Flash photography advice.

[rah]

Just got my first dslr and trying to get my head around flash photography.
I have a d80 and sb600.

I realize that front on flash looks pretty bad so I got the sb600 so I can bounce off the ceiling. I see that a diffuser is also available. Would this be better than bounce? What circumstances should I bhounce and when should I diffuse?

To end with a basic question,
How does the camera expose for the flash with a diffuser? Surely it can't meter after the flash has fired so wont it underexpose as it would be expecting the flash to be at full power rather than the diffused power? Do I need to adjust expore with a diffuser.

Thanks for any help.
I am learning lots from here!

[ATJ]

Bouncing off the ceiling will not only result in a change of the angle of the light, but will also diffuse the light. Typically, you don't need to use a diffuser if bouncing of the ceiling of similar.

A diffuser will give you a softer lighting, so you don't get harsh shadows. If you use the diffuser with the flash mounted on the camera, you will still get head on lighting, it just won't be as harsh. You may still lose shadows, though, as the light source will be very close to the lens.

With iTTL, the camera sends one or more short duration flashes before the main flash to assess how much light is bouncing back. It determines the duration of the main flash based on what it gets back. This will work with or without a diffuser. If you are using the flash in manual mode, you will have to take the diffuser into consideration when determining the power of the flash and/or the aperture of the lens.

[rah]

Thanks for that. It makes a lot of sense now.
Just to clarify though.

For on camera flash. If I can bounce, that is the best option. If I can't bounce , eg outdoors at night or if the ceiling/wall is coloured, I should diffuse.

You said with front diffuse you may still "lose" shadows. Did you mean you may still get shadows?

[PiroStitch]

The meter will give you a reading based on the amount of light which hits the meter in your camera (depending on the metering mode - matrix, centre weighted or spot). The amount of power from the flash will be dependant on this and the diffuser will reduce that power by about 1/3 or 2/3 stop, depending on the type of diffuser used.

Personally I prefer to bounce the light off a wall or ceiling rather than using the Stoffen diffuser.

Play around with the flash, try bouncing the flash off the ceiling as well as the wall and hold a piece of paper above your head and point the flash head into the paper.

Have a look at strobist.blogspot.com as well for some great tips and examples of using a flash for lighting

[ATJ]

For on camera flash. If I can bounce, that is the best option. If I can't bounce , eg outdoors at night or if the ceiling/wall is coloured, I should diffuse.

Generally, yes, but there is no one right answer and it all depends on what you are trying to achieve. The great thing about digital is that it costs nothing to experiment (as long as you don't experiment with important events). Walk around the house and try various options to see what you like and don't like.

You said with front diffuse you may still "lose" shadows. Did you mean you may still get shadows?

What I mean here is that you won't see the shadows if the light source (flash) is on the same line as the lens. The light and the lens are following the same path so all the shadows will be hidden. This will be more noticeable the further the subject is away. You could invest in a cable (TTL Remote Cord SC-28/SC-29) which lets you move the flash off the camera and control the angle relative to the camera.

[Reschsmooth]

When you bounce, you are effectively trying to create a large light source - ie. using the wall and/or ceiling as a reflected light source. Obviously, a light source which is quite a bit lower in power than direct flash.

That said, and the beauty of TTL flash metering is that the camera's meter will tell the flash how much light to through, bounced and all, to properly expose the subject.

Just remember, the bigger the light source (given a static light/subject distance), the softer and fewer the shadows will be.

[ATJ]

A couple of quick and dirty images (oh, boy, the bench is dirty) to show what I mean.

This one users the in camera flash and you can only just see the shadows. The subject is a bit close to show the full effect, but you can see what I mean.


This one has the flash off the camera and you get well defined shadows. If I stuck a diffuser on it, you'd still get shadows but they would be softer.

