My first star trail shot came out doubled?

RollsUp · 10-28-2009, 12:59 PM

Not a very interesting image I know, I'm still learning. I'm just wondering how this would have happened. It was a calm night, taken with my K20D, 16-45 @ 24mm w/o a filter, f5.6, 2678 sec. on a cheap tripod placed on my porch. I would understand if the tripod or camera had moved but wouldn't the eave with icicles be doubled too if one or both had moved? Plus there are a few star trails showing up under the eave too.

Thoughts?

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little laker · 10-28-2009, 01:24 PM

I'm wondering if you had any insects moving about.
I would imagine that if some of them glowed like fireflies they may cause those effects on the photo, and you may not notice them.

RollsUp · 10-28-2009, 01:33 PM

I've never seen any type of glowing bugs in my area. Besides the temp was too low for any sane bugs to be flying around in, 28 F (-2 C).

libbyh · 10-28-2009, 01:41 PM

Hmm... my first inclination would have been that the tripod had moved - and the blurred roofline to the side would seem to corroborate this, but that wouldn't explain why the star trails seemed to shif they way they did.

The only conclusion I can come to is that somehow the focal length was changed. Ie. he lens was somehow zoomed to only capture the sky and not anything else and thereby changing the pereived path of star trails.

Might I suggest trying to compose a similar shot but with a visual landscape? Shots of star trails tend to have much more visual impact when put in context with its surroundings and it'll also identify any areas of technique which need to be refined.

**Mallee Boy** · 10-28-2009, 02:59 PM

I'm with libbyh here. Something has moved. Dog or cat brushed against tripod? Maybe the tripod itself....a leg not tight, or centre post....or lens creep? Dont know if thats possible with the 16-45.

You'll just have to go and try it again.

pxpaulx · 10-28-2009, 03:06 PM

Originally posted by Mallee Boy

I'm with libbyh here. Something has moved. Dog or cat brushed against tripod? Maybe the tripod itself....a leg not tight, or centre post....or lens creep? Dont know if thats possible with the 16-45.

You'll just have to go and try it again.

I would bet on the tripod itself, probably a leg - especially at those temperatures. If the tripod just came from a warmer temp, the metal getting cold could cause it to contract possibly? The fact that there are not 2 rooflines just means it was not in the initial framing (or was, then wasn't). That is about the best guess I could give you!

Arpe · 10-28-2009, 04:43 PM

Looks like you forgot to wind the film on!

That's a weird one.

**Pål Jensen** · 10-28-2009, 04:48 PM

You can see startrails in front of the building. Theres only two posibilities: the stars are closer to you than the building or the camera/tripod has moved...

RawheaD · 10-28-2009, 04:54 PM

I bet that the lens changed focal lengths during exposure. You had the lens pointed up. You probably started off with a higher zoom. Then, the weight of the lens pushed it down. Looks like it happened more than once. Was the edge of the roof originally in your frame? Why did you choose 24mm? Wasn't it because you wanted to keep the roof out of your frame? Then, during exposure, it probably crept down to 16mm, maybe stopping around 20mm for a while :-)

Jerry Thirsty · 10-28-2009, 05:25 PM

If it were zoom creep the second set of arcs would still be concentric with the first, and you'd probably have radial lines or ramps joining them. I would say the camera/support moved and quite quickly too.

If you look at the bright white and blue short trails that are almost horizontal in the upper right, you will see they are the same stars that form the white and blue arcs below them near the bottom. And the three bright short blue arcs in the upper half to the left of center match the blue stars at the bottom as well.

kittykat46 · 10-28-2009, 07:57 PM

The clue is right there in the photo.
Most of the star trails align around one single point - that would be the North Pole.
There are other trails which are aligned in a totally different direction.

Sometime during the exposure the camera likely moved.
Try a more solid tripod in future, and make sure its footing is grounded properly.

aerodave · 10-28-2009, 08:36 PM

Originally posted by Jerry Thirsty

If it were zoom creep the second set of arcs would still be concentric with the first

Not true. If the center of rotation (Polaris) isn't in the center of the frame, it will move to a different part of the frame when the zoom changes, or maybe even out of the frame entirely. If it's near the top when zoomed out, it could disappear from the frame altogether when zoomed in. And then you'd end up with two sets of trails, each with a different center point. That's pretty much exactly what it looks like is going on in this picture

Notice that three critical points—the center of the frame and the apparent center of rotation of each of the two sets of star trails—lie in a single line. That's just what would happen if you changed the lens focal length without changing the position of the camera. If that change in zoom happens rapidly enough, there would be not connection between stars (the radial ramps you're talking about).

