dreamer
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How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:17 am

Fueled from all the great pictures here on anet and all the comments in the forum I believe someone here can answer my questions.

I took many pictures earlier in life, and have now taken it up again. My question is in general, I (think) remember from my older camera than when I used a flash it would automatically set the shutter speed to a certain setting (can't remember, but think it was 1/125) unless I used full manual setting. I might even remember this incorrectly.

My question is, is this still the case with more modern equipment, and on digital cameras, both SLR and compact?

Also I wonder how the ISO setting works on a digital camera, just as before? I

Thanks for any clarification on the flash issue.
still dreaming after all these years
 
ckw
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:50 am

To an extent it depends on the features of a particular camera, but in general, if the camera is in program mode, the shutter speed will be set to the max flash sync speed automatically (probably 1/200th these days).

Depending on the model, you may also be able to set the shutter speed in TV mode (to allow slow flash sync) - and of course, set anything you want in manual mode.

Don't forget the flash units themselves have become pretty sophisticated, making shooting in manual mode pretty simple. In effect, with a decent flash, you can set the camera to anything you like (provided you don't exceed the light output of the flash) and the flash unit will do a good job of giving you an accurate exposure.

ISO on a DSLR is effectively the same in principle as for film cameras, though the most recent models will generally result in a less grainy image than the equivalent film of an equal speed.

Cheers,

Colin
Colin K. Work, Pixstel
 
rotor1
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:53 am

As for flashes... most modern cameras can figure it out on their own. Shutter speed isn't terribly important, so long as its slow enough to sync with the flash and fast enough not to overexpose the shot with ambient lighting. Aperature and flash power usually work together to get a good mix... you can wing it on manual without a meter if you play around a lot, but its too much work not to let your $$$ camera off without earning its keep. If you want a certain effect, such as a slow syncro or mixed lighting shot (IE cockpit shot), it gets trickier. The most common one is the mixed shot, which is easy because the camera does most of the work -- meter on the outside, focus on the inside, and play around with flash power (via EV) if need be. Unless you're inside an airplane, don't plan on using flashes for av work... planes are too big and too far away.

ISO/ASA is the same as film. The sensitivity of the photographic medium. Higher ISO means you can use a faster shutter speed and/or a smaller aperature, and vice verse. You'll probably only mess with this stuff if you have a slow lens or a lens that likes a tight aperature (shooting through some lenses wide open at ISO100 can lend worse results than stopped down to F8-10 at ISO200) or in low lighting conditions.

-Mike
The best aviation photo I've ever taken was rejected by Airliners.net
 
diezel
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:55 am

Ever wondered why the shutter speed is set to a certain time?

That certain time is called the Flash sync time. It is the shutter speed at which the shutter is fully open in order to fully expose the film.

Most SLR's have a vertical travel shutter. There are two blades to the shutter, called curtains. At a slow shutter speed the 1st curtain will drop down and fold up at the bottom of the opening, then when the time has expired, the 2nd curtain will drop and cover it up again. When the first curtain is down and the second curtain has not yet started to fall down, the shutter is fully opened. At that moment the flash is fired, resulting in an evenly exposed image.

If the shutter time gets faster and faster, the shutter is never fully opened at one time because the second curtain falls down before the first curtain reached the bottom. So the film or sensor gets exposed by a slit of light. That slit travels from top to bottom. The fastest time the shutter is fully opened is called the flash sync time, which is usually 1/125 or 1/250.

Problems arise when you use flash with a shutter time faster than the flash sync time. A flash emits a short burst of light. Shorter than the time the shutter slit can travel from up to down, resulting in only the upper part of the film or sensor get exposed correctly.

There are however cameras/flashes which can deliver a number of flashes in a row resulting in faster flash sync time.

 Smile/happy/getting dizzy

Roel.

Never be afraid of what you like. (Miles Davis)
 
rotor1
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:56 am

Addendum - listen to Colin. He knows his stuff... plus, look how fast he types... he's gotta be good if he can type that quickly.

-Mike
Keyboard Grasshopper
The best aviation photo I've ever taken was rejected by Airliners.net
 
dreamer
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 5:49 am

Thank you Colin, Mike and Roel for refreshing my mind on the flash sync part, but how does that come to play with digital cameras? There is no curtain or moving part, so how does it make sure all of the image is exposed?

