AZ-EQ6 GOTO accuracy woes

[Snarf]

I have recently acquired an AZ-EQ6 mount but am struggling to get decent GOTO accuracy so need some help/advice. On the plus side the mount is tracking fantastically - I have taken 4 minute unguided exposures with my DSLR and the stars are nice and round.

I am using a refractor which has 1000mm focal length and I'm just using the hand controller with the skywatcher GPS attachment that sets the date and time. i.e. no PC software involved. I have disabled the auxiliary encoders as I don't need them and have heard they can be a source of problems.

I polar align using the polarscope which I find plenty good enough to get good tracking accuracy. When I turn the unit on the GPS sets the date and time and I select daylight savings on and I have the unit in the home position so weights down and scope pointing parallel up towards the north pole (I've used the spirit level to set the setting circles so I can get the home position more accurate). I've tried 1, 2 and 3 star alignments but always have the same issue - it succeeds but then when I slew to another star (even a close one) it is a long way off (i.e. nowhere near being in view even in 30mm eyepiece). The oddest thing is that after centering the star and completing the alignment if I slew away to another star and then back to the alignment star it still points way off! In my mind I at least expected that to work - I thought it would just have some offset map between the calculated astronomical coordinates and where you've told it is really pointing so I don't understand at all how this can happen. Late last night for example I did a 1 star align on Vega and then told it to go to Deneb and had to move with the hand controller the end of the scope up a good foot to find it! It's like its completely ignoring the alignment adjustment I have to make each time to find the star so any initial error never gets corrected.

Any ideas?

[rigradio]

Well...PC for sure.
SGPro+PlateSolve2: framing, centering, & start imaging less than 5min.
No need gps, nor star alignment.
Save your time & energy.
Justmy2cents

 

[cletrac1922]

You allowing for magnetic variation when setting up facing north

I use a compass to align the north leg of my EQ5 mount

Been in the southern hemisphere, bit different, and north leg has to face south

John

 

[david_taurus83]

What error do you get after your initial alignment?

[Snarf]

3 hours ago, david_taurus83 said:

What error do you get after your initial alignment?

You mean the polar alignment error? I haven't actually checked in the info for that on the hand controller as I've been pretty happy with the tracking in my photos. My understanding is the polar alignment shouldn't really affect the GOTO anyway as it knows what the polar error is from the movements you make with the hand controller when performing the star alignments. My problem seems to be that it just appears to ignore the input I give it during star alignment movements and carries on believing the stars are where it initially thought they were. e.g. If my polar alignment was 1 degree out then when I did the star alignment I'd have to move the scope with the hand controls back to undo that and find the star in its real position. Then surely the hand controller in future should know that it needs to always apply that adjustment to the position it calculates based on its catalog, the date, time etc.

[scitmon]

To me it sounds like something is wrong with the date/time/position info being fed in.  I would try without GPS just to rule that out.

[almcl]

Not sure how relevant this will be, but how accurately is your scope pointing at the North Celestial Pole when in the home position?  Can you see Polaris in the eyepiece?  In the finder scope?  If you can't, then the first slew is always going to be off.  That doesn't explain why the updates are failing, but it may help.

[david_taurus83]

34 minutes ago, scitmon said:

To me it sounds like something is wrong with the date/time/position info being fed in.  I would try without GPS just to rule that out.

I would try this advice. Does it display the time date and lat long after it initializes? I would disconnect the GPS and do a fresh set up using the hand controller. There is an app called SynscanInit 1.9 for android which tells you what to input.

[Snarf]

On 20/04/2018 at 14:26, david_taurus83 said:

I would try this advice. Does it display the time date and lat long after it initializes? I would disconnect the GPS and do a fresh set up using the hand controller. There is an app called SynscanInit 1.9 for android which tells you what to input.

