SStanford

Hi All, Feels like an age since I was last able to use the scope (late Jan!) but the skies were very clear tonight. I've been battling with obtaining accurate PA and I'm happy to have achieved PA error of 1.9 arc min according to PHD2 (log attached for reference). I'm using Stellarium scope and Stellarium to slew my EQ3pro. My understanding was, with accurate polar alignment, when slewing to a target on Stellerium the target should appear accurately in the scope FOV (correct me if I'm wrong). It seems that despite PA error of 1.9, targets are still quite far from the FOV. Do I need more accurate Polar alignment for this to happen? would I be better of just using saved alignment stars via EQmod at this point? S. PHD2_GuideLog_2021-02-27_181944.txt

Thanks Kens, guide logs below for reference. I'll apply the recommended minmove now. There was a lot of whispy cloud around last night and I feel this probably interfered with the readings. I'm also going to up the exposure times to 2 seconds rather than 1 to see if that helps. I'll aim for <5mins going forward. I'll chalk this up to the aformentioned clouds. Will the increased exposure time and a steadier atmosphere help the High-frequency Star Movement measurements? PHD2_GuideLog_2021-01-25_194449.txt

Calibration successful! thanks for your help all. Brief opportunity before the clouds rolled over tonight. With one issue resolved, two more pop up. All part of the fun. 1. I ran the guiding assistant tool and had two different outcomes. The second outcome was worse having tweaked PA via the Drift alignment tool (reducing recommeded exposure times from 2-4 seconds to 1-3 seconds 😐, unacceptable!) It also recommended amending the RA and Dec min move, before I apply these changes has anyone had any experience with these amendements? 2. The drift alignment tool is very tricky to manage. I had c.40 mins to play with Azimuth adjustment; when I got anywhere near a stable Dec line in the graph, the slightest adjustment in the Azimuth would cause the graph to give a wild reading. In fact, the lowest PA error I could get was 4.64' (38px), see image below. Any tips with this?

Thanks @Skipper Billy.

I've set RA & Dec rate to x0.80. Does it really matter if I were to put this up to x0.90? would guiding be more accurate at x0.50 for example? "sideofpier" is set correctly to "Pointing ASCOM" as is Guiding "ASCOM pulse guiding". I have also ensure that focal length and pixel size is accurate for the guide scope and cam in PHD2 (3.75 and 120mm (here)). At next clear night I'll be focusing on a portion of the sky +/- 20deg from 0dec and near the meridian. I'll also be slewing north via EQMOD at slew rate 1 for 20 seconds before running calibration. Should this not resolve the issue I'll be trying all the details outlined here and here. I'll post my results after.

Thanks both @michael8554, @kens. I'll make these changes and post my results.

Thanks @knobby. I havent tried any of these things yet! I'm a complete newbie with PHD2, do you know if theres a guide that'll gove some pointers in this direction? @KP82; I did indeed pick a star near the equator and meridian (just east of the meridian, North of the equator). Balance in bothe Dec and RA are good. @kens, thanks for these. I'll implement them tomorrow. Log files are detailed below if anyone can take a look? https://openphdguiding.org/logs/dl/PHD2_logs_b2VW.zip

Hi All, Lovely clear night tonight; first opportunity to use my ZWO ASI120mm which I recieved this week. Connected the EQ3pro Synscan to my comuter, controlled by Stellarium, slewed to a star in the South (which then starts tracking), Set-up PHD2, got a good focus on the stars, calibration running smoothly until it "steps north". PHD2 "steps east" (around x50), backlash (around x20) then "steps north" (around x60) before I get "Calibration failed" in the bottom left and the message: "Dec calibration failed: Star did not move enough". At the backlash stage on PHD2 the mount starts clicking every so often, as it does for the whole "steps north" process too 😬. I tried slewing to different parts of the sky but encountered the same failure three times. I'm completely stumped with this one so any guidance would be hugely appreciated! I've attached a screencap of the interface below in case theres anything I've overlooked here.

