Total noob question regarding flash speed

JohnN

JohnN

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Hi,

I thought I'd give the flash an airing in the real world and ended up with this:

120928_3061.jpg


Notice movement blur, I was expecting (not knowing much about flash) that the action would be frozen.

The settings are:

Focal length: 165.0mm
Exposure time: 0.0080 s (1/125)
Aperture: f/8.0
ISO equiv.: 100
Flash used: Yes (manual)
Whitebalance: Auto
Metering Mode: pattern
Exposure: Manual
Exposure Mode: Manual

Like I said I'd read so many times that flash will freeze action and in another thread someone said "how quick are your kids" - I guess very quick :D

As you can imagine the ones of the dog running were even worse!
 
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I would have were it not for being asked why I would need HSS as flash would freeze it.

To clarify this is what I was told:

You must have some amazingly fast kids that 1/200 sync speed plus flash duration wont stop.
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I'm guessing too much ambient light?
 
So presuming the flash is set on TTL, what setting would you have chosen to get this shot?
 
JohnN said:
So presuming the flash is set on TTL, what setting would you have chosen to get this shot?
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There isn't a setting that would have worked with this.
You should have used the fastest shutter speed possible, I'm not a Canon user but I believe that you could have shot at 1/250th, which would have been better than the 1/125th that you did use. Come to that, you could probably have got away with 1/500th - the 'black bar' that you would normally expect to see at the bottom of the image wouldn't have been visible/obvious in this daylight shot and the flash would have lit his face, which is really all that matters.

That would have helped, but using a low powered flash outdoors in bright light means that although the flash freezes the subject movement (up to a point) the blur that results from the much longer shutter speed undoes all that good work. The real answer is to use a high powered portable flash system that contributes more light to the shot than the ambient light.

And, whatever you do, if the subject is moving fast enough, if the camera isn't focussed properly or if the camera isn't held still, you still won't get a decent result.
 
Thanks Gary, I was trying out flash fill on a relatively fast moving subject and in that it was a total failure it was a success, it dismissed a myth from my head.

As it happens my flash is pretty powerful and HSS capable, which I know will lose some of that power.

Luckily my daughters not long back from school and bugging to go out on her scooter - I smell another test coming on :)

By the way on the 5D3 slow sync is only 1/200th, odd I know but thats the max speed now.
 
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Hello John,

Not an expert at all on flash but i'll have a go :lol:

You could close you aperture down a few of stops and shutter upto 1/250 or to where HSS takes it, but still might not be enough to kill the ambient.

It looks like quite a bright day, a few stops from Sunny 16 based on your exposure settings? Why not (*forget flash) just bump the ISO two stops and take your shutter to 1/500?

There is some reading here on effective shutter speeds with flash, but the environment for this to be effective is a dim room.

http://www.scantips.com/speed.html

*edit*
 
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JohnN said:
Thanks Gary, I was trying out flash fill on a relatively fast moving subject and in that it was a total failure it was a success, it dismissed a myth from my head.

As it happens my flash is pretty powerful and HSS capable, which I know will lose some of that power.

Luckily my daughters not long back from school and bugging to go out on her scooter - I smell another test coming on :)

By the way on the 5D3 slow sync is only 1/200th, odd I know but thats the max speed now.
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The thing is you're exposing for the ambient and then using fill flash, so your shutter speed will give you a full exposure despite what your flash 'freezes'. S you have 2 images - a blurry one from the 1/125 and a very sharp one on top of it. SO if you underexpose the ambient, your flash exposure takes precedence, or just use HSS so that the ambient freezes the action too - neither is right or wrong - it depends what you want to achieve.

About the myth - the flash will freeze your subject - but there's an entire blurry exposure from the ambient you never took into account.
 
Thanks all, I'll have a damn good read of both the site and over these replies a few times to let it sink in.
 
Cheers again.

The results of just upping the speed were much better, plainly it would help if I got spot of focus but it much better.

 
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John, the basic problem with your first shot is unrelated to either the flash or exposure settings, it's simply out of focus ;)
 
I didn;t think so, almost all the other shots from that test were also if you like out of focus, whereas later everything was fine - I could be wrong but if so then it was the worst set of missed focus shots I've ever had :)
 
JohnN said:
I didn;t think so, almost all the other shots from that test were also if you like out of focus, whereas later everything was fine - I could be wrong but if so then it was the worst set of missed focus shots I've ever had :)
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First shot is out of focus, no question. Focus is behind the subject. There could be other issues, masked by the OOF, but things like ambient blurring are actually not that visible (it's quite distinctive with flash) and I'm pretty sure you'd have got an acceptable result if only the focus was nailed. Subject is not moving very fast, you might have got some blurring on say an arm if that was swinging a bit more quickly, but probably nothing that would detract from the shot too much. Obviously a faster shutter speed would do no harm if you want 100% sharp, but a bit of blurring with subjects like that often looks good.

5D3 has a fantastic AF system. Servo AF would nail that every time.

Also get to know what your flash can do, HSS etc. With Canon, if you switch HSS on, it will only work when it needs to, ie over 1/200sec, and will switch itself in and out automatically.
 
You could be right although I cannot easily say where the sharp bit was and have now deleted the original so cannot do a zoom check sadly.

I always (well 99% of the time) use servo, so it wasn't that much of a noob mistake :D
 
Even servo is hit an d miss at times.
 
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