Maximum Bulb time

[BelGer]

Hi all,


I am planning to start taking log exposure photos, I have seen some tutorials and also some great ideas on youtube, so I am eager to start with this.


What I am wondering though, is what is the maximum time I can leave the shutter open, before destroying the sensor ?


I have seen and heard times of 30 minutes to 1 hour, but I am afraid that I will damage the sensor.


My camera is a Canon 40D,


anyone an idea what is the safest ( longest ) shutter time ?


Many thnx for your answers


Ger


belger.nl

[Dr Croubie]

I would not be thinking that there's a "sensor destruction" maximum time, the camera is smart enough to turn it off if it overheats (or should be). Max i've tried with my 7D is 12 minutes. (but i did do 4*3 minute, a 10 min, 12 min, 4 min, 30s, 10s, within the space of an hour, the 10 & 12 min were pretty much consecutive)


There's a difference between 'can' and 'should' though, I'd be more concerned about IQ, here's a100% crop of a shot i did with my 7D, iso100, 10 minutes. The noise is terrible (so is the diffraction and focus, but that's another thing). 40D is older, so having never used one, i'm still guessing it's got worse noise than the 7D for long exposures.


It's not all bad, I haven't used any noise-reduction, it's just the camera-JPG, i presume i could take out a lot of noise with RAWconversion, and dark-frame subtraction (the few shots i did in a row, the noise is in exactly the same spots), so it's no reason not to try... [H]


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[Fast Glass]

Longer than you want to stay awake. I have seen exposures as long as 12 hours!


John.

[tkerr]

What exactly are you planning on taking long exposures of?

One of my hobbies, which is what brought me to Digital Photography is Astrophotography. Astrophotography requires relatively long exposures, but nothing that might cause damage to you camera. Nevertheless, it's not the maximum bulb length you should have to worry about, but rather a maximum saturation limit, or Full Well Capacity. For that reason to extend median total exposure we shoot multiple shots and then stack them.

[BelGer]

Hi Guys,


Many thnx for your answers and help. Very helpfull, Thnx.


@ Tkerr, I will read that article you linked to thnx


What I was planning is :


( not sure if this is the correct english )


Make a picture of the night sky, were you will see the stars form a line ( half of a circle )


( Was thinking of starting with an exposure time of 15 minutes, not sure if this will be long enough though ? )


Other plans are ( but this needs not that long of an exposure ) to make multiple pictures of a skyline including the moon, and then see the moon phases. This will need some photoshop work, as I will have to stack the pictures on top of each other.


But for now, I have to wait until the summer kicks in, and the clouds and rain disappear....( Well Actually it is already summer here in the Netherlands, but my guess is that the weather gods don

[tkerr]

H





What I was planning is :


( not sure if this is the correct english )


Make a picture of the night sky, were you will see the stars form a line ( half of a circle )


( Was thinking of starting with an exposure time of 15 minutes, not sure if this will be long enough though ? )

That's called Star Trails. You can do it with long exposure, use ISO 100 with the largest aperture for your lens and let it go for as long as you want.
(1 Hour = 15° of arc.)
However, you can also do it with Shorter exposures as well. Something along the lines of just 2 to 4 minutes is plenty with a very short interval between each, and then you stack them all together..


If you have Photoshop you can load all your shots into Layers and change the blending mode for each to lighten. Or Select all the layers and convert to Smart Object. (Layer > Smart Objects > Convert to Smart Object)
Then you use Maximum Stacking Mode (Layer > Smart Objects > Stack Mode > Maximum)

Or you can download a application for making star trails using multiple exposures that is called Startrails. http://www.startrails.de/