Naked Science Forum

Non Life Sciences => Technology => Topic started by: neilep on 31/12/2009 12:07:51

Title: How do cameras synchronise shutter and flash?
Post by: neilep on 31/12/2009 12:07:51

Dearest Cameraologists,

As a sheepy I of course am used to the papparazzi stalking me and taking photos of me all the time.


Look, here I am enjoying a motorbikemobile ride and still a photo is taken....I mean why ?..I'm just riding my bike  !


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Me Enjoying Some Motorbikemobile Fun


What I would like to know though is the science behind flash photography !

How long does the flash of a camera flash for  ? and how is it calibrated to synchronise with the shutter so well ? We are dealing with fine tolerances yes ?

 Surely, just a minuscule difference in timing would mess the whole thing up so there must be a simple but very effective way of synchronising the two yes?...Every camera I have ever owned has never had a problem with synchronising the flash and shutter..even el cheapo ones.....how do they do it ?


Please send me photos of ewe flashing to aid in my study here.


Thank ewe



neil
It Seems At Night I Oughta Dash
To Avoid The Plight Of Photo Flash
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Title: How do cameras synchronise shutter and flash?
Post by: chris on 31/12/2009 12:12:22

The guy in the picture looks like he should be living in Wales...

Title: How do cameras synchronise shutter and flash?
Post by: Geezer on 31/12/2009 17:15:54

....and he's not even wearing wellies!

Um, re the flashy question: I'm not so sure about digital cameras, but I seem to remember that with old fangled photographic film cameras, the shutter is open for quite a long time and the flash determines the exposure, so the timing does not have to be very precise at all.

The same could be true with digital cameras because I think they keep the "shutter" open until sufficient light has been received at the CCD. You can test this by taking a picture in very low light conditions without a flash.

So, with a digital camera, it opens the "shutter" first, then fires the flash, then closes the "shutter" when it has received sufficient light - I think!

("shutter" in quotes because digital cameras don't have physical shutters.)

Title: How do cameras synchronise shutter and flash?
Post by: RD on 31/12/2009 18:01:47

Quote from: Geezer on 31/12/2009 17:15:54

... digital cameras don't have physical shutters.

Oh yes they do: digital SLR cameras are very similar to their predecessors which used "silver-halide technology" (a.k.a. film) ... http://en.wikipedia.org/wiki/Digital_Single_Lens_Reflex#DSLR_design_principles (shutter is "3" on diagram).

Title: How do cameras synchronise shutter and flash?
Post by: Geezer on 31/12/2009 21:34:43

OK, OK!

How about "most digital cameras don't have physical shutters, however, high-end SLR digital cameras do."

(I see you can actually disable the shutter even on SLRs so that you can view the image on the LCD sreen)

Does anybody make a digital adapter for SLRs? My Nikon is gathering a lot of dust!

Title: How do cameras synchronise shutter and flash?
Post by: RD on 01/01/2010 11:35:15

Quote from: Geezer on 31/12/2009 21:34:43

Does anybody make a digital adapter for SLRs? My Nikon is gathering a lot of dust!

Digital backs (http://en.wikipedia.org/wiki/Digital_back) were made for Nikon's (and other 35mm cameras) about a decade ago ...

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http://en.wikipedia.org/wiki/Kodak_DCS_400_series

A wee bit bulky by todays standards.

Nowadays you'd get a higher resolution image from a mobile phone camera.

Title: How do cameras synchronise shutter and flash?
Post by: Geezer on 01/01/2010 19:48:04

Maybe I could stuff a digital camera inside my Nikon  [;D]

Title: How do cameras synchronise shutter and flash?
Post by: neilep on 04/01/2010 13:05:17

Thank ewe Geezer & RD for shutter orientated answers.

I see ...shutter open..flash..close shutter !...There must be some clever stuff happening to accommodate the light that is coming in before and after the flash....Do ewe think the flash itself (on a basic digital camera) changes intensity ?

Title: How do cameras synchronise shutter and flash?
Post by: RD on 04/01/2010 16:43:59

Quote from: neilep on 04/01/2010 13:05:17

Do ewe think the flash itself (on a basic digital camera) changes intensity ?

On autofocus cameras the camera "knows" the distance of the subject and alters the flash intensity accordingly (by altering flash duration) so the focused subject is correctly exposed by flash. A less sophisticated solution is used on flash guns which have a light sensor and a thyristor (http://en.wikipedia.org/wiki/Sunpak_auto_zoom_600_flash) circuit which quenches the flash after enough reflected light had been sensed, but these can be misled if the subject is not of average brightness, e.g. a snowman, (you'll get 18% grey (http://en.wikipedia.org/wiki/Gray_card) snow if you don't add in exposure compensation).

Title: How do cameras synchronise shutter and flash?
Post by: RD on 04/01/2010 17:11:42

Quote from: Geezer on 01/01/2010 19:48:04

Maybe I could stuff a digital camera inside my Nikon  [;D]

You may be able to use your old Nikon lenses on a new Nikon digital SLR body, (with possibly some loss of function).

If you manage put an old lens on a new digital body it will effectively have a longer focal length,
(narrower angle of view), because the image sensor is smaller than a 35mm frame.
e.g. a 300mm lens for 35mm film camera will give a 450mm field of view on a new digital Nikon body.

http://photo.net/equipment/nikon/

So on a digital body your old wide angle lenses will become standard, old standard 50mm becomes short-telephoto, etc 
 

Title: How do cameras synchronise shutter and flash?
Post by: JulietWaugh on 05/01/2010 13:24:31

Well one thing i would like to tell that I am a big fan of photography so that way I find this picture very amazing and cool.