Photography News Issue 48

Photography News | Issue 48 | photographynews.co.uk

Technique

High speed flash sync in practice

This set of pictures was taken not to show that one unit is better than the other but to illustrate the potential benefit of having more power at your disposal, especially when using HSS outdoors and at longer light to subject distances. We used a Nikon D810 with 70-200mm f/2.8 zoom looking at the high speed sync output from a SB-900 Speedlight compared with a Pixapro CITI600. The distance from the Datacolor test chart was 3m. The camera was set to manual mode but TTL flash was used with a shutter speed of 1/8000sec with apertures as indicated – slower shutter speeds do have the benefit of more power. ISO was set to 200. These pictures have not adjusted in editing but left to show the differences in exposure. With the latitude of Raw there is clearly great potential for exposure and white-balance correction. The SB-900 does fine at f/4 but you can see the declining power issue from f/5.6 onwards. With the powerful CITI 600, you get a decent exposure at f/8.

Nikon SB-900, 1/8000sec at f/4

Nikon SB-900, 1/8000sec at f/5.6

Nikon SB-900, 1/8000sec at f/8

Pixapro CITI600, 1/8000sec at f/4

Pixapro CITI600, 1/8000sec at f/5.6

Pixapro CITI600, 1/8000sec at f/8

Images High speed flash sync has great potential for outdoor shooting and it is widely used by portrait and action photographers. The issue outdoors, though, is that flash has limited working range and even a powerful light can mean wide lens apertures, higher ISOs and eating through batteries. A powerful unit like the Pixipro CITI600makes life easier.

The design concept is ingenious, but there is much more. You can shoot TTL or manual within an 8EV range, from full power down to 1/128th output, there is high speed sync up to 1/8000sec (of which more later) and has an integral 2.4GHz receiver so meshes in with Pixapro’s ST-III triggering system. The Pixapro CITI600 is just like the sort of monobloc flashhead that you will find in studios up and down the country. Here, though, the unit is battery-powered and you can get up to 600 full power flashes on a single charge. You’re very rarely going to be shooting at full power so with TTL and lower power settings you are likely to get a great manymore flash bursts without having to recharge. Standard lightingmodifiers such as brollies, softboxesandbeautydishes fit happily into this S-bayonet head and we will be demonstrating this in our forthcoming features. The TTL version of the CITI600 is on sale for £650 or go for the manual only option for £450. The CITI600 is rich with features too and these include second (or rear-curtain) sync, multi-flash mode, flash durations between 1/220sec to 1/10,000sec and consistent colour temperature performance through its power range. There is also high speed sync, a feature found on all the units discussed so far; so perhaps now is a good time to delve into that feature in a littlemore depth and look at what it can do for your picture-taking. Shoot high speed sync Being able to correctly synchronise flash at shutter speeds higher than usual used to be the province of owners of leaf shutter cameras which also had the benefit that the flashgun’s full power range was available. But most cameras do not have the option of a leaf shutter and use a focal plane shutter instead. However, with high speed sync (HSS) flash, being able to sync flash at all shutter speeds, even at 1/8000sec, is common and readily available assuming you have the right kit. This means that you can very effectively mix bright daylight and flash for eye-catching results. So, for example, if the day is bright and you want to shoot a portrait at f/2.8 for a nice blurred backdrop (and you don't have a ND filter handy) and the subject needs a burst of flash to fill in some of those heavy shadows, that is now easy with high speed sync.

The time gap between the first and second curtains doing their job depends on the set shutter speed. At the correct flash sync speed, the gap between the two is long enough to have the whole sensor unveiled at the same time. At faster shutter speeds, however, the delay between two curtains ismuch shorter so effectively there is a slit travelling across the sensor. At very fast shutter speeds, this slit is very thin which is how you achieve such short exposures. With a non-HSS set-up this means flash shots taken above the correct sync speed are failures. But use a compatible flashgun and set HSS (Canon, Sony) or Auto FP (Nikon) mode, now you can get correctly exposed shots at every shutter speed. What happens now is that the flashgun pulses very rapidly, so rapidly that you can‘t see it, which means that the sensor is picking up light as the very thin slit of the focal plane shutter traverses across it. The downside of this form of camera/ speedlight HSS is that the pulsing flashgun uses a lot of battery, the output level is low which limits working distance and the flash can get warm with the risk of overheating if you are shooting lots. However, we are now seeing the same approach in studio type flash units, ie. from Profoto and Pixapro. Elinchrom and trigger makers Pocket Wizard use timing to give HSS froma single burst of flash timing the exposure to record a burst of light as it gradually tails off. The Pixapro CITI600 and Pixapro PIKA200 discussed previously give HSS with the optional £45 PRO-STIII T 2.4GHz remote trigger, available for Canon, Fujifilm, Nikon, Olympus/Panasonic and Sony. The advantage of something like the CITI600/PIKA200 over a speedlight is power, both in output and in respect of battery life compared with a set of AAs in a speedlight. As mentioned earlier, a pulsing speedlight is limited in power but something like the CITI600 has 600Ws of output so you will have a greaterworking range andmore options when it comes to aperture selection too. Check out the comparison pictures above. Over the coming issues, we will be exploring in greater depthwhat it is possible to achieve with this Pixapro kit both in and out of the studio.

On many occasions lighting needs no more than a speedlight slipped into the camera’s hotshoe

Above and below The Pixapro CITI600 gives power, impressive battery capacity and a wide range of power levels and flash durations. And it’s easy to use.

It is worth taking a closer look at high speed sync because the term is often used generically and, as with most broad brush strokes, the finer details get muddled and there are a great manyifsandbutswithdifferentmanufacturers tackling the issue in their own way. Let’s start simply. When a focal plane shutter fires, the sensor/film is exposed to light and when flash is used at the correct flash sync speed (mostly 1/125sec or 1/250sec) or slower the whole image frame is exposed at the same time. Fine, no problemwith flash here. But as we venture into shutter speeds above the correct sync speed, normal flash means you get blank frames or partially blacked out shots. This is because a focal plane shutter has two curtains and to make an exposure, the first one (often called the front curtain) opens to reveal the sensor and the second one (the rear curtain) follows very soon thereafter to end the exposure.

Above Pixapro offers a selection of radio triggers for wireless lighting control. Features include, depending on the model, an operating range of up to 100m, 32 groups and high speed flash sync.

The kit we used

Essential Photo is a leading specialist in selling studio equipment to the photographic, film and video industries. Pixapro is its lighting brand and a full range of products is available from speedlights and portable flash through to mains heads and generators. Over the coming issues, we’ll be exploring the opportunities presented by the Pixapro kit discussed here. essentialphoto.co.uk