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This may seem like a really stupid question (I certainly feel dumb asking it), but with a digital SLR, can you actually compose your picture using the LCD screen? If so, how does the image reach the imaging sensor, since it is being reflected to the eyepiece by the reflex mirror.
(This thought struck me when I say the double page advert for the Canon EOS300D in PP, where the photographers are at the footie match. The thing thatreally doesn't make sense is that they're at the back of the grandstand focusing on the pitch and they've got the built in flash popped up. What exactly is the guide number for the 300D?! 
)
I have the Canon EOS 10D and you can't compose with the LCD screen. It's there for reviewing purpose only.. unless someoe knows a way around this using the mirror lock up feature but I imagine that the 300D is like this also..
The hybrid SLR's from Olympus i.e. the E10 could use the LCD screen however..
Oh yeah.. forgot about the advert.. well... it's just an advert and they probably wanted to show that the camera has a built in pop up flash. It certainly isn't powerful enoughto reach the ground from there.. I think it has a GN of around 12 or 13
As for the pics on the LCD's I didn't notice whether they were representative of what was happening on the pitch or whether the LCD's all had slightly different ones.. representative of the fact that the people are probably reviewing pics they have previously taken rather than composing with the LCD
Thanks for that -- I don't feel so daft now!
With digicams that do allow light to hit the sensor during composition, how does the shutter work? Does the shutter curtain come down just before the exposure is made and then open for the correct exposure time, or is it controlled digitally and the sensor is switched on for the sepecified 'shutter speed'?
With digicams that do allow light to hit the sensor during composition, how does the shutter work?
To the best of my knowledge, these cameras don't have a shutter at all (which explains the optional "shutter noise" sound most allow you to use!). The chip in digicams is live - a bit like digital video cameras I guess - and the image that happens to be on it when - or soon after to be cheeky - the "shutter release" is pressed is what you get, so yes, your "or" option sounds good to me.
The following is copied from a website called how stuff works...
Film-based cameras must have a mechanical shutter. Once you expose film to light, it can't be wiped clean to start again. Therefore, it must be protected from unwanted light. But the sensor in a digital camera can be reset electronically and used over and over again. This is called a digital shutter. Some digital cameras employ a combination of electrical and mechanical shutters.
All the digital SLRs I have used (Fuji S1, S2, Canon D30, D60, 10D) do not let you do this, as the mirror has to sit in front of the sensor to direct the light up into the pentaprism.
The "electronic shutter" is not there either - the shutter on a digital SLR works the same as a film SLR.
The Canon advert is a little misleading.
Firstly the flash wouldn't reach, secondly with the 18-55mm lens you would be lucky to get the players the size of pin heads let alone as they are on the review screens.....you would struggle with a 500mm from the back of the stands even with the 1.6x field of view.
A word with the ASA I think !
As for the LCD the responses are correct. The DSLR does not allow for image composition from the LCD , although I have been asked this before, and I guess those with experience of compact digitals would expect nothing else.
Thank goodness we don't have people holding DSLR's 18" infront of their eyes with great big lenses on them composing via the LCD !
As for the shutter it doesn't exist the mirror does however flip out of the way (as in a film SLR) to allow the sensor to be exposed.
HTH
Mike.
Full blown Digital SLRs have an Electronically-controlled focal-plane shutter to control it's exposure just the same as a film based SLR.
However SLRs like the Olympus E10/20 which have a traditional mirror box viewfinder so you are looking through the lens as any other SLR, these have a combination shutter. Up to 1/640 sec. this uses a mechanical shutter but over this speed it will go into a Progressive Scan mode: up to 1/18,000 sec. The mirror will stop live viewing through the LCD but as you have a traditional SLR view through the viewfinder why would you want to?.
Baz
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