The lack of a double image in the roof just means it only showed up in the wider half of the exposure, and the longer-focal-length portion didn't have the roof in the frame.

So the question is: what woudl have changed the zoom setting of the lens? Sudden, and quick zoom creep seems unlikely. Maybe someone did it accidentally. Polar bear?

If I get bored, I can try to figure out what the angle of view (and thus the focal length) for each of the two apparent zoom settings is. I don't know what that would tell us, but it would be interesting.

captmacq · 10-28-2009, 09:17 PM

i think your all right looks like zoom creep and a bump. looks like to many stars within the early rings

aerodave · 10-28-2009, 09:20 PM

Now that I've investigated it more closely, I'm convinced it's not a case of changing zoom. It was definitely shifted down partway through the exposure quickly, all at once, and by about 20 degrees. How do I know this?

I took the liberty of identifying a couple recognizable constellations: the Big Dipper and Little Dipper, and showing them in the attachments. The first picture has a black line that "connects the dots" and forms the Little Dipper, with the end of the handle at Polaris. The connected points are the ends of each star's respective trail. Notice that these are bright stars sharing a common center of curvature...all belonging to the same half of the exposure, which I will call "Exposure A".

The second picture shows the same thing, connecting bright stars in Exposure B to show the Big Dipper. Note that it appears in the same part of the frame and actually overlaps the Little Dipper, which doesn't happen in reality. It also has a different center of curvature, so you know it was a different part of the exposure after the camera moved. At the time the picture was taken (based on EXIF data in the original picture) the Big Dipper would have been below (toward the horizon) Polaris by about 20 degrees. Therefore, that's how far the camera moved on the tripod. I know it was moved suddenly instead of gradually because there are no streaks connecting the two sets of trails.

Besides moving by itself, there is one other possibility... (No, not polar bears again!) Maybe the camera was set to do multiple exposures, and the OP tried to take two separate images but actually took one double exposure pointed at slightly different parts of the sky.

As a bonus, in the Little Dipper picture, I drew a line showing two stars that are 15 degrees apart in the sky. Using that line as a scale for the whole frame, I concluded that the diagonal field of view of the frame is about 59 degrees. This angle of view corresponds to a focal length of about 25mm on an APS-C sensor, which validates the OP's description of his shooting setup. Exposure B, where the Big Dipper is in the middle of the frame, appears to be at the same zoom setting as Exposure A. Notice the the white and blue stars at the end of the bowl of the Big Dipper (the pointer stars, Dubhe and Merak, for you astronomy buffs). They appear twice in the image: once where I have marked them in green for Exposure B, and they also appear the same distance apart at the bottom right of the frame as part of Exposure A. I know those stars at the bottom are the same because they clearly belong to Exposure A, as does Polaris, and they're in the right place relative to the Little Dipper. Since they're the same distance apart in both halves of the exposure, you can safely say the zoom ring didn't move.

pcarfan · 10-29-2009, 06:06 AM

This is irrefutable evidence of these pesky Martians travelling the universe in their star ships ...it's all a conspiracy, I tell ya!.....

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10-28-2009, 01:24 PM	#2
little laker Veteran Member Join Date: Sep 2006 Photos: Gallery Posts: 5,697	I'm wondering if you had any insects moving about. I would imagine that if some of them glowed like fireflies they may cause those effects on the photo, and you may not notice them.

10-28-2009, 01:33 PM	#3
RollsUp Veteran Member Join Date: Apr 2008 Location: AK USA Photos: Gallery Posts: 1,766 Original Poster	I've never seen any type of glowing bugs in my area. Besides the temp was too low for any sane bugs to be flying around in, 28 F (-2 C).

10-28-2009, 01:41 PM	#4
libbyh Inactive Account Join Date: Oct 2008 Location: Rochester, NY Photos: Gallery \| Albums Posts: 119	Hmm... my first inclination would have been that the tripod had moved - and the blurred roofline to the side would seem to corroborate this, but that wouldn't explain why the star trails seemed to shif they way they did. The only conclusion I can come to is that somehow the focal length was changed. Ie. he lens was somehow zoomed to only capture the sky and not anything else and thereby changing the pereived path of star trails. Might I suggest trying to compose a similar shot but with a visual landscape? Shots of star trails tend to have much more visual impact when put in context with its surroundings and it'll also identify any areas of technique which need to be refined.

10-28-2009, 02:59 PM	#5
Mallee Boy Site Supporter Join Date: Sep 2006 Location: South Australia Photos: Gallery \| Albums Posts: 3,904	I'm with libbyh here. Something has moved. Dog or cat brushed against tripod? Maybe the tripod itself....a leg not tight, or centre post....or lens creep? Dont know if thats possible with the 16-45. You'll just have to go and try it again.