[rah]

Ahh , I see your point.
I am obsessing about removing shadows rather than using shadows to improve effect.
The Sb600 can be remotely triggerd by the d80 I belive so I'll try mounting on a tripod and see what it can do.


PiroStitch: Thanks for the link, Ill have a look.

[gstark]

Oh that flash lighting were so simple.

The reality is that, like so many things, the basics are quite simple, but it can a long time to master the finer points.

First of all, you need to understand that the larger and more diffuse your light source, relative to your subject, the softer your lighting should be. That's why we try to diffuse the light by using modifiers like softboxes, brollies, and the like.

But as soon as we do this, it can and will have an affect on the relative power of our light source. This might not be totally undesirable though.

Ok ... D80, SB600. As already noted, when shooting in iTTL mode, your camera will send out, before making an exposure, a small burst of pre-flashes. The camera reads the light being reflected back to it from those pre-flashes, and because it knows how much power was used to send that burst, it can use that data to correctly calculate your scene's exposure.

To a point.

You always need to be aware of your subject and its surroundings when shooting, as these can have an affect on your exposure. Please have a look at the recent threads on using a light meter; they will do much to explain some aspects of the problem.


Now, given the exorbitant cost of shooting on your D80, the best way to learn is to simply start shooting, taking careful notes of what you're doing (and what you're doing differently) for each image, so that you can then look at the images and learn.

For a diffuser, look at how to make one yourself using cardboard and tissue paper.

Or use foam core board as a reflector.

Experiment with size and placement - proximity to subject, height, distance between background and subject ....

And remember that if the walls of your room are blue, pink, or yellow, seeing that colour impose itself within your images will be an expected outcome when you're just bouncing your flash off the walls or ceiling.

[Oz_Beachside]

I was given a nice rule of thumb the other day (and I was MOST PLEASED with its result/impact).

"The most flatering light, for a portrait, can be found setting the distance of light source to subject at the size of the softbox (diagonal measurement)."

of course this is a starting point, and move closer for further from there as desired.

it worked beautifully as a starting point for my flash photography on the weekend

thanks to Mike at Borge's in Port Melbourne.

[rah]

With iTTL, the camera sends one or more short duration flashes before the main flash to assess how much light is bouncing back. It determines the duration of the main flash based on what it gets back. This will work with or without a diffuser. If you are using the flash in manual mode, you will have to take the diffuser into consideration when determining the power of the flash and/or the aperture of the lens.

I have been playing around with the flash to get an idea of how TTL works.

If I put a tissue infront of the pop up flash my photos are underexposed.
Why doesnt the camera adjust for the falloff in light if it is emitting a preflash to guage exposure? The apeture of shutter speed doesnt change. (P mode)

[gstark]

If I put a tissue infront of the pop up flash my photos are underexposed. Why doesnt the camera adjust for the falloff in light if it is emitting a preflash to guage exposure? The apeture of shutter speed doesnt change. (P mode)

How many layers of tissue are intercepting the light?

What aperture are you setting?

What is the light-to-subject distance ?

How soon after one image are you shooting the next one?

These are all factors that can affect what you're doing. Too small an aperture, too great a distance, too much tissue .... all can reduce the flash power available to you, causing this sort of result.

iTTL will only work when it's given a full power flash, and only then within its stated parameters. We need to ensure that you're remaining within those boundaries.

[ATJ]

If I put a tissue infront of the pop up flash my photos are underexposed.
Why doesnt the camera adjust for the falloff in light if it is emitting a preflash to guage exposure? The apeture of shutter speed doesnt change. (P mode)

The tissue will reduce the amount of light the flash puts out. It is possible that you are cutting enough light down that for the given aperture, the flash is not powerful enough for the distance to the subject.

The two most important parameters for a given flash are the aperture and the distance to the subject. If you use too small an aperture or you are two far from the subject, the flash won't provide enough light. The power of a flash and putting a tissue or some kind of diffuser on the flash will also influence this.

