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WO ZS 73 with Star Adventurer

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#26 GabeS

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Posted 19 September 2018 - 01:52 AM

I would love to see your set-up indeed! Under "More Reply Options", attach your file in! Thanks a lot for your advice and help!

No worries. Sorry if it's tough to see what is what, I already had my equipment set up and it's dark outside. Glad I could be of help so soon after joining!

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#27 gfamily

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Posted 19 September 2018 - 07:05 AM

That's a good suggestion. Just out of curiosity, does the guidescope have to be physically very close to be the main scope for guiding to be accurate? And are the guider rings detachable from the main tube rings?

My fellow club member mounted his guidescope (a Skywatcher 6x50 finder with a MMC120 camera) on a ball head on the counterweight bar. 

 

Craig set up.jpg



#28 TelescopeGreg

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Posted 19 September 2018 - 06:17 PM

Um, I'm not thinking that having the guide scope point a different direction than the imaging scope is a good idea.  The guide scope ideally needs to see exactly what the imaging scope is seeing.  It's the whole idea behind the OAG system, right?  Otherwise it will be correcting for the wrong sets of movement.

 

Consider, for a worst case example, if the guide camera was pointing at Polaris, and using it as the guide star, while the imaging scope was pointing, well, anywhere else.  If you were perfectly polar aligned, the guide scope would see practically  no movement at all, even if the scope's tracking was turned totally off.  While being off just a little bit from the imaging scope is probably ok for most purposes (I've done this in order to get a guide star in from the edge a bit), the farther off it is, the worse your guiding will likely be. 



#29 GabeS

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Posted 19 September 2018 - 06:41 PM

Um, I'm not thinking that having the guide scope point a different direction than the imaging scope is a good idea.  The guide scope ideally needs to see exactly what the imaging scope is seeing.  It's the whole idea behind the OAG system, right?  Otherwise it will be correcting for the wrong sets of movement.

 

Consider, for a worst case example, if the guide camera was pointing at Polaris, and using it as the guide star, while the imaging scope was pointing, well, anywhere else.  If you were perfectly polar aligned, the guide scope would see practically  no movement at all, even if the scope's tracking was turned totally off.  While being off just a little bit from the imaging scope is probably ok for most purposes (I've done this in order to get a guide star in from the edge a bit), the farther off it is, the worse your guiding will likely be. 

No but you see, that's the exact reason why I sometimes point my guide scope somewhere different to where my imaging scope is pointing. I always will try to guide off of a star close to the celestial equator. Think about if I were trying to image M81 and M82, objects relatively close to the NCP. If there's an error in how my mount is tracking in the RA axis (the only axis it tracks and can be guided in), the guide cam will be much better able to detect that if it was looking at a star by the equator rather than a star nearby my target. I'm definitely not going to be pointing my guide scope closer to the NCP than my imaging scope is. As long as it's calibrated, I just can't see how guiding off of a star on the equator is going to be anything but beneficial when compared to guiding off of a star near my target. It's like your mount's tracking error gets magnified the best when the guide scope is looking at the equator.



#30 davidparks

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Posted 19 September 2018 - 07:36 PM

WO Z73 on AZ-GTi, EQ Mode with SkyWatcher Latitude Base.... now where have I seen that before...? Hmmm lol.gif

 

WO Z73 / SW AZ GTi
 
It’s an absolute joy to use.  Polar align with Sharpcap, guiding with PHD2, Goto, Platesolving, Wireless.  Easy to guide. Accurate.  I usually stick to 60 seconds stacked exposures, but you can find 10 and 15 minute exposure examples in my Gallery.
 
Stability:  Is it stable? Eh... yes/no, it is stable enough to do what I want to do, which is guided exposures anywhere from 30 seconds to 10 minutes. But the SkyWatcher Latitude Base is the weakest link.  A more stable EQ Wedge might be nicer, but I am able to quickly and easily align with the SW EQ Wedge and be off to the races.  I have a 12 lb. load (including counterweight)
 
For me it works, it works well, I love it... but you can always improve things waytogo.gif
 
Eagle WOZ73 294 20180613
Lagoon WOZ73 294 20180613
Trifid WOZ73 294 20180613
NGC7000 WOZ73 294 20180912
M31 WOZ73 294 20180917

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#31 davidparks

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Posted 19 September 2018 - 08:21 PM

Just another example of this scope on this mount...  not playing to any of it’s strengths... meaning the ZS73 is better at wider field deep sky, but c’mon, when have you NOT pointed any scope you had every type of target lol.gif

 

I had to use a Powermate 5x to get this with the ASI224MC camera, and I’m sure it could be improved upon.

