Guide to guiding with Maxim

[MartinB]

Guide to guiding with Maxim

One or two members have commented that although they have Maxim, they are sticking to PHD for guiding since the found the guiding utility in Maxim rather off putting. I decided to put together this quick guide to getting up and running with Maxim, it also covers some important guiding issues and how to address them. TheI guide relates to V5, the layout of the screens is different in earlier versions but you will get the jist.

You can set up most things during the day without cameras connected. Most of the time the default values will be fine.

Settings

Click the settings button to set: -

calibration time - determines the length of the slew in each axis. You need to be aiming for a minimum of 10 pixels shift in each axis. Dec is likely to show some backlash so the longer your time the better so long as the star doesn’t go off the chip. A bit of trial and error will see you with the right sort of time. If you are using a short focal length refractor you could start with 15-20 seconds.

Backlash – Leave the backlash for now (my mount has quite low back lash and I don’t bother trying to correct it).

Guide enables – enable them all unless you are doing something like measuring PE.

Manual calibration – ignore this

Autoguider control - I use guider relays but you can do pulse guiding through ascom direct (I have no experience of this).

Display mode – set to pixels if you don’t have your scope details entered into Maxim, otherwise select arc seconds.

Delta – check this to ensure you get a readout of variation from original position rather than the absolute co-ordinates of the guide star.

Binning mode. I normally use x2 with my lodestar.

Advanced

Under the advanced tab there are some settings you can tweak if you like that sort of thing

Minimum move – a bit like a steadying hand on a wobbly drunk. If your guiding seems a bit erratic you can stop it making corrections until it reaches a certain degree of error and also calm it down when it wants to through a real wobbly. CCDware have an excellent calculator for setting the appropriate values AutoGuider Calculator V4.00

Delay after correction – give the mount a bit of time to catch it’s breath. I’ve never touched this, always left at 0.1. Some mounts start to struggle if they don’t have this brief settle period.

Move commands – ignore these

Enable simultaneous RA and Dec corrections - I leave this unchecked. Some mounts (losmandy apparently) struggle to do this. Leaving unchecked slows the cycle a negligible amount.

Y is right ascension – by default X is RA and I leave this box unchecked. Updates of V5 have options here to control the axes which are reversed after a meridian flip, only “reverse x” should be checked.

Guide screen - Options menu

Select simple auto dark. This greatly reduces the chances of hot pixels messing up the calibration or guiding. When you click expose you will be asked to cover the scope (unless your camera has a manual shutter), the dark will then be taken, you are asked to remove the cover and a light is taken. It’s a bit of a faff but worth it.

Fine aggressiveness – If you check this the aggressiveness of the guide corrections can be adjusted to one decimal place. I’ve never found this sensitivity of adjustment to be necessary and it is more convenient to stick to integer values.

Guider setting criteria - The minimum 5 second guide settle delay applied by Maxim has always been plenty of time with my set up however when dithering exposures a much longer time is required. The time it takes to settle can vary depending on the amount of dither applied, the aggression of the guiding and exposure times. The setting criteria also allows you to start the next exposure when the guide star is within a certain distance from the track box centre. I have used this however if the correction required when coming back from the dither is in the same direction as the dec drift there is an over shoot when the backlash is being taken up and the dec drift isn’t corrected. Therefore if I am imaging at high magnifications, very revealing of guide errors, I tend to use the time delay and set it to 40-50 seconds when setting up the imaging sequence.

Track box size – I leave this set at 32x32. I don’t think there is anything to gain by making it smaller, It’s not an issue with fast downloading USB connections

Record cal images – I guess this allows you to save your calibration images, useful if you are having problems I suppose.

Connect cameras!

If you are able to connect Maxim to your mount do so using the observatory control. Also enter your site and scope details. If you have a stepper motored focuser you can connect this as well (allows appropriate adjustments to focus when filters are changed) To use maxim and planetarium software to jointly control the mount you will need an ascom hub driver, I use MaxPoint. The advantage of doing this for guiding is that the dec value will be set automatically and the tracking error readings can be in arc seconds which is more useful than pixels.

