Right then, well it seems you mostly did pretty well in the quiz from last week. The question was “What is the maximum sync speed of the EOS 50D?” The answer, as 73% of you got right, is 1/250sec.

So what is the maximum sync speed and why is it useful to know? There are two main reasons for using High Speed Sync – the first one being to make the background darker – in other words to achieve a shutter speed fast enough that the background (ambient) light forms less of the exposure, with the flash lighting the subject. We’ll deal with this more in a future post, as today we’re going to look at the second reason – the use of flash with fast lenses. The following two images were taken a couple of seconds apart. The lighting is exactly the same in both of them – a flash off camera to the left of the subject. They were taken on an EOS 5D Mark II with an EF 50mm f/1.2L USM lens. If you don’t use high speed sync flash, you end up with a situation where your shutter speed is locked at the maximum sync speed. This varies by camera, so here’s a quick list for the current models:
EOS 500D – 1/200sec
EOS 40D/50D – 1/250sec
EOS 5D/5D Mark II – 1/200sec
EOS 1Ds Mark III – 1/250sec
EOS 1D Mark III – 1/300sec

The problem with not going higher than the sync speed is that to get the right amount of light from the ambient light sources (ie to avoid overexposing the image) you need to stop down the aperture. This leads to image number 1 – not a bad shot, but too much of a distracting background.

1/200sec, f/11

If you enable high speed sync flash, then you can turn the shutter speed up – all the way to the maximum shutter speed  (up to 1/8000sec on most EOS models). That gives you picture 2: - a better image due to a less distracting background. Notice how the exposure and lighting are the same in both.

1/6400sec, f/2

The idea of high speed sync is that the flash fires several times rather than just at the start or end of the exposure. It needs to do this as the shutter only uncovers part of the sensor at a time during the faster than sync speed shutter speeds. Think of it as a moving slit passing over the image, since that is actually what's happening.

It’s not free though – you’ll lose some flash power as the flash has to work harder over a longer duration, so you may need to move your lights around to get them closer to the subject, or use more than one Speedlite to increase the amount of light available to you.

High speed sync is available on the Speedlite 550EX, 580EX, 580EX II, 420Ex, 430EX, 430EX II, Macro Ringlite MR-14EX and Macro Twinlite MT-24-EX.

Is it a sign that not many of you have EOS-1Series Mk III cameras? Or could it be you need to spend a bit more time with them really getting to know what they have in them and what they can do? (We can help with that if you do.)

Of all the entries we had to last week's quiz question, only 20% of you got it right. The question we asked was:

The answer is 57.

For those of you that said anything other than 57, it's back to school time for you (one or two of you should be ashamed as looking at the results I know you have EOS-1D Mark III cameras and you still got it wrong!). For the 20% that got it right, well done.

For those not intimately familiar with the camera, the EOS-1 Series Mk III breaks up the Custom Functions into four groups:

C.Fn I: Exposure (15 custom functions)
C.Fn II: Image/Flash exposure/Display (9 custom functions)
C.Fn III: Auto focus/Drive (17 custom functions)
C.Fn IV: Operation/Others (16 custom function)

This is largely carried through the entire current EOS range, although the number of custom functions available differs depending on the model. 

So why so many custom functions? The answer is simple - it provides professionals with the most ability to tailor the camera to their way of working and the work they're doing. For a pro, the camera is a tool to do a job. Being able to mould that tool to exactly the way you like to work makes it easier to do the job so having lots of available custom functions is a real advantage. 

If you've not yet entered this week's weekly quiz, go and do so. It'll require some thinking and maybe holding a camera in your hand, good luck! 

Have you ever got to a location, started shooting and realised after a few shots that you hadn't formatted the memory card and it still has images you've already downloaded? If you're short on memory cards (and if your using an EOS-1Ds Mark III or EOS 5D Mark II then you're always short of memory cards!) it can be a real pain as you realise you need to go through and delete each image one by one. However, on the EOS-1Series cameras, there is a solution: File protection.

Below the LCD screen is a button you've almost certainly never pressed - the protect/sound button. This button allows you to stop certain images on the card being erased, or record a short (up to 30secs) clip of sound with an image. 

So how do you use it? Simply scroll through the images in playback mode and press the protect button at each of the images you've just taken. Now go to erase settings and choose "Erase all". This will delete any image that is not marked for protection leaving you with a memory card that  contains the images you've just taken. When an image is protected, you will see a small key on the display for each protected image.

If you're on a camera other than the EOS-1Series models, then you don't have the protect function on a button. However, you do have a protect function in the menu system. Simply find protect in the menu (it is in one of the blue tabs) and then scroll through each image pressing the SET button when you get to an image you want to protect. 

There is one thing you need to remember about this though: it will not stop images being deleted if you FORMAT the memory card. Formatting will clear everything off the card including the protected images, so if you only want to get rid of those images you've not protected, make sure you use "Delete".