My first guide scope and camera, extremely fast delivery times by FLO, as always. Interesting that it came in the ZWO Planetary Camera box...

This is great, thanks! Will dedicate a few hours to this when I can.

As an update: Found an allen key long enough to reach the three grub screws to adjust the metal disk to loosen the RA axis. Once loosened, the disk cant turn more than a fraction and is very firmly stuck on the thread. I assume this can can be unscrewed further with a tool capable of fitting the two holes on the disk as shown above. As it is I'm only able to turn the disk using an allen key in one hole. Once the grub screws are loose the RA moves much more smoothly and loosely but once tightened again it goes back to how tight it was previously. I decided to balance my current OTA whilst loose then, once marking the dovetail and counterweight bar accordingly, I retightened the grub screws and reassembled the RA setting circle, polarscope and RA locking bolt. Out of curiosity; what is the purpose of the RA locking bolt? the mount will always be tracking in RA so why would anyone want this axis locked? As for the RA worm gear I loosened the two grub screws underneath the housing and attempted to bring the gear closer to the housing, eliminating the slight wobble. It seems to be as close as it can be but still wobbles as it did previously so I'll have to accept the backlash issue moving to the West (left on keypad). I don't think this should be too much of an issue however so long as I my targets (from parked) are selected clockwise, if that makes sense? Certainly learned a lot this weekend regarding the mechanical makeup of this mount!

@SiriusB; thanks for this. It seems I didn't need to mess with the Dec worm gear at all. I've just tightened the two black grub screws as shown below and it has removed all the movement (except the tiniest tick) in the dec axis. quick response in alternating directs with the hand control too. @kens; thanks again! the fact that the is no slewing at rate 1 to the west in RA explains why I wasn't having much success with DARV PA! With the Dec gears sorted, its clear that there is quite a bit of wobble in the RA worm gear. when turning the slo-mo handle back and forth the wobble seems to be on the gears axis. I can see there are two black grub screws underneath the axel in the housing; these have been tightened fully. And ideas how I can reduce this wobble? would unscrewing these and pushing the axel further into the housing and tightening sort it out? Additionally; I notice my RA is very tight when removing the clutches so whilst working on the above I thought I'd try and loosen this up. I've followed the excellent guide by @wimvb here but unfortunately my allen key isn't long enough to reach the three grub screws in the disk via the RA lock bolt. Before I start messing around with this which tool am I using to unscrew the disk as shown below? I'm conscious that I will likely need to re-grease the RA axis, can anyone make a recommendation for the best to keep this smooth?

I've added a few picture here to hel me explain myself. I'm completely new to backlash correction so let me know if I've overlooked something here! I've taken the covers off the RA and Dec motors to look for any noticeable misaligment in the gears but nothing immediately stands out. Dec motor gears engage in less than 1 second at rate speed 1 when alternating direction. Only concern here is that with the slo-mo controls attached, theres a good quarter turn on the slo-mo handle before the gears engage. Should this be tightened or is it a non-issue? If so; how do I tighten this to the gear? RA motor stragely doesnt work when pressing west (left) on the handcontrol at rate 1, only responds at rate 2 or higher. Any reason for this that anyobody knows? it takes the gears about 1.5 seconds to engage at rate 1 when pressing east (right) on the handcontrol from the opposite direction. Unline the Dec slo-mo; the RA slo-mo control is tight and engaged to the gears tightly. Would be hugely grateful if someone could offer some insight here

Thanks again @kens, Hopefully then I'll be able to reduce the error using PHD2 and the guide cam moving only in one direction from parked? If I can find a way to reduce the backlash too then all the better. Completely new to the issue so hoping I can find a decent guide somewhere for backlash reduction.

Thanks for this. Could I then take a long exosure without slewing the mount and adjust the alt/az until the trailling star is a single point? The problem I seem to be having is the mount isnt even resonding to insructions to slew on the lowest slew rate, which I'm hoing is a backlash issue (I've created a seerate topic on this). With FLO in stock of the guide scope and cam bundle (here) I ordered this last night so I'm hoping using PHD2 drift alignment function this will put my PA problems to bed! Of course now I'm concerned that my backlash problem will affect guiding and go-to in general 😬.

