AweSIM

@fifeskies you made some interesting observations and thank you for sharing your experience as well. You're right about the ROR blocking most artificial light sources in my neighborhood. But what surprised me the most was that even though the telescope will fit inside the room, it will still be able to see so close to the horizon. For me, the most fun part was programmatically generating a horizon for the room itself. Also, now that I have the horizon image, I can also use it to program mount limits in EQMOD, although that might be an overkill. 🙂

I've been wanting to construct an observatory on top of my house for a long time and am finally almost ready to build one. I settled for a roll-off roof design with the observatory being almost 10 feet by 10 feet and 7 feet high. I'd park my telescope in a horizontal parking position. My main concern was that what if I construct the observatory room too small or too tall so that it blocks out a good portion of the sky that would otherwise be accessible to me without an observatory. This post is more of a blog about my journey thus far, in hopes that others might find it interesting or useful. I came across an article online (don't remember the source, sorry) that showed how to show a custom horizon in Stellarium. I climbed onto the roof where the proposed observatory is supposed to be built and shot a 360 degree spherical panorama using Google Traffic app for Android. I exported the unwrapped 4096 x 2048 pixel image and edited it using Photoshop to make the sky transparent. An interesting problem I encountered in this process was that the horizon is not always in the middle of the image, so I needed to have a reference object in the same 360 degree panorama at the camera level. Being at the same level, it should touch the horizon, and this means that the top of this object should lie in the exact middle of the unwrapped image vertically. If it is not, the entire image can be shifted up or down till it is. Finally, I crafted a suitable "landscape.ini" file to reference the unwrapped image and define its Z-rotation and packed these assets into a zip file. Finally I imported it into Stellarium and viola! I could see my custom horizon perfectly. Stellarium now showed me views exactly as it would appear as if I stood at that spot myself. This step helped confirm if the spot I had chosen for my observatory was good or not (It was! Only 10 degrees above horizon was blocked, except south-east where almost 30 degress above horizon was obscured by trees). However, the issue still remained whether the observatory, once constructed, would block significant portions of the sky or not, and there was no easy way to test this. So I decided to put my software development skills to the test to address this. The proposed observatory is about 10 feet by 10 feet in size and about 7 feet high, with the scope placed in the middle of the room. With the walls so close to the telescope, parallax plays an important role. I created a quick programming project in TypeScript, included a good matrix maths base library, and created some 3D math classes on top of that to work with vectors, matrices and calculate ray-triangle intersections, etc. I created a basic 3D model of my telescope and mount such that the camera it looking out along the axis of the telescope, and can rotate like an equatorial mount along RA and DEC. I also created a very simple model of the proposed observatory with four walls, each made up of two triangles. The code loops thru each possible value of RA and DEC and computes where the telescope is pointing in the sky. It then computes if there is a wall triangle in between the telescope and its target. If there is, the code converts the direction the telescope is pointed at into polar coordinates (alt-azimuth) and plots a point on a graph where horizontal axis is azimuth and the vertical axis is altitude. If there is no triangle between the telescope and its target, it means that the sky is visible in that direction. This allows me to generate an 360 degree unwrapped panoramic image much like the horizontal I captured earlier. Using photoshop, I overlaid the custom horizon on top of the generated image to get the following image. This image clearly shows that the walls of the observatory don't obscure any significant additional portion of the sky, and hence the design is perfect from the perspective of viewing angles. Furthermore, we can also create a custom horizon out of this image and import it into Stellarium. Thank you for reading this. 😃

Thank you so much for the insight!

How were you able to tell? 😮 And how is the secondary easier to adjust than the primary? I thought it was the other way around.

I never knew that! Thanks for this document. I learnt something new today! 😃

Thank you for linking this item as well. I'll definitely keep an eye out for this item and I'm glad you picked the site I could actually purchase from. Thank you once again! 😃

Hi @vlaiv, thanks a lot for your valuable suggestions and some great insights. I didn't know that the backfocus of 55mm was an approximate value. How should it be dialed in and how can it be tested to see if its improving things or not? As in, is there a non-subjective way other than take an exposure, add shim, take another and judge whether things look better or worse? Thank you for understanding the constraints of my assembly as well. Indeed I need a female-to-female adapter and a M42-to-M48 adapter at some point in my assembly. Your suggestions about the solution make sense, and if I go ahead and purchase a rotator, I will act upon your advice definitely. As for why am I opting for a rotator instead of simply rotating the assembly myself is this: I have tried doing it exactly like youve said many times: taking an exposure, plate-solving to find rough orientation, repeat. But it is time consuming to get it right and everytime I loosen the screws and fiddle with the assembly, my focuser inadvertedly slips a bit and I have to go through focusing again and again. So I was thinking maybe a rotator that allows rotation without any resistance (on bearings) will be more helpful than my current technique. I even marked angles on my assembly using a pencil. Keeping your advice in view, perhaps a better option for me might be to ditch the rotator and fix my focuser first so it doesn't slip. Your thoughts? Thanks a lot! Asim Sohail

Hi @Waldemar, Thanks for the suggestion. I can see some problems with this that I hope you will address: The variable adapter you proposed is almost EUR 63 which is a bit expensive for my budget at the moment. My coma corrector has an M48 male thread whereas the camera has a M42 male thread. Since most spacers have a male thread at one end and a female thread at the other, I will have to use the stock 11mm M42 female-to-female extender supplied so that the camera + 11mm spacer exposes a female thread and the coma corrector exposes a male thread. Total spacing required in this case is 55 - 6.5 - 12.5 - 11 = 25mm. Since I have a stock 16.5mm M42-to-M48 spacer supplied with the camera itself, if I use it, the spacer required will be, once again, 25 - 16.5 = 8.5mm. I don't think there are many variable spacers within this range. Besides, as noted in #1, they are way more expensive. Thanks a lot! Asim

