Wednesday, 19 March 2008

Lastolite Umbrellabox vs. Shoot-thru

I routinely use a shoot-thru umbrella for portrait work, given I work on location for much of the portrait work I do. When I occasionally do something with a bit more time and looking for better quality of light, I like to use the Lastolite Umbrella Box. However, it's interesting to know how much of a difference the more expensive and slower to setup umbrella box actually makes.

First of all, a look at the two in action side by side. The Lastolite Umbrella Box is a touch larger than the Portaflash White Diffuser Brolly, but in practice it makes little difference a lot of the time because you can get it in closer to the subject.

Comparing the two, you can see that at the same power, the Lastolite Umbrella Box loses a lot of light compared to the shoot-thru umbrella. The umbrella box actually has a white interior rather than silver, so that's one of the big losses on top of the diffusion material. That said, it does give a great quality of light.

Lastolite Umbrella Box:

Portaflash White Diffuser Brolly:

Now for a little comparison for portrait work. I grabbed a rather good looking subject for this exercise. Firstly, the umbrella box. You'll notice that the control of the light on the background is pretty good. You've got the background going to black on the left, showing how much control you have with it. It is also not too harsh on the edge of light, so if you do want to light the background the way I have, you'll have a nice fall-off on the background.

You can see how I positioned the umbrella boxfor this shot.

Now for the Portaflash White Diffuser Brolly. As expected, there's a lot more light spill in all directions. If you look carefully at the left hand side, you'll now see a light switch on the rear wall which is showing up, but which was hidden in the previous image.

Here's a shot of the overall scene. Note the flare from the umbrella in this wide angle shot. That's a lot of spill, so it's something to note...the umbrella isn't actually stopping the direct source of light causing flare. Just something to be aware of!

So what's the diffence? Well, the first is that the umbrella boxuses up a lot of light, so if you're using small flashes, this can become an issue. Of course, with studio flashes, that's not so much of an issue given the extra power.

What's the benefit? Well, the quality of light is marginally better, but given you can get the shoot-thru brolly in nice and close, while still being out of the shot, you can still get pretty good soft light. There are also no sharp highlights with the Lastolite Umbrella Box, so if your subject has reflective surfaces, you'll find it better.

Another major benefit, as I showed here, is how much better control you have over the direction of the light. This means you can direct the umbrella boxsuch that the background is left dark, meaning you can control it better even in small spaces. This also has the benefit of meaning flare isn't nearly as much of an issue as it is with the shoot-thru brolly.

What about the shoot-thru brolly? Well it's cheap and fast to setup anywhere. It gives good quality light for the price (almost as good as the Lastolite Umbrella Box), and will easily become your mainstay for portrait work in most situations. Also, because it's just diffusing the light, rather than an additional bounce, it doesn't lose nearly as much light. The shoot-thru nature also makes it possible to control the size of the source by zooming in the flashgun, or moving it closer such that you choke the light. You can see an example of this in the previous entry.

Filling the brolly

I've seen it asked a couple of times now on different forums what "setting" the flashgun should be at for the best use of an umbrella. This question applies equally to reflective umbrellas and shoot through diffusing umbrellas - it's basically a case of how wide an angle you set your flash to in order to optimally fill the umbrella.

I've opted for a "shoot-thru" umbrella in this case because it makes it nice and easy to see what the light is doing. It's a relatively average 32inch white diffuser umbrella from Portaflash.

So firstly, what is happening as you zoom the flash head? Well, you're increasing or decreasing the patch of light that hits the brolly and therefore the area of the brolly which appears to provide diffused light on the subject. The bigger this patch of light is, the softer the light on the subject.

For this example, I set the flash relatively far from the umbrella. I could pull the umbrella in closer to the flash making the patch of light smaller if I wanted a less diffuse light source. In all cases I'm showing though, the flash was in the same position near the end of the umbrella stalk, with just the flash head being zoomed.

So firstly I set the 550EX (equivalent to Canon 580EX MkII) flashgun to 105mm. You see this creates a relatively defined patch of light in the centre of the umbrella.

Zooming out to 50mm, you see the patch is somewhat larger and also has a more pleasant softer edge. You'll also notice if you look carefully that there is a loss of light because the flash is now lighting a larger area of the brolly.

Zooming out again now to 24mm, we see the flashgun is now covering just about all of the brolly. If you want to use the full diffusion of the brolly, this is not far off an optimum setting, because the flash is covering just about all of the brolly and no more.

However, let's go wider. I now put down the diffusion cover on the flash that allows the flash to cover an area of about 17mm. You can see there's an incredibly significant loss of power now. What you can't see is that, although every inch of the brolly is lit now, so also is a large swathe of the room around the brolly, so a lot of light is being wasted. You also have to be careful you're not including this much brighter, undiffused light within your photograph. Suppose you light from the side of a subject, you could easily find that the undiffused light hits the background, and depending on distance, could actually be brighter than the subject. Not only that, but you can also find you end up with the shadow of the brolly appearing on the background, giving a nasty light/dark line up your background.

So what's best? Well the more you zoom out, the more you lose power, so if the idea is to over-power available light while only getting a little diffusion, then for a 32inch umbrella, 105mm is probably a good setting. If you want to really use the soft light of the brolly, then 24mm will probably give a good combination, covering all of the brolly. Going further than this is simply wasting light by spilling it all over the place.

I wouldn't of course recommend you use these values as gospel. Get your camera, flash and brolly, set the flash to low power, and take a few shots like these yourself to see how the light spill falls on the brolly. This will give you a much better feel for how the light is diffusing with your own setup.