Need help with taking pics at night... (long shutter)

[FlightIsPossible]

Hello, normally I would just go outside and figure this out for myself. But I am living in the city and there is tooooo much light pollution to get a reliable result. I am taking a very short trip to the desert, and I'd like to get some pics of the stars. My question/scenerio.(I apologize beforehand for my crap terminology/knowledge)........... Ok, so I would like to take pics of the stars with that neat "swirl" effect. I have taken a few before and was happy with the result. I was wondering if there is a certain(approx) amount of time that I can open my shutter that will give me a accurate idea of what my pic will look like after having my shutter open for an hour+. Example... can I open my shutter for 2 minutes to test my settings and would it have the same "lighting" result as if I opened it for an hour? I only want to open it for a long time for the "swirl" effect from the stars.

I am sorry if the question is somewhat confusing, I have no clue what I am doing, except having fun learning this stuff. I'd just like to save a lil time and be a little bit more prepared for this trip... more than I was for my last vacation... which I missed alot of pic ops cuz I suck.

I am using a Canon EOS 7D if that matters.

 

[Light Guru]

The Two Hosers Photo Show 107- Star Trails |

 

[KmH]

I was wondering if there is a certain(approx) amount of time that I can open my shutter that will give me a accurate idea of what my pic will look like after having my shutter open for an hour+. Example... can I open my shutter for 2 minutes to test my settings and would it have the same "lighting" result as if I opened it for an hour? I only want to open it for a long time for the "swirl" effect from the stars.

I suspect by 'swirl' you mean star trails which are caused because the Earth rotates on it's axis.

Do some basic math. The Earth rotates (makes a circle) once on it's axis every 24 hours. There are 360 degrees in a circle so 360° / 24 hours = 15° per hour. 15° / 60 minutes = 0.25° per minute.
So the Earth rotates 60x further in 1 hour than it does in 1 minute. Star trails will be about 30x longer in a 1 hr exposure compared to a 2 minute exposure.

So with a 2 minute exposure the star trail s will be much shorter than they will be in a 1 hour exposure.

The star trails may not be much brighter after an hour, because pixels can become saturated such that they cannot record any more light, but any light pollution will likely be brighter.

As it is, because the image sensor in your camera resists the electricity applied to it when it is turned on, it heats up. that heat causes thermal image noise.

So what people do to keep the image sensor cooler is take a series of shorter exposures so the image sensor can cool a bit between exposures, and then later add the series of exposures together into t single image.

Photo Stacking and Long Exposures - Part 1: Introduction | Shutter Photo Magazine

 

[FlightIsPossible]

Thanks for the 2 replies. I don't think I asked the question properly... nothing new for me... I am like a small child when it comes to this stuff... especially trying to explain myself.

I understand the effects from long exposure.... my problem is that I don't want to wait a hour+ for a long shutter, then review the pic to see that I have over/under exposed it... wasting a hour+ of my time. So I was wondering if I opened the shutter for 2 min(or whatever shorter time) would it have the same effect with the amount of light. I understand what it takes to make the "trails" effect... I just want to make sure I have the proper settings before I commit to a hour+ shutter speed. If I can test this with a 2min, rather than wait a hour+, it would be very helpful.

Once again, I am stupid and I know it... forgive me plz. lol

 

[JayJeep]

Try reading this post

http://www.thephotoforum.com/forum/articles-interest/276016-shooting-night-pictures-stars-stuff.html

 

[FlightIsPossible]

Woohoo! Thanks, I appreciate all the help, but that hit the spot JayJeep. I have been looking for a good article like that, every article I had found by myself just didn't answer the questions I had. Thanks!

 

[o hey tyler]

Thanks for the 2 replies. I don't think I asked the question properly... nothing new for me... I am like a small child when it comes to this stuff... especially trying to explain myself.

I understand the effects from long exposure.... my problem is that I don't want to wait a hour+ for a long shutter, then review the pic to see that I have over/under exposed it... wasting a hour+ of my time. So I was wondering if I opened the shutter for 2 min(or whatever shorter time) would it have the same effect with the amount of light. I understand what it takes to make the "trails" effect... I just want to make sure I have the proper settings before I commit to a hour+ shutter speed. If I can test this with a 2min, rather than wait a hour+, it would be very helpful.

Once again, I am stupid and I know it... forgive me plz. lol

I would suggest taking several 30 second exposures and stacking them to reduce noise and sensor heat. You'll have the same effect with a much cleaner image.

That way you don't have to take a single hour long exposure and come to find out it was over/under exposed. You can take shorter exposures, fine tune them, and layer them on top of one another for an identical effect.

 

[FlightIsPossible]

Thanks o hey tyler. I hadn't thought of that, but after I did a little bit of reading it seems like the best option. I appreciate ya mentioning the technique. Intervalometer awaiting shipment. That lil things gonna be handy, never knew those gadgets existed until today.

 

[jamesbjenkins]

Like Tyler said, taking a bunch of 2 min exposures and stacking them in post is the best idea for several reasons, noise reduction being near the top of the list.

 

[FlightIsPossible]

Thanks for the reply. Photo stacking is new to me, but I am certainly going to give it a try. I had heard about it over in the "macro" section of the forum, it never crossed my mind to use that technique for star pics. After doing some reading, it def seems like the best option. Can't wait to try it out. I assume photo stacking is fairly simple with the software. I am going to take the pics first, and attempt to stack them after I get back from the vacation. I appreciate the suggestions, I'd have been opening my shutter for 2hours+, like I did on my last star attempt(which worked with marginal results)