Star Trails - Any tips?

M

Morcomm

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Hi, I have attemted to do start trails for some time now, never with any success. I recently bought the Cannon 550d and attempted it again.

I love the 550D and upgraded from the 350D, but the 350D took way better star trails :confused:

30351393706134773375.jpg


That pic is super grainy, and it was shot on a ISO 100 for a 45 minute exposure.

Under the horizon of the shot is a city, so I understand that the conditions were no ideal.

What am I doing wrong?
 
K

koffiejunkie

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When you leave the shutter open for that long, especially in a light-polluted area, you are going to see some ugly stuff on that image. I spent a good deal of time cleaning up shots I took at 30 minutes in the city, and even then it didn't look great.

Another approach is to take a series of 30 second exposures and stack them. You can experiment with the time in between to avoid the sensor getting too hot.

 
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hilton

hilton

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What about driving out of the city for half an hour where there are no lights and redoing your work?
 
AstroTurf

AstroTurf

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I would also try get away from the city lights.

Find a friend with a farm or go to somewhere like rustewinter.
 
C

creeper

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Star trails are not an easy thing to do.

Firstly, get away from any rogue light. The karoo works well.

Now, the details:

A digital camera works with a microchip that captures light. So, if you run it at 45 minutes, it will heat up. The heat causes the noise problem. That is the reason for the noise. Normally, cameras have a Long exposure noise reduction, which essentially takes another photo with the shutter down and subtracts the noise generated from the orginal image. Saying that, the chances of your camera lasting an hour and a half (45 min x 2) is pretty much zero. The other light problems appearing is due to the mirror leaking light from the back of the camera. All SLR's do it, so cover up the eyepiece WITHOUT shaking the camera. Normally, you get a little black thing that slides into place (Nikon normally has it).

To get the twirly effect, point it to the magnetic south.

So, to summarise. Strong battery, no light from any other place.

There is another option. There is some software (called recall the name) that allows you to stitch multiple exposures of stars together to create a startrail
 
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koffiejunkie

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creeper said:
The karoo works well.
Click to expand...

You say it like you can put one in your pocket :)


creeper said:
Normally, cameras have a Long exposure noise reduction, which essentially takes another photo with the shutter down and subtracts the noise generated from the orginal image. Saying that, the chances of your camera lasting an hour and a half (45 min x 2) is pretty much zero. The other light problems appearing is due to the mirror leaking light from the back of the camera.
Click to expand...

Smarter people than me know how to do that in Photoshop. In other words, take a singe exposure with the lens cap on, and use that against your star images.

creeper said:
There is another option. There is some software (called recall the name) that allows you to stitch multiple exposures of stars together to create a startrail
Click to expand...

I know the astro guys love deepskystacker - not sure if it's more geared toward deep space kinda shots and if it's any good for what we're trying here.
 
hilton

hilton

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creeper said:
The other light problems appearing is due to the mirror leaking light from the back of the camera. All SLR's do it, so cover up the eyepiece WITHOUT shaking the camera. Normally, you get a little black thing that slides into place (Nikon normally has it).
Click to expand...

Canon has this on the neck strap.
 
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creeper

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koffiejunkie said:
You say it like you can put one in your pocket :)




Smarter people than me know how to do that in Photoshop. In other words, take a singe exposure with the lens cap on, and use that against your star images.
Click to expand...

The Karoo is only 600km away from Gauteng. If you have a pocket rocket, you'll be there in 4 hours. ;) (Edit, only noticed that you are in the UK), it is still only an additional 8-10 hour flight).

The trick in Photoshop is really easy. Take the camera with the lens cap. Take a photo with the cap on with the same time as the long exposure. Open the orginal image. Create a layer. Add the "cap" image on top. Change the layer to subtract and you have it. Play around with the opacity to get it perfect.
 
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koffiejunkie

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creeper said:
The trick in Photoshop is really easy. Take the camera with the lens cap. Take a photo with the cap on with the same time as the long exposure. Open the orginal image. Create a layer. Add the "cap" image on top. Change the layer to subtract and you have it. Play around with the opacity to get it perfect.
Click to expand...

Thanks, I'll give it a try. Is it necessary for the exposure to be the same length of time? If so, why? Just curious.
 
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creeper

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koffiejunkie said:
Thanks, I'll give it a try. Is it necessary for the exposure to be the same length of time? If so, why? Just curious.
Click to expand...

Try this.

Take a photo with the cap on for 5 minutes. You will see that the photo isn't black, but has some colour. This is due to the heating up of the sensor. Then take another photo for 5 minutes with the cap on. If you compare the photos, you will notice that the "noise" occurs at the similar place. If you subtract the colours, it should create a near black photo. The reason for the time is that if you need to subtract the noise, the noise of the "cap" shot should have the same intensity. The easiest way is by using exact same time that the orginal photo was.

Otherwise, just let the camera do the work for you.

PS. Note that you will always have a bit of noise on a Long Exposure with a DLSR. It is just the way it is.
 
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koffiejunkie

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Thanks creeper, I was assuming the noise is quite random, so that two shots of the same length wil yield different results. I'll try it tonight.
 
Dolby

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I tried for 45 minutes last night and there is too much noise :/

Even playing with PSE doesn't seem to reduce it sufficiently - so I think the best way is stacking. I also don't mind my 28mm 2.8 as sharp as I hoped ... so anything in the forgrouns isn't as sharp as I'd like either

*sigh*
 
bwana

bwana

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Dolby said:
I tried for 45 minutes last night and there is too much noise :/

Even playing with PSE doesn't seem to reduce it sufficiently - so I think the best way is stacking. I also don't mind my 28mm 2.8 as sharp as I hoped ... so anything in the forgrouns isn't as sharp as I'd like either

*sigh*
Click to expand...
Care to try again, in English this time? :p :)
 
Dolby

Dolby

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Oh wow ... Not sure what I was saying ;)

Apart from noise being an issue, the 28mm isn't sharp - so trees or anything in the foreground isn't sharp :/

EDIT : Rather, not as sharp as I hoped when focusing far
 
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