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DPChallenge Forums >> Tips, Tricks, and Q&A >> Star Stacking Legal?
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12/08/2008 02:15:14 AM · #1
According to the Advanced Editing rules...

You May:
"combine up to the allowable number of captures (1-10) either in-camera or in post-processing."

Does this mean I can take, say, 10 6-minute exposures and combine them in post to create an hour long star trail image?

The only thing in the rules that throws me off is...

You May NOT:

"combine captures of different scenes, move or change a feature between frames, or combine different captures to create a new scene."

It's the whole "move or change a feature between frames" that gets me. The Earth is rotating, thus the stars move between frames. However, since I'm not moving them myself and it's "natural subject motion" doesn't that make it okay? Or, am I falling into the rules set of the old Time Lapse challenges?

Someone who brackets exposures for an HDR of an ocean scene will have water moving from frame to frame, but that has always been legal. How would stars be any different, right?

Any thoughts?

Message edited by author 2008-12-08 02:17:32.
12/08/2008 02:19:14 AM · #2
42
12/08/2008 02:55:58 AM · #3
I don't have an answer but why not just take one 60 minute shot?
12/08/2008 03:13:23 AM · #4
Originally posted by bobonacus:

I don't have an answer but why not just take one 60 minute shot?


I agree
12/08/2008 03:21:24 AM · #5
Originally posted by bobonacus:

I don't have an answer but why not just take one 60 minute shot?


Less noise, different exposure, no sensor heat effects etc etc
12/08/2008 03:30:27 AM · #6
Two reasons for stacking:

1) No Noise / No need for Dark Frame Subtraction

2) Stacking images preserves the dynamic range of the scene, allowing for more freedom in regards to location. Star trail stacking allows me to shoot (almost) anywhere as long as the skies are clear. By shooting a long 60 min. exposure, I have to be in a really dark place. However, if i stack my images, I can create star trails that are just as long BUT preserve the dynamic range of the scene by not blowing out highlights.

The image below is a star trail image taken facing the Honolulu International Airport. I shot it, I believe at ISO 800 & f/5.6, stacking 56, 30-sec. photos - creating a 28 min star trail. For me to have shot a single exposure, I would've had to shoot at ISO 200, f/22 or ISO 100, f/16 to keep the airport/airplanes from blowing out. Also, the star trails wouldn't have shown up very well.

STRTRLS OVR HNL

Granted, shooting 56 exposures isn't legal for DPC. However, I could've created the same thing by shooting 7, 4-minute exposures at ISO 200 & f/8 (or ISO 100 & f/5.6 if you prefer).

Message edited by author 2008-12-08 03:46:32.
12/11/2008 06:59:30 AM · #7
Bump

Is it legal?
12/11/2008 07:10:02 AM · #8
there was a reply to this yesterday and my reply to Jovan have been deleted as well????
12/11/2008 07:35:21 AM · #9
Originally posted by marbo:

Bump

Is it legal?


I don't believe it's legal.
12/11/2008 07:41:59 AM · #10
Originally posted by Ken:

Originally posted by marbo:

Bump

Is it legal?


I don't believe it's legal.


That would be my interpretation of the rules as well

"create your entry from 1-10 captures of a single scene (defined as a scene whose composition/framing does not change). All captures used must be shot within the challenge submission dates."

If you were taking 10 x 10 minute exposures the scene would change due to the rotation of the earth. It doesn't really seem that different from any time lapse photography where you take 10 fast shots of a subject in different positions. The fact the earth's rotation is slow (relatively!) in comparison to a moving subject is irrelevant

Message edited by author 2008-12-11 07:42:37.
12/11/2008 07:46:56 AM · #11
Originally posted by bobonacus:

there was a reply to this yesterday and my reply to Jovan have been deleted as well????


I guess SC are having a vote on it.

I could do one single exposure but by stacking i can reduce the amount of light pollution.
Will stick to single shot until the result.
12/11/2008 07:53:47 AM · #12
Long exposure is ok
Taking up to 10 images of the same frame without moving the camera is ok
The scene calls for the natural movement of the stars to come in then out of the frame over a certain period of time.
I see no problem with doing what you intend to do. Good Luck.

