Long exposure limit

[Tsleel2811]

Rather stupid question, I think. I own a 60d and I want to get into astrophotography. I know the effective iso range is about 1000. Maybe 1600 if I'm good with lightroom noise reduction. the maximum exposure time is 30 sec. But in bulb mode I can leave it open indefinitely so long as I keep the button pressed. Most photography tutorials say that exposure times can reach upwards of 3 minutes if I want visible streaks. My question is as follows: can the sensor be damaged if I leave the Shutter open too long in nighttime conditions. I'm thinking overheating or too much light hitting the sensor.

Thanks for your input....

[TCampbell]

I routinely take exposures with my 60Da in the 5-8 minute time range.  But what's more... I'm really trying to grab a few hours worth of data.  So the shutter closes, writes the file, and a second or two later the shutter re-opens to start capturing the next file.  It's not a problem for the camera.

If I do this with Backyard EOS (astrophotography image-acquisition software) then it also reports the camera's internal temperature (there is a temperature probe inside the camera body).  On cold winter nights it doesn't even manage to get warm.  But on warm summer nights it might make it up to around 109ºF, but this isn't a problem.

As Ernie says... the camera will warn you or even shut down if it really gets too hot.

The best information I've ever read on the topic of noise was in the first chapter of the book "Lessons from the Masters" (edited by Robert Gendler but the chapters are all written by different authors where each author is considered *the* expert/master on that particular field of astrophotography).  But since "noise" is a general problem in almost every type of astrophotography they dedicated quite a bit of time on the topic and explained the quantum principles that cause noise to exist in the first place and how to use stacking to reduce noise.

The noise isn't just a simple matter of boosting the ISO.  It matters whether the boost is coming from analog (upstream) signal amplification within the imaging sensor or whether it's coming from digital (downstream) signal amplification by the camera or computer after the imaging sensor has already collected the data.  While any boost in ISO tends to also boost noise, it turns out the upstream amplification within the chip can boost the good signal significantly more than the noise and you end up with images that only have a tiny increase in noise for the ISO boost.  But each sensor model has some point where it can't boost anymore and has to resort to downstream (digital) amplification.  For the 60D that point occurs at ISO 800.

Most Canon models get to ISO 800... some models get to ISO 1600... and some models appear to get above 1600 -- nearer to 3200.  

[ebiggs1]

" It matters whether the boost is coming from analog (upstream) signal amplification within the imaging sensor or whether it's coming from digital (downstream) signal amplification by the camera or computer after the imaging sensor has already collected the data."

This is a point either ignored or unknown by most photograhers.

[Bryston3bsst]

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@ebiggs1 wrote:

Now for the correct answer.

With long duration of exposure more total and random pixels heat up.  This is because power is applied as long as the sensor is open.   Keeping the sensor powered longer means more heat will be generated.

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Now for the correction to the 'correct' answer.

The sensor doesn't 'open'.

[ebiggs1]

The intent was and as it is usually stated in this manner "open" if the shutter is opened.  The mirror is up.  Meaning the sensor is "open" to the world.  Clear?

[RobertTheFat]

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ebiggs1 wrote:

The intent was and as it is usually stated in this manner "open" if the shutter is opened.  The mirror is up.  Meaning the sensor is "open" to the world.  Clear?

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Perfectly. But I do think we have to credit you with inventing that usage of the word. A Google search I just did betrays no hint of it. Until it catches on, you may want to reconsider your inclusion of the word "usually".

[ebiggs1]

Bob
Boston, Massachusetts USA

Robert there you go again.  

SInce the early days of photography, the word "open" meant the film (in those days) was open to the world.  In those early days it was simjply a lens cap.  There were no shutters.  The photographer removed the cap and exposed the film.  Despite what google might say, it is a common term and 'usually' a clear meaning.

[TCampbell]

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@Bryston3bsst wrote:

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@ebiggs1 wrote:

Now for the correct answer.

With long duration of exposure more total and random pixels heat up.  This is because power is applied as long as the sensor is open.   Keeping the sensor powered longer means more heat will be generated.

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Now for the correction to the 'correct' answer.

The sensor doesn't 'open'.

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Technically "true" but Ernie's point (which is correct and valid) is the difference between the "active" vs. "inactive" sensor.  

When the shutter is closed the sensor is literally "off" (it's cold and if it was hot it's in the process of cooling down).  When the shutter is open the sensor is active and it's heating up.  

It's really the heat issue... there's a direct correlation between the physical temperature of the sensor and the level of noise as one factor that contributes to noise.  Dedicated astrophotography imaging cameras often have active cooling systems to drop the temp by 40-50º below whatever the ambient temperatures are just to drive down the noise levels.  That's usually not an issue for traditional photography becuse usually the sensor is only active for a fraction of a second.

[Tsleel2811]

Thank you very much for your help. I guess stacking is the way to go

[Tsleel2811]

This is the first time I'm hearing about this. Do I have any control over it?

[ebiggs1]

You always have options.  Photography is mostly a trade off.  You give to get and there is no free lunch.

Test your camera don't just rely on reviews you read on the ole inner web.