School me: getting faster than 1/250 flash sync speed

When using a flash, shutter speed is limited to 1/250.

I don't fully understand the mechanics behind this, but I'm thinking that's the limitation because the timing of the mechanical shutter is not precise enough to always catch the flash firing - that is, you could try to have the shutter open for 1/1000, but the flash might fire in the next 1/1000sec, and they don't perfectly line up so the flash misses the shutter. Hence the term, flash sync. Is this understanding correct? If not, what am I missing?

I vaguely remember reading that there are ways to get around this and use a faster shutter speed, but I don't remember what they are. High-speed sync? Is this a feature specific to certain camera/flash combos? I'm using a 60D and a 430EXII, wireless control via the pop-up flash.

Reason I'm asking: Yesterday I went out to shoot a zombie walk, and it was a beautiful day, almost no clouds, perfect bright hot sun. Beautiful days don't make for very good dreary, dark zombie pictures.

I had brought along my homemade beauty dish, and was wanting to try to light up portraits with the flash, while underexposing the background. The only way I was able to pull this off was by completely closing my lens down to f/22 and making the shutter as fast as it would possibly go while still syncing with the flash. However, I would have liked to be able to use a wider aperture to get a little tiny bit of background blur.

Any tips? What could I have done differently? Is this an appropriate usage of a high-stop ND filter? I have a 3-stop ND filter somewhere around here, I usually don't carry my filters with me since they are cheap-Os.

Here's my favorite of the set. We were in the shade but the background is in super-bright direct sunlight. There are a few more on my flickr.

IMAGE LINK: http://www.flickr.com …/nathancarter/5​795517044/

Its called Highspeed Sync. Its the lighting bolt and H button on your flash or the HSS choice on the camera menu.
It permits using higher shutter speeds by strobing the flash for the duration of shutter travel.
It costs about 2 stops of light but is useful in the situation you had for your shoot. i.e. keeping the flash close to the subject.

Canon's flash and camera manuals discuss it and there is a master class on the Canon site that goes into details about all the Canon flash functionality.

In brief, sync speed is the fastest shutter speed at which both curtains (sides of the shutter) are fully open at the same time. Faster than that, one starts to close before the other is fully open and there is no one moment at which the entire frame can be exposed by a momentary flash.

However, there is some safety factor built in and this is what Pocket Wizard's Hypersync capitalizes on: it optimizes the timing on a per-camera basis to get the fastest possible sync. It won't give you 1/2000 but it'll usually cut maybe 1/3 off the duration: 1/200 becomes 1/300 or so.

Faster than that, you need more than one flash of light and that is essentially what HSS is. Some power is wasted shining on closed shutter curtains, and the overall output is lower, but it does what it needs to do.

nathancarter wrote in post #12534450
Is this an appropriate usage of a high-stop ND filter?

Yes. As you found out, your ambient exposure is often too much. If you were at f/22, then your 3-stop filter would have given you f/8. Which is still a far cry from having a shallow DOF, but it certainly would have given you some breathing room. A six-stop filter would really make you happy here!

Don't shoot zombie walks in middle of the day

Seriously use powerful strobe and if you need to use wider apertures use ND filters. HSS mode will just suck power from already underpowered flash.

Thanks for all the advice.
I'll play around with HSS and see what happens, and pull out my 3-stop ND filter and mess with it too.

What happened to the image you posted? Why was it removed?

Interesting. I re-published it from Lightroom, so maybe that broke the link. It looks OK to me, maybe because it's cached. Thanks for the tip, I'll fix it.

This video really helped me understand HSS. It is a Pocket Wizard ad but it has great animations.


http://www.pocketwizar​d.com …wizard_controlt​l_optimiz/

nathancarter wrote in post #12537452
I'll play around with HSS and see what happens

Let us know, but IIRC, HSS won't work with the 60D's (or 7D's) wireless flash signals when the speedlite is OCF, only when the EX is attached to the hotshoe (or with a off-camera shoe cord).