Tareq
12/11/2008 07:54:59 AM · #13
Originally posted by marbo:

Originally posted by bobonacus:

there was a reply to this yesterday and my reply to Jovan have been deleted as well????


I guess SC are having a vote on it.

I could do one single exposure but by stacking i can reduce the amount of light pollution.
Will stick to single shot until the result.


I've never taken any long exposure star shots so could be way off the mark here but could you just create two exposures from your one raw file and then merge them in layers in photoshop so you have a dark exposure to hide the light pollution and the "correct" exposure for the stars?
12/11/2008 07:58:04 AM · #14
Originally posted by HighNooner:


Taking up to 10 images of the same frame without moving the camera is ok
The scene calls for the natural movement of the stars to come in then out of the frame over a certain period of time.
I see no problem with doing what you intend to do. Good Luck.


but, playing devils advocate, what is the difference between that and shooting 10 exposures of a person who moves around between shots? The stars are moving due to the rotation of the earth, but they are still moving between captures.
12/11/2008 08:02:58 AM · #15
that is exactly my point. Thats why I did what I did. Kirbic said star trails are legal from 10 exposures. So I thought whats the difference if a star or a swan or anything moving
12/11/2008 08:06:36 AM · #16
Originally posted by AlexSaberi:

that is exactly my point. Thats why I did what I did. Kirbic said star trails are legal from 10 exposures. So I thought whats the difference if a star or a swan or anything moving


Yeah, I agree, imho if the stars are legal then the swan would have to be legal too.
12/11/2008 08:10:49 AM · #17
Originally posted by bobonacus:

Originally posted by marbo:

Originally posted by bobonacus:

there was a reply to this yesterday and my reply to Jovan have been deleted as well????


I guess SC are having a vote on it.

I could do one single exposure but by stacking i can reduce the amount of light pollution.
Will stick to single shot until the result.


I've never taken any long exposure star shots so could be way off the mark here but could you just create two exposures from your one raw file and then merge them in layers in photoshop so you have a dark exposure to hide the light pollution and the "correct" exposure for the stars?


That might be possible. I`ve not tried stacking for the trails yet. From what i`ve read the trouble with one long exposure is the sky pollution gets so bright it drowns out the stars.

I
12/11/2008 08:30:19 AM · #18
What I don't understand is that people are allowed to bracket scenes for HDR in which natural subject motion does occur. You can find HDR's where the water, clouds or leaves on trees change from scene to scene but they've always been legal in the past. I don't see how stars moving from frame to frame are any different than clouds moving frame to frame.

Here's how I would classify it as legal. If some elements move from frame to frame during the 10 exposures BUT the scene doesn't looking any different than it would from a long exposure, then it should be legal.

If you took a long exposure of a person walking, then they would be a blur. That's how this is different than the time lapse photographs. Just as clouds, water, leaves, stars, smoke etc. etc. would blur. It should matter if you're stacking or taking a long exposure, the end result is the same. All I'm doing is taking one image, layering over another and changing the blend mode to "Lighten". That's it.
12/11/2008 08:37:10 AM · #19
Originally posted by Jovan:

What I don't understand is that people are allowed to bracket scenes for HDR in which natural subject motion does occur. You can find HDR's where the water, clouds or leaves on trees change from scene to scene but they've always been legal in the past. I don't see how stars moving from frame to frame are any different than clouds moving frame to frame.


I see your point but it is very rare to notice the movement between shots in HDR. In fact photomatix has options to try to stop this "ghosting".

Originally posted by Jovan:

Here's how I would classify it as legal. If some elements move from frame to frame during the 10 exposures BUT the scene doesn't looking any different than it would from a long exposure, then it should be legal.

