I started changing the imaging optics over to a 9.25″ SCT today (from the 80mm dual refractors).
The basic mounting was easy during daylight, but I couldn’t set up any of the actual optical train because I can’t see anything far enough away to focus except at night with the moon or stars. So I waited until evening to start piecing optical bits together. I plan to set up with a 0.5 or 0.63x focal reducer for now, and an off-axis guider. Ideally I’d like to use the Van Slyke 3-port guider because of its flip-mirror functionality.
Evening testing was not good. The scope has fallen ‘way out of collimation during the year of disuse, couldn’t get various parts to work together, couldn’t find the right focus distance, etc. etc.
Back to basics, and I’ll work through the steps one at a time. Each of these steps will likely be at least one evening. Basic plan:
Set up visually, no focal reducer, no camera, nothing, and get the collimation perfect.
Start with a rough collimation in daylight using mirror reflection
Then do out of focus “donut” collimation on a star next clear night
Add focal reducer to the chain, get working visually. Focal reducer has to go outside the Crayford focuser to keep the focus distance in range. 80 to 110mm from reducer to point of focus is the target.
Add camera with off-axis guider inserted.
It might be necessary to try putting the focal reducer outside the off-axis guider to keep the focus distance in range.
I liked the idea of the temperature sensor interface that let me tie a USB Thermometer to CCDAutoPilot, but didn’t like the idea that it was completely dependent on a single device.
The attached program, TempSens2, generalizes the handling of the input file and should work with any temperature sensor that, with its native software, produces temperature information in some kind of simple text file in real time. You fill out a bunch of forms describing the layout of the input file, and then the program translates the readings to a form that CCDAutoPilot can read.
I have tested it with 2 different temperature sensors (one in the $80 range, one in the $10 range) and have verified that it “should” work with a couple more, based on their online documentation.
The attached zip file contains the installer, which runs on Microsoft Windows XP or Vista (I haven’t tried Windows 7) and requires the .net framework. The installer includes help.
No guarantees, but I’d be interested in hearing from anyone using this.
After continued failures of autoguiding that all seemed to be cable- or connector- related, I tried a different approach.
My hypothesis was that the setup I had was fundamentally error-prone. The autoguider signal ran from the relay output on the camera to the guide port on the mount. This means that cable was in constant motion. The telephone jack type connectors used on both ends of that cable are unsuited for this – they don’t provide a positive lock, aren’t meant to be used in extreme temperatures, and certainly aren’t meant to resist motion.
So, I changed guider drivers. Instead of using the relays built in to the camera, I am using a GPUSB unit from ShoeString Astronomy. This with this setup, the small GPUSB control box is fastened permanently to the mount, and a short cable runs from the control box to the mount. Same connector, but no motion, so I hope it will remain more stable. I also thoroughly cleaned with mount-side connector with a small abrasive brush while changing the cable.
I originally thought the cable from the camera would be better since it meant one less wire running from the computer. However, that problem was solved by having only a single USB cable from the computer, running to a multi-port USB hub that is mounted in the space atop the pier. So adding the GPUSB device only mean an extra cable inside the pier platform, from the USB hub, not another cable to the computer.
Initial results: it seems to be working. I’m getting guiding on both axes again. Now I’ll need to spend some time calibrating backlash, aggressiveness, etc., again, because I messed those settings up with the previous guiding system, trying to make it work. I think this is going to be the winning approach, though.
It was a beautiful clear day and the sky remained clear through the night, we continue to have unseasonably warm weather, and the moon rose late, so last night was an ideal evening. Before dark, I mapped the horizon height all around the observatory, to configure Maxpoint and other software. Then, after dark, I carefully re-did the Gemini alignment routine on the mount, and overcame the pointing error problems I’ve been having. Finally, I put the 0.8x focal reducer into the imaging train to do some wide-field imaging, and recalibrated the focuser with this new setup.
One test image just for fun: a wide-field view of NGC 869/884, the Double Cluster. It seems to have worked well, including the automated filter changing, and alignment of the colours is good. As an image I’d like more colour depth and better colour calibration, but that will follow. Continue reading
Journal page, March 7
Clear all day and clear evening, and a wonderful warm spell has been going on about a week. Temp 8 degrees today. Did some pre-setup in the dome during the day, reloading drivers etc after having to re-image the observatory PC.
Out for imaging about 7:00 PM. Strange pointing problems continued with the mount, but I found a problem that I think might be the problem: the mount and software didn’t agree on epoch; software using J2000 and mount using JNow. I reset everything to J2000. That improved things a bit, but didn’t solve everything – right-clicking on plate-solved images is still not driving correct goto operations; must check the calibration of plate solving, image scale, etc.
Re-did autofocus calibration, about 5 V-curve runs. Did a test image on M45, trying to catch the reflection nebulosity. About 1 hour of images, LRGB. Guiding worked very well, +/1 1 pixel error. Rough guiding earlier in the year may have been related to cold temperatures making things run less smoothly? I gathered data until it sank below the hedge.
Quick look at the data indoors at end of session – seems to be some kind of smearing in the Green, resulting in a green gradient. I wonder if it was filter wheel problems registering wrong colours, will check that. In fact, I wonder if I have the Green and Blue filters swapped in the wheel. Once I get around to doing some G2V calibration I can firm this up; but will check the right filters are in place just to satisfy myself.
I’ve developed a small bit of glueware to allow a USB temperature sensor, a EL-USB-RT from Lascar Electronics, to feed temperature and humidity information to the CCD Autopilot application from CCDWare. It does this by copying the temperature sensor’s information to a file that simulates a Boltwood Cloud Sensor, so CCDAutopilot thinks you have one of those.
This application requires, and works with, the Lascar software that comes with the sensor, running on Windows XP or Vista. Free for others if you’d like to try it, no guarantees of any kind. Help is included.
Note: A Newer Program Replaces This One
Although this program is still available for download, it is very restricted in what device it can monitor. You would be better off to try this program – a newer one which can handle a variety of temperature sensors. It’s also free.