Going camping way up high this weekend and hoping to get some star trial shots. Looking for advice on how to find Polaris or what ever planet/star it is to make the circular pattern. I'm shooting with a 20D and have a 10-22, 24-70, 50, & 70-200. Which lens, F stop and aperture would you recommend?
Polaris is easy to find, if you can find the big dipper. the two stars that make the right side of the big dipper point directly up at polaris, when you draw a line directly through the two stars. Polaris is an extremely bright star, and quite obvious if you can spot the big dipper.
Or, just take a couple of exposures on a tripod, and you can move back and forth between them on the LCD and determine where polaris is fairly easily.
I would use the 10-22 at the wide end at around f4, iso 200-400, multiple 3 minute exposures
Here is a method I use which I posted here a while ago.
Things you will need (other than a camera):
1. Tripod
2. Shutter release or a way of pressing and holding the shutter without moving the tripod
3. Hand warmers and a way of wrapping them arround the lens, I use rubber bands. Or something warm to keep dew of the lens if it is humid.
NB dew will completely ruin your shots, I found out the hard way.
4. A fully charged relatively new battery for getting 1hr+use
5. A charged battery for working out composition and getting everything right before starting.
6. More warm clothing than you are likely to need.
7. 2 torches or one reliable one
8. A CLEAR SKY WITH LOW LIGHT POLUTION AND NO MOON
Why multiple exposures?
1. Noise is not proportional to exposure time and is more of an exponential. Combining lots of exposures will result in lower noise levels.
2. Contrast between the stars and the sky decreases as the exposure progresses. whilst the sky gets gradually lighter the stars are moving so they dont get any lighter at all.
3. Flexibility. It might be necessary to get rid of the first or last few shots for varios reasons sometimes passing clouds/ changing light levels at twighlight etc. Also this method allows you to have complete control over light levels of the sky via PS blending modes explained later.
The drawback:
There are miniscule gaps between the trails which must be corrected during post processing.
How do you want it to look?
If you want a dark sky and bright stars do lots of shorter (1-2 minutes) exposures. If you want brighter skies use less but longer exposures. Another thing you have to consider is how big a file you want. I never exceed 20 16-bit layers in one file, it kills my computer!
Technique:
Compose the shot using flash and shorter 30 second exposures on the highest ISO you have at the widest aperture.
Make your tripod as stedy as possible. I usually stamp the legs into the ground
Manually focus on infinity.
Set back to ISO 100-400.
Set the filetype to RAW
Set the aperture to its widest (as long as its not too soft)
Set the shutter to BULB
Double triple check everything, do some practice 5 minute shots, beleive me its worth doing I have skipped this step and payed the price.
Change the battery for the new one.
Start taking shots. (I take shots every 3-5 minutes based on the length of the music track I am listening to!)
Towards the end experiment with lighting the foreground.
Post Processing:
Open all files simultaneously in ACR or Lightroom
Synchonise them.
Alter the white balance (if you dont ACR will use the varying auto white balance settings your camera chose for each shot)
Boost the exposure if necessary
Boost the highlights in the curves dialogue box.
TURN SHARPENING OFF (if you dont do this the gap problem gets worse)
Save in a lossless format
Open all of the exposures in 1 PSD.
Set the blend mode of all of the layers to lighten.
Flatten the layers
Duplicate the layer
Set the blend mode to lighten again
Tranform the layer to fill in the tiny gaps.
Clone out the hundreds of hot pixels (which is more effective but also more time consuming than the black frame method)
Apply adjustment layers.
CarpeyBiggs wrote:
Polaris is easy to find, if you can find the big dipper. the two stars that make the right side of the big dipper point directly up at polaris, when you draw a line directly through the two stars. Polaris is an extremely bright star, and quite obvious if you can spot the big dipper.
Or, just take a couple of exposures on a tripod, and you can move back and forth between them on the LCD and determine where polaris is fairly easily.
Thanks for the wealth of info here also Alex Nail. Will print this out and give it a try.
I do not have Lightroom or ACR and know very little about them. I do have PS CS3. You think I should stay with jpeg or try raw ? At some point I'm going to have to learn layers as I'm struggling with that one also.
Bill, first, If you are going out this weekend, there will still be at least a half moon. It will still be quite bright and will prevent any long esposures of the sky after it has risen. So if you are planning on getting star trails you will need to do your worek before moonrise. you need to factor that into your calculations below. Now, if you want to experiment with longer exposures after the moon has risen for some interesting shots, that is fun too.
As for finding Polaris(north star) try this link. It has links to print out a star wheel/plainisphere. Once you align up the day/date/time, It will show you what is up in the sky, it will also show you how to locate Polaris. S+T Star wheel
AND, if you look to the south west just after sunset, you see a REALLY bright star low on the horizon, that is Venus. Then if you scan east to the south-southeast and see another REALLY bright star a little higher up, that is Jupiter.
As for making a circular star pattern, your 70-200 will not be very useful. Too narrow Field Of View. I would put the 10-22 on and take a look at your FOV and see if that is what you are looking at, next may be the 24-70 and then the 50. I would recommend you set your f-stop on the lens at least 1 to 1 1/2 stops from wide open and set your ISO at 200-400. This will allow for shorter exposures but minimizes noise.
As for trying to get a circular pattern, stars move 15 degrees per hour of time. Use that as your calculation for how long you want your star trails to be.
Also, I have seen several long exposures where the person exposed a series of shots and merged them in photoshop(I think). For example, 10 exposures at 15 minutes gives a total of 150 minutes when stacked. Which is abour 2 1/2 hours or about an arc of star trails of about 37.5 degrees. I cannot remember what the advantage was regarding multiple shorter exposures other than a noise issue.
ANOTHER thing, the longer the exposure, the more skyglow or background light you will get. So depending on how bright the nighttime sky is at your campsite, you may need to shoot a series of 10 minute exposures to limit the skyglow unless you are trying to highlight something on the horizon.
one thing of note. I doubt the users set the camera up for the secondary dark exposure frame. When I have seen the stacked images, there seems to be little or no gap between exposures.
I would recommend doing a search to see what else you can find on astrophotography on this forum.
OH, and have fun camping
...Clear, cold and fun.