A Practical Look at High Speed Synch

Come on all you Pentax Dads & Mums, the weekend is coming soon and that could mean a trip to the playground & park. Well, the fun shouldn't be only for the kids ... pack you own toys and be ready to catch some great lighting balanced images using some High Speed Sync flash techniques, and make the outing something truly special

The top of the slide is a great place to try this out, as is the wider area with lots of bright sky in behind. So grab your Pentax DSLR and an HSS capable flashgun and lets get going! I've used here my K7, gripped (great for stability), DA 18-55 f3.5-5.6 AL WR, and Pentax AF-540FGZ :

The problem with many 'normal' flash shots in these sorts of conditions is that the maximum flash sync speed (180th sec) can severely limit your ability to control the ambient (background) exposure, especially if you prefer a wider aperture, which will likely be desirable. Putting the camera on P with fill flash from the flashgun will likely result in something like this ....






Oh no Dad ... thats not good - you didn't set the controls properly. The shutter speed of 180th sec has overexposed the background resulting in a total washout! Yuck

Lets try that again. Now firstly it helps if you've got a total little poser and show-off to practice with ... luckily I've got one of those ... (clearly she takes after her mother :wink. Then all thats left to do is get the camera and flash set up - thats the fun bit. So, for this we're not going to use P mode at all (I was tricking you there), but rather switch to M mode (manual exposure) ... this will allow us to increase the shutter speed faster than 180th sec after the flash is set to HSS mode.

I tend to point the camera up towards the sky and press the green button - this will meter for the brightest parts and give us a good exposure for the sky, leaving our flashgun to correctly expose the foreground and subject. Leaving the AF-540FGZ in P-TTL mode gives us the option to apply flash compensation, and I would generally use -0.5 or -1.0 stop for this type of shot.

OK, so you've got your camera and flash ready, camera is showing ISO 200, f5.6, 1/640th sec (thats FAST ) .... push the button - Click / flash!!





Hey, now we're talking! This time the exposure of 1/640th sec at f5.6 has given us a nicely controlled background with detail in the sky, but the flash has lit up our little poser there and given that sparkle, and the whole thing is much more balanced ... happy Dad

Here's a couple more ...


Both at 1/400th sec at F5.6 ...









The technique is good out in where the views are wider, anywhere where the sky is dominating behind and you want to bring out your subject - here I tend to manually reduce the ambient brightness by dialing in around 2/3rd to 1 stop less exposure than my metering - so in this next shot on the hillside, my metering when pointing over towards the hills and sky gave me 1/300th sec at f6.3, but I carried right on and dialed in 1/640th sec, just to darken down and background and help my subject stand out - aided of course with that little bit of HSS fill - in ....






1/320th Sec f6.3






1/400th sec f6.3





OK - hope you've enjoyed the show .... and I hope you Pentax Mums & Dads, uncles, aunts, brothers, sisters, grandpas and grandmas, will all get out there and try some High Speed Syncing! If anyones got some examples to show then please feel welcome !

Excellent ideas Nigel, I rarely think of using my flash outside but must make an effort in future . The difference in results speaks for itself.
Beautiful young lady too, very photogenic.

Harry

Great little tutorial! I'll try this soon - thanks

Nice one Nigel

It's a bit of fun, but also a prod for getting out with the flash, or for those who were not aware of the practical benefits of HSS outdoors. I hope it might encourage others to have a go, because I love flash photography, it is great fun and very satisfying to see results that were not possible without it.

Thanks Alan and Stephen also

Great advice Nigel. You can also do similar with a manual flash, simply by reducing the power output of the flash. A bit more fiddly, but not too hard.

Regards
David

Also works on av using the AE-lock to set the exposure. And a PTTL cable and flash at arm's length will help with modelling.
David, I was under the impression the camera won't send a signal to a flash or a trigger if the shutter is faster than the sync speed, unless the flash is on HSS ?

You might be right Mark, I think I was referring to adjusting the flash output rather than specifically HSS. It's also interesting to explore slow speed sync at sundown or in a dimly lit indoor scene. Effects can be interesting.

Regards
David

The key aspect being explored here is the need to balance the lighting coupled with the desirable wider aperture for portraiture. If I didn't use HSS then, at the maximum flash sync speed of 180th sec, I would have to use an aperture nearer to f16 - f22 in order to produce the slightly underexposed background that works well in these situations. This would not give me the type of DOF ideal for this subject and environment.