10-28-2009, 03:06 PM	#6
pxpaulx Veteran Member Join Date: May 2009 Location: Twin Cities, MN Posts: 2,867	Originally posted by Mallee Boy I'm with libbyh here. Something has moved. Dog or cat brushed against tripod? Maybe the tripod itself....a leg not tight, or centre post....or lens creep? Dont know if thats possible with the 16-45. You'll just have to go and try it again. I would bet on the tripod itself, probably a leg - especially at those temperatures. If the tripod just came from a warmer temp, the metal getting cold could cause it to contract possibly? The fact that there are not 2 rooflines just means it was not in the initial framing (or was, then wasn't). That is about the best guess I could give you!

10-28-2009, 04:43 PM	#7
Arpe Pentaxian Join Date: Sep 2006 Location: New Zealand Photos: Gallery \| Albums Posts: 4,452	Looks like you forgot to wind the film on! That's a weird one.

10-28-2009, 04:48 PM	#8
Pål Jensen Site Supporter Join Date: Dec 2007 Location: Norway Photos: Albums Posts: 4,371	You can see startrails in front of the building. Theres only two posibilities: the stars are closer to you than the building or the camera/tripod has moved...

10-28-2009, 04:54 PM	#9
RawheaD Veteran Member Join Date: Dec 2008 Location: MA, USA Photos: Gallery Posts: 831	I bet that the lens changed focal lengths during exposure. You had the lens pointed up. You probably started off with a higher zoom. Then, the weight of the lens pushed it down. Looks like it happened more than once. Was the edge of the roof originally in your frame? Why did you choose 24mm? Wasn't it because you wanted to keep the roof out of your frame? Then, during exposure, it probably crept down to 16mm, maybe stopping around 20mm for a while :-)

10-28-2009, 05:25 PM	#10
Jerry Thirsty Forum Member Join Date: Sep 2007 Location: Bronson, Missouri Posts: 72	If it were zoom creep the second set of arcs would still be concentric with the first, and you'd probably have radial lines or ramps joining them. I would say the camera/support moved and quite quickly too. If you look at the bright white and blue short trails that are almost horizontal in the upper right, you will see they are the same stars that form the white and blue arcs below them near the bottom. And the three bright short blue arcs in the upper half to the left of center match the blue stars at the bottom as well.

10-28-2009, 07:57 PM	#11
kittykat46 Veteran Member Join Date: Dec 2007 Posts: 923	The clue is right there in the photo. Most of the star trails align around one single point - that would be the North Pole. There are other trails which are aligned in a totally different direction. Sometime during the exposure the camera likely moved. Try a more solid tripod in future, and make sure its footing is grounded properly.

10-28-2009, 08:36 PM	#12
aerodave Veteran Member Join Date: Aug 2007 Location: Dayton, OH Posts: 365	Originally posted by Jerry Thirsty If it were zoom creep the second set of arcs would still be concentric with the first Not true. If the center of rotation (Polaris) isn't in the center of the frame, it will move to a different part of the frame when the zoom changes, or maybe even out of the frame entirely. If it's near the top when zoomed out, it could disappear from the frame altogether when zoomed in. And then you'd end up with two sets of trails, each with a different center point. That's pretty much exactly what it looks like is going on in this picture Notice that three critical points—the center of the frame and the apparent center of rotation of each of the two sets of star trails—lie in a single line. That's just what would happen if you changed the lens focal length without changing the position of the camera. If that change in zoom happens rapidly enough, there would be not connection between stars (the radial ramps you're talking about). The lack of a double image in the roof just means it only showed up in the wider half of the exposure, and the longer-focal-length portion didn't have the roof in the frame. So the question is: what woudl have changed the zoom setting of the lens? Sudden, and quick zoom creep seems unlikely. Maybe someone did it accidentally. Polar bear? If I get bored, I can try to figure out what the angle of view (and thus the focal length) for each of the two apparent zoom settings is. I don't know what that would tell us, but it would be interesting.

10-28-2009, 09:17 PM	#13
captmacq Senior Member Join Date: Jul 2009 Location: fort worth tx Photos: Gallery Posts: 107	i think your all right looks like zoom creep and a bump. looks like to many stars within the early rings

10-29-2009, 06:06 AM	#15
pcarfan Veteran Member Join Date: Sep 2007 Location: Dayton, Ohio Photos: Gallery \| Albums Posts: 2,978	This is irrefutable evidence of these pesky Martians travelling the universe in their star ships ...it's all a conspiracy, I tell ya!.....