If you took a long exposure of a person walking, then they would be a blur. That's how this is different than the time lapse photographs. Just as clouds, water, leaves, stars, smoke etc. etc. would blur. It should matter if you're stacking or taking a long exposure, the end result is the same. All I'm doing is taking one image, layering over another and changing the blend mode to "Lighten". That's it.


That sounds like a great addition to the rules and makes perfect sense imho
12/11/2008 09:17:09 AM · #20
Originally posted by bobonacus:

Originally posted by AlexSaberi:

that is exactly my point. Thats why I did what I did. Kirbic said star trails are legal from 10 exposures. So I thought whats the difference if a star or a swan or anything moving


Yeah, I agree, imho if the stars are legal then the swan would have to be legal too.


It's all explained in that other thread guys. Your DQ wasn't because of the stars, it was for the swan. You can't use 9 pictures of stars and 1 of a swan and then stack them together, it's clear as crystal in the rules.

create your entry from 1-10 captures of a single scene (defined as a scene whose composition/framing does not change).
12/11/2008 02:25:23 PM · #21
Originally posted by bobonacus:

Originally posted by AlexSaberi:

that is exactly my point. Thats why I did what I did. Kirbic said star trails are legal from 10 exposures. So I thought whats the difference if a star or a swan or anything moving


Yeah, I agree, imho if the stars are legal then the swan would have to be legal too.


The claim is that the stars movement is a natural one.

check this DQ

' . substr('//images.dpchallenge.com/images_challenge/0-999/796/120/629087.jpg', strrpos('//images.dpchallenge.com/images_challenge/0-999/796/120/629087.jpg', '/') + 1) . '
12/11/2008 02:49:35 PM · #22
Originally posted by marbo:

Bump

Is it legal?

Not the way you describe it. Here's how I interpret this part of the rules:

The key factor in evaluating whether a composite image is "legal" under DPC's Advanced Rules is that any single one of the contributing frames should be essentially identical in composition to the final composite, except for technical aspects such as tone range, DOF, or noise. If any single frame is compositionally different from the final composite it's not legal.

You can stack the star trails, so that you have a noise-reduced image of six-minute star trails, but not combine them together to create a new, sixty-minute trail image -- that would be changing the composition, moving elements around to create multiple iterations, etc. -- specifically forbidden by this rule.

RegiStax
12/11/2008 02:56:02 PM · #23
This is still being discussed. Constructive feedback here can only help to generate a workable outcome to this question.
12/11/2008 03:01:01 PM · #24
Originally posted by GeneralE:

You can stack the star trails, so that you have a noise-reduced image of six-minute star trails, but not combine them together to create a new, sixty-minute trail image -- that would be changing the composition, moving elements around to create multiple iterations, etc. -- specifically forbidden by this rule.

RegiStax


I'll respond to this here because I think that it contains potentially misleading information.

1.) Whether a one-hour star trail shot is made as one exposure or many is irrelevant, as the captured scene will be the same.

2.) One of the express purposes of allowing multiple exposures was for noise reduction, and this is exactly why one would break up a star trail shot, *not* to "move objects."

3.)There is absolutely no way that one can "combine several six-minute trails" as you'd have to "de-rotate" the foreground in each shot, or let it be blurred, which is just the opposite instance of letting the stars "trail," and so would under this interpretation not be legal.

Message edited by author 2008-12-11 15:04:44.
12/11/2008 05:50:59 PM · #25
I don't see how star trails would be much different than clouds, and I know we're allowed some latitude in that.

Personally, I think there should be an exception for these naturally occurring moving objects. It becomes problematic for long exposure shots that you want to stack, and the moving clouds and star trails are the unintended result of combining exposures. But then that opens up the whole can of worms trying to determine the intent of the photographer.

But what do we do then if we take multiple exposures and combining them creates a star trail? Do we clone out the star trail? What if there are hundreds of star trails, essentially creating a background? We'd get into trouble for deleting a background.

A single exposure is possible, but then there are exposure and noise issues. And if we allow a bit of leeway for star trails, how much do we get? Again it a judgment call and SC gets enough heat over this stuff already.
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