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Desperate for long exposure help! :(


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Hi!

I have been using my 8" Orion Newtonian Astrograph on the Orion Atlas Mount for about a month now for AP purposes, and I'm in a bit of a rut. First, I should say that I love this setup, and I am not a total nube to AP (although clearly hopeless with the following problem). I have been stacking images using deep sky stacker, but have not been getting too much detail out of them. I am told that this is due to my very short subframes. I have only been able to get 30 second subs without trailing with this mount. I know that this mount is capable of far more. Everyone I have asked so far says that I should be able to get 3 minute subs WITHOUT autoguiding. (This is an important point for me, because I do not want to invest in an autoguider until I milk every last drop from this setup as it is first.) So, to summarize, here is my dilemma: I am clueless as to how I can use the Orion Atlas mount with go to SynScan controller to get 3 minute exposures without any star trails. Any tips/instructions?

Thank you so much!

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To use your mount without guiding then you need to get it as accurately polar aligned as possible - because unguided tracking performance is heavily dependant on that. You can achieve accurate alignment using the 'drift align' method with a reticle eyepiece - look it up because it's a long-winded explanation as to how it works and I'm not about to repeat it all here! A better method is to use the QHY Polemaster camera - a gizmo that attaches to your mount and allows you get quickly get within about 30 arcsec of perfect polar alignment. However, that costs money.

ChrisH

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As Chris says, you need to drift align your mount, until it will hold a star in the centre of an eyepiece or camera for a good 10 minutes or more.

Loads of guides and youtubes available, just find one you understand and go with it. Well worth the effort, even when you start to guide properly you will need to be nicely polar aligned.

Looking forward to your results :)

 

 

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After accurate PA you also need good balance, not too high load, stable tripod/mount (tighten bolts), low wind, pec, etc etc.

It should be possible, but may not be easy to achieve 3 min subs.

Good luck.

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The periodic error of the Atlas/EQ6 is pretty catastrophic at about 30 arcseconds, which is about 10x a premium mount's error. The genius of the mount, though, is that it guides out very well indeed and can end up very similar to a premium mount autoguided.

I have always regarded autoguiding as the life blood of astrophotography. (In this I include absolute encoder mounts which guide on their own encoders and a sky model rather than a guide star.)

Milk away if you insist, but I would get into guiding as soon as possible.

Olly

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I agree with the earlier posters on this thread - to get 3 min subs is a real challenge. I would dedicate at least 1 entire night just to perfecting the drift alignment and proper mount balancing. But as Olly says, you should be considering auto guiding as this will allow you to really get the most out of the mount.

HTH Dan :happy7:

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I have known an EQ6 do 2 mins unguided with ~1" pixels, but I suspect that is the exception rather than the rule. But maybe you have larger pixels, given the scope is around f4 - depends what camera you are using?

NigelM

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With cheaper mounts, you have to expect larger quality variation between units of the same model. The reported 1" unguided results may very well be a lucky unit. Furthermore it will depend very much on the load and focal length you put on the mount. I can get exposures of several minutes on my EQ3 Pro, if I only use a lens with my camera. It's lighter and has a much shorter FL, so it's less sensitive to tracking faults (but of course, will never reach 1"/pixel).

As Olly already wrote, guiding is the safest way to ensure longer exposures. But having a tuned setup with accurate polar alignment, backlash and periodic error correction, and good balancing will prepare for easier guiding, once you take that step. I consider it all part of the learning curve in astrophotography.

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Try drift alignment.
I believe you can with that mount!


I have tested my AVX+AT65EDQ+60D unguided for 3min (untrained PEC).
Here is the result -> 3 min exp

Read this article carefully until you understand what's going on -> Drift Alignment
Note:
-Pay attention ONLY to the star's drift in DEC, not in RA.
-The mantra is "UP RIGHT" for Northern Hemisphere.

You will find a Drift Alignment Simulator in that article.
Practice with it. DO NOT USE the cheat button! :icon_biggrin:

Hope that helps...

Ketut

 



 

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On 4 August 2016 at 07:56, rigradio said:

Try drift alignment.
I believe you can with that mount!


I have tested my AVX+AT65EDQ+60D unguided for 3min (untrained PEC).
Here is the result -> 3 min exp

Read this article carefully until you understand what's going on -> Drift Alignment
Note:
-Pay attention ONLY to the star's drift in DEC, not in RA.
-The mantra is "UP RIGHT" for Northern Hemisphere.

You will find a Drift Alignment Simulator in that article.
Practice with it. DO NOT USE the cheat button! :icon_biggrin:

Hope that helps...

Ketut

 



 

Here's a question, which I have not been able to find a satisfactory answer to - and I believe from my research her the past year or so isn't actually possible.

How can you reliable drift align when you have no sky visibility E<>W or below 70degrees?

 

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14 hours ago, iapa said:

Here's a question, which I have not been able to find a satisfactory answer to - and I believe from my research her the past year or so isn't actually possible.

How can you reliable drift align when you have no sky visibility E<>W or below 70degrees?

 

Set your mount's altitude correspond to your latitude location. I set mine to 8 degree since I live in Denpasar City (8°40'27.2"S).
If you want more accurate, find a location nearby with same latitude until you have visibility E<>W. Adjust your mount's altitude there. Atfer done, bring back your mount to your original location.

My house -> 8°40'27.2"S
My dark location -> 8°15'48.5"S
I rarely need to adjust my mount's altitude between those two locations. If I can recall it, some altitude adjustments needed between those locations only when I imaging an object low in North or South.

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thanks for the response, unfortunately my CGEM DX does not readily lend itself to moving - unless I happened to have a largish flat bed vehicle, which unfortunately, by dearly beloved tells me I am not allowed :(

 

 

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