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Old Jan 9, 2011, 10:58 AM   #1
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Default Shutter speed Question

When using the flash on the Sony A55 is the shutter speed limited to 1/160 of a second?

Or is there a way to increase the shutter speed using the flash?
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Old Jan 9, 2011, 11:10 AM   #2
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That's the x-sync speed of the camera.

You'll find similar limitations with any SLR type camera using the built in flash with a mechanical focal plane shutter design.

Otherwise, you could get dark bands in your photos due to shutter curtain travel (because the sensor would never be fully exposed to the flash at faster shutter speeds). Here's a page with information about Focal Plane Shutter designs:

http://www.mir.com.my/rb/photography...lane/index.htm

Now, you can use an external flash with High Speed Sync (a.k.a., FP mode for Focal Plane shutter mode) ability to get around it (for example, the Sony HVL-F42AM).

Then, the flash will "pulse" the light over a longer duration while the shutter curtains are traveling across the frame. On the downside, use of High Speed Sync reduces flash range. Here's how that works:

http://www.photozone.de/hi-speed-flash-sync

If you're indoors, you probably don't need anything faster than 1/160 second to freeze action with a flash anyway (and you could use much slower shutter speeds than that and still freeze action at lower ISO speeds).

That's because as long as settings for ambient light exposure give you an image that's a few stops underexposed (way too dark) without the flash on (as would be the case in typical indoor environments at something like ISO 400, f/5.6 and 1/100 second), then the flash itself can freeze the action (because the subjects would only be properly exposed during the short flash burst length, which is usually 1/1000 second or faster).

IOW, unless you're trying to use a flash for fill in bright lighting outdoors, you won't need anything faster than 1/160 second to freeze rapidly moving subjects.
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Old Jan 9, 2011, 11:33 AM   #3
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Thanks Jim. I thought that was top speed for the built in flash. I vaguely remember having to have the right shutter speed set on my old Nikkormat "synced" to the external flash. That was MANY years ago.

After taking shots indoors in AUTO with the flash I noticed blurring - shutter speeds at 1/10 or 1/15. So no more AUTO mode for indoor stuff. I t had me wondering what the top setting was for flash shutter speed.

A lot new tricks to learn for this old dog!!

Thanks
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Old Jan 9, 2011, 11:51 AM   #4
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Yea... I normally go manual exposure when using a flash. That way, I can dial in more appropriate settings.

Most non-dSLR models use a simple shutter design and tend to make use of a sensor's electronic shutter feature. So, you can get away with faster shutter speeds using a flash.

But, when you get into an SLR or dSLR, then the limitations of a focal plane shutter come into the equation. Once you go faster than a certain shutter speed (1/160 second with your A55), then the sensor (or film) is never completely exposed. This limit is known as the x-sync speed (and 1/160 to 1/200 second is typical with an entry level dSLR model now).

Instead (once you go faster than the x-sync speed), you end up with a traveling slit of light from the shutter curtains opening and closing. Since a typical flash burst length is 1/1000 second or faster, then you'd have black bands in your images if you tried to use a single flash burst at faster shutter speeds (because of the shutter curtains in the way). So, the only good way around it is to design a flash that "pulses" the light over a longer duration (which is what a flash that supports High Speed Sync/FP mode gives you). Again, here's how that works:

http://www.photozone.de/hi-speed-flash-sync

Built in flashes just don't have the power to allow that feature (and not all external flashes support FP mode either, so be careful to buy one that does if you need that feature).
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Old Jan 9, 2011, 3:51 PM   #5
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Thanks again - I think for the time being the 1/160 will be ample for my indoor use.
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