Intermittent Bad Subs with Skyguider Pro - Forums

Topic starter

Oct 16, 2021

Hi folks:

I bought a Skyguider Pro about 11 months ago, and I am starting to think I might have got a bit of a lemon. I have a really high rate of rejection past about 60 seconds. I'm not currently guiding.

I am able to polar-align with accuracy, but I find that about one in every three or four subs show out-of-round stars. The other subs have perfectly round stars. The longer I expose, the more subs need to be thrown out, but the same pattern of round and out-of-round stars persists. This suggests to me that the issue is intermittent and not related to polar align accuracy. Whatever is happening happens every 2 minutes or so, maybe, and if it happens during an exposure that sub is ruined, but then some subs it doesn't happen - so the longer the subs, the greater the chance the mechanical "event" occurs. At least, that's my reasoning.

I have had this issue with the mount since I purchased it, and it hasn't gotten any better or worse over time. I know a lot of you can get 2-3 minute subs with round stars even at my focal length (360mm) without guiding, so it seems fishy that my mount is showing this intermittent glitch.

Is this consistent with a bad polar alignment? Is it, perhaps, a mechanical issue? Backlash? Poor balance? Wind? Vibration? I'm flummoxed. I'm planning to start guiding soon, but I'd love to sort this issue so that my guiding is not always fighting it.

Thanks in advance for any suggestions! I've contacted iOptron support too. It would be great to get to the bottom of this!

CS,
Mark

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Ian McIntyre

Oct 16, 2021 · Edited: Oct 16, 2021

I have only once done a sequence with subs greater than 55 seconds and the stars were pretty soft. No obvious trail, just soft. But I am pretty new to this and it could have been related to any facet of my newness. One of the big things that I was not doing early on was not being super vigilant with my leveling, so I had pretty bad drift.

In your case it sounds like something mechanical. To happen in a cyclic nature like that sounds like a gear slipping or having some imperfection. If it was bad polar alignment you would drift and have trailing rather than just out of roundness. I suppose if you had an out of balance load it could make the clutch slip. Mine seems pretty secure, so much so that I really have to fight to turn the release ring, even with a very conservative hand tightening.

Are you using the stock base or the William Optics upgrade? Sometimes I consider the upgrade as I find play in the dec. I have to really crank down on the lever that secures it. I could see that effecting the motion, but not in the pattern you are experiencing.

Hope you find a solution. Now I'm going to keep an eye on my images for abnormalities.

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Mark Germani

Topic starter

Oct 16, 2021

Ian McIntyre:
Are you using the stock base or the William Optics upgrade? Sometimes I consider the upgrade as I find play in the dec. I have to really crank down on the lever that secures it. I could see that effecting the motion, but not in the pattern you are experiencing.

Thanks Ian! I’m using the stock base. I’d like to get the WO base, but I honestly don’t have to many issues with my base, AFAIK. It’s a little dodgy, but with some fussing I can get it where it should be.

Of course, there is the possibility that something is shifting after I’ve aligned and started the imaging run. The clutch seems pretty solid though, so maybe something else is moving.

Your stars look good - I wouldn’t worry!

CS,
Mark

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Ahmed Waddah

Oct 17, 2021 · Edited: Oct 17, 2021

I use the SGP with my Redcat 51 and I can do 5 min subs all night unguided. I used to get trails from 90 sec subs so I did get the WO mount base (Improved my Polar Alignment) and I got a tripod leveler (level using a 2 axis bubble level) which had a great effect on overall balance and polar alignment.

I did a polar scope calibration test where u point your center reticle at a distant point (flag pole) and turned 360 and the point moved from its place but when I researched and emailed Ioptron got this reply:

"If the object stay at the center of crossed hairs, or inside 4” circle, it should be OK. There are three small set screws for adjustment. Do not over tighten them or you’ll damage the dial holder."

I didn't attempt to calibrate the polar scope and haven't had an issue since. So you can start by checking the polar scope alignment.

http://www.ioptron.us/Support/SGP_PolarScopeAlign.pdf

Mark Germani

Topic starter

Oct 17, 2021

Thanks Ahmed!

I did check my polar scope, and while it does appear to be slightly off-centre of the RA axis (the image wobbles as I rotate the scope) the object I focus on never leaves the centre of the reticle, which according to my reading suggests that it’s ok, and should be left alone.

When you were getting trails above 90 seconds, were they consistent - all or most of your subs - or were they intermittent and mixed with subs with good stars, as is my issue currently?

Cheers,
Mark

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Ahmed Waddah

Oct 18, 2021

I usually got trailing stars with the exposure time I wanted (120" and 180"

So I worked on balancing my setup bottom up and getting polar alignment spot on! Like I told you the tripod leveler and WO wedge helped and now I can do up to 5 min provided there is no wind or my setup is sheltered from wind. I even tried a single 8min on a still night and it was good! I know people who say the SGP and SA cant do more than 2 min consistent subs with a 200mm/250mm but others that use my same setup told me that I can push it to 5 min and I did! I am not sure the SA can do more than 3 min but I might be testing that with a friend soon.

You must know I travel to a bortle 2-3 location and I don't shoot from the city. I think 1-2 min is what people who shoot from the city using filters but since I go to a dark location I have to push the exposure!

Mark Germani

Topic starter

Jan 7, 2022

Just to update this thread…

I managed to get a replacement mount, as my Skyguider was deemed to be faulty after communication with iOptron. The replacement is MUCH better, and produces unguided subs @ 2 minutes much more reliably. I was even able to get a very passable 4-minute sub once!

I have ordered the replacement base from WO, and I look forward to seeing what, if any difference that will make.

CS,
Mark

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