After building the observatory, I eventually got around to making it water tight. I just got sheets of rubberized canvas and made skirts around the roof's 2x4 frame so that the skirts cover the gap and extend a bit over the walls on all four sides. Upon water testing this with a garden hose it held up pretty well. Unless we have a rain with winds strong enough to make the rain come close to parallel to the ground, there should not be a problem (and this never happens in california).
The base of the walls, where the frame meets the asphalt of the roof was also completely sealed using roofing cement on all sides. This makes sure that water does not seep inside from the bottom edges.
I also noticed that I needed a bit more ventilation and added two more of those solar fans from solarwholesales.org. This time I added them at the apex of the roof so the air is being circulated by two fans in the center and two fans near the edges. This seems to be working very well as well. We've been having a few 100 degree days lately and the insides easily stay 15 degrees or so cooler than the outside.
Also for a while now, I have been contemplating making the system I have (Celestron C8 on an Atlas EQ-G mount. QHY8 and Hyperstar III) a little more versatile. Of course I could always operate the scope in f/10 config by attaching the camera to the back, but with a f/6.3 reducer/corrector, I could also operate it in that mode effectively giving me 3 different configurations. A quote from the Celestron website on the f/6.3 reducer: "For the Celestron reducer with a focal length of 284mm working at f/6.3, the spacing is 105mm. For Celestron accessories simply screw the reducer onto your scope and view at f/6.3. For aftermarket uses the compression ranges from about 0.7 at 50mm spacing to about 0.5 at 225mm spacing." Given this, I got the following items: 1) Celestron f/6.3 reducer/corrector 2) SCT to T-Thread adapter. Got the 55mm version 3) 10mm T-Thread extension
I already had a 20mm T-Thread extension and from the QHY dimensions
I have a total spacing as follows: 55mm Thread Converter + 20mm Extension + 10mm Extension + 20mm QHY8 = 105mm spacing between Corrector and CCD Chip. The QHY8 has 7.8 um x 7 .8 um pixels with 3110x2030 total pixels and 3032x2016 active pixels. Using this calculator and the active pixels, I get the following: At f/2 Hyperstar setup: 16" FL == 40.64 cm FL == 406.40 mm FL == 199.8' x 132.8' FOV At f/10 Visual Back setup: 80" FL == 203.20 cm FL == 2032.00 mm FL == 40.0' x 26.6' FOV At f/6.3 FR Visual Back setup: 50" FL = 127 cm FL = 1270.00 mm FL = 63.9' x 42.5' FOV
I could also change the spacing using the various spacers I have and get these additional combinations ( comp = 1 - Spacing/FR FL. For Celestron f/6.3 FR FL = 284mm): 75mm = 1 - 75/284 = 0.74x 85mm = 1 - 85/284 = 0.7x 95mm = 1 - 95/284 = 0.67x
Which translates to: At f/7.4 FR Visual Back setup: 59" FL = 149.86 cm FL = 1498.60 mm FL = 54.2' x 36' FOV At f/7 FR Visual Back setup: 56" FL = 142.24 cm FL = 1422.40 mm FL = 57.1 x 38.0' FOV At f/6.7 FR Visual Back setup: 54" FL = 137.16 cm FL = 1371.60 mm FL = 59.2' x39.4' FOV
I am not sure if these additional configs are worthwhile to attempt, but it's interesting nonetheless. Maybe I can use the FOVI in Sky6 to see what suits best. Although, I should point out, the Celestron documentation indicates a different range for the same range of spacing.
Been on a hiatus for a while now, but meanwhile I have been scheming to construct an observatory. The detached room we have in the backyard provided for a very good skyline and height to build this. After researching on the web, I pretty much narrowed down my decision to something like this (or this). After talking to Richard Shell from STI, and looking around for the right shed, I finally decided on an Arrow Newport Shed from HomeDepot which was on sale for 230$. Richard suggested that instead of the 2x4 and 1x4 rails, he is now using garage door rails and it works much better. But this would add some more engineering to the project and so I decided to do this with 1x4s and 2x4s with castors.
