0

Computer controlled OTA and DSLR

Orion SpaceProbe 130ST

I obtained a Rich-Field Refractor with an aperture of 150mm and a focal length of 750mm along with a iOptron MiniTower mount that wasn't in what you would call 'perfect working condition' some time ago and this post documents how I went about restoring it.

Entry 01 : Problem Identification

Issue #1 : Issues with the GoToNova hand controller that is supplied with the MiniTower. Red backlight on the screen remains on but the information that is displayed tends to be somewhat intermittent. Unplugging and plugging in the connector cable occasionally helps but the issue normally will reoccur shortly after. I plan to open the back cover of the GoToNova Hand Controller again and try to reinforce the ribbon connector once again. I should be able to gently pull back the two grey/black tabs on either side of the ribbon cable connector in order to remove it. I'll then be able to reseat the ribbon once again by pushing down the grey tabs.

Issue #2 : Two of the legs in the stand can't be extended for some reason probably due to being in storage for a long duration. Initially thought that this was caused by a fusing of the joints due to heat since part of the outer layer seems to be coated with rubber, but found that this was not so once the joints were separated with my knife. Seems that the issue lies within the legs themselves. Nothing that good old WD40 can't fix hey?

Issue #3 : I will need to obtain a finder scope and an eyepiece set for the telescope.. or will I? A finder scope may not be required if the OTA and the GoToNova Hand Controller are able to be remotely controlled from a computer (as long as OTA alignment is not an issue) and a set of eyepieces are not required if I instead connect my DSLR to the diagonal and use it as prime focus. The liveview on the D90 is nothing great so will also need to establish a feed from the camera that runs back to the computer for image stacking using DSS. Magnification will still be an issue though as the focal length of the telescope is only 750mm.

Entry 02 : DSLR

I was pleasantly surprised that the T-ring (Nikon 1.25" T-ring) for my Nikon D90 screwed right into the diagonal prism that is connected to the telescope focuser and that the D90 could be attached for prime focus photography without the need for a T-adapter. Still unsure if the focusing tube has the required length for prime focus (as was the case with the Orion SpaceProbe 130ST) but if so, could possibly be remedied with a 2x Barlow. Problem here is that the T-ring will not connect directly to the Barlow which would mean that a T-adapter will be needed anyway.

Another concern is the additional weight once the DSRL is attached as prime focus. The OTA was already bottom-heavy due to the large star diagonal that was already attached. Normally the off-axis loads are counterbalanced by shifting the attachment point of the OTA with the mount. Problem is the attachment point on the OTA itself is not long enough to do this. This will mean that the OTA may not be entirely stable on the altitude axis and may have to work a bit harder when rotating due to the effects of gravity. I will have to look into a permanent fix for this at some point in the future (anticipating this to be somewhat costly). Since the MiniTower is an Alt-Azimuth mount, counterbalancing on the second axis is also required but this can easily be achieved using the counterbalancing weight provided (or a secondary telescope if attached).

*I will still need to look into getting an extension tube for eyepiece projection setup at a later date once the eyepiece set and a 2x Barlow have been purchased.

Entry 03 : GoToNova Controller

I thought that there was a chance that the issue that I was facing with the GoToNova could be overcome with a simple firmware update and figured that there really wasn't any harm in doing so (as long as I got the right version and make of the controller matched correctly).

I managed to fix this by going to iOptron's website, selecting the 'support' option at the top of the page, and then choosing the 'MiniTower/MiniTower II/MiniTower Pro' category. The USB2COM driver was at the top of the list and I chose the first one (CP2102) since I am running a 32-bit OS. I then went to the Device Manager to verify that everything was installed correctly (was using COM5 - COM is basically the name given to a serial port that will refer to the virtual port that is created by the USB-to-Serial adapters).

I then went back to the iOptron software/firmware update page, chose the category 'MiniTower 8401 hand controller firmware' and downloaded both the 'iOptron Downloader 2.01' as well as 'MT 8401 HC firmware (Ver090701)'. Launching the iOptron Downloader, choosing the right serial port and selecting the firmware version was very straightforward but I had issues after that as I needed to reset the GoToNova Controller and this could only be done through the Controllers interface (which is what I was having issues with). Ended up obtaining the manual for the controller and navigated the menus by just using the directional pads and listening to the beeps.