If you are not planning to change the orientation of your guide camera you can get on and calibrate immediately after alignment. This can be handy since your eventual guide star may not be a good calibration star. It is much easier to find a decent calibration star by moving the mount than it is by adjusting guide scope rings. Of course, if you need to rotate the guide camera (when off axis guiding) you will need to do the calibration after framing and then reframe (one of the reasons why OAG can be a pain).

In V5 the camera control window has 3 tabs, expose, guide and setup. Under the expose tab your guide camera will normally be camera 2. Select your guide cam and run 1 second exposures using continuous mode. Move the scope using the mount motors until you find a suitable star for calibration.

Suitable calibration star

Bright but not more than 2/3 saturated, somewhere between 20 000 and 40 000 max pixel value as measure using the info palette.

No neighbouring star of similar magnitude which could confuse the calibration

Not a double!

No adjacent hot pixels

Centre your suitable star. Select the guide tab. Make sure camera 2 is checked. If you have connected maxim to your mount auto scope dec will be checked. If not you should enter it manually at this point.

Now set the exposure value in seconds (probably the same as you used when organising your calibration star – at this point we aren’t thinking about the eventual guide exposure). Check the expose tab and click start, if you have selected auto dark in the options menu you will be asked to cover the scope then click ok. A dark is taken and you are asked to remove the cover, click ok and the light is captured. The image appears and values appear for the guide star coordinates. With the info palette showing you can confirm that these coordinates match the ones in the info palette. If, for some reason they don’t you can click on your chosen star to change to the correct co-ordinates (very unlikely that this will happen). Once you have confirmed your guide star, check calibrate and press start.

The star is first moved in RA at guiding speed, an image is taken and the new co-ordinates recorded. A move is made in the opposite direction and another image taken. Maxim creates a red line with each guide move as a visual check. Hopefully it returns to within a couple of pixels of it’s start value. It then repeats the process in dec. Depending on how the gears were meshed the star may fall short of returning to it’s original position due to backlash. If you repeat the calibration the dec move will have to be taken up in both directions and the star should return to it’s original position. Doing this however does mean the calibration under estimates the amount of movement achieved in dec for a given correction and this may need to be catered for by reducing dec aggression. I normally don’t worry too much about evening out the backlash when calibrating. The only time I find backlash is an issue is when correcting large tracking errors that intentionally arise after dithering.

Choosing a guide star

Once calibrated, find and frame your target. Select camera 2 under the expose tab and see what you have on the guide chip.

Guide star requirements

Good signal. I prefer to have a max brightness of greater than 10 000 ADUs but at a push, especially if constrained by off axis guiding you can get away with less.

Not too bright. I prefer to stick to less than 40 000 ADUs since I worry that a lack of linear response of NABG chips may affect the precision of the centroid calculation.

No adjacent hot pixels

No adjacent bright star

Not at the very edge of the chip.

Play around with different exposures and binning x1 or x2 until you are happy with the signal and position of your guide star. Now select the guide tab. Enter the exposure time and go into settings to check you have the correct binning mode. Remember to enter your dec position. Check camera 2 and Exposure and start, doing an auto dark if necessary. Click on track and see whether the star chosen by maxim is the same as the star you want. If not, click on the star you want to change the coordinates. Choose the aggression settings, 7 for each is probably a good starting point. Click on graph to bring up a visual display of tracking error and then, making sure track is selected click start.

The little arrow at the bottom left of the graph box allows you to adjust the parameters. You can swap between scope and camera axes as well as adjusting the graph scales. An RMS tracking error can also be shown.

Aggression settings can be adjusted on the fly. If you have good polar alignment you can set the dec to a very low value, I sometimes just use values of 1 or 2. Watch out for jagged over corrections and reduce aggression if you think the guiding is over correcting. When you have the graph at smallest scale – ½ arc second, expect the graph to look very bumpy, don’t let it upset you!

