Guiding v2

After many months of waiting I finally have some new gear (more later).  I’m back to problems with guiding.  PHD worked perfectly on the Tak FS 102 NSV with my SBIG ST402ME (9 micron pixels) and my Planewave Ascension 200 HR mount.  The the focal reducer I was running gave me an arcsec/pixel ratio of about 3.  Deviation from zero was max 0.4 pixels on a bad seeing night.

Enter the new gear – OfficinaStellare 400mm F 3.8 RILA.  Focal length is 1520mm.  The guidescope now sits on a MMOAG with my Proline.  The guiding was lousy!  More like averaging 3 pixels variation.  Now the stars in the guider where not very round – they where lousy not even oval.  First step adjust the angle of the prism/mirror on the MMOAG. One small piece of folded over tape later (under the back edge of the blocks that hold the prism) and my stars now look like ovals.  Tracking improved a lot.  Average deviation from the mean is < 0.5.  Now I use PHD 2.0 because it’s easy and I’m dumb.  Alas it does not seem to support binning – come on Craig.  The SBIG on this rig has an arcsex/pixel ration of 1.22 – not good in Sydney sky’s.  So I went back to Maxim DL for guiding and binned 2×2 (arcsex/pxiel now surprisingly 2.44).  My guiding even with all the high cloud last night was great – deviation from average max 0.2 pixels.  Yeah!

Training the scope for guiding in Maxim is still a pain – some times it misses the star altogether, sometimes the stars become stripes etc BUT regardless it guides really well.

Arduino Based ASCOM Rotator

One to many cloudy nights has spurred me into action. My imaging setup is getting closer to automated but I’ve had a distinct missing link, the ability to choose a guide star from within my astronomy applications. Since adding the MOAG and updating my guide camera I’ve added a Takahashi CAA rotator and it provides excellent manual rotation.

The reason I selected the CAA was price and aperture. I did look longingly at a number of electronic rotators.

Automation of the rotation was another issue. There seems to be lots automation for mounts and focuses but nothing for rotators. Google was not my friend. So I decided to write something. This is very much a work in progress but so far I have adapted the code from the SGL Automation guys and attempted to make it rotator specific. It supports ASCOM v6.

The ASCOM interface for rotators is reasonably simple, Move, Position, etc and the ASCOM documentation and templates are excellent. Well done standards guys, shame us health professionals can’t get our act together as we’ll as you have.

First go was to get the basics operating: Arduino, USB to serial driver, stepper motor, easy driver motor controller a couple of belts and a pulley. Check out the photos below.

I’ve only tested it with Maximdl using my bench setup as yet, but it seems to work well.

The bench setup.

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The arduino (note the resistor is for the reed switch, keep reading).

The reed switch and magnet.

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Reed switch and magnet.

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I was having trouble this weekend determine the number of steps to make 360 degrees so I dug up an old reed switch, found a very small magnet and introduced homing and a step counter into the software, as of Sunday night it all appears to work.

The Arduino Project and VB in the solution - ES - works but its still a little messy to release, but here you are anyway.

Code in action below

Sample rotator screen shots with debug

 

More experiments with collimation – an alternate approach

Can anyone tell me why this shouldn’t work? I brought a Hotech SCT collimator a week or so ago, I was sick of not being able to accurately collimate using the out of focus star method. The Hotech was quite easy to use but my final collimation was worse than before, just poor operator I suspect.

I started looking at 60 second shots and the stars were clearly badly collimated, the longer the exposure the worse the star looked, and it’s not the tracking. Out of sheer frustration I started taking 1 second exposures continuously and began twiddling the secondary mirror knobs. The star began to get smaller, and smaller and smaller and more evenly shaped. It ended up with a perfect circle at 400%. The star was out of focus, but not so much that it looked like a doughnut.

So next step run the autofocus routine, the star (it was mag 5) shrunk still more and was still perfectly shaped. Collimation fixed. Now when I’m on on either side of focus or in focus the star is a nice circle. Why can’t we do collimation this way all the time? It was nice and easy and produced a great result.

Guiding using Maxim dl

See update below.

I’ve been trying for weeks to get guiding to work perfectly in Maxim DL. I’ve just upgraded to v5.22 in case it was a bug.

Here’s the scenario. I’ve recently added an 8 filter wheel extension to my QSI 583. I also added the guider port. I’ve attached my Orion autoguider (with lense) to act as an off axis guider. I’ve had real problems getting Maxim to calibrate the guider using the stars I’ve selected. With my combination I’ve found that with pixel intensities in the star of greater than about 160 then the little red L would appear reliably every time.

Over the last couple of nights nothing I did would get it to calibrate, even on the brightest stars. I tried replacing the USB cable (I was getting desperate), playing with the previously good settings but to no avail.

I went back to PHD and it worked first time on much fainter stars with the old cable. I know when I’m beaten PHD it is.

21/11/12 I’ve just acquired an ST-402 and got it working as a guider. Guess what all the problems experienced under Maxim dl guiding are gone. In short buy a better guide camera.

Temperature focus compensation FLI Atlas

My FLI Atlas is a lovely focuser however it does not have temperature compensation.  After many frustrating nights ducking out to fix my focus after one or two images I decided to do something about it.  Enter Maxim DL Scripting.

I figured I could read the temperature of the focuser store it in a file on disk and then at the end of the next image read the temperature again and compare it to the one I wrote to disk.  If the difference was substantial (i.e. some number in my case 0.2C) I could move the focuser an specific amount.  In my case for the LX 200 it measured up to be about 0.19mm per 1  C.

