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Old 28-05-2014, 08:48 PM
malau (David)
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Star trail sometimes when expose longer than 30 sec with telescope

Hi all,

I have an unmod 600d, skywatcher BKP 150 (or something) f/5, EQ3-2 mount, orion driver motor which set to 2x speed.

I use DSLR method to do the polar alignment and just wonder why when I taking some photos which expose longer than 30 sec (sometimes is shorter) it has star trail? It doesnt happen to all photos but random.

Will that be either my scope is not balance correctly or the wind as I do it in balcony... or what else can it be? I will try to upload some sample photo later....

p.s. the star trail not very long when zoom to 100%
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Old 29-05-2014, 10:05 AM
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cometcatcher (Kevin)
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I recognise that. It's the Leo triplet!

Why are you using 2 x speed?
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Old 29-05-2014, 01:29 PM
malau (David)
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Quote:
Originally Posted by cometcatcher View Post
I recognise that. It's the Leo triplet!

Why are you using 2 x speed?
LOL yes. It's the Leo triplet.

I think I misunderstand the orion manual. the 2x,4x,8x speed is for tuning to the right position.....

I found out Orion may ran out battery last night but still small star trail (not as long as this example and is straight) appears randomly....
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Old 29-05-2014, 02:30 PM
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cometcatcher (Kevin)
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Yes, 2x and greater is only for corrections.

Most mounts don't track perfectly and will trail sooner or later. An EQ3, well you would be lucky to get 30 seconds without corrections. To stop the trailing you will need a guiding system, a guidescope with a camera and software, a stand alone guider like the Synguider, or a guidescope with illuminated reticle eyepiece and guide manually with your eye.
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Old 29-05-2014, 04:01 PM
malau (David)
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Quote:
Originally Posted by cometcatcher View Post
Yes, 2x and greater is only for corrections.

Most mounts don't track perfectly and will trail sooner or later. An EQ3, well you would be lucky to get 30 seconds without corrections. To stop the trailing you will need a guiding system, a guidescope with a camera and software, a stand alone guider like the Synguider, or a guidescope with illuminated reticle eyepiece and guide manually with your eye.
Cool thanks. Atm I normally do 15 sec or so without trailing.. the reason why I asked is I saw other people can do e.g. 5mins but I may forget they may have guidescope..etc so I thought I can do the same
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Old 29-05-2014, 06:39 PM
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That's actually a bit odd.
Usually star trails are as bright as the initial star - these are feinter
The are 2 stars in every trail instead of one at the start of the trail (which should be indistinguishable from the trail.
It looks to me like the mount is moving quickly from one position to the next thus the feint trailing, then staying put before moving again - thus the 2 bright stars.
And the trail off is longer than the distance between the double star images.
Am I seeing things that aren't there?
Can anyone else comment on this please?
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Old 29-05-2014, 07:24 PM
malau (David)
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Quote:
Originally Posted by Regulus View Post
That's actually a bit odd.
Usually star trails are as bright as the initial star - these are feinter
The are 2 stars in every trail instead of one at the start of the trail (which should be indistinguishable from the trail.
It looks to me like the mount is moving quickly from one position to the next thus the feint trailing, then staying put before moving again - thus the 2 bright stars.
And the trail off is longer than the distance between the double star images.
Am I seeing things that aren't there?
Can anyone else comment on this please?
Thanks for the reply. After I posted this last night I found that the drive motor light is flashing - battery getting low and not sure if that may caused the issue. However I have a straight light line of trail (short one) sometimes if expose more than 30 sec... see if there is a chance I take some sample tonight if can get a break from the cloud...
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Old 29-05-2014, 10:43 PM
malau (David)
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Here is what I tried tonight with 30 sec... most of the pics look like this
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Old 30-05-2014, 11:47 AM
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Quote:
Originally Posted by Regulus View Post
Can anyone else comment on this please?
Drive errors, flex and wobbly mounts don't always make for straight lines.
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Old 30-05-2014, 12:57 PM
malau (David)
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Originally Posted by cometcatcher View Post
Drive errors, flex and wobbly mounts don't always make for straight lines.
Thanks. Which means I have to send it to repair?
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Old 30-05-2014, 11:05 PM
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Which means I have to send it to repair?
Nope. It's all perfectly normal for a light duty mount loaded heavily.
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Old 31-05-2014, 12:31 AM
malau (David)
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Originally Posted by cometcatcher View Post
Nope. It's all perfectly normal for a light duty mount loaded heavily.
*Phew*... good to hear.

Really thanks for the comment everyone. I am practicing everynight when weather is permitted.

I reseated the drive motor tonight and seems a bit better... managed to get some photos which is 45 sec.. but I mainly make it as 25s instead and seems ok.

I guess now I have to back to learn how to PS the pics after DSS.....
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Old 31-05-2014, 10:57 AM
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Remember to expose only long enough so the stars don't show trails, even if that's only 10 or 15 seconds. You can't do much with trailed frames.
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Old 01-06-2014, 10:15 PM
malau (David)
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Thanks for everyone their contribution.

I also did some google search after you guys comment and I found that my EQ3-2 mount has periodic error (or something like that) so it will never be perfect. I may stick with as long as I can expose without trail (probably around 30sec I guess) however consider if I need many hrs worth of pics will be a PITA
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