The graph is a bit hypnotic. Try playing around with aggression settings, minimum and maximum moves and even backlash. However, if your mount is performing reasonably, your PA is good and you have a reasonable guide star tweaking the aggression is really all you should need to bother with.

Now you can just click between the exposure and guide tabs to keep a check on things. Information on the guiding status is available under the exposure tab and vice versa.

After a couple of runs Maxim soon starts to feel very straight forward.

Happy to hear of any other tips and please let me know if I've made any glaring errors or said anything incomprehensible.

[Starjumper]

Hi Martin that sounds very methodical, as soon as I get some clear skies I shall give this a go, thanks.

John

[roundycat]

An excellent primer for guiding with MaxIm, well done. Thinking about the time it must have taken you I know now why I never bothered.

Two things I would take a very slight exception to;

1. Under the Guide Screen - Options Menu you mention the delay after dithering. I have noticed the dither overshooting quite often. I might set it to 2 pix and some moves go to 3 or even 4. Either way I set the delay to about 4-5 times the guide exposure. That is rarely more than 25-30 seconds. (my guide exposures are usually in the 3-5s region).

2. In a treatise on guiding Roland Christen says to never check the Dec value box. I have done both and don't find a big difference.

The Max move can be used to neutralise the mount's response to wind gusts. I think Min will tend to smooth out guider response to very small moves so acts a bit like agressiveness.

An excellent piece of work, well done again.

Dennis

[Neil I]

An excellent guide Martin. I'm sure it will be of great help to new, and old, Maxim users

I've recently started using Maxim for guiding as I could never quite get PHD guiding as I wanted. I did have second thoughts about using Maxim after seeing the interface as it looks far more complicated than PHD, but after trying it a few times I found that it really isn't that difficult to use, and it gives excellent results.

Cheers

Neil

[Euan]

Great stuff, Maxim can be a bit of a headache to get working but it's really worth it in the end

One thing that still bugs me is auto meridian flip. Sometimes this messes up and I have to check the box manually, I've never managed to figure out why and just worked around it when it happens

[kookoo_gr]

one question i have the qhy5 guide camera. in orrder to connect it i use cmos camera from the setup camera. in order to guide my mount via the autoguider port which setting at autoguider output should i use? currently i use phd and CdC with EQMod to control my mount

[MartinB]

Thanks guys.

Dennis, thanks for the comments. I normally dither using the guider and use 1 pixel. It will have me back within the 4-5x guide exposure as you say and sometimes I would be ok with 20 seconds but if the backlash needs taking up after this I've found it can be longer. I guess the solution would be to start using some backlash compensation.

I've read Roland Christen's comments about Dec and they do make sense esp if you are having over corrections. I thought about including something about this but thought it might all get too complicated and I might trip myself up!

Sorry kook but I can't advise on PHD. However, if the QHY5 has a guide port you should be able to connect this to the guide port on your mount and use guider relays. Well that is what you would do with Maxim

[sam81]

Thanks guys.

Dennis, thanks for the comments. I normally dither using the guider and use 1 pixel. It will have me back within the 4-5x guide exposure as you say and sometimes I would be ok with 20 seconds but if the backlash needs taking up after this I've found it can be longer. I guess the solution would be to start using some backlash compensation.

I've read Roland Christen's comments about Dec and they do make sense esp if you are having over corrections. I thought about including something about this but thought it might all get too complicated and I might trip myself up!

Sorry kook but I can't advise on PHD. However, if the QHY5 has a guide port you should be able to connect this to the guide port on your mount and use guider relays. Well that is what you would do with Maxim

I came across this topic in a web search trying to narrow down my Maxim woes. I hope it isn't too much trouble bumping such an old topic.

My issue seems to be wave-like patterns in my X-axis (Right Ascension). My Dec seems to be ok for the most part. I'm using a 6" reflector on a CGEM with Lodestar off-axis guiding.

I have a feeling it might be due to bad polar alignment but I'm practicing on getting that down correctly by using ASPA (all star polar align).

Do the wave-like patterns in RA bring anything immediately to mind?