Well, I already found the solution for the sidereal speed problem and not being able to make an alignment, it was my mistake when entering the coordinates in their place, although they were the correct ones, I was changing their places, the latitude in the longitude and vice versa, I was telling the gemini that I was in another part of the planet, once I realized my mistake I corrected it and yesterday I had an excellent night, being able to handle it with the pc and cartes du ciel, so it was my fault that the mount worked wrong.

Oh, forgot to mention that if going strictly visual you should look for a used GM8 with a #492 digital drive and spend the money you saved over a Gemini on the Nexus DSC.

If you shop carefully you should be able to find a used GM8 digital drive and LWT you could be into the whole thing for under $1,500-$1,700 including a new DSC.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

LOL,? this is what happens to people with a full G11G and HD or FHD who image. They want to go and observe visually and the HD/FHD and 10+ extra pounds of G11G vs GM8G becomes very real not to mention that even the relatively svelte FHD while an amazing solid tripod while imaging is a heavy, bulky tripod and major overkill for visual.use and the LWT can more than double your weight savings.?

Ken if you do not plan to image using the much more compact lighter GM8G and LWT setup they will be more than adequate for up to a C11 SCT or something like a TEC140. I have been using 10" LX200 and C11 SCT OTAs on my old GM8 now a GM8G for many years without issue. I also use.it.with the bespoke Parallax/AT130 SDT apo which at 28+ poumds naked is heaviwr than the C11.?

Is the GM8G as solid in the wind with nearly 30 pounds in the saddle? Of course not but it is about 20 pounds lighter and stows a lot easier in modern car trunks than my G11G and FHD or Berlebach Planet and it is hard to see a difference at the eyepiece.?

I long ago added Astro Devices 310K encoders and the crazy good Nexus DSC with SkySafari6 Pro for simple push-to observing. This is they way these mounts were meant to be used, balanced and clutches left free to push the scope around the sky with two fingers.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

I have (or, hopefully, had) the same problem that I just posted in this thread?(also check the link in it).? I have the two-piece worm block.? After checking the alignment of the blocks, I concluded that I had to shim the blocks on the outside/bottom in order to get the bearings aligned properly.? It is a bit difficult to judge the alignment as there is some play in the bearings and squeezing the blocks in the middle vs. a bit off to the side makes a difference.? I use the cover plate to visually compare the alignment against, when squeezing the blocks (everything off the mount of course).? After one test it looked like the 76 s error was reduced quite a bit, and the autoguiding errors had improved a lot resulting in equal RMS whereas before this it was always larger in RA resulting in elliptical stars.? This is just from one test so take it FWIW.

I presume that when you loosen the cover / one-piece assembly screws the blocks will have some play around the screw axis which will let you do the same.? If you just shim the outer block at the outside bottom area, that should be easy to try and see if it improves things.? You want to first tighten the bottom screws to pull the shimmed block down then tighten the cover screws, or else the last part of the cover screw turn can actually skew the position of the block - and it only takes a tiny little bit to skew the bearings enough that you will get the 76 s harmonic.? Then you can either loosen the bottom screw or leave it depending on whether you want the SLW enabled or a fixed configuration (or whatever Losmandy's instructions are - I don't have the one-piece worm assembly).? Not guaranteed to work but it seems to have worked for me (my 2-block assembly that may be different enough from yours that this idea has no merit).

Check also if the bearing is intact, who knows a bearing ball may be damaged - I have one, awaiting new bearings now.

I am looking at adding a TAK TSA-120 refractor to my kit as? a good scope and to travel with. To support this I see a couple of options to mount it - (1) to buy a GM8 w LW tripod or (2) buy a LW tripod for my G11G.

Would anyone have an experienced perspective on the (2) choice? If it is an option, is the spreader a must have?

Appreciate your constructive insights.

Thanks,
Ken

I was able to setup again last night and take some more test runs. Following Mark's suggestion, I recorded three runs with Hysteresis: 0, RA aggressiveness: 50 at guide rate: 0.5x. I did this for 3, 2 and 1 second exposures. I also did an additional test using 2 second exposures with the default PPEC algorithm.