 

Jupiter 20180524

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#32 bobzeq25

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Posted 19 September 2018 - 08:53 PM

Um, I'm not thinking that having the guide scope point a different direction than the imaging scope is a good idea.  The guide scope ideally needs to see exactly what the imaging scope is seeing.  It's the whole idea behind the OAG system, right?  Otherwise it will be correcting for the wrong sets of movement.

 

Consider, for a worst case example, if the guide camera was pointing at Polaris, and using it as the guide star, while the imaging scope was pointing, well, anywhere else.  If you were perfectly polar aligned, the guide scope would see practically  no movement at all, even if the scope's tracking was turned totally off.  While being off just a little bit from the imaging scope is probably ok for most purposes (I've done this in order to get a guide star in from the edge a bit), the farther off it is, the worse your guiding will likely

Yet another unintuitive fact about AP.  As a practical matter (ie with any reasonable misalignment), it doesn't matter much, if at all.   The setup above your post is fine.

 

It is true that calibrating PhD2 at high DECs is less accurate, but that's about it.  If your target is at high DEC, PhD2 will also work less well, equally less well.  Misalignment changes nothing.

 

People slew guidescopes to get better guidestars all the time.  There's no significant penalty.


Edited by bobzeq25, 19 September 2018 - 08:58 PM.


#33 TelescopeGreg

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Posted 19 September 2018 - 09:17 PM

Yet another unintuitive fact about AP.  As a practical matter (ie with any reasonable misalignment), it doesn't matter much, if at all.   The setup above your post is fine.

 

It is true that calibrating PhD2 at high DECs is less accurate, but that's about it.  If your target is at high DEC, PhD2 will also work less well, equally less well.  Misalignment changes nothing.

 

People slew guidescopes to get better guidestars all the time.  There's no significant penalty.

Interesting.   How far off from the imaging scope can one be, before things start to be a problem?

 

Thinking about this some more...  In GabeS's case, guiding in RA only, I would think the direction you move off of the imaging scope would be the prime factor.  If you moved it to one side or the other in RA only, then I guess the tracking would be the same, and the off-angle of the guide scope would have no effect.  If moved in Dec only, then one would be magnifying or reducing the apparent star motion as a percentage of how far you moved it.  If you are guiding in both RA and Dec, then things get a bit more complicated, especially if you have any sort of backlash issues with the mount.  However, when you have that flexible of a mount for the guiding system, differential flexure could become the primary issue, swamping any inaccuracy in the tracking of the guide star.

 

Agree totally about PHD2's calibration at high Dec angles, and found that it "reminds" you of that if you try otherwise (or in my case, if ASCOM gets confused due to a USB connection reset).



#34 dciobota

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Posted 19 September 2018 - 10:16 PM

Greg you're right, if your guidescope is pointing in a significantly different direction towards celestial north then guiding would suffer.  Just like you mentioned, if the guidescope pointed at the celestial north then there would never be any guide commands (except dec, which in your case would be turned off).  This is indeed intuitive, not as otherwise suggested.

 

Another issue would arise if the guidecam sensor is not aligned with the dec/ra axes.  In that case the ra calibration would be insufficient, since it will only partially correct for ra movement.  It will also be partially affected by dec drift as well.

 

Rule of thumb for me is to keep the guidescope reasonably well aligned with the imaging scope, +-10 deg or so.  This gives you a large field to pick a good guide star, especially with the faster smaller guidescopes out there nowadays.

 

Hope this helps.



