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Old 16-09-2016, 02:36 PM
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gregbradley
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Autoguiding parameters

I thought I would put it up for discussion what autoguiding parameters you find works best for your setup (it would be good to mention what setup you have to keep in context).

I am using a 670nm infrared filter screwed onto the end of my SBIG STi autoguiding camera (I find it cuts through the seeing better) and I generally don't have trouble finding a guide star (except recently with the frickin Helix which seems to be in a barren part of the sky).

I use Sky X, CCDsoft and have used PHD2 for autoguiding. Sky X is good until one night it stopped guiding prematurely for an unknown reason.
CCDsoft is very reliable mature software.

SkyX now allows to adjust the aggressiveness on X and Y both positive and negative moves. I think this is a nice feature. Often one axis seems to have larger errors than the other. You can watch it for a while and see it if it is swinging too much from + to - and ajust to suit to tame it a bit.

For my Paramount ME and AP1600 I run them similarly. min move of .01 arc secs and max move of 2. I tend to use 4 second guide exposures sometimes 4, sometimes 6 if the guide star is dim.

I calibrate often and definitely after a meridian flip. I believe if you calibrate near the meridian it will stay true over the bulk of the sky. I can't say I have done that except for after a meridian flip.

I set aggressiveness low at around 6. If its good seeing Roland Christen recommends upping the aggressiveness.

I try to pick a brightish star but not too bright and not a double star if I can avoid it.

I use autodarks (this is where the STi shines as it does autodarks so easily).

I find I get better guiding if I use 1x1 binning rather than 2x2. I also focus my MMOAG guide camera fairly closely. That has to be done after the main camera is fully in focus to be accurate.

I have my scopes well balanced in both axes and don't have stuff on top of it messing with the centre of gravity.

Cable management can be a hidden source of problems so I try to keep them somewhat tidy but not as tidy as I see some photos of people's rigs.

I use Tpoint to get exact polar alignment. I do a model of about 35 points then follow the Accurate Polar Alignment routine then do another new 35 point model and repeat until Tpoint says its good enough no more adjustments are needed. This is often on the 2nd model. I then do a large TPoint model; my current one is 349 points and I have done one that was 439 points. I active Tpoint and activate tracking adjustments. I find it can make the difference to get round stars versus a bit off.

I also find I need to redo my Polar Alignment every now and then for some reason (perhaps minor shifts in the soil after wet weather?). So it lasts for maybe 3-6 months then a redo when stars start to egg up.

I use a Pempro PEC curve.

I recently regreased my PME and I noticed PE reduced. I should redo my PEC after that but I am getting round stars so no rush.

So in summary my successful actions are:

1. Use a reliable software. Reliability is more important than bells and whistles.

2. Exact polar alignment is time well spent.

3. A proper PEC curve is time well spent.

4. Good balance.

5. No cable tangle.

6. Good calibration.

7. 4-6 second guide exposures on a high end mount and probably much shorter on a less high end mount. I used to go for 1 second exposures with a Tak NJP and I would get better results.

8. Good focus on your guide camera.

9. Use 1x1 binning if you can for your guide camera and low aggressiveness except on nights of good seeing.

10. A 670 infrared filter screwed onto the end of your guide camera can help cut through the seeing at the expense of slightly dimmer guide stars (not so much an issue for me with CDK17 or Honders 12 inch F3.8 as they are really bright scopes but it probably would be for a small refractor).

11. Don't pick double stars or too bright, pick a round tightish star. If you get bad errors try another star,k they are definitely not all equal.

12. Don't confuse eggy stars from bad tilt/tip or miscollimation for guide errors. Similarly don't confuse slight blooming of bright stars for guide errors (hello Starlight Express Trius 694).

13. PHD2 is quite a sophisticated guiding program. Sky X is good too and has dither.

14. I have gotten good results from guide scopes but MMOAG has consistently been the best guiding accessory for me. OAG is the way to go so far.

What do you find successful?

Greg.
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  #2  
Old 16-09-2016, 04:06 PM
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Peter Ward
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CCDops
AO-X with exposures as short as the guide star allows (3-10 hz seems to be the sweet spot)
Provided I haven't rotated the camera, then calibration vectors seem to work well for weeks... if not months.
Haven't redone the polar alignment in years......

Guess I'm simply not trying hard enough
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Old 16-09-2016, 08:56 PM
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Atmos (Colin)
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I guess I was pretty lazy when it came to auto guiding setting. I had two lots of setting depending on what software package (SGP or MaxIM) and which laptop I was using. One laptop would change direction after a meridian flip and the other wouldn't, things like that. Setting were the same as far I could tell!

In PHD2 I used 0.5-1s exposures and just whatever PHD suggested I should.

In MaxIM DL I used a bunch of different settings. I actually found that sometimes 0.1s exposures, aggressiveness of 8, min move of 0 and max move of 0.3. The 0.3 was calculated from my uncorrected PE (I'd never attempted to correct for it), meant that even with the star jumping all over the place with sky conditions the mount couldn't jump too far in any single movement but would still be able to compensate for PE.

I found this worked best for my setup at 660mm with my EQ6 and guide scope BUT it was also the most unstable (guide camera dropouts) so I didn't use it unless I was babysitting it. If I wasn't, 1s exposures and MaxIM default settings (aggressiveness of 8, min move 0.01 and max of 2).
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Old 16-09-2016, 10:23 PM
DJT (David)
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I use MaximDL and use parameters mostly calculated using the resource on CCDWARE plus a bit of trial and error depending on seeing.

http://www.ccdware.com/resources/autoguidercalcv4.cfm

With the short focal length refractor, as I have a self guiding CCD for LRGB but behind the filters I take advantage of that so no guide scope or OAG but its not so good for NB. I can get away with guide exposures every 8 seconds at this focal length, usually binned, prefarring to avoid moving the mount too often if I can help it.

For the GSO RC8 I use an MMOAG which is excellent. Guide Star shapes are crud due to the combination of curvature you get with those scopes alongside the size of the chip (stl6303) but you can work around that and I get good results. Depending on what stars I can pick up for guiding I set the exposure length for around 6 seconds.

Good thread, Greg.
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  #5  
Old 17-09-2016, 10:58 AM
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Merlin66 (Ken)
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I guide on-axis (reflective slit) on a C11 at f10 and NEQ6pro using a Lodestar camera 1x1 binning.
I've used PHD (1&2) for many years, but now let AstroArt control the cameras and the guiding.
The slit gap is usually around 25micron and I guide for ten min subs....
No issues, no drama.
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