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Star trails: 15 minute exposure

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skp

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Hello all!

I shot this one 2 days ago, on a very isolated farm, the sky was very dark and you could see A LOT of stars! So i felt like sharing :-)

Almost 15 minute exposure (actually, it's 14 minute, 20 seconds)... Sorry for the hot pixels, couldn't help on that, it was very hot (90F)... I'll try that again in southern hemisphere winter!

For those who are interested: this was shot in the countryside of the city of Panambi, State of Rio Grande do Sul, Brazil. Full EXIF is preserved on the image file.

Any tips on how to improve that in any way? I'd appreciate it.

Minor post-processing in Photoshop (Levels, Decreased saturation, resized, a little USM'd).

Please comment! Thanks.



Stephan.
 
Why isn't the house spinning? ; )

Which camera? I didn't know that the 300D could expose that long

Looks good. Would be cool to see long exposures with a tracking mount tho
 
Very nice idea indee, maybe try next time F/8 instead of F/5.6 ? It would give you a bit more sharpness, but then I'm not certain it would make any difference. Also you would need to expose 30 min to get the same level of effect.

I have a question for you, since you live in Brazil, here in the north hemisphere, we would use the North Star to make these, centering the lens onto the north star, and the rest of the stars would circle around like you did there. What's the star you use in the south to do the same ? I forgot the name of that star which is close to the true south pole.

Cheers

--
Eric Cote

More photos here too :

http://community.webshots.com/user/drhangar
 
Hi there!

Thanks for the advice... I have tried f/8 but got dark results... in fact even with f/5.6 the picture was very dark, i had to brighten it up on PS, that's why it has all those noise.

In June when it's winter i'll try an 1 hour exposure, hope i can get less noise... Although it's very hard for me to go to this place (this farm belongs to my aunt, actually I live in a big, 1.5 million people city).

As for your other question... I don't know the name of the star we have here, i don't know if there is any star at all! To achieve this alignment, first i used a compass to find the south magnetic pole, then I made a 5-minute exposure to "find" exactly the true south pole, after that I decided to shoot the picture with the camera pointed a bit to the left, to show the house... If you don't show anything but sky on the picture, without horizon and important objects, the picture becomes boring =
Thanks again for the advice!
Stephan
 
Rob,

That's really a good idea... I've seen some people using this technique, would like to use it too, but I don't know how to layer 2 pictures on PS, i'll try to find out how to... It would really make a beautiful final picure!!!!

Stephan
 
Hello, look carefully at your picture, there's a star just to the left of the true south, and I believe its this one. There's a name for that star. Same applied for us, the North Star is not actually at the true north pole, I think its about 57 arc min off it , but this always changes since the earth axis slightly changes. Also the earth axis actually wobbles, but its very minuscule and with a wide angle lens like yours it will not show.

I think you're on the right track, maybe longer exposure, F/8, then remove the noise, increase contrast, so the sky will be more black.

Cheers !
skp said:
Hi there!

Thanks for the advice... I have tried f/8 but got dark results...
in fact even with f/5.6 the picture was very dark, i had to
brighten it up on PS, that's why it has all those noise.

In June when it's winter i'll try an 1 hour exposure, hope i can
get less noise... Although it's very hard for me to go to this
place (this farm belongs to my aunt, actually I live in a big, 1.5
million people city).

As for your other question... I don't know the name of the star we
have here, i don't know if there is any star at all! To achieve
this alignment, first i used a compass to find the south magnetic
pole, then I made a 5-minute exposure to "find" exactly the true
south pole, after that I decided to shoot the picture with the
camera pointed a bit to the left, to show the house... If you don't
show anything but sky on the picture, without horizon and important
objects, the picture becomes boring =
Thanks again for the advice!
Stephan
Click to expand...
--
Eric Cote

More photos here too :

http://community.webshots.com/user/drhangar
 
Eric CAN said:
I have a question for you, since you live in Brazil, here in the
north hemisphere, we would use the North Star to make these,
centering the lens onto the north star, and the rest of the stars
would circle around like you did there. What's the star you use in
the south to do the same ? I forgot the name of that star which is
close to the true south pole.
Click to expand...
My astronomy isn't that great but I think I know a rough method to find the south pole. The distinctive Southern Cross circles the pole and it's long axis roughly points straight towards it. You then measure in about 10 degrees from the bottom cross and you're aiming for the pole.

I HOPE that is close to correct.... nervous

--
Not a Rebel but a DKiss(er)
http://community.webshots.com/user/engyrob
 
Rob Lenghaus said:
Rob Lenghaus said:
I have a question for you, since you live in Brazil, here in the
north hemisphere, we would use the North Star to make these,
centering the lens onto the north star, and the rest of the stars
would circle around like you did there. What's the star you use in
the south to do the same ? I forgot the name of that star which is
close to the true south pole.
Click to expand...
My astronomy isn't that great but I think I know a rough method to
find the south pole. The distinctive Southern Cross circles the
pole and it's long axis roughly points straight towards it. You
then measure in about 10 degrees from the bottom cross and you're
aiming for the pole.

