I got my mini lathe today!
It looks great next to the SX2 mill.
Now I can start making more worm wheels. Watch this space…..
A couple of weekends ago, late on a Sunday afternoon I decided that the time was right to open up my 600D. I suppose I was in a hurry and couldn’t wait any longer. The clear glass replacement filter has just been sitting there and I was already prepared with all my tools and silicon, etc.
So I did it.
Opening the camera up was pretty easy. I used the following websites to guide me along:
A large number of very small and delicate connectors have to be disconnected.
Eventually the CCD assembly can be removed.
This is the complete filter and imaging chip assembly, before I took it apart (and almost broke it…)
The piezoelectric element is removed here..
And here I was too impatient and broke the IR cut filter. The crack line can be seen from top left to bottom right. I should have ready the instructions in more detail! Take it from me, don’t be in a hurry when you do this. Fortunately there was no damage to the imager chip and after I cleaned all the filter glass fragments off the CCD surface I could start the assembly process again.
The clearglass filter replaced both the IR cut filter and the piezoelectric filter element. I have now modified the camera to a full spectrum camera.
Pieces of the IR cut filter. This is not the way to do it!
Inside of camera, looking at the back of the shutter.
Putting it all together was reasonably easy. The most difficult part was to get the imaging assembly in the correct position to allow the auto focus to work properly. I will have to make some more adjustments to get the auto focus to be more accurate. It can wait as I mostly use manual focus for astrophotography anyway.
A big sigh of relief when the camera fires up and still works !
A weekend later and I was testing the camera under an almost dark sky. Nothing spectacular but just confirming that it all works as it should.
Orion Nebula (M42 / M43)
Large Magelanic Cloud (LMC)
Coalsack with the Southern Cross and two pointers
And, the evening would not have been complete without a image of Carina.
This project is never going to end…..
I have been very busy at work over the last 10 months and have done very little with my projects or even observing under the night skies. Over the Christmas break I started a little project to add a declination axis on the tracker to be able to install my Orion 80ED. It looks a bit weird but it works a treat.
The new dec axis is based on another 20mm mild steel rod that is clamped in a 40 x 40 x 80mm aluminium block that is mounted on the RA axis. This dec arm is currently locked in place by tightening the split block with two allen key screws. Not very elegant but rock solid. The dec axis is long enough to handle a counter weight but when I used it, I did not have any counter weight on and the system handled it without any worries. I think that it may be able to take my Meade 8″ SCT telescope if I add a counter weight as well.
When I tested the new setup I was battling like crazy to get a guide star in view and in keep it in focus. It would really be a good idea to buy a proper guide camera to do the job properly. The webcam is ok to start with but it’s frustrating when you are trying to change to a new target quickly. The sensitivity of the webcam is not great. In a dark sky it works reasonably well but in a polluted sky it’s no good. Hopefully I can afford to spend a few hundred dollars on a dedicated autoguider camera with a ST-4 port, it would make the guiding experience much easier. Does anybody have any recommendations for a good camera?
I almost forgot, I have now effectively locked down the RA axis and I don’t have a clutch on the RA axis. I have to drive RA with the motor to point in any particular direction. I have added a switch and some new code on the stepper driver box to allow me to change the stepper motor speed to slew the RA axis faster or slower. It works well but I wont be able to handle a crowd at a star party with this setup!
I finished the construction of the new tracker to the point where I could test it under a suburban night sky.
I mounted a piece of angle iron onto the RA shaft and mounted two camera ball heads on it; one for the imaging DSLR and one for the webcam autoguider.
To align the mount I use a green laser pointer that is mounted on a bracket that sits directly on the RA shaft. This allows me to to align the mount very accurately to the SCP. I was very pleasantly surprised with the stability of this new mount. There is almost no vibration or oscillations in the mount, even when touching the mount or adjusting the settings on the camera. It is reasonably heavy but it will also be able to carry quite a payload. At this stage I have only tested it with a DSLR but the next step will be to load it up with an Orion ED 80mm to see how it performs. Maybe it will take a 8″ SCT optical tube as well …..
Due to the very light suburban conditions I only took a few photos to see how the tracking and autoguiding work on the new mount.
