Flash technique question
I'm going back and re-reading those tutorials that cmason linked a while back but in the meantime...
1. What is the difference between
A. second-curtain sync
B. "ordinary"
and WHY would one use one or the other?
2. What is the effect of the 1/200 shutter setting in AV priority when using the flash? And how do I adjust exposure accordingly (or does the camera do that once the setting is selected in custom functions?)
Fwiw, I'm using a Rebel XT + 420ex.
I'm loving the 420 and get some great pictures with it. I think I've got a handle on how to use FEC, but above and beyond that any successes are usually on the program setting and seemingly more by accident than design - I'm not fully understanding what settings to use to get which effects, and at the moment I want to get some SPECIFIC effects with it. By choice. On command :rofl
Lastly:
3. How would I get the effect where I use a long(ish) shutter to get some motion blur, but the flash manages to capture one moment clearly within that? I can't find an example of what I mean, but I know what I"m trying to achieve...
1. What is the difference between
A. second-curtain sync
B. "ordinary"
and WHY would one use one or the other?
2. What is the effect of the 1/200 shutter setting in AV priority when using the flash? And how do I adjust exposure accordingly (or does the camera do that once the setting is selected in custom functions?)
Fwiw, I'm using a Rebel XT + 420ex.
I'm loving the 420 and get some great pictures with it. I think I've got a handle on how to use FEC, but above and beyond that any successes are usually on the program setting and seemingly more by accident than design - I'm not fully understanding what settings to use to get which effects, and at the moment I want to get some SPECIFIC effects with it. By choice. On command :rofl
Lastly:
3. How would I get the effect where I use a long(ish) shutter to get some motion blur, but the flash manages to capture one moment clearly within that? I can't find an example of what I mean, but I know what I"m trying to achieve...
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I still need help on questions 1&2, but after reading for the last hour I gather the technique I refer to in #3 is "dragging the shutter". So far so good - I get the concept.
HOWEVER... how do I figure out what the "normal" setting is (ie what the camera would choose) so that I can then set the shutter slower than it thinks is right without actually overexposing it? Clearly I need to understand this well enough that I can set it in manual, but without a starting point (ie what the "correct" exposure would be), I'm clueless.
Thanks in advance for (you should pardon the pun) any enlightenment!
In this instance the flash goes off as the shutter is coming down, instead of as it's going up. When using a slower shutter speed this gives the effect of blurring everything prior to the flash and then freezing the last moment in time crystal clear.
See here:
http://oreilly.com/images/hacks/digphotohks/figs/dphk_0414.jpg
Ordinary is just the opposite - flash goes off as the shutter is opening (going up) so that the frame has exposure compensation. This works because flashes have a spin-up/spin-down time that provides extra light. If you've ever used an overhead projector it's the same concept. Even though it's fast the light is not *instantly* on or off. It gets hot, hits peak, and cools all in a split second. Firing at the shutter going up leaves all the residual of the cool down time in the frame.
As for #2 you'll need someone more experienced with your camera. I've always shot Nikon (sorry...)
"Your decisions on whether to buy, when to buy and what to buy should depend on careful consideration of your needs primarily, with a little of your wants thrown in for enjoyment, After all photography is a hobby, even for pros."
~Herbert Keppler
"Normal" flash sync is first curtain. The flash is triggered when the shutter curtain is fully open or just before (depending on the actual shutter speed.) What most people don't realize is that with a focal plane shutter the first curtain has to move through and then the second follows. The lag of the second curtain is dependant on the shutter speed. What this means is that if you have a shutter speed of 1/200th, the frame is actually only completely clear for probably 1/500th of a second before the second curtain starts to traverse the frame. (With a more "professional" shutter that has a flash sync of 1/250th, the frame is only completely open for about 1/600th sec.) Most modern compact electronic flash has a flash duration, at full pop, of 1/600th or a bit faster, so that is the real limit to match.
