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Old 22-06-2015, 07:25 AM
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Autoguiding tips and tricks

I thought I'd start a thread about autoguiding to get some ideas going on that may be helpful.

One question I have is time delay. I noticed Martin Pugh mentioned once he uses a 1 second delay after corrections in his autoguiding. I don't know if he does that all the time or just some of the time.

Anyone noticed any improvement in guiding from doing that? I have done that when using shorter guide exposures and if its windy or bad seeing.

I guess it would help more on a mount that had a bit of backlash or was struggling a tad as it would give the mount a chance to settle.

I often see the guide corrections start off a bit high drift down a bit and when its nicely aligned, balanced it just pops down into a lower range. I think this is a similar thing as the bounces and momentum of the mount wears down gradually.

The first thing I learnt about autoguiding is its not a solution to bad polar alignment. It tends to be as good as your polar alignment and balance.
So I spend a fair bit of time on getting the polar alignment as good as possible.

I thought of a potential good accessory someone could make. That would be a polar alignment scope with a CCD camera in it so you could plate solve the image when its pointing at the SCTParea and adjust until the reticle matches exactly. Just like you do manually but without the crouching down and the dim SCP Octans stars.

I'd like to hear some opinions about Min/Max move and what aggressiveness you use under what conditions.

A few points I use are if the seeing is not so good it makes sense to use longer exposure times for less often corrections. It would also make sense to set the max move lower so you are not trying to correct the seeing variability.

If the minimum move were too low then the mount would be correcting mostly for seeing and the correction would be meaningless as we only want to correct for drift and periodic error of the mount.

I use CCDSoft and about to switch over to the Sky X. It all works in Sky X now but haven't used it as clear nights are not common and I don't want to find out I did not know something and I got no data overnight!

Here is a quick summary of what I do:

1. Concentrate on polar alignment and Balance.
2. I calibrate the autoguider often. At a meridian flip or if I move too far away from the last location imaged.
3. I find the selection of the guide star makes a huge difference to the guide errors. I am often surprised at how much guide errors can drop if I simply select another star. I usually pick a guide star that is not too bright and is very round and no double stars and without another similarly bright star too close by that could confuse the autoguider about which is the guide star. I often use the auto button in CCDSoft to select the star and use that for calibrating. I add a 1 second delay when calibrating otherwise on SB mounts which move fast I can get a streaky star whilst it does the calibration and I don't want that.
4. I vary the exposure length but the better mounts when best setup I tend to go a bit longer. Currently I am using 3 seconds on the PMX and the Honders and 4-6 seconds on the PME with the CDK17.
5. Off axis guiders have been the best autoguider solution I have used so far.
6. I am looking to achieve guide errors that range from .02 to .5 that will give round stars. Errors greater than .5 on average will give elongated stars. Errors averaging over 1 are a waste of time and the stars will be unacceptably elongated.
7. The most accurate polar alignment tool I have used is T-Point and its polar model feature. The Sky X has added a feature recently called accurate polar alignment with T-Point where you adjust the mount until the bright star is centred in the image. It seems good. Pempro polar alignment wizard is another good tool I have used if I have trouble using T-Point (T-Point can be a bit fussy and hard to get going sometimes at least for me).
8. Sometimes elongated stars are not guiding related and its tilt of the camera, sag in the imaging train, wrong spacing to reducers and flatteners. Of course autoguiding is no solution to heavy wind.
9. Make sure everything is tight, all adapters are seated properly, the scope is mounted securely and balanced well, the counterweights are tight and try not to use counterweight shaft extensions and keep the counterweights up as high on the shaft as you can. There could be a discussion here about is it better to increase the number of counterweights and have them higher up the shaft or less and have them lower down the shaft.
10. Refocus often as it affects the OAG stars as well. I haven't found tight OAG focus to be vital but it does help.
11. As far as autoguiding software goes I'd like to hear opinions about which ones work best. CCDSoft has been my goto software and its very familiar to me.
12. I don't have any backlash settings on my autoguiding, I use direct guide (for SB mounts) and I use 50-75 as the setting for the calibration. That could be increased if its a wide field scope like an FSQ. I currently am using aggressiveness at 3. I find when PA is perfect, balance is perfect then you are only doing gentle corrections and don't want to overcorrect.
13. It pays to watch the correction errors and if you start seeing + to - too often then its just correcting the last correction so turn down the aggressiveness or increase the guide star exposure time.
14. I use auto darks on my SBIG STi guider ( a fabulous guider and my favourite of alltime, SBIG really got that little sucker right). If not hot pixels can throw off the software and are often brighter than any guide stars and you can get crazy large corrections all of a sudden.
15. Once I have autoguiding working well as above I add Protrack to the corrections as it corrects for slow flexes whilst the autoguider corrects for PE. With my CDK17 that takes stars to the final roundness I am after.
16. I sometimes use a .6X (I think its .6 it may be .5X) reducer that attaches to the end of the STi. This makes guide stars brighter and more guide stars so that is a worthwhile accessory.
17. I have also used a 750nm IR filter attached to the end of the guide camera to see if guiding in infrared cuts through the seeing better. I find it dims the stars quite a bit but still useable on many occasions but the improvement to guiding was not always seen. So I tend not to use it. Perhaps a better IR filter that allows everything above 750nmto go through is the go. This one is an Edmunds Optics one and they have several. Its worth experimenting as a simple way to incorporate the IR cutting through the seeing effect.
18. I have no experience with AOs at this time but am about to use one.
19. Don't overload your mount and keep it in good condition. Keep screws that tighten in good condition and stripped heads or missing screws need to get replaced.
20.. As far as minimum/maximum move is concerned I use .1 and 3.0. I sometimes lower that to .2. If its windy I would lower that as the larger numbers are simply wind caused and once the gust is past the mount should settle. Too low and actual PE corrections needing to be done get missed. Too high and non PE errors are being corrected like wind gusts.

