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  #21  
Old 02-09-2011, 01:24 PM
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Terry B
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Quote:
Originally Posted by DavidTrap View Post
Terry is quite correct - it shouldn't affect PHD if it's not square - it will just make things look bad on the screen.

What are you options for AG speed? Mine has 0.25x, 0.5x and 1x sidereal rate for guiding corrections. I don't think it would make too much difference as PHD will "calibrate" at what ever speed you have set.

DT
I have tried various AG speeds. I use EQMOD and guidemaster rather than phd but it shoudn't make much difference.
I fiddled with the DEC worm on my mount to try to reduce backlash. This is quite touchy. By making the worm tighter you can reduce the backlash but it seems to take a bit more "strength" to make the mount move at all. It slews perfectly well at higher speeds but at very slow speeds it will stall. I found that if I use 0.25x or 0.5x the mount would stall at certain points and not actually move in RA. I turned the speed up to 1.0x and it works. The guiding is the same. When you calibrate the software will just give shorter pulses.
I then tried loosening the worm slightly and this stopped the stalling at the expense of more backlash. A compromise that I think is inherrent in the quality of the mount (EQ6). Hopefully when I get my new mount (NJP) later this year this will become unimportant.
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  #22  
Old 02-09-2011, 05:23 PM
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hotspur (Chris)
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Ok Terry and David,thanks.

Terry the mount is a brand new Vixen GPD2 EQ mount,on a cast iron pier on a cement block that goes 1000mm into ground,and polar alignment is good.

It would seem.the issues are operator error.It would be unlikely the mount has issues.The motors are MT2 original motors that come with Sky Sensor 2000 PC.
this is second hand.(may be the motors could have issues??)

Going by the information,thankfully supplied,It seems to be looking like the settings of the backlash I had,is the cause.But unfortunately I cannot test,as major smoke in sky,plus cloudy weather

Hope tomorrow night is clear.
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  #23  
Old 02-09-2011, 07:29 PM
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hotspur (Chris)
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re Calibration

Just wondering what RA aggressiveness setting is a good place to start at?.Looking at it, I noticed it has been set 100,may be that has been too much.

Also,the calibration step for the guide scope.I have a small Borg 50 mm 'finder guider' style scope.That is only 200 mm long,I had the calibration step set at 950,it says the shorter the scope the higher the number-I think it goes up to 1500.

Any 'finder guider' AG'er's out there?

Thanks Chris

Last edited by hotspur; 02-09-2011 at 07:32 PM. Reason: detail
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  #24  
Old 02-09-2011, 08:12 PM
Alchemy (Clive)
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Are you using phd?

Can you set the guide speed ie 0.5 sidereal

I set my aggressiveness to 10%, but I do use a g11 you may need quicker if the mount is less accurate.

Watching the screen calibrate will give you the idea, just set it so you can just determine movement in the calibration routine.

If you're not using phd..... ,meh ... cant help
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  #25  
Old 02-09-2011, 09:18 PM
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Quote:
Originally Posted by Alchemy View Post
Are you using phd?

Can you set the guide speed ie 0.5 sidereal

I set my aggressiveness to 10%, but I do use a g11 you may need quicker if the mount is less accurate.

Watching the screen calibrate will give you the idea, just set it so you can just determine movement in the calibration routine.

If you're not using phd..... ,meh ... cant help
Yes,Clive using PHD.

I've just been outside,in observatory,I am just about to shut it up,its blowing a gale.But I put backlash to 0,and the mount and controller behaved very similar to when I had it 300,a little time lag between pressing button to manual control.but not a issue.

I checked PA,and it was out a bit,so lined it up.Hopefully tomorrow I will be able to try some guiding.The RA agresiveness had been set at 100,so will turn that down.

There could be hope that,this could work properly.

Cheers Chris
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  #26  
Old 05-09-2011, 10:33 AM
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re AG'ing

Had a go last night.

these are the settings I had changed RA aggressiveness settings on 50% rather than 100%.

Backlash comp set to 0

the 'calibration step' in PHD set to 1300,it was on 950,the smaller F length of gude scope-the bigger the number needs to be,I am using a 'finder guider'style scope approx only 200 mm long,or shorter.

See 4 images and there crops immediately following them.Image 1 was on the object for well over half an hour,before I took this image,this is what I would like to achive 80% of the time-is that plausible?

The other images,were not on the objects all that long before I took the images,after 1 (I had to change a battery),so that is why view in 2 and 3 is different,even though it the same object.

2,3,and 4 do show some trailing,but appear better than last weeks episode.

MAy be the experienced AG'ers here can assess these,and see if there is any meaningfull improvement.what else could I do to improve?? may be lower the aggressiveness???,I spoke to another owner of this same mount (a Japanese made Vixen GPD2) he has lower aggressiveness set.

May be lower calibration step amount again?

The seeing conditions were not the best last night,cloud about,moisture in air,moon light.But I just wanted to see I could minimize the star trailing etc from last week.