Hi All, With ongoing issues related to slewing in the EQ3 pro it's quite clear that there is some significant backlash. I understand there is a way to repair this myself; does anyone have details of guide for the EQ3 pro to reduce the backlash? I also understand that the lubricant is important to reduce backlash. Can anyone make any recommendations here too? Thanks again!

Quick update on this: Clear skies tonight; setup eager to get the DARV process underway and PA accordingly. Not as easy as it looks! Its clear theres some significant backlash on the mount as in slew rate 1 there is no noticeable trailling as to make adjustments as outlined here. In addition to this, Slewing West as instructed makes stars trail in an downward direction, rather than left as outlined in the tutorial. With no success with DARV I gave Synscan PA error another bash too, selecting stars first from the East then to the SE/S. Still getting wildly incorrect PA error. With no other options avilable its clear I can only buy my way out of the PA alignment hole 🤷‍♂️. I'm hoping that using drift alignment via PHD2 and a guide scope (eyeing this) will resolve this one and for all!

Music to my ears! I'll try DARV when next have clear skies.

Just to continue my previous post; with regards to DARV, I have view of stars in the east starting at about +15°-20° from the horizon (and no view of the west). As this is quite a bit away from 0Dec do you think this will be an issue?

Sorry to keep bumping this thread! I've just been informed elsewhere that the 2 or 3-star alignment method will produce "very poor results". Quote: "If you are aiming for AP (which is the goal of this specific forum), you will have very poor results with this method you're trying to implement, even if you get a zero PA error as reported by synscan. 2 and even 3 star alignment has cone error and other things affecting it's accuracy. If it was as simple as using a 2 star alignment then we would all just be getting PA from plate solving somehow. It is not how it works." So without the view of 0Dec with the DARV alignment in the East and with the Synscan PA error function being useless, which other options do I have?

Good point; I'll be sure to stay in this direction moving from the two alignment points.

Thanks @MercianDabbler; it seems clear that my issue is due to backlash (a term I've just learned this afternoon!) From further reading online I'm seeing that others have had issues with Backlash in the EQ3pro. I was approaching the stars in different directions: from parked position to Rigel (in SE, so from North to SE) back to Pollux (in E, so from SE to E). This I assume will be accounting for a fair bit of the PA error inaccuracy. For my next attempt I'll be sure to go in the same direction, however, I'm not too sure which two directions I should use exclusively on the hand control. Is this just a trail and error to see which gears are engaged in whichever direction you try? Elsewhere an interesting point was raised with regards to the +/- PA error in Synscan; is the handset reporting the error, or the required correction?

@happy-kat I have seen this, about a month ago I followed a similar instruction as outlined by @Terrierist here. A quicker way to get rough polar alignment for my purposes was to simply activate the reticule on StarWalk 2 APP and hold this against the polar scope until Polaris sits in the cross hairs.

Hi all, I had some clear skies last night so I tried the two-star alignment process via Synscan with my EQ3 pro, adjusting the alt-az according to the pa error. I didn't have much success! I was running the alignment on Rigel then Pollux and I'd always get very strange results on pa error. The figures would put the alt and az in +/- double digits alternating with each iteration on the two-star alignment process. I'm thinking this may be due to my slewing of the mount via the hadset for correction: when slewing in an opposite direction it takes a while for the mount to respond (as the gears engage) but I assume the handset registers the action despite lack of movement. Would there be anyway to offset this? I'm thinking that if I only use two directions on two stars in a single direction (I.e. From East to South or vice versa), therefore no need to backtrack the direction on the headset... Also, in what direction am I moving azimuth when it says +/- in pa error? With altitude I'm assuming it's straight forward as it's numbered. Any guidance would be hugely appreciated!

Thanks @wimvb, very helpful. Can you make any recommendations with regards to light pollution filters?