Greg.

Last edited by gregbradley; 22-06-2015 at 07:55 AM.
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Old 22-06-2015, 09:03 AM
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Hi Greg,

Thanks for sharing. You've mentioned some really good points here, on a subject which always deserves discourse.

Quote:
Originally Posted by gregbradley View Post
One question I have is time delay. I noticed Martin Pugh mentioned once he uses a 1 second delay after corrections in his autoguiding. I don't know if he does that all the time or just some of the time.

Anyone noticed any improvement in guiding from doing that? I have done that when using shorter guide exposures and if its windy or bad seeing.

I guess it would help more on a mount that had a bit of backlash or was struggling a tad as it would give the mount a chance to settle.
I've never used this feature, but it makes sense that it would help in situations where the mount has significant backlash or is under heavy load.

Quote:
The first thing I learnt about autoguiding is its not a solution to bad polar alignment. It tends to be as good as your polar alignment and balance.
So I spend a fair bit of time on getting the polar alignment as good as possible.
This is something that can't be stressed enough and these are probably the two most critical factors in successful auto-guiding. Since I don't yet have an Obs, I usually spend one night setting up, refining polar alignment and auto-guiding, and then spend the following night imaging. It always pays to go that extra mile with the polar alignment.

Quote:
I thought of a potential good accessory someone could make. That would be a polar alignment scope with a CCD camera in it so you could plate solve the image when its pointing at the SCTParea and adjust until the reticle matches exactly. Just like you do manually but without the crouching down and the dim SCP Octans stars.
This is a really good idea and could be easily implemented. Dion over at Astronomy Shed demonstrated a basic CCD (I think it was a modified Phillips TouCam) connected to an EQ6 polar scope. Assuming the required source images are available at that focal length, incorporating plate solving would be simple enough. The real killer app would be to have motorized alt/az adjustments which take directions from the plate solving output!

Quote:
I'd like to hear some opinions about Min/Max move and what aggressiveness you use under what conditions.

A few points I use are if the seeing is not so good it makes sense to use longer exposure times for less often corrections. It would also make sense to set the max move lower so you are not trying to correct the seeing variability.