Thanks for all the advice folks, I will give that a go next time I'm out with it. The date and time it shows on the handset as set by the GPS are spot on I've checked that. I should probably double check the position is getting set correctly too as you say though as if that is wrong it could explain a few things! I use SynscanInit for Android already to help me get Polaris in the correct position in the polar scope. What I am somewhat confused about though is the home position - if the polarscope is pointing at Polaris then surely the telescope won't be exactly as its mounted somewhat higher up although parallel (or very close to parallel)? Also does it matter which side the knobs are on for holding the dovetail on the scope? I always put them on the left side in the home position as I look toward the scope facing north. I might also try the PAE at some point and see if that helps at all.

[david_taurus83]

When doing a 2 or 3 star alignment, after the first star, does it get the next star in the field of view? Have you tried with the encoders enabled? I've not used it on mine, but these mounts have a quirk where if you use the polar align feature on the handset, after the alignment the GOTO positioning is way off. The cure it seems, is after a star alignment, to get the mount to park itself, switch it off and switch back on and your good to go. Something to do with the encoders getting confused. I've set mine up once for observing, but I use a Polemaster and then a 1 star alignment. Not had any issues and GOTO accuracy is good.

[Snarf]

22 hours ago, david_taurus83 said:

When doing a 2 or 3 star alignment, after the first star, does it get the next star in the field of view? Have you tried with the encoders enabled? I've not used it on mine, but these mounts have a quirk where if you use the polar align feature on the handset, after the alignment the GOTO positioning is way off. The cure it seems, is after a star alignment, to get the mount to park itself, switch it off and switch back on and your good to go. Something to do with the encoders getting confused. I've set mine up once for observing, but I use a Polemaster and then a 1 star alignment. Not had any issues and GOTO accuracy is good.

Well the last time I tried no it couldn't get the 2nd or 3rd star in view. In fact it never seems to improve at all as if it just ignores my centering completely. Recently I've been just trying 1 star alignments as I figure if it can't get that right then it won't get anything more complicated correct. I've not tried it with the dual encoders on of late and I haven't use the polar align feature of the handset just manual polar alignment with the synscaninit app. I read read the whole manual last night and this morning and one thing I noticed in it is about a warning it displays after the alignment about stored cone and/or NP error. I've seen that message come up so I wonder if the cause could be some dodgy stored cone/NP error values that are being applied. It seems you can just set them manually to zero so I will give that a go as well.

[wimvb]

Cone and np error shouldn't matter. Just for completeness, here's my procedure, which gives me spot on goto accuracy, even with a barlowed 17 mm eyepiece:

- Set up tripod. Aiming north leg to polaris.

- Level tripod, using a small builders level

- Mount switched off. Setting circles in correct position. Mount in parked position (pointing due north, cw bar down).

- Turn on mount. Use synscaninit for location and time input. Make sure north and east/west hemisphere are correct.

- 2 star alignment. First star with 25 mm eyepiece, finetune with barlowed 17 mm eyepiece with homemade crosshairs. Also adjust finderscope now.

- Align 2nd star with barlowed eyepiece.

- Note polar misalignment.

- Use synscan polar alignment routine to improve pa.

- Repeat 2 star alignment, and check polar alignment error.

This procedure should give you a very accurate goto alignment. The pa accuracy after two iterations of polar alignment is good enough for (guided) imaging. Usually, if the pa error is small, even the first alignment star is within the fov of the 17 mm eyepiece.

I never slew the mount manually when it's switched on, but only use the synscan hand controller.

Hope this helps.

 

[michael8554]

On 20/04/2018 at 00:01, Snarf said:

The oddest thing is that after centering the star and completing the alignment if I slew away to another star and then back to the alignment star it still points way off! In my mind I at least expected that to work

To my mind this seems a reasonable test, even if the alignment map is incomplete it should go between two stars already mapped.

Is the error in RA or Dec or both in this test?

If your encoders are optical  one may be miscounting ticks due to dirt or grease or a fault.

Michael 

[Padraig]

Hi Snarf, 

how did you get on with your goto, as I have similar issue and only starting out with a new az-eq