Here's a recap of the RMS results:
3 second exposures: RA 1.16" / Total: 1.24"
2 second exposures: RA 1.00" / Total: 1.33"
1 second exposures: RA 0.81" / Total: 0.93"
PPEC 2 second exposures: RA: 0.79" / Total: 0.90"

The total RMS looks like it's skewed higher by some strong deviations in Dec. I had to setup from scratch last night and it looks like my polar alignment can use some work. The RA RMS definitely looks like it's trending lower with lower exposures, however it looks like this confirms Mark's suspicion that this is the 76s error. Is there any other way to mitigate this through guiding or does this require mechanical adjustments? Any suggestions on next steps are most welcome!
-Frankie

Here's a screenshot from the PHD Log Viewer Analysis for the 1 second exposure run:

Derek,

That's a nice setup and those are some pretty good guiding results. Glad that's working out for you and thanks for sharing! It seems likely though that my issue is not related to my guide scope, so the investigation continues.

-Frankie

I have been getting the 76 second harmonic in RA fairly consistently and so far, my efforts to get rid of it failed.? I took a good look at the blocks while keeping the worm properly aligned (squeezed the blocks as much in the middle as I could).? Overall, the block alignment is near perfect except in the vertical plane through the worm axis.? Namely, the blocks appear to tilt up slightly on the outsides which could be enough to cause an unbalanced pressure on the worm bearings.? This was also noticed ?where, after the author shimmed the outer blocks, the 76 second harmonic was significantly reduced.? So, I tried the same.? I made some shims from the foil lid of a sardine can, 2 layers in thin strips glued to the block bottom's outer area (both blocks).

Here are some results without shims (using the Ekos autoguider in openn loop and a Scilab curve fitting program that fits a polynomial trend plus 2 harmonics).? The 76 second harmonic is very clear with an estimated amplitude of about 3".


Here are some results with shimmed worm blocks.? The 76 second period is much less pronounced with an estimated amplitude of 0.66", still some but quite a bit less.? The 240 second harmonic is now dominant with a decent peak to peak value that can be guided out and reduced further with adaptive PEC.


The estimates are not exact because of fitting artifacts but they are consistent with the visible reduction of the 76 sec harmonic.? The autoguiding was also a lot quieter without the periodic spikes that I used to get.? The error RMS in RA and DEC are about the same, previously RA was always worse.? I have to do it a few more times so hopefully it's not a fluke but it looks encouraging.?

If any of you have tried similar experiments I would be interested to hear about the results.? For sure, worm block alignment is tricky and can have a big impact, so it takes practice and needs to be done with care.

开云体育

开云体育

Frankie,

First, you have too many features already enabled (such as dithering) - that makes it harder to see what is going on with what matters, the mount mechanism.
Likewise, while trying Yet Another Feature (YEF) may clear up your problem I wouldn't bet on it and, at worst, it will just further confuse things more.

Looking at the session starting at 22:21:17 in your log it looks to me as if there is a strong periodic error (about 4 to 6 arc sec peak to peak based on your pixel pitch of roughly 3" per pixel) with a period of about 25 guide exposures between
the zero crossings of the downward (or upward) trends.

I'm old fashioned and looked at the Log in Excel. The units are guider pixels.



Since your guide exposures are 3 seconds, that comes out right at 75 or so seconds. It appears to be the classic (and dreaded) 76 second error problem.
The usual cure, excluding hardware changes, is to carefully adjust the worm. I assume you have the one-part worm blocks since your unit is new.
My G11 has the old two-part worm blocks so I can not advise on how to do that.

I suggest you disable everything other than simple Aggressiveness (aka feedback) and set it to 50%. In particular, turn off Hysteresis and Dithering.
They just confuse the picture of what the mount is doing mechanically. In particular, Hysteresis can sometimes 'fight' Aggressiveness. That is why, with a
Hysteresis of 0.1 (your setting) the Aggressiveness is so high: 0.70. With no Hysteresis the Aggressiveness would be in the range of 0.5.

I'd then set the guide exposure to 3, 2 and 1 second trials as a test with 50% guide rate in the mount.

Why do I suggest these things? Because while shortening the guide exposure can result in more atmospheric scintillation in some cases (it is highly environment/atmosphere dependent) it makes the system more responsive and samples (for analysis) the mount/sky/guider behavior more frequently. The validity of that data, of course, is partly contingent on how stable your seeing is. You can get a handle on that by just tuning off guiding and look at the DEC component - detrend the data and look at the residuals - those will be the atmospheric component.