If the minimum move were too low then the mount would be correcting mostly for seeing and the correction would be meaningless as we only want to correct for drift and periodic error of the mount.
Some good advice right there. Extending your guide camera exposure time can help "average out" the effects of seeing on the guide star.

I never really saw much gain from adjusting the min/max values, until I started using AO. Because AO usually relies on fast guide camera exposures, the star will obviously bounce around a lot more. Increasing the minimum movement threshold instructs the AO to ignore the high order atmospheric scintillations, since we can't correct for those, even at 10Hz. Neglecting to do this when the AO is running at something like 10Hz results in a constant clatter of the actuators, as the unit desperately tries to correct for every minor change in the guide stars appearance.

To see how the min/max values would influence the operation of the SXV-AO, I set the guide camera exposure time to 0.01s and took a single 30 minute exposure of Antares, whilst using it as the guide star via the ONAG. In preparation, I increased the min movement variable until the AO actuators stopped going berserk and then tweaked it so that significant changes in the guide star, such as the effects of low-order seeing, would be corrected. It addressed the issue of "chasing the seeing"; Antares itself and surrounds were very well defined, but this diminished in an almost radial fashion towards the edge of the field (1.162 arcsec/pixel, 0.9 degrees field radius).

Brett

Edit: Apologies, Greg. Didn't mean to jump in before you'd finished editing!
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Old 22-06-2015, 09:36 AM
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http://www.ccdware.com/resources/autoguidercalcv4.cfm

I've used this to set my values in MaxIm DL.

I use the SBIG Remote Guide Head nowadays as I've got narrowband filters installed in my STL-11000M so the values for MaxIm DL guiding are set based on the RGH and FS-60CB, and not the FSQ-106N and STL-11000M.

H
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Old 22-06-2015, 09:41 AM
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some good info there Greg.

I too recalibrate PHD every new portion of the sky I enter for imaging.

when centering or framing the object I always end with up and right to reduce backlash effects.

how does plate solving go with OAG? my OAG stars aint star shaped that is for sure!

Cheers

Russ
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Old 22-06-2015, 09:44 AM
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Myastroshop.com.au used to retail an adapter that fitted a malincam/GStar or similar to the polar scope of the EQ6 and maybe others. Not sure if it is still available.

But, with a good compass (with mag. deviation offset) and a good inclinometer, is it even necessary? using the tools just mentioned, I always get to within a couple of minutes of the pole, and then adjust with an iterative alignment or a drift alignment. Takes maybe 30 minutes all up to get to within a few seconds of the pole.
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Old 22-06-2015, 09:45 AM
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I agree about recalibration. Don't care what some "exspurts" say - I recalibrate EVERY new target, and I ALWAYS have round stars. Period.
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Old 22-06-2015, 10:02 AM
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H, are those min/max moves applicable to BOTH axes of movement?

If I enter my parameters (using an 8 arc sec per pixel guidesetup - yeah, it's wide ), it generates a min of 0.033 and a max of 0.133 - do I set these in maxIM to BOTH axes the same?

Now guys, what about anti-stiction - on or off? How many cycles?

Also, do you set the scope declination or not? Is it necessary if we re-calibrate each target? I have NEVER set it, never had an issue.
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Old 22-06-2015, 10:14 AM
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Hey Lewis,

The default MaxIm DL values are identical for both axes, so, yes, I've just copied my values to both axes, too.

However, at the moment, I'm suffering from some anomaly that's causing my guide graph to go haywire on the RA axis. I'm not sure if I've lost balance, but, it's driving me nuts. Will have to spend a little time sorting that out.

I've asked the wife if I can buy a Paramount MX+; the laughter that ensued meant "no", I'm assuming.

H
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Old 22-06-2015, 10:53 AM
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Quote:
Originally Posted by LewisM View Post
H, are those min/max moves applicable to BOTH axes of movement?

If I enter my parameters (using an 8 arc sec per pixel guidesetup - yeah, it's wide ), it generates a min of 0.033 and a max of 0.133 - do I set these in maxIM to BOTH axes the same?

