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Long exposure limit

Tsleel2811
Enthusiast
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....
21 REPLIES 21

Bryston3bsst
Enthusiast

Doing astro you should use a remote shutter release so you don't touch the camera with the shutter open. And you shouldn't have to hold the release in bulb. I use a Vello remote and the shutter stays open without holding after a few seconds and a second press will close it.

 

My understanding too is the best star trails are the result of stacking many 30 second exposure as oppsed to leaving the shutter open for 3 minutes. Plus that time duration would require a tracking device to compensate for the earth's rotation.

 

And please note...I am not an astro guy. I'm sure a more experienced astro person will probably chime in here.

Tsleel2811
Enthusiast
I should've specified. Im using a remote as well. I guess stacking would be the best. But my question is can the sensor get ruined of left open for too long at night time

Tsleel2811
Enthusiast
And I don't need to use a smart tracker because me desired result would be the earth standing still and the stars moving. So a regular tripod would do. I'm using a heavy one (Manfrotto) so it stands firm anyway


@Tsleel2811 wrote:
And I don't need to use a smart tracker because me desired result would be the earth standing still and the stars moving. So a regular tripod would do. I'm using a heavy one (Manfrotto) so it stands firm anyway

Actually, you may want to use a tracker, if you want to have circular star trails around the North or South pole stars.

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"The right mouse button is your friend."


Waddizzle wrote:

Tsleel2811 wrote:
And I don't need to use a smart tracker because me desired result would be the earth standing still and the stars moving. So a regular tripod would do. I'm using a heavy one (Manfrotto) so it stands firm anyway

Actually, you may want to use a tracker, if you want to have circular star trails around the North or South pole stars.


In astronomy class in college we were taught that there is no South pole star. Have they found one in the meantime?

Bob
Philadelphia, Pennsylvania USA


@RobertTheFat wrote:

@Waddizzle wrote:

@Tsleel2811 wrote:
And I don't need to use a smart tracker because me desired result would be the earth standing still and the stars moving. So a regular tripod would do. I'm using a heavy one (Manfrotto) so it stands firm anyway

Actually, you may want to use a tracker, if you want to have circular star trails around the North or South pole stars.


In astronomy class in college we were taught that there is no South pole star. Have they found one in the meantime?


https://en.wikipedia.org/wiki/Pole_star 

 

There is a star, Sigma Octantis, that is used for aligning telescopes in the Southern Hemisphere.  Like Polaris, it is not precisely aligned with the Earth's polar axis, and is visible to the naked eye.  It is not as closely aligned with the Earth's axis of rotation as Polaris.

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"The right mouse button is your friend."

kvbarkley
VIP

No, the sensor will be fine. But if it does heat up you might get more noise and "hot" pixels.

 

I think that video overheats because of all the digic processing and readout, not the actual light gathering. For a still image, nothing much is happening when the shutter is open.

TCampbell
Elite

I have a 60Da which is Canon's camera specifically designed especially for astrophotography (the standard 60D filter is replaced with a different filter which allows more full-spectrum light through and dramatically increases sensitivity in the "reds" (camera's designed for normal photography actually trim the visible light spectrum to mimick the sensitivity of the human eye and the human eye isn't actually particularly sensitive to reds.)

 

It turns out the ideal ISO setting for a 60D is ISO 800. 

 

But there are a few things you need to know to go along with this.  I'm doing astrophotography of "deep sky objects" (DSOs).  I'm not shots of the Milky Way over landscapes at night.  Because of this difference... I either attach the camera to a telescope like I did for this shot:

 

Andromeda & Companions

 

Or I put the telescope on a "tracking" head (apparently I haven't uploaded a prior example and that shot is on my other computer).  But the "tracking head" just means you're using a normal camera + lens combination but the "head" is rotating at the same rate that the earth is rotating -- but in the opposite direction (it cancels out the movement of the sky so you can take very long exposures without the stars "smearing" due to the rotation of the Earth.)

 

BTW, the shot above is not a single image... I shot many 8-minute long images and those are then combined using a stacking process.  The color and contrast details are "stretched" to exaggerate them (otherwise the image would mostly just appear as a black & white).  So to be clear... this NOT what you get straight out of the camera.  The adjustments above cause the younger & bluer stars to look more "blue"... and the older and more yellow stars appear more "yellow".  (So the color differences aren't made up - but they are exaggerated).

 

I do have some examples of images that where the colors are not exaggerated -- they really do come out of the camera looking pretty vivid.  It all depends on the object.

 

The reasons ISO 800 turns out to be ideal is because this is the magic ISO for a 60D which maximizes the "upstream" signal amplification and minimizes the "downstream" signal amplification.   This tends to produce the strongest "signal to noise ratio" (SNR) and astrophotography is all about maximizing the SNR.  The reason we shoot a LOT of images of the same object is to improve the SNR even more.

 

The image-aquisition steps to astrophotography are somewhat nit-picky... and the image processing process is even more nit-picky.  

 

There are numerous web-tutorials that can help... I have found the "photographingspace.com" website and "DSLR-astrophotography.com" website seem to have quite a bit of good info.

 

Your camera is very capable of capturing fantastic images... but it will require some work on your end (it require work no matter which camera you use.)

 

 

 

Tim Campbell
5D III, 5D IV, 60Da

ebiggs1
Legend

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.

 

Duration related noise effects thermal noise. Increasing the ISO requires amplification, which requires more power.

Basically in a given shooting environment, increasing ISO has the greatest adverse effect.

 

The camera knows when it gets too hot.  It will shut down until temps normalize.

EB
EOS 1DX and 1D Mk IV and several lenses!
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