The AG seemed to work better,no loosing star all the time like last week.no noisy steps in mount/motors when guiding.

all images 5 min exp,except the last was at 6 min,focus was a little out

Thanks for any pointers-Chris
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Last edited by hotspur; 05-09-2011 at 10:44 AM.
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  #27  
Old 05-09-2011, 01:15 PM
Alchemy (Clive)
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Well it's an improvement, I'm not familiar with the mount you are using in the sense ei haven't nor have I fiddled with one.
Ive covered all the potential physical movement points.

At this point I guess you just have to pay careful attention to the guide screen whilst guiding. Just check how the star moves. If it's erratic you may need to turn it down.

There are lots of things one can do to improve things.

You can do unguided tests with phd outputting the guide data which can then be analyzed ( for this just disconnect the guide camera ) this will give you indications of what going on..... I have the program details at home but not here. Analyzing your mount will give you invaluable information, you can also do this while imaging and get an output of the mounts performance by the star trails. From memory you actually need the polar alignment to be poor to do this, the wiggles in the star trails will repeat every cycle thus giving you an idea of the periodic error in the mount.

Certainly a useful thing to do in nailing down all your issues.

On another note, I did some imaging last week ( Friday ) just having a bash at the western veil which is fairly low here so didn't expect great results. Calibrated the gear etc, left it running whilst I went inside to watch the box. I have a computer inside which allows me to monitor goings on in the observatory, so after an hour I had a squiz ..... It looked like your images.... Doh .... Turned out the USB cable to the guidescope had some moisture and stuffed the connection, with the GPUSB on mine to get it reworking it needs to be dried and computer rebooted, I figured the problem and just closed up shop for the night. Sometimes it can be the smallest thing. The giveaway for this was that the red light on the GPUSB was stuck on and not flashing with the updates, although the guide program was doing it's thing.

Keep plugging away you will get all the details sorted sooner or later.
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  #28  
Old 05-09-2011, 04:35 PM
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Quote:
Originally Posted by Alchemy View Post
Well it's an improvement, I'm not familiar with the mount you are using in the sense ei haven't nor have I fiddled with one.
Ive covered all the potential physical movement points.

At this point I guess you just have to pay careful attention to the guide screen whilst guiding. Just check how the star moves. If it's erratic you may need to turn it down.

There are lots of things one can do to improve things.

You can do unguided tests with phd outputting the guide data which can then be analyzed ( for this just disconnect the guide camera ) this will give you indications of what going on..... I have the program details at home but not here. Analyzing your mount will give you invaluable information, you can also do this while imaging and get an output of the mounts performance by the star trails. From memory you actually need the polar alignment to be poor to do this, the wiggles in the star trails will repeat every cycle thus giving you an idea of the periodic error in the mount.

Certainly a useful thing to do in nailing down all your issues.

On another note, I did some imaging last week ( Friday ) just having a bash at the western veil which is fairly low here so didn't expect great results. Calibrated the gear etc, left it running whilst I went inside to watch the box. I have a computer inside which allows me to monitor goings on in the observatory, so after an hour I had a squiz ..... It looked like your images.... Doh .... Turned out the USB cable to the guidescope had some moisture and stuffed the connection, with the GPUSB on mine to get it reworking it needs to be dried and computer rebooted, I figured the problem and just closed up shop for the night. Sometimes it can be the smallest thing. The giveaway for this was that the red light on the GPUSB was stuck on and not flashing with the updates, although the guide program was doing it's thing.

Keep plugging away you will get all the details sorted sooner or later.


Ok,Clive the graph output software you mention may be worth ago.The light on AG camera was blinking so does not appear to be a connection issue with that.

Maybe as you suggest lower the RA aggressiveness again-I think the chap I spoke with said he had his Vixen GPD2 and guider running at 40 or 20 percent correction,and he may have had the correction step set up at 1500,not the 1300 I had it set.

If that new setting still gives results as above images show.Not sure where to go then.I may ditch the lot and buy a big dob and argo navis.Certainly a lot less headaches.

I've seen plenty of people use these AG's and not had the issues I have had.Been trying to get this up and running over last four months with no success.There was a chap that use to come for astro photography nights,and was able to advise,but he has since moved on from the hobby,and bought a fresh water kyack,and well its left me up the creek without a paddle.
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  #29  
Old 05-09-2011, 05:10 PM
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DavidTrap (David)
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Chris - the graph is part of PHD. You click on one of the menu items across the top and scroll down to "enable graph" (or something like that)

DT
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  #30  
Old 07-09-2011, 11:21 PM
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An interesting thread. Autoguiding is a black art.

Here are some tips that I have learnt. I have only used PHD briefly and it seems very user friendly and does some things automatically. I use CCDsoft.

Basics:

0. Balance:

If you have a guide scope on top and then balance with the scope horizontal it may still be unbalanced with the scope at an angle as the centre of gravity shifts. Make sure it is balanced at an angle which is where you actually guide anyway.

Under balance I would include cable drag and cable management. Poorly handled cables or transformers dragging on the mount can throw off autogudiing or result in 1 out of 3 images being no good.

2. Alignment:

Perhaps less important but still a basic. Have your mount level where you can - it all helps. If on a tripod make sure it won't sink in soft soil under the weight.