HSS resolves this, although its worth pointing out that the power needs are higher in HSS mode than normal flash, so your range of possible flash to subject distances for each aperture/ISO combination is reduced ... In practical terms with a powerful flash it just means you will need to remain fairly near to the subject.

Thanks for the tutorial, lovely explaination, and beautiful model

You're very welcome, it was fun to do, and I am finding HSS flash photography very rewarding .... And yes, I'm lucky to have my little poser there ... But like most of the best models, she don't come cheap

Mark, regarding the Av mode and using AE-lock ... this does seem to work, and I suppose could be a practical way to get a quick, say one-off HSS flash. In general though I find manual working with the green button for metering the ideal practise.

I agree that with the flash on you need HSS activated to get the speed above 180th. Also, with the Pentax flashgun the only flash mode available with HSS active is P-TTL. I wouldn't have thought HSS operation was compatible with manual flash mode anyway, but it would be interesting to hear if any third party flashes do provide it in other modes?

I'll make this a Sticky, for a while at least, to give those interested a chance to have a look at an interesting and useful idea.

Nice practical examples

It is interesting that the flash in P-TTL mode is automatic even if the camera exposure mode is M. It is a nice way of controlling things.


There is another, automatic way

The exposure compensations are cumulative...

So, set the overall Ev to -1 and set the camera's Flash Ev to +1, with the flash in HSS mode. IIRC the compensation on the flash itself is added to the camera's Flash Ev compensation (which is useful, but irritating that it doesn't get remembered!)

That way, the camera will expose the ambient to one stop under, and the flash will be 'right'.

Additionally, the camera's flash exposure mode gives additional settings. Particularly in dim conditions you should switch to Slow-speed Sync (lightning bolt and "Slow"). That way the ambient exposure should be the same as without flash, and the flash will add some 'pop'. You may want to restrict or control the ISO too.

If the subject is moving quickly, and you've opted for really slow shutter speeds for ambient, then use the "Trailing Curtain Sync" instead of "Slow".

In the normal "Flash On" mode (just the lightning bolt) the camera's exposure will ramp up towards the exposure level for flash.



The Pentax dSLRs have a long standing bug/feature/irritation where the exposure meter will not flash to indicate overexposure when using flash not in HSS (i.e. if the ambient is say 1/500s, ISO400, f/2.8 and you turn the flashgun on it will show 1/180s, ISO400, f/2.8 - and the shot will be massively overexposed). Would have been nice if the exposure meter blinked to warn!

Sorry for the rambling... haven't had my second cup of coffee

Matt

Thanks Matt Hoping it will inspire others to want to try it out and go get a Pentax Flashgun!

You're right about the convenience of having automatic flash functioning and manual exposure control together - a great combination!

Regarding the exposure and flash exposure compensations, I have decided on a little convention in terms that is logical and keeps clarity, (I think - tell me what you think ) ... where we control ambient exposure by setting a value that is in 'stops' away from the meter centre, then I term that 'EC' (Exposure Compensation), and where we control flash power output by setting a value that is also in 'stops', I term that 'FC' (Flash Compensation - which is the actual Pentax term I think).

I don't think Pentax use 'Exposure Compensation' but there's a logic to that term, as of course the adjustment is making a 'compensation' for the meters failings! So we have EC and FC - in most practical scenarios then EC will be controlled by shutter time value and FC by applying the compensation in stops on the flash unit or camera (as you described above).

I don't think we can call manual power output settings (in M flash mode) 'Flash Compensation', because there is not an actual 'compensation' being made against any measure, and also the unit of control is different, being a fraction (1/4th, 1/16th etc) of full power - (not 'stops') - so in manual flash mode both the thinking and the terms need to be different. The term I use then for manual flash mode is 'Flash Power' - it then becomes another constant just like aperture, ISO & distance. (FC is never a constant because it is directly linked to a variable, the metered flash output).

Matt, do you agree with me that HSS is probably incompatable with manual flash mode? I'm making this assumption becasue flash output needs to be measured in HSS and shut off when enough has been given, . Manual flash mode would not allow a metered control over this I'd assume?


No problem, I certainly enjoyed it .. and let me tell you, I have a little hunch that we might all soon be getting a new excuse to have many more Pentax flash ramblings, right here on PU !