Flashgun help please!

[VxDuncan]

Hi All!
Could do with some pointers. I'm a deadicated High-iso warrior, used to shooting pretty much in aperture priority mode adjusting isos as needed.

As I can't run to a D700 and have been invited to loads more weddings I conceded and bought an SB600 flashgun to help in dim situations. Currently reading through the manual but was hoping for tips to get me upto speed a bit quicker. I understand the principles of bouncing, diffusion etc, but I don't get how to adjust the gun to mix natural light with flash.

Do you use full manual with the flash and set shutter fast enough to avoid camera shake but still record some natural light, or can I continue to use AP mode? It doesn't seem to allow for the flash on top and suggests silly exposures. I usually try to avoid program and full auto modes if at all possible.

Also if you're allowed to use a flash in a church is it likely to work if I bounce it or will the ceiling be too high?

I thought I knew my camera inside and out but feel like a total beginner again! Camera is a Nikon D80. Thanks in advance...

[rustyspit]

A complicated topic, and to some extent you'll have to play with it to understand how it works. I'm no expert, but here's how I think about it (with a D70 and SB800), assuming that the flash is in iTTL mode (I wouldn't bother with manual flash, unless you're doing clever things with multiple flashes or macro stuff..):

You need to think about shutter speed slightly differently when using the flash. The duration of the flash pulse is extremely short - much shorter than any shutter speed you are likely to be using, so exposure of the parts of the picture that are illuminated mainly by flash (i.e. the bits that are closer to you) will not be affected by the shutter speed setting. Of course, the exposure of the parts of the picture that are not reached by the flash works in the usual way. In other words - a faster shutter speed will make the picture look 'stark' with a bright foreground and dark background, a slower shutter speed will allow the camera to collect more ambient light from the background, and give a more balanced exposure. Bear in mind that you can sometimes get away with slower shutter speeds than usual when you use the flash - it tends to sharpen things up a bit. You can also create some nice effects by using really slow shutter speeds with flash, e.g. this was handheld at 1.3sec:


The ISO and aperture settings determine the usable range of the flash - if you use a large aperture and a high ISO the exposure requires less light, so the flash will be able to illuminate a subject that is further away than if you had used a small aperture and low ISO. Again, the parts of the picture that are not reached by flash will be exposed in the normal way, a wide aperture and higher ISO will give a brighter, more balanced background to the picture than a narrow aperture.

So in principle a slow shutter speed, wide aperture and high ISO will give the most even balance between foreground and background illumination. If you're trying to bounce the flash off a high ceiling, or reach a long distance you will stand the best chance with a wide aperture and high ISO. Of course the usual trade-offs involving noise at high ISO and depth of field at large apertures work in the usual way.

The Nikon flash system has 2 TTL (through the lens) metering modes - iTTL and iTTL-BL. Both modes will fire a brief pre-flash before the shutter opens to determine how much flash should be used for the main exposure, using the normal metering system. As I understand it, plain iTTL will attempt to provide enough flash illumination to correctly expose the subject as determined by the metering system without regard to the ambient light. iTTL-BL is a balanced fill flash mode that will attempt to balance the flash output with the ambient light. Bear in mind that if the picture is under-exposed without the flash, then it may well also be a bit under-exposed with the flash in iTTL-BL mode (not too sure how this works?).

Wow - that was quite long, I hope it makes some sense?

Edited to add:
Aperture-priority and program modes will continue to work as if the flash wasn't there, so you can use them for in situations where you already have enough ambient light, but you want to use balanced fill flash to fill in the shadows. If you want to use the flash to directly illuminate the subject of your photo, you need to switch to manual aperture/shutter control.

Edited by rustyspit on Wednesday 16th July 22:50

Edited by rustyspit on Wednesday 16th July 22:54

[VxDuncan]

Wow, thanks for the great reply - made more sense than the manual! Need to do a lot of practising before being comfortable using it in anger I think. Seems I need to start learning the iTTL-BL mode and how to apply falsh compensation. Back to the manual. Usually I know exactly how to get the result I want, but feel I've stumbled into a black art! Been playing with firing it remotely - quite cool...

Thanks again for the post. No doubt I will report back.

[chris.mapey]

A quick work around (I have a D70 and SB800) is you can still use the flash modes on the camera to control the flashgun (slow / rear lighting etc)

It's worth having a play with those as well. (Push & hold the flash button on the camera and turn the scroll wheel to run through them)

HTH

Chris

[Simpo Two]

VxDuncan said:

I understand the principles of bouncing, diffusion etc, but I don't get how to adjust the gun to mix natural light with flash.

Do you use full manual with the flash and set shutter fast enough to avoid camera shake but still record some natural light, or can I continue to use AP mode? It doesn't seem to allow for the flash on top and suggests silly exposures.

Also if you're allowed to use a flash in a church is it likely to work if I bounce it or will the ceiling be too high?

Rustyspit has a better grasp than me on this one but here's the Simpo version:

Fill flash in Nikon-speak is 'TTL-BL'. I suppose (flash of genius) (no pun intended!) that BL means Balanced Lighting. This means the flash gives less power and allows the ambient light to do more of the exposure. However there are times when this is still too fierce, for example early dusk, and you can balance it further manually by dialling, say, -2EV on the flash and +2EV on the camera until you get the result you want.

Another way is to use the camera on manual exposure, set the shutter speed and aperture you want and let the flash sort out the rest (if it possibly can). However if you set the flash to manual as well, then there's nothing left in the system to do any thinking so your exposures will be bonkers unless you adjust accordingly.

Flash in church is dire. No way will it bounce (possibly with a D700 or D3 set to very high ISO?) and if you point it forwards and blast it, the first three pews will be like Hiroshima on 6/8/45 and the back of the church will still be dark. Double processing can help but it's still far from ideal.