Star Trail Help

Prasham

Armchair Traveller :(
Another problem I am facing is about focusing. The CHDK is activated without switching on the sensor or lens. Once I key in all the desired values, I have to push the click button and the camera comes to life. Initially its in the wide angle position and the shutter speed, ISO, aperture etc are punched in beforehand. It just starts clicking images as set in CHDK and doesn't let me zoom or focus. Hence I believe that if I add some object in the foreground (like in most start trail shots) the camera might focus on it instead of the stars :( Any suggestion?

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I've shot 50 pics of 32 secs shutter speed with F/3.4 & ISO 200. I will stack them tomorrow and post here. I believe it will be better than what I shot yesterday.

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Here's the stacked pic....

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This pic is better compared to the last one and hence I understand that I should increase shutter speed further and try again. BTW coincidentally I composed this image with polaris in mind and it seems i wasn't too far. A little more towards north and I just might get lucky.

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Some good news... I had posted about Dark Frame Removal in CHDK forum for my camera. There is a option to shut it down. I'll take a few shots after shutting off the Dark Frame and see if it works that way.
 

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Prasham

Armchair Traveller :(
Finally I've been able to capture decent star trails in my P&S with help of the experts here. Thank you. A better composed pic will be uploaded in a few days.

@ Hensil: I had the Long Exposure Dark Frame option cancelled while taking the below pic and have not added a dark frame of same shutter speed. Will adding 1 dark frame decrease the noise in the pic?
 

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hensil

Guru
Does the position of stars change every day? Say for example if I shoot few shots of 1 min every day at same time & keeping the tripod in the same position, will I get a continuous star trail?
Prasham,
I hope you are not pulling our legs.:) Its not the stars that are moving but the earth that is revolving. And honestly I did not understand your question.
Henry

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Finally I've been able to capture decent star trails in my P&S with help of the experts here. Thank you. A better composed pic will be uploaded in a few days.

@ Hensil: I had the Long Exposure Dark Frame option cancelled while taking the below pic and have not added a dark frame of same shutter speed. Will adding 1 dark frame decrease the noise in the pic?
My compliments! This is a good picture for any camera and for p&S it is excellent.
I'd say just forget the dark frame and shoot the way you are doing, try good composition. Anyway, let me explain the concept of dark frame. The single black frame has be of the same setting as your all other timelapse frames. That means no sort of auto exposure, all manual mode. Now the software will subtract each of the frame shot in timelapse from this black frame. The idea is, when the sensor is exposed for a longer duration it generates heat. This heat causes noise/distortion in the image that is so much that the pictures becomes useless. To eliminates this heat noise the camera records immediately a black frame exactly of the same duration and settings. This cause the same distortion in the black frame. Then the camera combines the two files and mathematically subtract the distortion giving a much cleaner picture.
If you are shooting 50 long exposure in timelapse of the same settings, then instead of recording black and subtracting after each frame you shoot without the black frame and then in the end just shoot one black frame and let the software do the subtraction. I guess this software is not free.
Henry
 

zack2137

Leh'd and how!
Congrats Prasham. I haven't yet gone through the thread in detail, but in city lights with a P&S, this is excellent learning!
 

vinay_sinha

Active Member
Tried out star trails for the first time yesterday night. The results are not that satisfactory though I did get the trails. One thing I remember having forgotten is to switch off the IS. The aperture was 2.8, ISO 800. Seeking advice for improvement :)

Exposure 2.jpg


Exposure 6.jpg


The first image has been created by stacking 10 shots, shutter 4 sec
Second image by stacking 100 shots, shutter 2 sec
 

Chetan Kulkarni

Super User
I think you have got an excellent set of images for a first try.What I would suggest is to do two things:
1) Make sure the Polaris is a part of the frame so that you get the entire circular trails in your image. The starting part of this thread has some notes about finding the Polaris.
2) Most important part is to get something in the foreground. The star trails should be a part of the image but you need to have a subject which grabs your attention. See if you can compose the images accordingly.
 

hensil

Guru
The pic. is very good for the first try. As Chetan said you need better composition, you have nailed the exposure. Try some more.
Henry
 

zack2137

Leh'd and how!
The quality is nice but the composition, not so much. Tanveer once suggested an easy trick to locate the Pole Star. On the big dipper (the one that looks like the spoon), the pole star is the brightest star right above the last two stars on the spoon part.

Finding the Pole Star
 
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