First star tracks

[yamadak13]

I just went out to do a star track shot. I've never tried a shot like this before and I didn't leave the shutter open for very long so I could see what was happening. Can someone explain to me what caused these purple spots in the upper corners and what can I do to make it better next time?

 

[Sw1tchFX]

10 minutes is quite a while on a digital camera, and you probably should have made it 20-30 minutes with Long-Exp NR on.

The purple spots is amp noise. Basically, the electronics around your sensor are heating up and everyone knows, heat=noise. Long-Exp NR was created to eliminate it. The only trick is that your 10 minute long exposure would be made into a 20 minute one so the camera had 10 minutes to create a similar noise pattern so it could subtract it from the image.

 

[yamadak13]

10 minutes is quite a while on a digital camera, and you probably should have made it 20-30 minutes with Long-Exp NR on.

The purple spots is amp noise. Basically, the electronics around your sensor are heating up and everyone knows, heat=noise. Long-Exp NR was created to eliminate it. The only trick is that your 10 minute long exposure would be made into a 20 minute one so the camera had 10 minutes to create a similar noise pattern so it could subtract it from the image.

Thank you. I forgot all about the Long Exposure NR switch.
Can this heat cause damage to the sensor?

 

[DannyB]

That is MUCH better than anything I have gotten so far.

I will be getting some of the stars this weekend while camping. I am going to try it by taking many 1-2 minute long shots and then layering them together. I have heard it works pretty well.

 

[yamadak13]

That is MUCH better than anything I have gotten so far.

I will be getting some of the stars this weekend while camping. I am going to try it by taking many 1-2 minute long shots and then layering them together. I have heard it works pretty well.

That layering sounds like a good option. I don't have the slightest idea how to go about layering them though.

I'm wondering if there were too many stars visible to get the right effect. I would have liked to stay out longer but I was in an old gravel pit quite a ways out. When I started hearing rocks rolling down the walls from animals walking around the rim I decided to pack it up. There is getting to be too many wolves around here the past several years.

 

[DannyB]

There is a program someone posted that helps out with the layering. Keeping the shutter open for a shorter time will also reduce the amount of stars you will see. I'll be searching for that program and if I find it I will post it up here.

 

[realitycheck3907]

I would have liked to stay out longer but I was in an old gravel pit quite a ways out. When I started hearing rocks rolling down the walls from animals walking around the rim I decided to pack it up. There is getting to be too many wolves around here the past several years.

Are you serious? I probably would've never been out there to begin with. hehe. Daytime sure, night no way.

 

[dklod]

What is the ideal aperture to use with star shots??

 

[Garbz]

Can you damage your sensor: yes do these with care.
What's the ideal aperture: f/1.0, Infact a Nikon made a Noct-Nikkor 50mm f/1.2 just for this purpose. But it is unaffordable. No really. 30 years old and still goes for $4000US on ebay. Shoot as wide open as you can. More light = more stars unless you're in a light polluted area.
Image Stacking is very very easy: http://www.tawbaware.com/imgstack.htm and has the practical upshot of being able to cut through light pollution: http://farm2.static.flickr.com/1353/773160897_fae20200db_b.jpg (2 hour equiv photo less than 5km from the city centre)

 

[XsCode]

These guys use/create software specifically designed for stacking short exposures.

http://www.qcuiag.org.uk/

 

[josealb]

As already said this purple on the corners is noise from the amplifier. Digital cameras are quite bad for getting long exposures. The best thing you can do is use your lower ISO setting (minimal amplifying) and take shots no longer than 5 min to blend them together on the pc.

If you're interested I've got a tutorial about shooting star trails in my blog.

Hope it helps :mrgreen:

 

[yamadak13]

Can you damage your sensor: yes do these with care.

Any certain precautions I need to be taking to avoid this damage? Or do I need to not keep the shutter open for more than a certain period of time?

Thank you to everyone who helped out here. I've learned a lot reading through this info.

 

[DannyB]

Well looking and the radar, I have clear skies tonight I'll have to give it a shot with the layering method

 

[DannyB]

Ok, this was only 10 minutes worth (ten, 1 minute long exposures) out of my backyard just to tryout the image stacker. ( http://www.tawbaware.com/imgstack.htm ) Wow! I was shocked at how well it stacked and how simple it was to do I know its not great quality or anything but it was just to try it out and I had plenty of light pollution around so I wasn't expecting much anyways.