I am happy with the performance of the mount. The stars are mostly round. The stepper motor has a nice quiet hum and the worm and worm gear seems to hit it off quite well without binding. It all works quite smoothly. I must also mention that the autoguiding software from Stark Labs; PHD Guiding (http://www.stark-labs.com/phdguiding.html) works beautifully and I could focus on the imaging and let the software and webcam look after the tracking.
I guess the next step is to take this new setup out to a dark spot under a clear sky and see what it can do. I can’t wait!
I have now made a new worm gear and worm with a 10×2 ACME threaded rod (10mm diameter with a 2mm pitch). I milled a few slots into a section of the ACME threaded rod to try and make a tap. It works quite well but this “ACME tap” cannot start the aluminium worm blank in the same way as the M10 thread would.
This meant that I would have had to manually cut or saw the starter slots into the blank for the ACME thread to lock onto. It’s quite a bit more work with about 200 odd slots to cut! Eventually I got a M14 tap with a 2mm pitch and I started the worm with that until there were well defined teeth in the worm wheel. I then changed to my home made ACME tap and continued until the worm gear was done. A new ACME worm was then mounted on the guider with two pillow blocks that I used previously. The assembly is quite heavy but very solid.
The worm has not been cleaned up yet. I still have to spend some time with the worm gear pair and some metal polish and let them work themselves into a smooth finish. There is a small section on the worm that is not great and I will avoid using that section when I use the tracker under the stars.
The tracker will be mounted on a Meade wedge at first until I make a more solid wedge out of a few steel plates. The orientation of the tracker’s RA shaft is 90 degrees different to the normal. Fortunately the Meade wedge can adjust far enough and I can reach the southern celestial pole with this unconventional configuration.
The thick aluminium plate will be cut smaller at the top end to allow for the mounting of a DSLR camera and a guidecam on a ball head. Later I will have to figure out a way to mount an ED80 and a Meade 8″ SCT optical tube on the RA shaft.
I have made some progress on the new mount. See the photos below…
I have learnt quite a few new lessons already. One important lesson was not to cut the M10 thread too deep into the worm gear disk. It causes the M10 worm to bind very easily when the worm/gear assembly alignment is not absolutely perfect. I have now ordered a 10×2 mild steel threaded rod with an ACME thread (10mm diameter with a 2mm pitch). The ACME thread is much more suitable for a worm gear than the M10 type thread.
I still have to figure out how to mount the tracker onto my Meade tripod. I have a few ideas and will have to try it out soon.
The other important item that is stil outstanding is the bracket for the camera and guidecam on the end of the RA shaft. It should not be a problem.
If you have been reading my blog you will know that I love building things. I almost like it more than using things. So, after my recent experiment with a tracking mount I decided to start again, from scratch, to try and make a more robust, heavy weight mount that will not complain when I load it up with cameras and scopes. I also use the iOptron SkyTracker a lot but you cannot load it up too much.
The previous tracking mount is shown in one of my previous posts, Look at https://starsinphotos.wordpress.com/2014/09/23/diy-autoguider-for-long-exposure-astrophotography-part-2/ . This mounts works surprisingly well but it looks like a dogs breakfast, it’s sensitive to bumps and it is too bulky to transport easily.
My new design will be more solid with a steel based design rather than aluminium. Its harder to machine but the design is relatively simple so it is quite easy to make. I have decided on a few design parameters that will make the design robust and will not require any skilled machining capability (apart from the worm wheel and gear). I will also make a new worm gear combination (130mm diameter with approximately 270 teeth. The previous one I made was not very accurate and it only tracked smoothly for about 3 hours at a time, then I had to “rewind” the RA axis to get to the start of the good section on the work gear. My stepper controller design have buttons for a fast forward and rewind on the RA drive.
The new tracker design is based on a square section of 125mm mild steel U-channel with two pillow block bearings that holds the 20mm steel RA shaft.
It should be possible to get the steel supplier to cut the U-channel to the correct length when you buy it but I got an offcut cheap and had to spend a few hours to get it nice and square. The U channel and the 20mm rod cost me $10. The two pillow block bearings was a bit more expensive, the two of them cost about $60.
