Star Trails

[bradrjames]

Hi

I was experimenting with star trails a while ago, this is a shot I took that I was happy with. Once I started to have a closer look at the shot I noticed that there were heaps of small red dots all over the shot. This was not only when I viewed it on the computer but also when I viewed it on my camera (Zoomed all the way in)and when I printed it. I have cropped a section of the shot, so I hope you can see these red dots.
Does anyone have any idea what these are? If so how do I shoot really long exposure and not get these dots.

[coffee]

Yes, it's either dead or hot pixels. Most likely hot ones. It's happends when using very long shutter times. Do a search on it as find out more.

[bradrjames]

Thanks for that, I will check it out. :-)

[dkippen]

brad - do you remember what your settings were? On my computer at work, I'm not seeing the spots. I've done a couple of star trails and off the top of my head I think I shot at f/8 for 45 minutes and I don't recall having red spots. I'll try and get one posted later today.

[bradrjames]

Hi Debbie

I really can't remember what my settings were, it was about 18 months since I took the shot. At a guess I think I would have set it at about F11 and I think I left the shutter open for about 1 hour.
I will load this shot up onto my gallery where I can have it at a higher resolution, you should be able to see the red spots then. The reddish glow you can see on the trees is from my camp fire, I stoked the fire just before I closed the shutter, maybe this had something to do with it?

I would love to see your shots!!! Let me know when you have loaded them up:)

[coffee]

What I read is most all sensors will have hot pixels. They just aren't that noticable with normal everyday shots, just long dark captures. If you have a canon DSLR there is an undocumented way to rest the hot pixels. I've tried it and for some reason it works. Unless they are dead one. That would be rare though.

First do a search to a very small program that will map out where the hot ones are. There are many little free programs out there that will do that. Take a long exposure with the lens cap on, say 5 seconds or so. Run that picture through one of those programs and fine the hot ones. Then with the lens cap on, set your camera to "clean sensor" and leave it that way for 5-10 seconds or so, then turn your camera off. take another shot like the first one and run that through the hot pixel finder program and you will see there won't be anymore hot pixels.

[dkippen]

Brad - here is my first try at star trails, other than a bit of sharpening, straight out of the camera. These were taken the end of July in Ely. Both were shot at f/4.5 with a wide angle, the first one for about 20 minutes (the bugs were AWFUL) and the second one for about 35 min.

[jerryph]

Wow, an hour... not sure I would want to subjecet my dSLR to that regularly, but I would not have an issue using a film camera to do this. It seems like this is quite hard on the sensor.

Eventually more burnt pixels will result if you do this regularly.

[dkippen]

Jerry - these were taken on two different nights. But yes, I do believe it can be demanding on the camera. Because of where I live, I need to go way up north to get star trails, so it's not something I'll be able to do a lot of.

[bradrjames]

Thank you all for your help :)

I had no idea I would be doing my camera any harm....I guess that why I am doing this course. :)

Debbie I loved your star trails!!! I have now posted the start trails on my gallery, you should be able to see the red spots on that.

Thanks again guys for your help :)

Brad

[jerryph]

Jerry - these were taken on two different nights. But yes, I do believe it can be demanding on the camera. Because of where I live, I need to go way up north to get star trails, so it's not something I'll be able to do a lot of.

As long as you are not getting pixels so hot that they show in the pics, or are getting more dead pixels, its fine.

This is one area where film cameras really have it over digital (no sensors to overheat).

Something silly that I was just thinking about... if the average shutter speed of your pictures is 1/2 a second, having your shutter open for 1 hour give the equivalent wear on the sensors of taking 7200 pictures... except the sensor NEVER will get that hot a 1/2 second or less at a time. Most of my pics are in the 1/125th-250th or faster. At 1/250th for me, that would be equal to taking 14,400 pictures... yikes! :eek: :p :D