To test it properly, you should a) use manual and set the aperture to its maximum (smallest f/stop) and b) keep the camera/flash closer to the subject.

[Reschsmooth]

In summary, placing the tissue over the flash, you might end up halving the power of the flash. If your i-TTL metering says the flash needs to fire at full power, but that full power is cut in half, you will get an underexposed shot.

As others have said, move the light source closer or widen the aperture or increase your ISO.

[rah]

Ok I see.
The camera cant compensate enough for the reduced flash light, ie it wont reduce the shutter speed autmaticlly to 1/10 or even 1 sec etc. I expected that it would, thats my mistake.

[ATJ]

Ok I see.
The camera cant compensate enough for the reduced flash light, ie it wont reduce the shutter speed autmaticlly to 1/10 or even 1 sec etc. I expected that it would, thats my mistake.

First of all, shutter speed makes no difference how well the flash lights the subject (unless you go beyond the flash sync speed). A flash on full power has a duration of around 1/1000 second and the lower power settings just reduce the duration.

Second, how does the camera know that you put a tissue over the flash? The only compensation the camera will make is to increase the duration of the flash. But if the flash is already at full duration and there isn't enough light, there isn't enough light.

For flash photography, manual is usually the best, so you can can control the aperture. Controlling the aperture means you can make sure there is enough power in the flash, but also you can control DOF and use available light (controlled with the shutter speed too) to fill the background or for other effects. Note that for flash fill situations, aperture priority may be of value.

[rah]

You're all going to put me in the too stupid basket soon!

I do actually get it now. You have all been very very helpful.

Thanks.

I'll keep experimenting, Ill play around with aperture priority and iso and see how I go.

[gstark]

You're all going to put me in the too stupid basket soon!

Not while you're asking good questions, and listening to the answers being offered.

I'll keep experimenting, Ill play around with aperture priority and iso and see how I go.

Play with aperture settings, but in manual mode. But definitely keep experimenting. Flash scares a lot of people because of its percieved complexity, but once you get it, you'll be surprised at how easy it really is.

One other thing that we've not canvassed is for you to check that your flash unit hasn't been set to a low power mode. That too can cause these symptoms ...

The camera cant compensate enough for the reduced flash light

I can't say that; I simply don't have enough facts to make that call. What we've been doing is highlighting points where problems may occur. It's up to you to check those points, and either confirm that there's an issue in one of those areas, or tell us what your settings were, so that we can further diagnose the problems for you.

FWIW, if you use a tool such as Nikon View, it will tell you many of the settings with which your image was made. You just need to look at the EXIF data. And posting it with your image can often be of great help for the rest of us.

[ATJ]

Another recommendation is to learn to make use of Guide Numbers. While they may look a bit daunting, they are actually very easy to use and you can much more easily predict what is going to happen.

The SB600 that you have has a guide number of 30 (metres) at ISO 100 (when the zoom is set to 35mm). Knowing this means you can calculate what the aperture should be for full power knowing the distance of the flash to the subject. For example, if the flash is 5 metres from the subject, the correct aperture is f/6. You get this simply by dividing 30 (the guide number) by 5 (the distance) giving you 6. If the flash was 2 metres from the subject, the aperture should be f/15 (30/2 = 15).

Even if you are using TTL, this is helpful to know as you know the smallest aperture you should use. For example, if you are 2 metres from the subject (with the flash on the camera), an aperture of f/16 will probably mean under exposure and f/11 would be safer.

Of course, if you are using a diffuser (a proper one or just some tissue), this will reduce the light output and so change the guide number in use. Similarly, if you bounce the flash, you will get a reduction in the guide number - although you could guess the total distance of the flash and choose an aperture based on that. For example, if you bounce off the ceiling and the centre of the bounce is 2 metres from the flash and the subject is a further 2 metres from that, assume 4 metres and go with f/7.5, but it would be safer to open up a stop, so go with f/5.6.