NEQ6PRO E/W drift max/min question

[coldlegs]

Could anyone who has used or owns an neq6pro mount tell me what the maximum (or minimum) drift (sec/sec) either east or west you get after correctly polar aligning and balanced the mount is? I'm trying to get a general idea of the tolerance of this is as I'm getting about 0.5 sec/sec with mine and think that may be far too much but I'm not sure yet. I haven't done a PEC and fed that back in to eqmod yet and I'm curious to know what the basic mount does or for that matter how much a PEC can correct for.
Thanks
Stephen

[RobF]

Well theoretically you can get it down around zero if you're spot on Stephen. How are you measuring your drift? Even assuming you are pointing perfectly at the South C pole, you'll need to have perfect balance, no flexure, great seeing, etc.

If you're guiding for astrophotography, then its more the rate of change that matters. Assuming you're talking arcsec/sec, as a guide my HEQ5Pro moves through about +/17 arcsecs over a 8min worm cycle even if its aligned "perfectly" (i.e. that's a rough indication of its PE). Some would say there's actually a benefit in being slightly off to one side so that your guiding is constantly tweaking your DEC axis in one direction, thus avoiding backlash when your mount tries to reverse DEC tracking.

[coldlegs]

Rob
I was about to reply with more detail when it dawned on me what the problem could be. I run a fairly long (8metres) cable out to the scope and although the red power light is solidly on at startup it does tend to flash during driving. The manual says it means the power is low and I think this voltage drop may be the cause of the mount tracking slightly slower than it should be. I'll check it out over the next week or so and report back.
Stephen

[coldlegs]

Rob
I checked the power at the mount and found 11.7v which was slightly low, so increased it to 13v but found no change in the drift. Drift aligned the mount then did some PEC data runs and noticed on the K3CCDtools screen the drift was about -18.5arcsec/min. The PEC analysis says the R/A trend is Y=0.3087X +- 11.5 but I'm not sure if this the same thing I'm chasing. Rob, what is your PEC R/A trend? I included a screenshot of the PEC analysis for member comments so everyone feel free to jump in. Discovered that the lunar rate had less drift (+10.2) than the sidereal rate (-18.5) and got so frustrated at trying to figure out what's wrong that I took a bunch of shots of the orion nebula by flipping from sidereal rate to lunar rate to keep the image centered over 30 minutes. Still this is no long term answer. Rob, if you aligned everthing perfectly, then switched to “lunar rate” what would the expected star drift in arcsec/minute be? Would it be +28.7 (-18.5 + 10.2)? I guess what I'm trying to work out is what the rates in arcsecminute are for sidereal and lunar rates. I tried using the eqmod “custom rate” and tried everything from 0.0000001 to 30 and the stars drfited/streaked far to fast. The dec rate was left at 0. I am at a complete loss as to how to use the custom rate function and what numbers would be a useful starting point, so if anyone is listening help would be greatly appreciated.
Regards
Stephen

[RobF]

Hi Stephen

When I read back through your original post, I think you're fundamentally concerned your guiding isn't right and want to compare with other people?

PE is nice to sort out, but if you're relatively new to this game its probably better that the conversation focuses on what guiding software you're using and what sort of performance it shows on the tracking graph it shows. FWIW, your PEC looks about average for an EQ mount I would say. You may be able to improve it with PEC or mechanical tweaking, but would suggest you look at other things first, specifically:

- what camera and scope combination (main and guiding) are you using?
- critically look for flexure (e.g. guidescope focuser and mounting)
- are you using a guidescope or off axis guider (or 2nd chip)
- how good is your balance in every dimension?
- guiding parameters (you can get a lot of improvement by changing the guide interval, max/min movement, etc)

All this stuff really needs to be systematically tweaked over many months (or years :D) of careful monitoring.


Getting back to your last post, its relatively unlikey the sidearal rate of your mount is a major issue. Its good that you've eliminated power as a problem. Depending on your guiding and main OTA setup, next goal I would suggest is to try and get your guiding error down under a few arcsecs max variation during an extended exposure (>5mins). Do you have any images from your last guiding session?