Now guys, what about anti-stiction - on or off? How many cycles?

Also, do you set the scope declination or not? Is it necessary if we re-calibrate each target? I have NEVER set it, never had an issue.

I haven't heard of anti-stiction, is that something in Maxim? I have never used Maxim.

I think you've got your image scale wrong. Its highly unlikely its 8 arc secs/pixel. Most setups are .5 to 2 arc seconds per pixel or an FSQ may be as much as 3.5. You can get a free download of Wodaski's image scale calculator. I use it all the time. Its very handy. Especially if you are evaluating various cameras on your scope.

Greg.
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Old 22-06-2015, 10:56 AM
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Quote:
Originally Posted by rustigsmed View Post
some good info there Greg.

I too recalibrate PHD every new portion of the sky I enter for imaging.

when centering or framing the object I always end with up and right to reduce backlash effects.

how does plate solving go with OAG? my OAG stars aint star shaped that is for sure!

Cheers

Russ

I don't plate solve the OAG guide camera only the main imaging camera through the scope for T-Point. Oh are you referring to the idea of plate solving a cam attached to a Polar Scope.

The main problem would be making sure its mounted very squarely or it would introduce error.

It may not even need to be plate solved - just make it easier to see the stars, the Octans Trapezium stars. They are hard to see even at a dark site. But a plate solve would let you know where you are and where you need to go as The Sky X can overlay your image on the star chart.

Greg.
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Old 22-06-2015, 11:03 AM
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Quote:
Originally Posted by Octane View Post
Hey Lewis,

The default MaxIm DL values are identical for both axes, so, yes, I've just copied my values to both axes, too.

However, at the moment, I'm suffering from some anomaly that's causing my guide graph to go haywire on the RA axis. I'm not sure if I've lost balance, but, it's driving me nuts. Will have to spend a little time sorting that out.

I've asked the wife if I can buy a Paramount MX+; the laughter that ensued meant "no", I'm assuming.

H
You just really need to make a little checklist for possible errors:

1. Polar Alignment OK?
2. Scope balanced in both axes?
3. No cable drag or obstacle?
4. Autoguiding on a single star not a double?
5. Guide rates correct? (.5 sidereal is common).
6. Guide exposure length about right? (1-4 seconds is usual as much as 6 on a high end mount, shorter on a not so good mount like 1 second).
7. Are you getting flexure? Adapters all tight, when you press on the imaging train does it flex?
8. Guide scope flexure?
9. Something loose?
10. Autoguider not calibrated?
11. Getting hot pixels that the software confuses with the guide star? (sudden large errors like 13.5 are hot pixels) Use auto dark subtract.
12. Something wrong with your mount? Gears meshing too tight or too loose, some play , something stiff and tight needs loosening or regrease.
13. Tripod/pier not stable. Mount not levelled and way out?

Greg.
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Old 22-06-2015, 11:06 AM
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Quote:
Originally Posted by Octane View Post
Hey Lewis,

The default MaxIm DL values are identical for both axes, so, yes, I've just copied my values to both axes, too.

However, at the moment, I'm suffering from some anomaly that's causing my guide graph to go haywire on the RA axis. I'm not sure if I've lost balance, but, it's driving me nuts. Will have to spend a little time sorting that out.

I've asked the wife if I can buy a Paramount MX+; the laughter that ensued meant "no", I'm assuming.

H
Thanks for the link. Its telling me I should use .5min and 2 max.

I'll try that. I use .1 and 2 at the moment. I have used .1 and 3.
Come to think of it .1 is a bit low as anything under about .2 would be questionable as to whether its PE. I just know when I see errors ranging from .01 to .4 I am going to have beautiful round stars with a 9 micron pixel camera and 1159mm focal length.

At 3 metres focal length that would be .2 to .8 errors. Over 1 then its eggy stars.

Greg.

Quote:
Originally Posted by LewisM View Post
H, are those min/max moves applicable to BOTH axes of movement?