Maxim dl scripting is pretty straight forward except when it comes to the Focuser.  If you create the object directly you can end up with two instances of the focuser object so what I did was use the Generic Hub and pointed Maxim to this and the Hub I pointed to the FLI Focuser.  The code is setup accordingly.

I run it at the end of each image (configure under Autosave->Script).

Code attached as a vbs so it only works under windows.  Download it from here it’s only a few lines.

FLI Filter Wheel

There’s always something new to learn. I just got a set of Astrodon’s LRGB Tru Balance E-Series filters. I installed them in my FLI CFW3-10. The mechanics of fitting them was very smooth. The different width locking nuts is very clever. When I installed the filters I did notice a position 0 on the wheel and thought nothing of it. I setup the filters in positions 1-4, LRGB respectively. I then fired up Maxim and configured the filter wheel. Positions 1-4. I then proceeded to take a short series of unguided 180 second shots of M20. The pictures were lovely but when I combined them I noticed that the stars in the luminance frame where enlarged. Why? yes you guessed it, it appears that the filter wheel positioning counts from 0 and Maxim counts from 1. Same position.

Never mind, next time.

Planewave Ascension 200HR Pointing

Great progress so far. This mount is great. Last night was PointXP night. I tried the instructions in the manual for calculating the 6 point model so it would provide the differences from polar alignment. It involves initially using the Scitech exe, chart menu option then selecting a star and doing and initial align (one button click). My scope pointed miles away from the selected star, perhaps it was the Southern Hemisphere thing. So I manually slewed to the star did an initial align and then all the subsequent stars appeared on the image (which is about 20′x 15′). Most were within 5 arcmin or so of center. The stars got closer to the center as I went, by number 3 it was pretty close every time. Not bad at all.

I do however have lots of trees around so not all the stars displayed on the chart menu were visible. Naturally the Sitech chart can’t display everything. So I gave up. I wanted to get the magic number of turns the pointXP displays so you can align your mount more accurately. So I gave up on the 6 point model and just went for the complete pointing option. I did an initial star alignment, followed the instructions for making a script for a PointXP model and let it do it’s thing. Initially I tried a 30 point model and the code crashed, twice. I reduced this to 27 points and it worked really well. I increased the exposure time to 6 seconds as the default of 3 seconds did not work for Sydney skies. The modelling took about 30 minutes to run, and about 6 of the points where failures because of trees. The results indicated that my polar alignment was out by about 2 arc minutes in both axes (where a 10 minute run in PemPro indicated about 20 arcsec, why?).

The end game was pointing and tracking. Pointing is within a 10 arcsec everytime. Tracking errors as reported by MaxiumDL are not bad either. Peak to peak is about .2, and I have yet to balance my scope!!!!

Watching the PointXP do it’s thing is a pleasure to behold with a hit within 1 or 2 seconds everytime you can get an image of stars.

Great job guys. Most impressed.

Ascension 200HR Southern Hemisphere configuration

The mount is installed and Polar aligned. The alignment was done initially with a laser pointer (toward sigma Octans) and then using PemPro polar align. It took a while to get there, but the mount is brilliant.

The documentation that came with the mount was a collection of A4 pages which although a little amateurish are actually pretty good. There is nothing in the documentation about Southern Hemisphere alignment. The Sitech documentation on Dan Gray’s site is however comprehensive. It looks like the software that comes with the Planewave has slightly diverged from Dan’s.

The Yahoo Group was very helpful.

When I started on my configuration the instructions are to perform a “Initialise Scope Using Homing Switches”, which with the default configuration sends the scope pointing directly at the North celestial pole. So to get it basically working there needs to be 2 changes. See screens below.

Change 1. This is based on the SciTech manuals. Essentially this configuration change works out (for Sydney Latitudes at least) like this: Using the ServoConfig.exe, “Edit Parameters” menu option then “Get Configuration from Controller” tick the invert motor encoder direction, invert motor direction and invert scope encoder, in both RA and DEC. See screen shot (from v 1.2 of ServoConfig).

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Update the Flash Ram from ServoConfig (Edit then Misc and Action) and all should be well. With this change the scope will track, undergo a PointXP model etc.

The home page of ServoConfig should now look like this:

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Change 2. From the Planewave support guys. To get the controller to “Initialise Scope Using Homing Switches” in the Southern Hemisphere, successfully you need to untick the two check boxes see highlighted below.

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As soon as you do it all just works.

Installation of the Planewave Ascension 200HR mount

After 11 months of patience my Planewave mount turned up. The idea was to replace my G11 temporarily so I could get used to working it then put a 20″ scope on it and host it at a dark site. I’ve brought a FLI Proline 16803 etc to go with the new scope as well.

First impressions where BIG! It’s a monster compared to the G11. It’s heavy as well the crate was almost 200kgs. Physical setup was a breeze but it was so big I replaced my pier, with a 10″ wide with 3/8″ wall thickness pipe. Thank goodness the concrete block beneath was huge to start with.

Pictures below

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The father in law and creator of the pier, oh, and also the engineer who made the mount plates etc.

G11 Deluxe Hand Controller Cable

I have a Losmandy G11. It’s old now, but with the odd upgrade it still works OK. I had a problem with my deluxe hand controller, I must have dropped it one to many times and the cable at the hand controller end was dodgy. How hard can it be to replace the end, better than waiting for a cable to arrive?

Its taken all today but its finally working. The trick was in the Losmandy doco on page 83 it described the pin outs – which are straight through – but it notes that pins 12 and 13 should only be connected to ground for use with a serial connection (the port can be used for both serial or the hand controller). However to use it for the deluxe hand controller you have to wire all the pins including 12 and 13 along with with soldering the ground to the shield of the plug.

I was so relieved when it worked. All tested just fine, what else are rainy Sundays for?