#35 davidparks

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Posted 02 October 2018 - 06:42 PM

I just took delivery of an iOptron Alt-azimuth Adjustable Base.  Though I havn’t used it in the field yet, I can already tell it is an improvement over the Skywatcher Star Adventurer Latitude Base for the 12lbs of weight I have on the AZGTi mount (not including the weight of the AZGTi itself).  I’m sure the Latitude Base works well for the Star Adventurer mount it was designed for, and it has worked well enough for my application for the most part, however, when the latitude clamp was loosened to allow for adjustment, there was some slight instability.  Nothing that couldn’t be worked with, but it was there.  With the iOptron Base, the latitude adjustment is both smoother and more stable.

 

The iOptron is somewhat shorter, with a wider latitude joint, which probably accounts for the improvement in stability, although we all know that quality can vary on the same item, so it may be that some samples of the same product are better than others.  These two bases are close enough in performance that quality control on individual samples should be considered, and could make the difference (They are THAT close).  Of course, with a lighter payload, you may not ever notice the difference...


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#36 DCWZ

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Posted 02 October 2018 - 11:51 PM

Thanks for the input!!! So in general, would the iOptron SkyGuider pro? William Optics offers them as a package. The only reason why I leaned towards the Star Adventurer is that I can use generic batteries without being limited to the battery life of the internal battery (which, as I read, is non-replaceable, correct?).
In terms of tracking and guiding, would the SGpro be superior to the SA? How about actual payload capacity (I heard that the SGpro is sturdier)? Ease of usage compared to the SA? If anyone has experience on this matter, please do offer your opinions! Thanks!

#37 james7ca

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Posted 22 November 2018 - 05:29 AM

I know that this is a pretty old thread, but I wanted to offer some additional comments about guiding on a star that is a great distance from the center of the imaging field.

 

First, as far as the guiding rate itself, it really doesn't matter how far the guide star is offset from your imaging field because the rate will be exactly the same as long as you are using an equatorial mount with perfect polar alignment and with zero atmospheric refraction (however, "perfect" polar alignment is almost impossible and the only place you will have zero atmospheric refraction is in outer space -- or if you happen to be pointed directly at the zenith). So, under those highly improbably conditions any corrections to the guiding rate will work correctly regardless of where the guide scope is pointed. That said, the apparent movement of a star decreases as you get closer to one of the celestial poles and therefore to get accurate guiding you need to be able to detect far smaller offsets (errors) which will make guiding harder and that's one of the reasons why PhD prefers to be calibrated on a star that is closer to the celestial equator (and not nearer to one of the celestial poles).

 

Next, atmospheric refraction can be a pretty significant factor when trying to track a star and thus if the guide star is "suffering" a greater or lesser amount of atmospheric refraction than the main imaging camera that will change the apparent tracking rate over time (as the degree of refraction changes, and it will as a star rises or sets from its meridian).

 

Also, any field rotation that happens because of a non-perfect polar alignment will be magnified by the distance that the guide star is offset from the imaging field. I'm pretty sure this is a completely linear relationship, so the error would double if you offset the guide star by twice any given distance (going from one degree offset, to a two degree offset, to something that could be much greater if the guide scope is completely misaligned to the imaging field).

 

What all of the above means is that you really don't want to try to guide on a star that is a great distance from the center of the imaging field. Thus, in practice some of the earlier statements were wrong or at least incomplete.

 

Of course, if your image scale is very low (meaning a very short focal length lens) then your guiding or tracking doesn't need to be that good, so you may get acceptable results even when there is a large offset between the guide star and the imaging field.

 

As for any field rotation, you can use the following online calculator to see how much that can/will affect your image.

 

  http://celestialwond...xErrorCalc.html


Edited by james7ca, 22 November 2018 - 06:35 AM.


#38 yoandresmza

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Posted 24 November 2018 - 04:49 PM

Hi DCWZ, did you consider get MEADE APO70 instead WO ZS73? Is lighter (about 2kg), faster and don't need a flattener, but is more expensive of course. I think it's a great option to combine with the SA.

#39 CrossoverManiac

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Posted 03 December 2018 - 01:01 PM

I just took delivery of an iOptron Alt-azimuth Adjustable Base.  Though I havn’t used it in the field yet, I can already tell it is an improvement over the Skywatcher Star Adventurer Latitude Base for the 12lbs of weight I have on the AZGTi mount (not including the weight of the AZGTi itself).

Do you notice an improvement over using the Sky-Watcher Latitude Base?




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