I HOPE that is close to correct.... nervous

--
Not a Rebel but a DKiss(er)
http://community.webshots.com/user/engyrob
Click to expand...
 
Hi Stephan -

That is an excellent shot of star trails. You can remove the hot pixels by taking a dark frame of equivalent exposure and then subtracting it in photoshop. The only catch is that you have to take the dark frame immediately after taking the shot, you cannot go back later and do it.

Incidentally, the 10d and 300d are the first cameras able to do 15min exposures with so little noise and hot pixels. I bought the 300d specifically to do astrophotography - I have yet to see any digital camera that can compare.

Try THAT with your D-70!

--
Don't ask me, I'm NOT an expert!
http://public.fotki.com/digiastro/
http://www.freewebs.com/jjacobson/
 
The nosie removal in the photoshop CS RAW convertor is also good at removing ot pixels as has be shown by other star trail posts.
DigiAstro said:
Hi Stephan -

That is an excellent shot of star trails. You can remove the hot
pixels by taking a dark frame of equivalent exposure and then
subtracting it in photoshop. The only catch is that you have to
take the dark frame immediately after taking the shot, you cannot
go back later and do it.

Incidentally, the 10d and 300d are the first cameras able to do
15min exposures with so little noise and hot pixels. I bought the
300d specifically to do astrophotography - I have yet to see any
digital camera that can compare.

Try THAT with your D-70!

--
Don't ask me, I'm NOT an expert!
http://public.fotki.com/digiastro/
http://www.freewebs.com/jjacobson/
Click to expand...
 
Rob Lenghaus said:
That looks really good.

It just occured to me that you could possibly layer many 15min (or
5min or whatever) exposures to get REALY long trails without so
many hot pixels???
Click to expand...
There is a recent Sky and Telescope article that discusses doing just that. It was a 2004 issue but I'm at work and can't recall which one. A search at Sky and Telescopes web site didn't find it as they seem to be a few issues behind. If you're interested let me know and I'll search for it tonight when I get home..

--
© Steve Mattan
http://www.stevem.smugmug.com
 
Nice work!
Congrats!
skp said:
Hello all!

I shot this one 2 days ago, on a very isolated farm, the sky was
very dark and you could see A LOT of stars! So i felt like sharing
:-)

Almost 15 minute exposure (actually, it's 14 minute, 20 seconds)...
Sorry for the hot pixels, couldn't help on that, it was very hot
(90F)... I'll try that again in southern hemisphere winter!

For those who are interested: this was shot in the countryside of
the city of Panambi, State of Rio Grande do Sul, Brazil. Full EXIF
is preserved on the image file.

Any tips on how to improve that in any way? I'd appreciate it.
Minor post-processing in Photoshop (Levels, Decreased saturation,
resized, a little USM'd).

Please comment! Thanks.



Stephan.
Click to expand...
 
Eric CAN said:
Very nice idea indee, maybe try next time F/8 instead of F/5.6 ? It
would give you a bit more sharpness, but then I'm not certain it
would make any difference. Also you would need to expose 30 min to
get the same level of effect.

I have a question for you, since you live in Brazil, here in the
north hemisphere, we would use the North Star to make these,
centering the lens onto the north star, and the rest of the stars
would circle around like you did there. What's the star you use in
the south to do the same ? I forgot the name of that star which is
close to the true south pole.

Cheers

--
Eric Cote

More photos here too :

http://community.webshots.com/user/drhangar
Click to expand...
--
Clicker
 
The dark frame subtraction method is so easy to do that it seems churlish to look any further for a remedy for hot pixels and other sensor noise. It also has the advantage that it's a specific fix for that problem, rather than a generic noise reduction technique (which might compromise other aspects of the image, including removing faint stars - not what you want to do here!).

DB
Kallus said:
DigiAstro said:
Hi Stephan -

That is an excellent shot of star trails. You can remove the hot
pixels by taking a dark frame of equivalent exposure and then
subtracting it in photoshop. The only catch is that you have to
take the dark frame immediately after taking the shot, you cannot
go back later and do it.

Incidentally, the 10d and 300d are the first cameras able to do
15min exposures with so little noise and hot pixels. I bought the
300d specifically to do astrophotography - I have yet to see any
digital camera that can compare.

Try THAT with your D-70!

--
Don't ask me, I'm NOT an expert!
http://public.fotki.com/digiastro/
http://www.freewebs.com/jjacobson/
Click to expand...
Click to expand...
--
DB
 
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