From time to time I have mentioned Stellarium as my favorite astronomical software. It functions as a personal planetarium, in particular allowing me to do three things:
1) It allows me to see what it was I saw in the sky any time in the past. So, I can take a picture of the night sky and later on use Stellarium to identify asterisms, stars, or planets I don’t recognize.
2) It allows me to see what the night sky will be like on any night in the future. This allows me to plan my astrophotography shoots in advance, selecting ahead of time those interesting things I want to try to photograph. It lets me see which nights will be moonless, or if there is a moon, when it will rise and set. It lets me see where in the sky certain objects are at any time of the night so I can plan my astrophotography session.
3) It allows me, right at the site the very night I’m taking pictures, to see where things are relative to me. Since I can enter my location by latitude and longitude easily obtained from my phone, I can more easily find what I want to look at or photograph than if I was using paper charts. I can also definitely answer questions from people around me as to what this or that is and show them on the laptop screen all the parts of the constellations, for example.
New comets and satellites are easily added to the program’s database, allowing me to easily and quickly hunt them down in the night sky. Playing with Stellarium, I can look into the future to see if there’s anything interesting that I might want to go see or photograph. I don’t have to wait for it to be announced on the news the night before or something like that. I can browse the internet and if I find some interesting astronomical event, I can simply fire up Stellarium, virtually go to my favorite remote sites, and see if it’s going to be visible for me and at what times locally. For example, it may not show me the Orionids meteor shower itself, but it will show me where in the sky the radiant is and when I’ll be able to see it. I can then use that to plan an outing, either stargazing or astrophotography for myself or someone else. Of course, I actually do both every time, the night sky is so wondrous and eternally fascinating.
I do indeed use other tools as well, such as The Photographer’s Ephemeris, Flash Earth, Google Earth, GPS and the ubiquitous internet. By and far, though, Stellarium is my premier astronomical tool and is the reason for this particular blog entry.
After three tries, I have finally managed to get a panorama that does justice to one of my favorite astrophotography sites, the one I call Sands Basin Overlook. Located a mere hour’s drive from my house, it’s up in the Idaho Owyhees. It has a reasonably dark sky and is high enough that the horizon is more or less at what appears to be eye level. That gives me a site with almost a full hemisphere of sky. I’ve often thought of creating a landscape from this site for use with Stellarium, first for myself and once I have it fully verified and working, then for all Stellarium users that might want to use it.
Three tries because, as I’ve mentioned before, I can shoot panoramas but in this case I wanted a perfect pano for a very specific use. Previous versions had too much curvature to use due to using the fisheye lens, or significant differences in exposure, or…. All things that will happen to any photographer when he or she digs down to get one perfect shot. Murphy likes to tag along, ya know?
This time, though, I went to the Sands Basin overlook for the express purpose of shooting that panorama. Again, Murphy tagged along…a critical part of my post photography session for panoramas is…drum roll, please…stitching them together. My intent was to go out to Sands Basin Overlook, shoot a pano sequence, pull it up on my laptop, stitch it, verify it, and correct the next series of photos as required. I was using a relatively new laptop and forgot to put my stitching software on it.
I had no way to verify the shots. I could look at them individually, and in my head put them together, but way out in the middle of nowhere I didn’t have the software to actually do so and no way to get it.
So, I did what any good photographer does. Bitched about it a bit then buckled down and went to work. In the end I wound up with ten pano sequences with two different lenses. Then we packed up and enjoyed a leisurely cross-country back road drive home.
Out of those ten panorama possibilities, five of them were actually good enough to use. Of course, some were better than others for my purpose, but I was still extremely happy to get a 50% success rate, especially as I was using the fisheye as one of the lenses. Indeed, the pano I decided to go with was taken with the fisheye.
None of the 10mm fisheye panos were usable, they had far too much curvature. The two 17mm panos were both usable. The general recommendation is to use a 50mm or longer lens, but my fisheye at 17mm worked better than my 50mm. The 17mm, on my Pentax bodies, equates to a 25mm lens on a 35mm film camera. So, 25mm works.