Another benefit of a shorter guiding exposure is that the guider+mount can chase and correct any worm error more easily. A longer exposure allows the error to build up, assuming it is reasonably smooth. Testing with a shorter exposure (again, assuming your skies are not too turbulent) will give visibility into that. If you can get away with a 1 second exposure it may cut your RA error in half or more.

Likewise, Hysteresis tends to decrease the speed with which the guiding can react to errors. Dithering just jogs the mount between exposures - it can only confuse matters at this point. Potentially dithering can require that the mount takes a little? time to settle down again. It may be a cause of part of the problem. And I say may - nothing is guaranteed. But again, it is just another feature than may be confusing the fundamental issue, although looking at that log session it appears to be a periodic error problem.

I'd also suggest, as a courtesy, that you put one session per guiding log file, or at least tell us which time hacks we should be looking at.
Weeding thru many sessions with different parameter changes buried in them makes it hard for you (and those who want to help) to dig thru the logs.

Best regards,

Mark Christensen

Hi? Dale,

Thank you for the response. Yes, your assumptions are absolutely right. The PHD guide logs were not from an imaging session, but were strictly to get results for analysis. I started out measuring guiding performance for about 20 minutes and then ran the Guiding Assistant, which turned off guiding, so I could measure the raw performance for another 20 minutes or so. I should have mentioned that specifically in my initial post when describing the logs, sorry about that!

I will try out your suggestion tonight to use PPEC algorithm with the 76s period, with auto-adjust off and will try and post a new PHD log with the results.

Thanks again for your time and feedback!
-Frankie

Hi Brian,

it was a while ago, and I believe that was the error; and I don't believe that I the calibration finished before (I think it is 100) steps.? The log file on 27 June was refers.

I have since re-installed PHD2 to the previous version, and on 16 Jul I was merely doing a quick/rough run? to see if the re-install of PHD had any effect (yes) - forecast/actual was only for 90 mins or so clear sky.? The PHD log on 16 Jul refers (PE turned off, well in the rush, I forgot to turn it on).

To be honest, I don't think there is likely to be anything in this data, other than it confirms the re-install of the software worked.? It surely doesn't indicate PHD was at fault on the night that I had troubles (I believe that I must have done something, irrespective of whether I repeated the issue the following night - sorry lost that log).

The reason I reinstalled, was that an OP on the PHD site had something similar, and the advice was to 1: delete and re-add the config, or 2) re-load PHD to earlier vers.??

I am happy to continue on from where I am (re=baseline per help paper if needs be).? Sure if your experience sees something obvious that I did/did not do - then advice of that would be appreciated.?

My plan is to progress to predicative PEC algorithm (I think there are some settings somewhere from another post), and do some imaging and see if I like the results before bothering anybody further.


Phil

Hi Frankie,

Looking at your Phd2 log, Section 10 appears to be continued guiding after the calibration and GA, rather than an actual imaging session showing your issue directly. Roughly the first half of the graph up to about frame 415 or so shows RA 0.87" and Dec 0.55" - not too bad, but after that things go south as the actual guiding output from Phd2 got turned off, and it seems you are tracking the mount's raw behavior without the guiding.

Maybe I'm being naive about your intent here; that you were actually measuring the unguided response of the mount.

Maybe try using the PPEC RA guide algorithm with "Auto Adjust period" off and the period set to the largest periodic error which looks like 76s ?

(Help from the group sure helped me sort out similar issues!)

Dale

Hi Derek,

Thanks for the reply! There is a very slight bit of play with the counterweight shaft. Here is an image of my how my new guide scope is attached.?
?

I had taken a look at those guide rings you posted a link to on Losmandy's site. Did you notice any appreciable difference in guiding accuracy after you installed them? I'm curious how well they perform.?

Thanks,

Frankie

?

开云体育

--

Hey Brian:

Do you screw the Hutech adapter all the way down to it's shoulder??

I have the 10" Sky-Watcher Quattro 250P and from the 200P manual (I couldn't find a 250P manual) the focuser end of the draw tube is M54.5 X 1 mm. I bought the Hutech adapter, but it's threads and size seem to be M54 X .75 mm. It does thread into the draw tube but it doesn't thread all the one down to the Hutech's shoulder.

I'm curious how your using it?

Bill