Questions on shutter and mirror

[molested_cow]

Two questions: first of all, are shutters and mirrors the same thing?

1. On SLR camera, the mirror reflects the image to the view finder, at the same time the shutter keeps light out from the film. When you hit the trigger, the shutter opens and the film is exposed.
For DSLR, the mirror still exists in order to reflect the image to the prism and view finder, however, do image sensors need mechanical shutters? Are they electronically activated or some sort?

2. I always hear about long exposure draining battery. I use SLR and I've never had problem with low battery even when taking long exposures. So what's the relationship between shutters and battery drainage? How is this different for DSLRs?

 

[thingsIsee]

They are not one in the same, but a DSLR and a film SLR work the same. The mirror has the same function and operates the same. Push the shutter bottom the mirror swings up then the shutter opens exposing the film/sensor.

The battery on a DSLR has many more things to operate from the film SLR. For long exposure shots draining the battery again both SLR and DSLR long exposure shots will drain the battery faster, but the digital camera has more to power then film does.

 

[Big Mike]

1. On SLR camera, the mirror reflects the image to the view finder, at the same time the shutter keeps light out from the film. When you hit the trigger, the shutter opens and the film is exposed.
For DSLR, the mirror still exists in order to reflect the image to the prism and view finder, however, do image sensors need mechanical shutters? Are they electronically activated or some sort?

2. I always hear about long exposure draining battery. I use SLR and I've never had problem with low battery even when taking long exposures. So what's the relationship between shutters and battery drainage? How is this different for DSLRs?

Many (most actually) digital sensors don't need a physical shutter. Most point & shoot digital cameras don't have shutters, the sensor is always getting light when active...and that's why they they let you view the image 'live view' on the screen.
Some new DSLR cameras now have that feature, but they hold up the mirror and open the shutter when you activate that mode.
One of the functions of the mirror, is to direct some light to the AF sensors...so when you activate live view on a DSLR camera, the AF must use a different method, which won't be as good as 'normal'.

There are a few DSLR cameras with electronic shutter systems. The Nikon D70 for example. They do have an advantage, in that they can sync with flash at much higher speeds than cameras with mechanical shutters.

As for the power usage with long exposures...besides the drain from the sensor & processor being active...the shutter also draws power when open. It other words, it uses electromagnets to hold the shutter open.

 

[molested_cow]

Got it, thanks!

 

[Garbz]

There's a bit more to Mike's comment that is missing. Digital sensors don't strictly NEED a shutter for certain sensor types, but it does help improve quality. When sensors are read out in anything but perfect darkness it is possible that high contrasts start blooming and bleeding, and in the worst case will actually completely stuff up the readout of the entire row of pixels. So yes a shutter is needed, and in some lower-end models at higher speeds it actually serves no other purpose than to blank out the sensor during readout.

As for power consumption. My D200 will sit in standby for more than a month without emptying both batteries. I get about 400-500 shots off in a session too. However a long exposure will drain the battery within 2 hours continuous.

 

[KmH]

Or you can use multiple camera bodies with a different lens on each, so you don't have to change lenses.

That's what a lot of sports shooters do.