Maximum Bulb time

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

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


John.

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.

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

Quote:

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Originally Posted by BelGer

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 ? )

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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/

Good information tkerr on the brief photoshop how to. What other kind of shots is stacking good for?

http://www.belger.nl/images/stories/...bg (Large).jpg.


I have used "some kind"of stacking with this picture.


Although I did it a bit more time consuming :-) ( since this was one of my first experiments with Photoshop )


What I did was take all the shots into photoshop, Took 1 picture as the basis, and then "cloned" parts of the other picture in this "Base" picture. This is of course a bit of a puzzle.


I also have made something like this of a man who is attacked by a German Sheperd. ( not sure what the correct English is ) in Dutch it is called "Pakwerk" Maybe a Dutch reader can help me with this ? Anyway, it is not attacked in a bad way, but this was for police dog training :-)

Quote:

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Originally Posted by freelanceshots

Good information tkerr on the brief photoshop how to. What other kind of shots is stacking good for?

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It's a common practice for most Astrophotography. Stacking multiple exposures vs a single or only few longer exposures improves the S/R(signal to noise ratio).


Camera: Canon EOS 50D
Exposures: 45x 180 seconds at ISO 800


http://i68.photobucket.com/albums/i3...5-pleiades.jpg

Quote:

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Originally Posted by BelGer

http://www.belger.nl/images/stories/...28Large%29.jpg.


I have used "some kind"of stacking with this picture.


Although I did it a bit more time consuming :-) ( since this was one of my first experiments with Photoshop )


What I did was take all the shots into photoshop, Took 1 picture as the basis, and then "cloned" parts of the other picture in this "Base" picture. This is of course a bit of a puzzle.


I also have made something like this of a man who is attacked by a German Sheperd. ( not sure what the correct English is ) in Dutch it is called "Pakwerk" Maybe a Dutch reader can help me with this ? Anyway, it is not attacked in a bad way, but this was for police dog training :-)

---

You can achieve the same thing loading all your images into Layers, select all the layers and convert to Smart Object just like I described above. Instead of Maximum Stack Mode you might have to choose Minimum Instead. Saves you from all that cloning.

I have plenty of experience with the multiple images joined into one image to give the effect of progressive movement where I've even gone a step further and done it with a panning image. At first that is what I was kind of considering image stacking to be but when I read on the Internet I learned that its best for photographing the sky at night.


Found this webpage (http://keithwiley.com/astroPhotography/imageStacking.shtml) and it helped me to understand better. Simple right?!?!

Quote:

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Originally Posted by freelanceshots

I have plenty of experience with the multiple images joined into one image to give the effect of progressive movement where I've even gone a step further and done it with a panning image. At first that is what I was kind of considering image stacking to be but when I read on the Internet I learned that its best for photographing the sky at night.


Found this webpage (http://keithwiley.com/astroPhotography/imageStacking.shtml) and it helped me to understand better. Simple right?!?!

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It's been a while but I am familiar with that web site and the information contained within.
Simple?
Well, If the conditions are right and you have all the right equipment it can be. Capturing all the image data, (Light Frames, Dark Frames, Bias, and Flats) is relatively easy, but time consuming. Then you need the right stacking software! One popular application is Deep Sky Stacker. That makes things easy as far as Calibration and Stacking of everything goes. The hard part comes when you need to process all that stacked image data to bring it to life. Unfortunately just stacking a bunch of shots isn't going to do that for you.

Hi Tkerr.


Thnx for the tip.


At that time I did not know this was possible, I will try that method again on the same image, maybe I can also see some change in quality.


Again thnx for tips.


( By the way )


Coming back to my first question this post started with :-)


I also have send Canon an email asking the same question about the maximum Bulb time.


They told me that the camera should turn off automatically when it starts to overheat, or when it detects damage may come due to overheating.


Well.... keep my fingers crossed lol :-)


I have planned this weekend a trial of my long exposure project. Hopefully the weather gods are with me :-)


Ger

Quote:

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Originally Posted by tkerr

Stacking multiple exposures vs a single or only few longer exposures improves the S/R(signal to noise ratio).

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Many people make this claim, but it is not true. There are several good reasons to stack, but improving SNR is not among them.


Photon noise is not affected at all by stacking (ie, 10 one minute exposures stacked or one ten minute exposure will have the same photon noise and same signal, and thus the same photon noise / signal ratio). Read noise is actually worse when you stack.

I don't care to start an argument about it here, but there are numerous other more experience photographers than I who would. Shooting does increase the s/r but won't remove every kind of noise. For that is the reason you also shoot and use Darks, Bias/offset frames, and Flats for proper stacking and calibration.


This is just one resource, I can supply hundreds more.


http://www.astropix.com/HTML/J_DIGIT/COMPEXP1.HTM





You go ahead and shoot a 10 minute exposure and compare the level of noise to 5 x 2 minute exposures stacked and tell me which has less.

Quote:

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Originally Posted by tkerr

I don't care to start an argument about it here, but there are numerous other more experience photographers than I who would.

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I'm well aware of that. I don't really want to argue either and I mean absolutely no disrespect, but a lot of great astrophotographers (whose results make mine look laughable) say just what you are saying. I believe they are confused or misinformed.


(For example, flats correct uneven illumination, but unless I'm sorely mistaken, they don't do a thing to SNR)


The article you posted seems ro me to be exactly right- but unless I misunderstood, it is comparing a single image with several images of the same exposure time (eg, 1 one minute exposure vs 4 one minute exposures). Of course in this case, the stacked image will have a higher SNR. But if you made a single image with the combined exposure time of all the stacked image and compared it to a stacked image (eg, 1 four minute exposure vs 4 one minute exposures), the signal to photon noise ratio would be the same. The stacked image would have more range, but it would not have less noise. The formulas in the article you linked to (together with the fact that photon SNR in a single image goes like 1 / sqrt (exposure time) ) agree with what I'm saying.








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