@vlaiv, I really look forward to your advice on this. 😃

Hi! A while ago, I acquired a ZWO ASI294MC Pro and a SkyWatcher F/5 Coma Corrector for my SkyWatcher 8" Newtonian telescope. The coma corrector requires a backfocus distance of 55mm which was straight forward to achieve: Camera (back focus = 6.5mm) 11mm M42 (female to female) extender (11mm) 21mm M42 (male) to M42 (female) extender (21mm) 16.5mm M42 (male) to M48 (female) extender (16.5mm) Coma corrector with a M48 (male) thread This all adds up to exactly 55mm which was all perfect. However, I've been thinking of getting a M42 CAA 360 ° Rotator Camera Angle Adjuster or a similar M48 one. Both of these have an extension thickness of 12.5mm. Furthermore, the length of the male thread on the rotator is 3mm while the female thread is 5mm long. If I opt for the M42 rotator, I have only 1 option: it will have to replace the existing 21mm spacer with an additional 8.5mm (21 - 12.5) spacer which is a very odd spacing and I can find no satisfactory option on AliExpress (which is I'm forced to buy items from as only it ships to Pakistan). My new assembly should become: Coma corrector 16.5mm M42-M48 extender (16.5mm) M42 SPACER (8.5mm) (16.5 + 8.5 + 12.5 + 11 + 6.5 = 55) (I can break the 8.5 down into (4 + 4 + 0.5) or (5 + 3 + 0.5) but both seem odd M42 ROTATOR (12.5mm) 11mm extender (11mm) Camera If I opt for the M48 rotator, I have only 1 option and that is even worse: it will come between the coma corrector and the 16.5mm extender and the 21mm extender will be replaced by some other extender. This option is bad as the M42 female thread on the rotator is only 5mm long whereas the male thread on the coma corrector is 6mm long. This means there will be a gap of (not exactly) 1mm in the assembly. So my spacings become: Coma corrector (male M48 6mm) Empty space (1mm approx) M48 ROTATOR (female M48 5mm) (12.5mm) 16.5mm M48-M42 extender (16.5mm) M42 SPACER (7.5mm) (1 + 12.5 + 16.5 + 7.5 + 11 + 6.5 = 55) 11mm extender (11mm) Camera Does my "spacer math" check out? How do I go about solving this problem? I don't see anywhere outside this assembly where the rotator can go. On one side is the camera, while on the other side beyond the coma corrector, there is the focuser entrance. Also, the coma corrector simply slides into the focuser and I don't see how I can attach the rotator outside this assembly area. I would love to hear the thoughts of you awesome people who might have the same combo as this (Coma Corrector + Rotator + ZWO ASI294MC Pro) and would love to see how you guys have approached the problem. Finally, if having these weird spacers is the only way, which option should I go for? And given 8.5mm or 7.5mm of spacing, is there a preferred way of building this spacing (4 + 4 + 0.5) or (4 + 0.5 + 4) or (3 + 5 + 0.5) or (8 + 0.5)? Thanks a lot! Asim Sohail Pakistan

Thank you so much for sharing this. I will try to order one for my scope asap. It looks really effective. I just hope they ship to Pakistan. 😃

I wish I couldve done that. In Pakistan the sun is very hot I dont have anything to shade my telescope from the sun or rain. =(

Hi @r3i! This is a very interesting video! It looks quite simple. I even had a go at it just now with the ASCOM simulator and it works! I'll test it out with my actual gear the next time I go out and report back (which may be a couple of days as I managed to injure my spine just recently carrying my gear back and forth between my house and the observation deck on my roof every night =( ). Thanks for sharing this! 😃

Hi @Jiggy 67! Thanks for the heads up! I'll look into it. Can you also advise if using the parking feature can help avoid the hassles of alignment? Up till now, I've always had to polar align and then align after setting the scope up. But if I make an observatory so that I don't have to tear down my setup after every night, can I somehow reuse the previous night's alignment? I know having a permanent setup will help me avoid the hassles of polar alignment. But what about star alignment? Thanks!

Hi! I am planning to construct a small roll-off roof observatory for my telescope rig. I've found that when parked in its default home position, the top end of the telescope is almost 6 feet above the floor. This means that: My construction cost would be a bit high since my observatory would need to be at least 6 feet tall. For some viewing angles (like when the OTA is near horizontal, the observatory walls and roof might block some areas of the sky. However, I've seen some pictures on the internet where people have parked their scopes such that the RA axis is horizontally pointing to either East or West, and the Dec axis is also horizontally pointing to either North or South. This is great! It means that if I can park my scope in this position, my observatory would need to be only about 4 feet tall instead of six feet. It also means that once taken out of this parked position, almost all areas of the sky would be accessible to me. The issue is that I'm not aware if it's possible to change the default parking position on the SkyWatcher NEQ6 Pro mount. I can manually slew the telescope to this horizontal parked position and then switch the mount off. However, this means that when powering the scope up the next time, I wouldn't be able to allow the scope to resume from its parked position. Is there any way that I can change the default parking position for SkyWatcher NEQ6 Pro? Thanks! Asim Sohail ---------- EDIT: Here is how I connect my telescope to my PC. I use a Serial-2-USB cable to connect the hand controller to my PC. I set my hand controller to PC Direct mode and then use CDC and PHD to connect to the mount via ASCOM EQMOD. And I'm looking for a way to modify the default parking position so that whenever I want to park my mount via the hand controller or the EQMOD software interface, it should always park in the horizontal position (RA and Dec axis horizontal).