Polaris Star Trails

Canon 40D
Tokina 11-16 f/2.8 @ 11mm f/4
ISO 200

164 30sec exposures (82 min) & 1 dark frame
combined with startrails.de

Color

Can definately say you got your polarscope aligned

Very nicely done!

just interested in why you would need a dark frame?...i want to get into star trails too

The dark frame helps cut down on the noise.

I also have a question.
I get people asking me why I just don't do one long exposure vs. doing the multiple short exposures. Can someone give me the pros and cons of of both ways please?

Thanks for the comments!

The one thing that does come to mind with long exposures is you tend to get hot pixels show up in the dark sky, because ( I think) the sensor gets pretty warm.

boost_dependent wrote in post #8083151
I get people asking me why I just don't do one long exposure vs. doing the multiple short exposures. Can someone give me the pros and cons of of both ways please?

Two reasons:

1. Noise is integrated as an essentially linear function of exposure time and you reach a point that the really dark areas will become pure noise.
   
2. With extremely long exposures, any foreground objects (like trees) will eventually wind up being greatly overexposed.

nipper wrote in post #8085733
The one thing that does come to mind with long exposures is you tend to get hot pixels show up in the dark sky, because ( I think) the sensor gets pretty warm.

That's one of those urban legends that is based on a misunderstanding of of the term hot pixel -- the term "hot" refers to the effective analog gain and not the temperature. Each photosite on a CMOS image sensor has its own isolation amplifier that converts stored charge into a voltage. It is impossible to manufacture a sensor in which each of the ten to twenty million amplifiers have precisely the same gain -- add to this, the variation in light sensitivity between photosites and also finite differences between each of the micro lenses over each photosite. The end result is that the longer the exposure, the more apparent the differences in gain between individual photosites.

Wow, you guys have stars down there? Its bloody twilight all the time past 11 oclock up here! I'm jealous you actually get to see stars, nevermind make trails!

That's one of those urban legends that is based on a misunderstanding of of the term hot pixel -- the term "hot" refers to the effective analog gain and not the temperature. Each photosite on a CMOS image sensor has its own isolation amplifier that converts stored charge into a voltage. It is impossible to manufacture a sensor in which each of the ten to twenty million amplifiers have precisely the same gain -- add to this, the variation in light sensitivity between photosites and also finite differences between each of the micro lenses over each photosite. The end result is that the longer the exposure, the more apparent the differences in gain between individual photosites.[/QUOTE]

Now in English please.:p

nipper wrote in post #8090891
Now in English please.:p

If you take too long of an exposure with a digital sensor, then it will turn out poorly

nipper wrote in post #8090891
Now in English please.:p

dcad10 wrote in post #8091483
If you take too long of an exposure with a digital sensor, then it will turn out poorly

Excellent job of translation!

My wife keeps telling me that when she asks what time it is, she does not want to know how to build an atomic clock.

Thanks for the answer(s)... that helped out.
Some other people I know were saying their Nikon D700 would be able to do a single long exposure just fine, unlike my 40D. Something about the full frame and in camera noise reduction and the high ISO performance that it has.

Yes, down here in Pensacola, FL we do have stars LoL although the light pollution sucks! Polaris is about 30deg for us.

Invite them to show you. Set up cameras side by side and the rule is that they must do a single 82 minute exposure while you do 164 half-minute exposures. Of course, the loser must buy the winner a nice expensive dinner.

Very nice !

Nice shot. One question- do you take the dark frame prior to taking the multiple shots, or after your done with it?