If I enter my parameters (using an 8 arc sec per pixel guidesetup - yeah, it's wide ), it generates a min of 0.033 and a max of 0.133 - do I set these in maxIM to BOTH axes the same?

Now guys, what about anti-stiction - on or off? How many cycles?

Also, do you set the scope declination or not? Is it necessary if we re-calibrate each target? I have NEVER set it, never had an issue.
Quote:
Originally Posted by Octane View Post
http://www.ccdware.com/resources/autoguidercalcv4.cfm

I've used this to set my values in MaxIm DL.

I use the SBIG Remote Guide Head nowadays as I've got narrowband filters installed in my STL-11000M so the values for MaxIm DL guiding are set based on the RGH and FS-60CB, and not the FSQ-106N and STL-11000M.

H
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Old 22-06-2015, 11:08 AM
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Quote:
Originally Posted by gregbradley View Post
I haven't heard of anti-stiction, is that something in Maxim? I have never used Maxim.

I think you've got your image scale wrong. Its highly unlikely its 8 arc secs/pixel. Most setups are .5 to 2 arc seconds per pixel or an FSQ may be as much as 3.5. You can get a free download of Wodaski's image scale calculator. I use it all the time. Its very handy. Especially if you are evaluating various cameras on your scope.

Greg.
Greg,

That's using a mini-finder-guider with a focal length of 210mm (8.3"), and a Lodestar with average pixel of 8.3 microns - so, if I use the (8 x pixel size)/focal length, this seems to indicate 8 arc sec per pixel. Unless I am doing something VERY wrong or misunderstanding!

MaxIM has the anti-stiction feature. Their manual is less than elaborate in this regard, so I have always ignored it.

I have had issues in the past with MaxIM reporting no movement in Y - I had attributed most of that to backlash (almost eliminated now), so am starting to wonder if the image scale of the guide image is too small at the default settings to effect truly precise guiding. I shall try the adjustments above - IF my maths is right, hopefully tonight.
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Old 22-06-2015, 11:41 AM
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Oh I see. Yes that is about 8.3 arc secs/pixel.

And that works OK?

What focal length and scope are you imaging with?

I have the STi lens guiding kit and I found it did not work at 1050mm focal length reliably. Most often it gave eggy stars and very occasionally round ones.

Greg.
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Old 22-06-2015, 11:48 AM
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Greg,

My Running Chook image was done using the guider setup I have described, but with an f/8 refractor as the imaging scope. I now have an FSQ-106 again.

I have considered going MOAG or longer FL guidescope, but still undecided. Maybe just add a barlow to the mini-guider Though, with the guidescope being f/4.2 to the telescope's f/5, I thought it should be compatible enough?
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Old 22-06-2015, 04:20 PM
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I don't know Lewis, it seems a bit skinny to me.FSQ is a short focal length scope but its ultra sharp. How much of that ultra sharpness are you giving away to differential flexure? I would suggest a substantial amount. So you spend a bomb on ultra sharpness but don't actually receive it in the final image. A 1x1 binned 16803 images is several screens wide and shows up even the smallest guide errors. A displayed image is substantially reduced down from that massive size so it can hide some of these guide errors. I have had 2 FSQs and getting ultra sharp round stars is not necessarily totally easy either.

I am not a fan of guide scopes although I do use one sometimes on my CDK17 with its reducer. MMOAG is so much superior its not even close. Guide scopes invariably flex to a greater or lesser degree and reduce resolution of the final image.

A barlow is just another thing that can flex. I only use screw adapters not eyepiece holder type fittings. They often flex and they come become loose if they get cold.

Greg.
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Old 22-06-2015, 05:24 PM
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Not sure about flex with my guide scope setup Greg, as I do NOT use standard guide rings; rather, I use rings that fit the finder guider's OTA precisely (securing the tube with 6 grub screws), which is mounted to a mini-vixen dovetail, clamped to the main OTA rings.

