I've been gone a while but wondered if anyone could tell me why the star trails are blue? I was at a recently night photography class in Las Vegas and had my first experience doing light trails. It was lots of fun but I can see I have still a lot to learn. I miss all my friends here and hope all are well
@mikegifford 20. It's my first attempt. I can hardly wait to try it here with the lighthouse and more images...perhaps longer in each capture too. It was really hot there so we kept it to 2 min exposures. I bet I can do 3 min here when the clouds pass and we have stars visible again.
Fabulous Jane! Especially as a first attempt. It looks fantastic. Well done! I'm sure Alexis @abirkill would be able to answer your questions. Coincidentally he has posted a stunner today. http://365project.org/abirkill/365/2014-09-17
Beautiful shot, Jane! I really like the light trails to really show the depth in the foreground landscape, too!
I think there are a couple of reasons why the star trails are blue in this shot. The first one is to do with the white balance of the photo. I'm not sure if you shot on automatic white balance, chose a manual white balance in camera, or tweaked the white balance when processing the raw file(s). However, I suspect that the white balance for this shot was relatively low, probably around 4000 Kelvin, or if set on the camera, a setting such as tungsten or fluorescent.
This is a very cool white balance -- it will correct the warm white light of a tungsten (standard) light bulb so that it looks pure white, rather than warm-white, but for objects that are already cool-white, it will push them further into the blue end of the spectrum.
Bear in mind that, if you are shooting with automatic white balance, you'll get a pretty random result that may or may not be what you want. Automatic white balance sensors, like autofocus sensors, are only rated to work down to a certain light level, which is much higher than you get on a starry night. While the autofocus not working correctly is immediately obvious (the camera doesn't focus!), the auto white balance not working is a lot less apparent -- you just end up with a shot that might not have an accurate white balance value, no warning is given.
You can correct this by either setting a manual white balance in the camera, or by altering the white balance when editing the raw file. However, even here there's no real correct answer -- the white balance should be set to match the temperature of the light hitting the camera, but the light hitting the camera here is from stars of all sizes and temperatures -- you will have some red giant stars with a temperature of around 3600 Kelvin, and some main sequence (dwarf) stars that have temperatures of upwards of 50,000 Kelvin! Both of these settings can be correct, but obviously you can't use both in the same shot!
If you are looking for 'accurate' colours, about the best you can do is calibrate the shot so that the white balance matches that of the Sun. While the Sun isn't visible, it's still what we, as humans, are most familiar with, so this will give a shot that most accurately reflects the scene as our eyes would see it. To do this, you would set a daylight white balance setting of around 5500 Kelvin, either in the camera or when processing the raw file.
However, be aware that this will end up with quite a dull, brown/grey sky. If you strive accuracy then you may like this, but personally I prefer the sky to appear more towards the blue end of the spectrum in my shots. It's all really to do with how you want to portray the final shot, as the artist responsible. Certainly you may wish to try a daylight white balance, but don't feel that you need to stay there -- experiment with what works best for the shot in question.
The second reason why the stars will appear blue is something that I touched upon above -- stars have a wide range of temperatures and apparent colours! Our eyes do not have great colour sensitivity in low light situations -- the rods, the bit responsible for vision in low light, are not colour-sensitive. Cameras, on the other hand, have no such limitations -- they can see colours just as well in the dark as they can in mid-day, provided the exposure is correct. This is why aurora shots look so colourful on the camera compared to when seen with the eye -- the colour is there, the eye just doesn't see it as strongly. The same applies with star photos -- the camera will pick up the various colours of the stars that your eyes just see as 'white'.
While the colour of the sky between the stars suggests that the white balance is mostly responsible for the blue tint in this shot, even when you use a daylight white balance, bringing the sky to a more neutral colour, although the stars will get a lot whiter, you will still see more blue-white stars than you will yellow-white stars. This is because, although the Sun is about average for a star's temperature, really hot dwarf stars emit much more light, so tend to show up from further away.
I hope that gives some tips, let me know if you have any questions!
@abirkill Alexis, you are so kind to explain this all to me. And I like the low Kelvin look for everything else so I will leave it as is. I peak at your album every once in a while and am almost without exception blown away both by your shots and by your generosity in sharing how you got them. What an asset to the world you are
Beautiful shot, Jane! I really like the light trails to really show the depth in the foreground landscape, too!
I think there are a couple of reasons why the star trails are blue in this shot. The first one is to do with the white balance of the photo. I'm not sure if you shot on automatic white balance, chose a manual white balance in camera, or tweaked the white balance when processing the raw file(s). However, I suspect that the white balance for this shot was relatively low, probably around 4000 Kelvin, or if set on the camera, a setting such as tungsten or fluorescent.
This is a very cool white balance -- it will correct the warm white light of a tungsten (standard) light bulb so that it looks pure white, rather than warm-white, but for objects that are already cool-white, it will push them further into the blue end of the spectrum.
Bear in mind that, if you are shooting with automatic white balance, you'll get a pretty random result that may or may not be what you want. Automatic white balance sensors, like autofocus sensors, are only rated to work down to a certain light level, which is much higher than you get on a starry night. While the autofocus not working correctly is immediately obvious (the camera doesn't focus!), the auto white balance not working is a lot less apparent -- you just end up with a shot that might not have an accurate white balance value, no warning is given.
You can correct this by either setting a manual white balance in the camera, or by altering the white balance when editing the raw file. However, even here there's no real correct answer -- the white balance should be set to match the temperature of the light hitting the camera, but the light hitting the camera here is from stars of all sizes and temperatures -- you will have some red giant stars with a temperature of around 3600 Kelvin, and some main sequence (dwarf) stars that have temperatures of upwards of 50,000 Kelvin! Both of these settings can be correct, but obviously you can't use both in the same shot!
If you are looking for 'accurate' colours, about the best you can do is calibrate the shot so that the white balance matches that of the Sun. While the Sun isn't visible, it's still what we, as humans, are most familiar with, so this will give a shot that most accurately reflects the scene as our eyes would see it. To do this, you would set a daylight white balance setting of around 5500 Kelvin, either in the camera or when processing the raw file.
However, be aware that this will end up with quite a dull, brown/grey sky. If you strive accuracy then you may like this, but personally I prefer the sky to appear more towards the blue end of the spectrum in my shots. It's all really to do with how you want to portray the final shot, as the artist responsible. Certainly you may wish to try a daylight white balance, but don't feel that you need to stay there -- experiment with what works best for the shot in question.
The second reason why the stars will appear blue is something that I touched upon above -- stars have a wide range of temperatures and apparent colours! Our eyes do not have great colour sensitivity in low light situations -- the rods, the bit responsible for vision in low light, are not colour-sensitive. Cameras, on the other hand, have no such limitations -- they can see colours just as well in the dark as they can in mid-day, provided the exposure is correct. This is why aurora shots look so colourful on the camera compared to when seen with the eye -- the colour is there, the eye just doesn't see it as strongly. The same applies with star photos -- the camera will pick up the various colours of the stars that your eyes just see as 'white'.
While the colour of the sky between the stars suggests that the white balance is mostly responsible for the blue tint in this shot, even when you use a daylight white balance, bringing the sky to a more neutral colour, although the stars will get a lot whiter, you will still see more blue-white stars than you will yellow-white stars. This is because, although the Sun is about average for a star's temperature, really hot dwarf stars emit much more light, so tend to show up from further away.
I hope that gives some tips, let me know if you have any questions!