We were getting a new roof constructed on the detached roof and my roofer was kind enough to listen to what I needed and built me a counter leveled platform for my shed. He also installed braces for the 4x4 columns. The platform were built with these dimensions (this is from the shed manual):
The platform and brace for the columns eventually ended up looking like this: Platform from the front Platform from the back 4x4 column brace
The platform is counter leveled to correct for the slope in the roof and make it flat. And the braces are leveled as well. The height difference between the two braces (because of the slope in the roof) was corrected for by using different length 4x4 columns. Anyways before we get ahead of ourselves, I had to buy all the lumber. braces, castors etc. for the roof frame, the rails and the columns. I drew up this design before acquiring the lumber: This changed a bit as I started building, but the roof frame was pretty much spot on. As you can see from the above, the roof frame and the part of the rails on which the castors ride are made of 2x4 bars. The side stops on the 2x4 rail is made of 1x4 bars and the rail support in the back is made of 4x4 columns (attached to the 4x4 brace in the bottom)
Basically, when constructing the shed off of the instruction manual, you just skip the parts where the roof is affixed to the walls through the wall channels. Instead the roof is constructed in completion and attached to the 2x4 frame using wood screws. The rest of the building (base frame, walls, wall support channels, doors etc.) are again constructed according to the manual. One the walls are all standing up, you build the rails on top of it and then place the roof on top of the rails. The rails were originally going to be build with a complete four sided frame with the two side portions running further back so the roof can roll off to the back. But then I realized that I did not need all four sides. In fact I only needed the two sides on which the castors would roll. So eventually I just ended up doing this. Also the length I used finally for the rail 2x4s was 139 inches as opposed to what I had in the diagram to begin with. On either side of these 2x4 rail supports (which are laid flat on the roof, screwed with wood screws through the side wall channels and supported and screwed into the 4x4 columns in the back), I used 1x4 bars to provide for wheel stops, so that the roof does not slip off the 2x4 rail by moving sideways. This creates a depressed channel in each rail in which the castors ride. Blocks of wood are also screwed in these channels on either end so the roof can only move so far in either direction The rail design using the 2x4 for castor support and the 1x4 for wheel stop on the sides forms this depression in which the castors ride Here are the end stops which make sure the roof does not travel more than it should. 4 such blocks on the 2 rails make sure that the roof only goes so far in either direction Castors sitting inside the rails The 2x4 castor supported is screwed on to the wall channels from underneath using wood screws
I then built a pulley system using nylon ropes and metal rope eyes so I could pull the roof on and off from below without having to climb up on the roof. Basically it uses two pieces of rope on either side so that there is no rope in the center obstructing the view and uses metal eyes and rope knots to acheive the right forces to move the roof in either direction. Each side is composed of 3 eyes. One of the roof frame (eye 2) in the front and two on the rail system one in the front (eye 3) and one in the back (eye 1). The rope passes through the eye 1, enters eye 2 where it's knotted and then passes through eye 3 and then back out through eye 1. These four ropes then pass through two additional eyes on a beam fastened between the 4x4 columns and reach the ground in the back where they can be reached and pulled on. When the top ropes from the two sides are pulled, because of the knot on eye 2, the roof starts rolling off. when the bottom ropes on the two sides are pulled, eye 3 directs the force forward because of the knot in eye 2 and hence the roof starts rolling forward. It is important to note that when the roof has completely rolled on eye 2 should be a little behind eye 3. The forces act in such a way that when rolling the roof on, the forces on eye 2 act horizontal only as long as it is behind eye 3. Once it gets on top of eye 2, the force becomes vertical and the roof won't move anymore. Some pictures might help: A full view of the ropes inside the building. This is the right side looking from the front of the building Eye 2 and eye 3 setup when the roof is completely rolled on. Notice the knot on eye 2. This is what lets the forces direct the roof on and off Eye 1. This eye is used to just direct the ropes out of the building while staying on the edges These eyes in the back take all four ends of the ropes and direct it down from where they can be acted upon. You notice that ropes from one side of the building go through one eye. The two eyes here are centered so that there are no lateral forces when yanking on the ropes. The length of the two pieces of rope from either side (top part or bottom part) are tied together so they form two coherent pieces, one which moves the roof off and one which moves it on A view from the back of how the ropes travel behind the building Another view A view from down below where the ropes will be used to roll the roof on and off
And here's with the roof off and on:
When the roof is off there is a pretty good, clear view of the sky, and the telescope should be able to slew to it's limits through the zenith. The view to the back is not much limited either (the horizon is above the level to which the rolled off roof obstructs the view and the roof itself is not very tall, even with the castors and the frame. Atmost 6~8 inches)
Another idea I had (what with 100 degree days in NorCal these days) is to have some forced ventilation in this observatory. I found these solar powered vent fans which were a great fit. I installed two of these in the center roof panels after cutting the right holes. Caulked it afterwards to be water tight. They work great! The solar panels can be seen on the outside view from the inside
A full view of the observatory:
And a video of it in action ;)
Also to control the power on/off remotely, I am using this wireless power controller in the observatory. Using this I should be able to turn everything on/off remotely without having to get up on the roof Also the insides of the observatory will be lit with this work light and red CFL spiral, in case I do need to go up there to tweak something
One final problem I need to figure out is the water tightness of the building for realistic rainy situations. The sides which have the rails should be fine: But the front and back might not be: One of these days I am going to climb up there with a garden hose and see where I need to do some work to block out rain. Most probably some plastic sheets will do the trick, but I need to test first. Of course I will have to do this before I put any equipment in there :)
It's a beautiful thing. This is 16x10min subs. 60 Flat frames and 40 bias frames. I took the Flat frames with 0s exposures in Neb2 and so used the bias frames as flat darks as well. I think the flats are coming out nice, as evident in the lack of a central halo.