Thus (shown on now sold FC-100):
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Old 22-06-2015, 06:46 PM
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Hi Greg,

Well, I'll be most curious to see if you actually do better with a min move of .5 when you are obviously getting good results with .2. By setting .5 are you not essentially saying that a guide star movement of .5 pix is to be totally ignored and not corrected? Yes, I suppose one could argue that seeing of 2 arc-sec would blur that anyway, yet, I constantly hear and read complaints from people that gripe about a RMS already lower than the min move they have set. Maybe I don't understand something but if you set the min move to .5 then you won't even correct until the star has moved .6, and then if aggression is set to 3 it will move in the correct direction .2 or so. So how would that translate into a good RMS? I personally think a better way to combat poor seeing is to increase exposure (as you have mentioned in the first post). Where we part company is that I think slightly higher aggression might be necessary as the exposure increases due to the fact that the mount might have drifted further away during the longer exposure.. If the aggression is set too low the correction might not be large enough. Anyway, in my limited experience that seems to work for me. I've found with my MEII I can do long exposures (6-10+ seconds) and that works usually much better than short. But, I think to do that you need good PEC and good Protrack.. You might want to see how long you can go with just PEC + Protack. Even if it is "only" 30 sec one could argue not to make corrections every 5 sec! I think if you start to use TSX for guiding once you calibrate I don't believe you need to recalibrate unless you change something on the guide camera.

Peter
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Old 22-06-2015, 08:15 PM
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Quote:
Originally Posted by LewisM View Post
Not sure about flex with my guide scope setup Greg, as I do NOT use standard guide rings; rather, I use rings that fit the finder guider's OTA precisely (securing the tube with 6 grub screws), which is mounted to a mini-vixen dovetail, clamped to the main OTA rings.

Thus (shown on now sold FC-100):
If you are getting round stars then you are there. I've seen some Honders setup that use the Baader vario finder scope with an AP made special set of rings to attach it.

Roland from AP has said that guide scopes should be attached to the OTA body not the rings. When you think about it the scope could flex slighty with regards to the rings and its the scope you have to match not the rings.

But if you are getting round stars like these guys using the Baader vario finder as a guide scope on the Honders then you are there. If not then this would be something to look at.

Greg.
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Old 22-06-2015, 08:20 PM
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Hi Greg,

Well, I'll be most curious to see if you actually do better with a min move of .5 when you are obviously getting good results with .2. By setting .5 are you not essentially saying that a guide star movement of .5 pix is to be totally ignored and not corrected? Yes, I suppose one could argue that seeing of 2 arc-sec would blur that anyway, yet, I constantly hear and read complaints from people that gripe about a RMS already lower than the min move they have set. Maybe I don't understand something but if you set the min move to .5 then you won't even correct until the star has moved .6, and then if aggression is set to 3 it will move in the correct direction .2 or so. So how would that translate into a good RMS? I personally think a better way to combat poor seeing is to increase exposure (as you have mentioned in the first post). Where we part company is that I think slightly higher aggression might be necessary as the exposure increases due to the fact that the mount might have drifted further away during the longer exposure.. If the aggression is set too low the correction might not be large enough. Anyway, in my limited experience that seems to work for me. I've found with my MEII I can do long exposures (6-10+ seconds) and that works usually much better than short. But, I think to do that you need good PEC and good Protrack.. You might want to see how long you can go with just PEC + Protack. Even if it is "only" 30 sec one could argue not to make corrections every 5 sec! I think if you start to use TSX for guiding once you calibrate I don't believe you need to recalibrate unless you change something on the guide camera.

Peter
I don't know Peter, that's just what the CCDWare min max move calculator came up with as I have never used those settings. Next clear night.

I agree higher aggressive settings may be needed for longer guide exposures. It sounds right but when your mount is really spot on not a lot of correction is needed. So whatever works. Its something to check when you are guiding which gets the better result.

Its hard to check several variables at once on guiding hence the thread to pick up some new ways of guiding, more refinement.

Recallibrating may not be that important as well with CCDsoft and I presume the Sky X. I tend to do it anyway and usually after a median flip or at least check the reverse X box when flipping the meridian.

Greg.

Greg.

Greg.
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