So now I have the RA shaft mounted and it feels VERY solid. I am thinking that I might be able to load my 8″ SCT OTA on to the mount if all goes well. The new 140mm worm gear will fit onto the 20mm shaft on the left (or bottom) side and the camera / scope mount will be on the right (top) side. The stepper motor and worm will be below the U-channel on the bottom.
I am going to try and build the tracker without any ability to adjust for altitude polar alignment. In my opinion, its too hard to get a very solid mount if you add the adjustment elements to the design. This mount will be mounted on a fixed altitude block that is centred on Adelaide (35 degrees south). I will use the Meade tripod legs to make large changes to that and small changes will be made by an adjustable tripod foot consisting of an adjustable pipe flange that can be rotated to make small adjustments on the tripod leg facing south. Azimuth will be adjustable with the Meade tripod head bolt. I may go so far as to include a method for making small adjustments to the azimuth as I have battled with that in the past.
For accurate polar aligment I will keep on using my green laser pointer on a small aluminium bracket that attaches to the RA shaft itself. This implies that I can achieve very good polar alignment with a mount that may not be perfectly square and with bearings that are not fitted very accurately on the mount. It’s legal to use a green laser pointer in South Australia if you have the correct documentation with you.
My existing stepper controller and autoguider works well and I will use it again for this mount.
Update 22 January 2015:
I have now got two new 130mm diameter aluminium “blanks” for the new worm gear. This time I had them professionally machined so that they will be 100% square on the 20mm shaft, unlike last time…..
Over the next few days I will cut the worm gear and a new worm. I will post some photos when it is done.
Update 27 January 2015:
Yesterday, I cut the worm gear and it turned out much better than before. I have 279 teeth on this disk and hopefully they will be quite smooth after I have polished them.
The new tracker is slowly coming together now…
Now for the worm….
I will update this post as the mount gets built over the next few weeks.
Comments and questions are welcome…
I have received a request to describe the autoguider electronics a bit better so I went back and opened my controller box and drew out the circuit.
Link to a pdf page with circuit diagram: Circuit Diagram of DIY Autoguider Ver 2
There are a few tricky issues with the circuit:
1. Polarities: The RA direction is sometimes confusing to get right but it is easy to do a test and swap two connections around or tweak the Arduino code to correct it.
2. ST-4 connection to laptop parallel port. Many laptops do not have a parallel port anymore. I used an old laptop I had available. You probably do not want to use a new laptop outside in the dew anyway…
3. Stepper motor; I used a stepper motor with microsteps (1/16th steps). This makes the tracker/ guider movements smaller and less jumpy. Similar to a much larger ratio gearbox.
4. The tracking speed can be calculated and programmed in easily. I found that my calculated stepping rate was spot on and well within the autoguider’s range to correct without working too hard.
5. I used a webcam based autoguiding camera that I modified myself. You can probably use any autoguiding camera, or if you want to try, modify your own webcam to fit on a suitable lens.
For more details, look at previous posts with the same title (Parts 1 to 4). A copy of my latest Arduino code is also available.
If you need or want more information, please ask, I will do my best to answer quickly.
I tried the upgraded autoguiding tracker again on Wednesday and the results improved quite a bit. I used a 250mm lens to image the LMC. The following is a photo of the PDH graph showing the tracking error. The error is a small fraction of pixel. It has improved a lot since the previous test where the typical tracking error was ±3 pixels.
The resulting images of the LMC are not great due to the light polution but the tracking is starting to show promise.This is a single image (no darks or flats) taken at 60mm, f/2.8, 120 seconds and ISO 800 showing some round stars. Some cropping, levels and stretching was done with Lightroom 4.
This is the setup I used:
I used a Canon 18-55mm lens for the guide webcam. Tracking accuracy will improve a lot if I increase the focal length for the guiding, maybe use a 18-135mm. The zoom works well on the guide camera to find a suitable guide star.
The advantage of this mount is that it can take a bit of weight. I tried to mount an Orion EON 80mm on and it did not complain too much. Maybe I will need to modify a bracket to make sure the camera mount ball head cant slip with the 80mm scope. I will try that next.
Here is the latest version of the Arduino sketch: Stepper Motor sketch (pdf download)