Once the dust had settled and to my dismay, I found that the firmware update had not fixed the issue meaning that the source had to be hardware related. Time to fiddle with the ribbon connectors!

Entry 04 : Stellarium

Since there were so many issues with the Controller and since I had yet to obtain a finder scope for the OTA, I realized that if control over the OTA could be established using a computer instead, then the Controller itself would not be required for navigation.

To do this I would first have to ensure that the Planetarium Software (Stellarium) that I was using was able to detect the OTA and in order for that to happen, the architecture would have to be in-place. After installing the ASCOM platform (ASCOM Platform 6SP1) which was obtained from http://ascom-standards.org/ and the iOptron ASCOM drive (iOptron ASCOM Driver category under 'software/firmware updates' on the iOptron Support page), I was still unable to find any option in Stellarium that matched the mount that I was using.

It turns out that a third party program is needed to provide the interface between Stellarium and the ASCOM telescope drivers (the one I used was called 'StellariumScope'). Installation was very simple and the interface detected and connected to the OTA very quickly. Stellarium wasn't able to detect the OTA until I updated it to version 0.11.3 though as I was still running a fairly old version. Control over the OTA via Stellarium was there once everything was setup and configured properly but was severely limited to just synching and slewing. Further testing needs to be done once the telescope's alignment is configured correctly.

Entry 05 : Bahtinov mask

During the last stargazing session, I realized that the live view on the D90 was not sensitive enough to support real-time focusing. To get around this, I will most likely need to resort to making a Bahtinov mask and shoot continuous exposures using something like MaximDL or Nebulosity. Further testing with the DSLR controls will need to be done once MaximDL or Nebulosity have been installed on the computer.

* The vector template for a 150mm aperture and 750mm focal length OTA has already been generated.

Entry 06 : Ribbon Connector

Opened up the back cover for the GoToNova Hand Controller in order to access the ribbon connector that lead from the PCB to the LCD screen. There were 2 black tabs on each side of the connector that were securing it in place so had to gently (and dexterously) pull them both back so that the ribbon connector could be removed. Slotted the connector back in and secured it by pushing the black tabs back in on each side. Started the GoToNova up and it worked! I ended up playing around with the menus on the controller and the GoTo (and slewing) ability of the MiniTower for several hours and the LCD display worked fine throughout.

Entry 07 : Stellarium Navigation

I was initially pretty disappointed with the telescope controls through the Stellarium Telescope Control plug-in as it seemed severely limited. From the first glance it looked as if objects could only be located by typing in the Right Ascension and Declination and then clicking 'slew' which would in turn direct the OTA to that position in the sky, albeit very slowly. I ended up finding out that the best (and by far the easiest) way to navigate the OTA to a celestial object was to just click on the object in Stellarium and then hold down CTRL and press '1' (since I was slewing the primary OTA). I then found that the speed of the slewing itself could easily be adjusted by pressing one of the numerical keys on the GoToNova Hand Controller, 1 being the slowest slewing speed (almost not noticeable) and 9 being the fastest.

I also ended up installing Redshift 6 Premium just to test the telescope controls but quickly ended up reverting back to Stellarium after finding it not very user-friendly. However, the telescope controls for Redshift 6 Premium picked up the drivers for both the iOptron mount and the ASCOM Platform without any issues.

Entry 08 : Crayford Focuser

Identified another issue but fixed it within minutes. I found that the 2 speed 2" Crayford focuser that is attached to the Dielectric Star Diagonal was sliding out of focus very easily and tended to do this when aimed at locations with high inclinations or that were located close to the Zenith. This was probably exacerbated by the additional weight of the DSLR that was attached to the 2" to 1.25" eyepiece adapter. The issue was easily remedied by tightening and loosening the Tension and Locking bolts on the underside of the Crayford focuser accordingly.

