Maximum Bulb time

[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?!?!

[tkerr]

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?!?!

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.

[BelGer]

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

[Jon Ruyle]

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

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.

[tkerr]

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.

[Jon Ruyle]

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

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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