Have your guidescope square to the camera and it should be seeing what the scope is seeing. Take an image with your scope and one with your guider and adjust until square or at least make sure it is parallel with the OTA.

If you have a portable setup and image at the same location but lug your gear out each time then try to make the polar alignment repeatable. By this I mean put markers on the ground for the exact position of the tripod or tape marks on your mounts RA and Dec scales etc.

With my dark site mount I found I could take it down there, shove a torch on the polar alignment scope or a laser and it would hit the ceiling. I placed a small piece of electrical tape on the ceiling. I would simply adjust the mount until the laser or torch (laser was better) was on that mark. That would take about 1 minute and it was back to being aligned where I had spent a couple of hours getting it right and marking the ceiling for next time.

3. Flexure:

If you are using a guide scope then you are one step away from the actual image you wanted guided ie the main camera's image. So anything that could make the guide scope shift slightly form what the main camera sees will mean the autguider will be moving the scope away from what the main camera images. Screw fittings, loose focusers, weak mountings of the guide scope, heavy guide cameras, dragging guide camera cables and transformers, main OTA and camera weakly fitted or not totally secure or loose focusers will mean it will be very hard to get round stars at 10 min exposures. Get everything tight, strong and rigid. Threaded adapters are better than eyepiece slide in with tightening screw type adapters.

3. Polar alignment has to be really really accurate. You can buy a cheap screen overlay from Andy's Shotglass Astronomy site called Star Targ.

Using that it becomes easy to polar align using your CCD cam or DSLR if you download the images to a computer.

Otherwise use a reticulated eyepiece and drift align until you have it veyr close.

There is free software to assist with polar alignment like PoleAlign Max. There are others.

PemPro has a polar alignment wizard that is really hot and worth the cost of the program just for that. They have a free trial.

Software Bisque T-Point is also very very good and takes it to a high level of accuracy but that is more for a permanent mount.

I have found in several years of imaging that the most important thing in autoguiding was the polar alignment. You can fiddle with software all you like but if your Polar Alignment is off then you will go nowhere.

Time spent on improving polar alignment is the most productive thing here you can do.

How good do you want it?

Perfect.

4. Only now do software settings come into it. Guide exposure times are important. Work out by trial and error which give best results. I found with my NJP 1 second guide exposures gave best results. The Paramount seemed best around 4 seconds. In poor seeing it is better to use a bit longer as the guider can chase the seeing.

Aggressiveness - If polar alignment and balance are good and the correct guide exposures for your mount are being done then this should be perhaps medium like 6-8. Too high and the mount will overcorrect. Watch the guide errors. You see a - go to a heavy + after one correction it probably means you are overcorrecting. Back it off.

There is an article about how to set backlash setting. I think its at the CCDware site, or Maxim site.

5. Guide star selection:

The first thing I do if I see bad errors and my setup has been working fine is to select another guide star. Don't select double stars. You want one that is bright enough to survive a small cloud but not bloated and too bright. Sharp and tight and fairly bright.

6. Callibration.

The software needs to know how much of a correction moves the mount a known amount. Pick a star that is by itself, that is quite bright. Set the callibration time long enough so the movement between callibration exposures is 50 pixels at least. Sometimes it improves autoguiding to recallibrate at different parts of the sky or on the other side of the meridian. It depends on how well your mount is guiding.

7. Min/max move:

I usually set this to .1 and 1. I figure a correction needed more than 1 is an error or blip in the seeing or wind and not periodic error. Under .1 and I don't want to correct it as it probably has not moved to be worth it.

8. PEC:

If your mount supports it then PEC takes you that last little step is the PEC is uneven.

9. Offaxis guiders or self guiding is better than a guide scope. Offaxis guiders are the modern way to go as the guide camera is in front of the filters and you can do narrowband. Also you have higher quality guide cameras and its easy to pick up a guide star.

10. If you've done all the above then you need to reduce your mount's PE.
A better worm (some have upgrades available). There is an ad at Andy's Shotglass Astronomy to coat gears of mounts with a hi-tech low friction coating that is supposed to dramatically reduce PE. Perhaps that is worth a shot (I don't know if it works, just saw the ad).

Join Yahoo Groups for your mount to get tips specific for that mount.

I had a Vixen Sphinx once. The mount was very stiff in rotating in one axes. That had to be adjusted as it came out of the factory too stiff and that caused issues. I don't know about other Vixen mounts.

I hope that helps.

Greg.
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  #31  
Old 08-09-2011, 08:28 PM
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re AG

Thank you Greg

For taking the time to give a very informative post-Yes,I does appear the thread is very useful for many trying to get AG going smoothly.

I have had the good fortune to talk with Clive,talking on phone really gets things sorted.

Unfortunately,there is so much smoke in air,I cannot test.But it certainly does appear the RA aggressiveness settings are too high,even at 50% on the Vixen GPD2-the AG os over correcting,so will back off to 20%

Also-a big mistake I made-the calibration step,I was under the impression this setting applied to the guiderscope,but its the imaging scope it applies too.I had the setting at the wrong end.

So between those two,-now understanding that,I hope to have improvements again.

The mount is all PA etc-its all in observatory, Greg,But will go over your post and check points you mention.

Thanks Chris
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