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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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cuivienor
professor emeritus


Reged: 10/07/10

Loc: Tokyo, Japan
First time trying on a GEM (SmartEq Pro)
      #5840592 - 05/04/13 07:03 PM

Hello,

Last night was the first time I tried imaging with my smaery eq pro and vixen vmc 110L, Meade DSI Pro II mono.

I tried only with 30 seconds and 1 minute stubs, but I noticed that while some stubs were absolutely perfect (thus the mount alignment should be good enough), many stubs show significant (around 2 pixels) drift in either left or right direction (roughly corresponding to the RA axis). There was no more wind during those exposures than the perfect ones. It almost looked like the RA motor was sometimes going too slow and sometimes too fast...

Anyone can tell me what causes this? Maybe the tube was not balanced well enough?

Thank you very much for your input!

Yannick


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BKMaynard
super member
*****

Reged: 02/21/13

Loc: Cahokia, Il. (st.louis area)
Re: First time trying on a GEM (SmartEq Pro) new [Re: cuivienor]
      #5840657 - 05/04/13 07:58 PM

It's called periodic error. All mounts have it to some degree. Most mounts have a way to tame the error using periodic error correction (pec) or use an autoguider to keep the mount tracking properly.

Edited by BKMaynard (05/04/13 07:59 PM)


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Jeff2011
Pooh-Bah
*****

Reged: 01/01/13

Loc: Sugar Land, TX
Re: First time trying on a GEM (SmartEq Pro) new [Re: BKMaynard]
      #5840696 - 05/04/13 08:35 PM

Yannick,

With my Celestron AVX mount and 430mm focal length refractor, I was able to get 27 out of 27 good shots at 30 seconds but at a minute and a half only got 4 out of 9 good ones. Different mounts will get different results. But it is periodic error which has to do mainly with the quality of the worm gears in your mount. Autoguiding will solve your problem. Some mounts like mine have periodic error correction capabilities, but you need a guide camera in order to record the error that the mount can then use to correct the error. But ths is not a perfect science and guiding is always recommended for longer exposures.


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cuivienor
professor emeritus


Reged: 10/07/10

Loc: Tokyo, Japan
Re: First time trying on a GEM (SmartEq Pro) new [Re: Jeff2011]
      #5840768 - 05/04/13 09:24 PM

Thank you very much!

Now it looks like I have to get an auto-guider!

Thank you for the clarification,

Yannick


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rigel123
Postmaster
*****

Reged: 06/29/09

Loc: SW Ohio
Re: First time trying on a GEM (SmartEq Pro) new [Re: cuivienor]
      #5840827 - 05/04/13 10:07 PM

Hey Yannick, long time no see! Glad to see you are getting some time under the stars!

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cuivienor
professor emeritus


Reged: 10/07/10

Loc: Tokyo, Japan
Re: First time trying on a GEM (SmartEq Pro) new [Re: rigel123]
      #5841208 - 05/05/13 07:11 AM

Hi Warren,

It has been a while indeed! I have been terribly busy with work and with my now 2 and a half son (those creatures tend to consume a lot of time) but finally am getting some astronomy time.

I still have my LS-8, but it sits for the moment unused in favor of my ETX-125 and Vixen VMC 110L on SmartEq Pro (the latter being a very recent addition), which are simply much faster to set up than the LS-8 (I need to carry the gear up some stairs, and am too worried about adverse effects should I leave the LS in a weatherproof case on the balcony). I also have a small 70mm ED refractor and reducer/flattened coming soon (so many thing happening).

Hopefully I'll get some imaging practice with guiding soon!

Yannick


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*skyguy*
Carpal Tunnel
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Reged: 12/31/08

Loc: Western New York
Re: First time trying on a GEM (SmartEq Pro) new [Re: cuivienor]
      #5841223 - 05/05/13 07:40 AM

The relatively long focal length of the Vixen VMC110L (1035mm) will greatly magnify any periodic tracking errors inherent in the SmartEq mount. You'd probably get better imaging results using a scope with a shorter focal length. Success and Good Luck with your imaging!

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cuivienor
professor emeritus


Reged: 10/07/10

Loc: Tokyo, Japan
Re: First time trying on a GEM (SmartEq Pro) new [Re: *skyguy*]
      #5841227 - 05/05/13 07:47 AM

Thanks Skyguy,

That's what I figured out as well - long focal lengths telescopes are the only thing I have until my Blanca 70mm refractor arrives next week! One I have that, I'll try for a while without guiding and decide whether I need the autoguider package or not...

Thanks,

Yannick


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