But this image just has too many stars in it!! I don't know how to reduce them. Also I wonder how can I do a better job of data acquisition for this. Should I go longer on each exposure?? or do shorter, more numerous subs? Light pollution is definitely screwing me over to some degree. But there is a glimmer of hope.
After some feedback from Sander about there being enough data, and to just add processing, I decided to take another stab at this. With the same data as the previous post. And here's the result:
I used the Red Channel as a luminosity channel and some iterations of Histograms, Curves and Noel Carboni's "Enhance DSO" script. All in all very happy with it. Thanks for the suggestion about processing Sander.
After cleaning the corrector, remounting it etc. I decided to check if everything was ok yesterday night. Tried to image Soul Nebula (IC1848). Here's what I achieved: My flats have gotten much better as can be witnessed in this image. I also too Flat Darks this time around. So here's the skinny on this: 17x10min light frames, 60x0.1s Flats, 40x0.1s Flat Darks and 40 Bias frames. All in all a pretty decent image assuring me that things have not gone horribly wrong. The collimation looks pretty good as well. Although this image probably needs much longer exposures time on each sub frame. Will have to come back to this target.
Yesterday, in an attempt to bring the sweet spot back to the center (as noted in the previous post about flats etc.), I tried recollimating the Hyperstar. After an hour or so of frustration, and lost collimation etc. I realized that the threads of the hyperstar had stuck to Hyperstar conversion kit in the corrector plate. I guess this was because of my attempts to get a better angle for the collimation screws on the Hyperstar. The collimation screws on the Hyperstar really need to be more accessible. They are hard to reach, especially when using a camera such as the QHY8 which has a profile which covers the screws from the top. Anyways, this whole thing meant that I now had to remove the whole corrector plate and rescrew the baffle tube to the conversion kit ring. What a hassle! But the silver lining is that since I had the corrector out anyways, I ended up cleaning it pretty good. One other thing that was stuck was the nose piece of the QHY8. I guess I lost whatever seal it was providing to the CCD. Now I will have to see if frosting problems will rear their ugly head. Finally as of tonight, I am back to my old IDAS-LPS-P2. And the Hyperstar seems collimated and I think I have the corrector centered properly. So the sweet spot should be back in the center. To collimate I started with the hyperstar completely flat and I need very little effort to bring it to collimation. One other thing that I ended up fixing in the process is the way the Robofocus was attached to the scope. I was using 3M mounting tape, which was rated for 2 pounds. I went to Home Depot and got Scotch mounting tape rated at 5 pounds and the robofocus seems to be a lot more stable now.
As I type this I imaging IC1848 (Soul Nebula). Hopefully it will turn out good enough to post. We will see...
Recently I bought the Astronomik UHC filter to try and mitigate some of the light pollution problems I had been having. I have not posted a single image that was taken after obtaining this filter although I did do many runs of data acquisition. The problem being that in even data acquisition, after stacking them, I notice these diffraction color bands. At first I thought it was because of the flats, which I corrected as indicated in my last post. And even after that I notice the bands:
After some discussion on the QHYCCD yahoo forum, turns out that this is because of the steep light paths the the f/2 hyperstar system entails, combined with the large CCD chip used to image. The data is there as can be seen from the red channel:
The other channels show severe banding. Green:
And Blue:
As can be seen, the flat looks ok but is just not able to correct for these diffraction bands:
And the bands make it very hard to correct for it and bring out the details. People indicated that the Baader 35nm Halpha filter migt do a better job. The reason being that the steep light path basically shifts the wavelength by about 6nm and this leads to diffraction patters resulting in the color bands. The Baader 35nm, being pretty wide for a Halpha filter still captures the Halpha even though the shift happens and hence should preserve the data while cutting out all the light pollution. I tried stacking them without flats as well, to rule out the flats and the same problem exists. But oh well!! After 200$ for the Astronomik UHC, I think I am back to using the IDAS-LPS-P2
One thing that can be noticed here is that the chip seems to be offcenter. This was indicated by Sander after seeing my flats. I think the collimation effort pushed it a bit off-center. I can try and recollimate to bring it back to the center, but for now I think I am going to continue with this setup and the LPS to see what kind of results I get.
Posts