With most subjects you want to use a faster shutter speed, partly to control ambient light, and partly to control both camera shake and subject motion blur.
With an object like a car at night in motion it is often advantageous to use a longer shutter speed in conjunction with the electronic flash. You can expose so that the lights of the car streak to show motion and then the electronic flash is used to stop the motion of the car. The problem is that if you use first curtain flash, the car will seem to stop before the lights, making the lights trail forward from the car.
With second curtain flash, the lights will trail behind the car, which makes more photographic sense and it looks like the lights lead to the car.
"Drag shutter" can be used with either first or second shutter and is used to expose a non-moving subject with both flash for the subject and longer shutter primarily for the background, giving a more balanced overall exposure. Drag shutter usually implies a longer shutter speed than flash sync speed.
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My final question remains, however: when wanting to shutterdrag to catch both motion blur and a sharp moment, how do I *meter* so that I can ensure the correct exposure and not simply wind up with an overexposed shot? Do I take an ambient exposure and then switch to manual and decrease by ?? stops? Can I set it in shutter priority with a slowish shutter (what's a good working speed for this effect?) and hope the flash compensates adequately?
I only have the meter in my camera, so I'm trying to figure out how I would do this... by design (instead of happy accident!). Fortunately, in the situation I'm anticipating I won't have to do it superfast (I'm not shooting a wedding or event where it would require speed and accuracy of execution,m thank goodness!), but I'm wondering how to do it so I don't waste tons of time and shots figuring it out by trial and error.
Thanks again for all the help!
In order to balance light between ambient and incident (flash) yes, you need to know the exposure value of the ambient light. Both Manual mode and Aperture Priority (AP or what Canon calls "Av") modes may be used with somewhat different results.
I turn off the flash momentarily if in AP mode and that makes the camera think that there is no flash installed, allowing the reading of ambient light alone. I adjust the aperture and ISO according to the percentage of ambient light versus flash. The flash can then be further tempered by FEC adjustments. You still have to watch the histogram and "blinkies" to manage the final exposure.
Manual mode I usually reserve for more controlled light and ambient light that has less variability.
Pathfinder has a great explanation here:
http://www.dgrin.com/showpost.php?p=292152&postcount=7
... and he points to links with even more information here:
http://www.dgrin.com/showthread.php?t=70330
Moderator of the Cameras and Accessories forums
There are some great links there, that explain everything about your 430ex (or your 580ex II or other Canon flashes), that the manuals omitted. The modern flash systems of the Canon system are quite sophisticated, but not intuitive. ( to me anyway, and from the number of questions I am sure I am not alone here
If you do not KNOW precisely what the flash and camera settings do, you will not guess them correctly ( I speak for myself here, as these links are where I finally figured the Canon flash system out too ) - the behavior of the flash will be highly unpredictable. But if you understand the underlying philosophy of the Canon system, the flash becomes very controllable and quite useful. I won't leave home without my ST-E2 and my 580ex
Moderator of the Technique Forum and Finishing School on Dgrin
::scuttles off to read and experiment some more::
Just as an aside...it's usually a good idea to just leave your camera in 2nd curtain synch all the time. The reason is, it will only impact you when you are exposing ambient light enough to see the blur.
You have two choices:
1) Use normal (1st synch) which means the subject will be stopped by the flash and then trail the motion in ambient light or
2) Use 2nd synch, which will allow the blur first and then freeze the subject at the end of the exposure.
The advantage to 2nd synch is that by freezing the subject at the end of the exposure, it's impossible to have the ambient blur go across / over the interest of your photograph (assuming the frozen subject is the key of the composition). With 1st curtain synch, the chances are excellent something is going to move past the main subject AFTER it has been recorded with the flash - resulting in a blur distraction overlapping your subject.
SO...unless you're going for a specific effect, just leave your camera in 2nd curtain synch...you'll be happier
- Gary.
Moderator of the Technique Forum and Finishing School on Dgrin