To take good panoramas, certain steps are vital. Those steps ensure a minimum of post production work and ensure whatever stitching software you use has the best chance of success. For me, those steps are:
1) Use manual focus so that depth of field, etc. remains same through every shot. I used infinity which for my camera/lens setup is everything from 10-20 feet on out. That works here because I want the horizon sharp.
2) Use manual white balance. I set mine to sunny and to cloudy for different panos. I believe the cloudy setting gave me a warmer result that I liked. If you leave the white balance on automatic, it will change the colors between shots and that will most likely be evident in the final pano. It’s best to use as much manual control as possible. If you don’t have sunny/cloudy pre-sets, the equivalent temperature settings are around 5000K and 3000K if I remember right.
3) Use manual exposure times. This can be arbitrary but it’s a good idea to use a fast exposure. I used 1/350 seconds which allows me to do a quick panorama series with minimum light or movement changes. In this case, movement wasn’t an issue since the only real movement was the clouds and I would be removing the sky.
4) Use manual ISO settings. I wanted the best quality photos I could get and had plenty of daylight so I used 100.
5) Use manual aperture. I wound up using f/8. This was determined by looking at the brightest, darkest, and random places on the scene, using the Tv mode. For each point looked at, note the aperture the camera recommends then average them out. I lucked out as virtually all mine were f/8 with the settings from 3) and 4) above.
6) It’s critical that your tripod is leveled. You don’t have to be anal about it but get it as good as you can. For me this meant going back and forth adjusting my tripod legs while moving the camera around the 360 degrees of horizon that would become the pano. This is, of course, with 0 degrees of up or down tilt.
7) The recommended photo overlap is anywhere from 20% to 50%. In this case, because of the nature of a fisheye, the overlap in the pano I eventually decided to use came out close to 30% and consisted of 8 photos for the entire 360 degrees of horizon.
For stitching, I use any of Microsoft ICE, Hugin, and Autostitch. Each has advantages and of course disadvantages. In this particular case, I used Microsoft ICE. Zooming into the resulting panorama I did not find any edges or anything that stood out that I needed to adjust. Sweet! Every pano stitched together and the only issues were the extreme curvature on five of the ten. Two more had minor curvature that I could tweak if necessary, but the remaining three needed no tweaking. Selecting from those three was simply a matter of picking the one I though best.
Now came time to review the process I needed to follow to create my Stellarium landscape. I used two guides to determine what I needed to do from this point on out. The first guide is an overview of the main points that need to be done. Since this one does not include the details of image size and package contents, I also relied on the Stellarium wiki for the necessary specifics, in particular section 3.
I used GIMP to remove the sky from my panorama. It was a tossup when to resize the pano but I decided I wanted to work with the full size pano (at 21216 by 4028 pixels) to remove the sky. That means a lot more work on the skyline removing the sky, but it also means that when I add the extra transparent sky area and reduce the image to 2048 by 1024 as called for it will have no sky in it at all. For me, that was worth it. Others may see that as overkill and reduce the pano size first and most likely end up with just as good a job.
I also used GIMP to “pull” the ground down to the bottom of the end result. This is my first attempt at a Stellarium landscape, so I’m having to learn as I go. In this case, I perhaps should have taken more shots of the ground closer to me as well since I have to create a certain size PNG for the landscape. To keep the horizon true to what I see, the pano I took doesn’t “bottom fill” properly.
I already had the Sands Basin Overlook GPS coordinates and altitude keyed into Stellarium so it was a simple matter to recover that data when needed to create the .ini file. If you create a panorama for use with Stellarium as a landscape, be sure and record both the location and the altitude. You need that to have Stellarium present you with a true image of the sky at that location.
I definitely plan to put this personal landscape up on stellarium.org eventually after I use it a bit and make sure it’s correctly showing the site and properly aligned.
So far, I’m fairly happy with the results.