I started a discussion with a co-worker, I claimed that his pictures could be less sharp when taking pictures outdoor inn bright light using flash (to avoid dark shades) because the picture would be exposed at a slower speed, then as I was telling him that I became very unsure about my knowledge of the topic as I really don't know much about how it works in digital cameras.

Are there sites out there that know more details about how different cameras work? Nothing in my manual talks about flash sync.

It seems most are using digital cameras here at anet?

toril
still dreaming after all these years
 
AndersNilsson
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 8:21 am

Airliner photography is not a crime.
 
ckw
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 8:32 am

In the case of DSLRs, the camera is essentially the same as a normal SLR - there is still a shutter in front of the sensor, and most of what you know from shooting film is directly transferable.

Cheers,

Colin
Colin K. Work, Pixstel
 
wietse
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 8:34 am

Colin, for advanced flash photography, would you say the 1/500 flash xsync of the Mk1 is an advantage over the 1/200 of the Mk2?

Wietse
Wietse de Graaf
 
ckw
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 9:31 am

Well I don't find it so, but I believe some sports photographers find it a limitation when using fill flash in certain situations (eg. think of a pole vaulter coming over the bar shot from underneath).

However, with the 550EX there is a flash mode which lets you sync at ANY speed on the Mk2 - this is done by the flash firing a rapid series of flashes providing in effect an almost continuous burst of light over the entire period of the shutter travel. The penalty for this though is a significant reduction in the range of the flash.

Cheers,

Colin
Colin K. Work, Pixstel
 
dreamer
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Wed Jul 28, 2004 4:31 pm

You guys are the experts and very good teachers!
Anders, thank you for excellent site addresses, I have already looked at them, and bookmarked them! I can tell that very much has happened since I last was active.
Amazing what they can do automagically now!

-toril
still dreaming after all these years
 
timz
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RE: Shutters Travelling Vertically?

Thu Jul 29, 2004 7:17 am

Do SLR focal-plane shutters really travel vertically nowadays? If so, why the change from horizontal?
 
AndersNilsson
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Thu Jul 29, 2004 7:40 am

I found this explanation at http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=004oty"Vertical run shutters use a series of slats instead of the two curtains used in horizontal run shutters. Almost by definition these are metal although I believe some manufacturers have experimented with plastic or carbon fibers. The slat construction permits a higher electronic flash synchronization speed than horizontal shutters allow. It also makes them even more delicate - there are frequent cries of woe from people who have poked their shutter with an unwary finger and find they've displaced a slat."

Anders

Airliner photography is not a crime.
 
ckw
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Thu Jul 29, 2004 7:46 am

There is a very simple practical reason - traveling vertically, a shutter only has to cover a distance of 24mm - horizontally, 35mm. With shutter speeds of up to 1/8000th of a second, and high flash sync speeds, factors such as inertia, acceleration etc. become significant factors - hence modern shutters are made of thin titanium foils or similar materials arranged in a series of blades rather than the traditional cloth (or metal) "curtain".

Cheers,

Colin
Colin K. Work, Pixstel
 
dreamer
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Thu Jul 29, 2004 10:41 pm

and do digital cameras have the same type of shutters as regular cameras?
I'm impressed with the high sync time.
still dreaming after all these years
 
wietse
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Thu Jul 29, 2004 11:17 pm

Digital SLRs have the same kinds of shutters you find in regular film SLRs. Consumer digicams often have a shutter mechanism where the sensor is turned on for as long as the shutterspeed. So a quick turn on/turn off instead of a conventional shutter system.

Wietse
Wietse de Graaf
 
dreamer
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Fri Jul 30, 2004 1:36 am

So to sum it all up, I can pretty much think of a digital camera as an analog one?
Thanks again guys!
-toril
still dreaming after all these years
 
wietse
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RE: How Does Flash Use Impact Shutter-speed/aperture?

Fri Jul 30, 2004 2:23 am

You can think of a Digital SLR as an Analog one. Digital consumer cameras (with fixed lenses) are not the same, although they mimick the workings of analog cameras.

Wietse
Wietse de Graaf

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