[coldlegs]

Rob
I'm not guiding. This is a 6"newt on the mount with a toucam at prime focus. Nothing else. The mount is levelled, balanced and ccd drift aligned until no movement over a two minute period either straight up or just above the western horizon. No matter what I do it will not keep up with the western movement of the stars. It always has a -18.5 arcsec/minute r/a drift which effectively means the stars drift west by 18.5arcsec/minute and seems to be excessive to me. I'm not sure if guiding would even be possible given the drift rate. During a one or two second guiding exposure the stars would drift about 0.7arcsec and I don't know if that's too much for guiding. Is it? So I'm trying to determine if it is excessive and/or where problem lies. Is the right ascension motor/electronics in the mount faulty? I know it is usually the user at fault but assuming it's the mount, how do I prove it? That's the rub and what I'm trying to do. Hence the attempt to find out
1/ r/a rate in arcsec/min (to compare with current measurements)
2/ lunar rate in arcsec/min (to compare with current measurements)
3/ Does eqmod constantly send pulses to the mount during normal sidereal rate tracking and I'm losing some due to my long cabling.
4/can I play with the custom rate and if so how?
Basically any data that would allow me to determine the nature of the fault (if there is one).
Thanks for the replies
Stephen

[coldlegs]

Rob
Found some old CCD drift alignment pictures that tell the story. The procedure is from
http://www.astrophotoinsight.com/public/ccd-drift-method .
Regards
Stephen

[Merlin66]

On the EQMOD Y! forum there is some discussion about the firmware version ( V1.06 I think) and the lack of fine tracking control.
Can you check your mount's firmware version from the utilities menu??

[coldlegs]

My hand controller reports the software version is 03.27 which I think is the latest(?). One of the eqmod screens reports that the mount version is 000402. Not sure if that's the latest NEQ6PRO but it was purchased last August, so it's reasonably new.
Stephen

[RobF]

Hmm, looks like I jumped to the wrong conclusion re guiding. I've looked up a tracking log from last night, and my HEQ5 was correcting (mainly slowing) in RA around 7 arcsec/min with reasonable polar alignment (err, that means dumping it straight on the marks I've made on my outside tiles...!).

I know its RA drift of concern, but can you just confirm you're not tracking directly overhead for PA, but rather at intersection of meridian and celestial equator (i.e. 0 degrees DEC)?

[peter_4059]

Stephen,

There is a rate measurement utility and adjustment capability in eqmod. You should try posting your question on the eqmod yahoo group as the developers are very proactive at troubleshooting these issues.

Peter

[coldlegs]

Rob
Good question. That may be my problem. I'm not pointing due south at zero dec but straight up (ah dummy!!). Well slightly west of straight up. I'll have to read up the eqmod manual to see how to set the scope to due south at zero dec. And I'll have to wait for clear skies to do it. It's been a bad year this one. Here's hoping the next is better.
Thanks Rob
That reminder may have solved it.
Regards
Stephen

[Merlin66]

Slight correction...in the southern hemisphere zero dec and Pointing NORTH.

[Visionoz]

Stephen

Based on your posted PE graph from PERecorder several posts before, it looks more likely that your mount's PE is actually aro 30arcsecs peak-to-peak and therefore the average is aro 15-20arcsecs which is quite normal for the EQ6 -auto-guiding will definitely be able to guide out for you

It is when the graph is not sinusoidal that you should be worried about your PE

Yep your drift alignment is still not spot-on when you still have drift - generally it is better if you test the alignment for drift for at least 5mins rather than 2mins to ensure that it is 100% spot-on

HTH
Cheers
Bill

[coldlegs]

Quite right. "pointing north".

QUOTE=Merlin66;679920]Slight correction...in the southern hemisphere zero dec and Pointing NORTH.[/QUOTE]

[coldlegs]

Well folks, Ive managed to get between the clouds and gather some more data. Noticed that the r/a drift got worse the further away the declination was from the south celestial pole. I believe this is due to K3ccdtools drift explorer measuring the dift with a constant field of view whilst the rate at which the stars move across a given field of view varies from almost zero near the scp to quite fast at zero declination (assuming the r/a drift is slower than the sidereal rate). If the r/a rate was perfect i.e. the same as the sidereal rate , then there would be no drift at all. Hence the error gets bigger the more positive the declination is. So I did a spreadsheet of the r/a drift error relative to the difference between the SCP and the declination setting and found a constant error which is about -1.5% of the sidereal rate so I'm convinced my mounts r/a drive is slow. Earlier I has tried to use the EQMOD custom rate (“comet button”) to correct this error but got “very fast” and “faster” results until I realised the default sidereal rate is +15.041067 which works fine in the northern hemisphere but down under the mount is postioned backwards pointing south so a minus sign is needed i.e. -15.041067. I didn't get enough time to test out adjusting the rate but preliminary tests indicate it will work. Have included a pic of the spreadsheet for any one with a calculator. Please let me know if there are errors.
Stephen