30 seconds max, why?

Since making some night shots and some experiments with infrared of 120 seconds exposure time,
I've being thinking why they only offer a max of 30 seconds.

Why can't or won't they offer a longer exposure time, it seems so simple to me to extent it.

What's the point, in doing that. Cost effective it only raises the price, and how many people are having a benefit of that. The shutter speed should than look like: 30 sec, 60sec, 2 min, 4min, 8 min. Just use bulb. You are experimenting anyway.

Martin.

Use Bulb and a cable release for longer than 30 seconds.

The point is that it would be easier and you dont need to buy a electronic remote were you can set the exposure time for the bulb.
It's all done electronicly so they can easly change it in the frimware without (much) extra cost I believe.
I'm sure there are more users that go over an exposure of 30 seconds, so why not give us an extented exposure time?

The steps arent going so steep as you discribe Martin, after 15secs they take step of 5secs so after 30secs would come steps of 10 till a minute.

That's not right, I think. The way electronic shutters work, in conjunction with the light meter and aperture, is basicly always by doubling or halving the amount of time in sequence. I think there is more tech-wizz. involved as you might think.

Martin.

The shutter is held open by electrical power and the longer the shutter time the more power is consumed. Bulb also consumes power and the limit of film camera batteries was usually about 8 hours becaue of this.

In a digital camera very long exposures also heats up the sensor.

Bit most of all as shutters have for a long time been designed with a 30 seciond limit this will have more to do with film and a thing called reciprocity failure.

That is, at very long exposures the normal relationship between shutter speed and aperture breaks down. If an exposure is correct at say 1 secod at f11 then you would expect an equivalent to be 2 seconds at f16, but you will find it needs to be morw like 4 seconds. An expected 30 secondexposure might be more like two minutes to expose film correctly.

So a timed very long exposure was worthless.

Thank you John, that was informative
I've looked reciprocity failure up and it was an interesting read, I didn't knew that.
With the digital age we have the problem that the sensor gets hot and increase noise and it wouldnt be so good for the lifetime of the sensor either.

I do use bulb to have longer exposure but it would be far easier if you can set that exposure time in your camera, it will save you the cost of the remote.
The theory behind the exposure time can be calculated, there is just a formula behind it so that won't be the problem.
So... what's the thing that stops manufacuters of letting us set longer exposures, is there even somthing?

WEll we've stated the reasons. Apart from anything else it might need a new shutter design, and why do that when the existing shutters were fine?

I'm not so sure it's a feature that many people would want. It isn't difficult to count off the seconds!

The shutter is controlled electronicly by the firmware of the camera and we use the same shutter in bulb so it can handle longer exposures.
Although you're right that it would be a feature not many will need and those needed can countdown so that would be a valid reason but also the only reason why...

I would have thought it was more down to the limits of the metering system. Although you can do longer exposures, the meter cannot accurately measure very, very low levels of light (you'll notice the flashing values - indicating out of range).

However, on "M" mode it would, I suppose, have been possible to increase the available shutter speeds... though when you get longer than 30seconds it doesn't matter if you do 60 or 63 seconds! (Remember each "stop" is a doubling of time - so from 30 to 60, to 120, to 240 are all one stop).

As John says, though, beyond 30 seconds and the CCD can get very warm - introducing all kinds of noise, and uses quite a chunk of power (so the batteries can get quite hot)! The K20D is better in this respect - having a CMOS sensor rather than CCD.

Matt

Personally I would like longer shutter times, but I would quite happily settle for Bulb but with an on board timer, of which some cameras already have.

My take on this would be to use shorter exposure times and "stack" the images using software. That would get around the problems of heating the sensor etc.
I presume these long exposures would be taking place in dark environments? Exactly the conditions to show up the noise from the sensor, so some editing would be needed anyway.

I come at this from a slightly different angle of wanting to get some decent astro shots (not managed it yet) and it is interesting to note that long exposures don't seem to be recommended for this anymore. Multiple shots stacked, with dark shots also then "deducted" to take away any noise is the way to go (apparently).

There was an interesting article in the December issue of the "Sky at Night" magazine on how to take astro photos with a DSLR. This should also apply to long exposure shots of any sort.

Thanks Matt, Steve & Father Ted

yes I've notice the flash icon Matt, I thought it was that he wants you to pop up the flash because of the sharpness of the image, to prevent blur by moving the camera.
It still looks like it meters just fine against the 30 secs though, just need to experiment a bit with that.

Father Ted, that stacking sounds very interesting, surely for the infrared. The K10D and up have an uv coating on the sensor so there isn't coming much uv-light trough and since the number of red sensor isn't that much they are pretty noisy.
Do you've an helpfull link for me in to the matter, it would be very helpfull?

About astrophotography, I've readed that shots taken from the Andromeda Galaxy were 200 mintes at f/8

If I remember correctly, digital cameras built for astrophotography have special liguid cooled sensors.

Specialist astro cameras tend to be cooled in one way or another, ( depending on how deep your pocket are ).

Stefan, I'll have a rummage and see if I can find a link.