND filter? Nevada desert?

I use flash at 1.4 when I am shooting gigs where the stage lighting is not super bright....mostly small venues.

Using rear curtain with rock bands you can freeze the action as well as exaggerate it.

So thats an example where I have used flash @ 1.4

Joel