So, to recap :

Issue #1 - Fixed

Issue #2 - Unresolved

Issue #3 - In Process

Issue #4 - Fixed

Issue #5 - Fixed

Entry 09 : MaxIm DL

I installed Cyanogen's MaxIm DL Version 5 and was able to connect to and control the Nikon D90 once I had the DSLR connected to the computer using a mini-USB cable, however was very annoyed at how cumbersome things became due to the length of the cable. The detection of the D90 was automatic and no drivers had to be installed.

Setting up the camera was also relatively straightforward. The option to setup two cameras was given and is normally used when the primary camera functions as the main 'imaging' camera and the secondary camera functions as the autoguider. Once in the 'Camera Control' menu, I clicked on the 'Setup' tab and entered the Nikon D90's settings under 'camera 1'. Once this was done, I clicked 'Connect' on the far right side of the menu.

Exposure settings were found under the 'Expose' tab. Planning to focus on celestial objects by taking continuous exposures every few seconds and making slight adjustments to the focus depending on how the three angled diffraction spikes line up using the Bahtinov mask. The Bahtinov method should be an easier, faster and more accurate way to achieve perfect focus if compared to the focus statistics that MaxIm DL generates for each exposure. These focus statistics are based on the maximum pixel value (Max), the full width half maximum (FWHM), and the half flux diameter (1/2 FD) and the focus can be adjusted based on these variables.

Another useful option that I encountered was the 'subframe' option. This basically lets you see just a selected portion of the sensor frame. Using this option will end up speeding up the download during the focusing itself as well as helps isolate the target (the star) that is being used.

* I will need to test the auto guider abilities of MaxIm DL as well as how well it stacks exposures.

* I will also need to look into powering the Nikon D90 from an external power adapter. This is just to ensure a continuous use with no risk of the battery discharging.

Entry 10 : Tripod

Finally managed to disassemble the entire tripod but it ended up being a huge physical effort. Reassembled it after cleaning, polishing and applying WD40 for lubrication. Also tested out the dual OTA setup successfully. Will need to buy 2 screws to ensure that the secondary OTA is affixed to the mount securely.

Entry 11 : Stargazing Attempt 1

The skies were fairly cloudy with quite a bit of light pollution despite going out onto the roof. Only stars brighter than magnitude 2 were visible. Spent a while setting the OTA up due to the sheer awkwardness of the location and ended up spending a few hours trying to align the scope using single point and dual point tracking using Spica, Arcturus, Mars and Saturn and still could not get the GoTo slewing ability to work well. Didn't have a compass to point it exactly South which could have been the reason (balancing was ok).

Was really tricky finding the positions of objects without a finder scope as the lowest magnification I had was a 25mm eyepiece (30x magnification for the 750mm focal length of the OTA). I ended up just looking at Saturn with a 10mm and a 2x Barlow since the moon will be in the area in the next week or so. I will also need to get a power cable reel for ease of access.

Entry 12 : Bahtinov mask completed

Finally completed my Bahtinov mask! Used a generator that I found online to create the template with the correct measurements based on the OTA dimensions (aperture and focal length) and printed this template out. Cut out the slots using the same measurements from a piece of thick, sturdy, black cardboard and ensured that this could fit into the hood/cover of the OTA. The cover can be used as it has a secondary (smaller) opening that is used for lunar/solar observations to cut down the light entering the OTA. Have yet to test the efficacy of the mask for focusing though..

The generator used can be found here.

Entry 13 : Eyepieces

Finally completed my full set of eyepieces! Managed to procure a 4mm, 6.5mm, 10mm, 15mm, 25mm, and a 40mm which will end up giving a magnification from 18.75x all the way up to 187.5x. Also scrapped the idea of a finderscope as the low magnification given by the 40mm should suffice to give a view wide enough for region location.

Entry 14 : Dismantling

I completely dismantled the OTA to prepare it for the spraypainting process. Was able to get in and give it a good clean at the same time. The picture shows the parts that will not be spray-painted, namely the primary OTA lens, the bracket mount, and the Crayford Focuser.

Representin' at the #500teleskop event hosted by Planetarium Negara. Unfortunately, the weather wasn't too kind to us so we ended up looking into windows of office blocks seven kilometres away.