I have since moved on to using Astrophotography Tool and the integrated plate solving using ASPS and PlateSolve2. The information below is still relevant, especially if you’re using BackyardEOS or BackyardNikon, but I find plate solving through APT easier and more reliable.

• This is a basic setup to get you going and solving relatively quickly.
• More advanced settings will help you solve a bit quicker, but fiddling with them off the bat could just lead to frustration.
• Configuration and explanations of the more involved settings can be found down the page after the basic setup.
• These are just a baseline, and what works for me. You may need adjustments according to your setup to be fast and accurate.
• Plate solving with the use of narrow-band filters will most definitely require changing advanced settings depending on the area of sky you’re imaging.
• Let me know in comments or email if these work for you so I can learn and/or adjust the post to fit more people.

Astrotortilla is an incredibly useful tool, with a confusing setup. The purpose of this software is to center the object you want to image within one arc-minute of the center of the field of view. It does this by taking an image of the sky you’re pointed at, overlaying that on a database to determine where you’re pointing, then calculating where you want to be and slewing the scope to the correct position.  The application requires some thought prior to installing. Follow the steps below to hopefully get an accurate setup specific to your equipment. Once configured properly, you’ll never be left out in the cold searching for a target again.

1. Download the application installer from SourceForge
2. Visit the Sky At Night field of view calculator site by clicking here. If you don’t see your equipment listed, or anything equal, click here to visit the astronomy.tools FOV calculator. You may find some equipment on one and not the other, but they both have custom options.
3. Enter the information for your OTA and imaging camera using the drop-down menus. My scope wasn’t listed, but the Omni XLT150 has almost the exact specs.
4. Note the FOV numbers. Astrotortilla uses these at the time of install, and during the configuration.
5. For the Narrowest Level drop-down menu, enter the range that covers 20% of the smaller value. In my case, 1.14*.2=.228. For the widest Level, select the range that covers the larger number in the FOV calculator – 1.70 in my case.  The Astrotortilla setup uses these numbers to download the corresponding databases used in solving your image. Get this right the first time, as it’s a pain in the butt to correct afterward.
6. Click next through the screens and allow it to download the necessary files. This could take some time.
7. When opening for the first time, these are the default settings. This is where things get confusing. If you leave these settings, your image may solve once in a while. If it does, it will take several minutes.
8.  This is the field of view that Astrotortilla is expecting to search. Enter numbers slightly outside of your range, but not more than a half degree or so and try to keep the same mid-point you had with your original numbers. The default levels of 0-179 are set to the entire visible sky!
9. We’re working in Degrees, so leave the field degwidth alone
10.  The original search radius is set to 180 degrees. This will essentially take the entire sky into account. I set mine to 25 degrees because my GoTo is just terrible. It might work slightly faster if you narrow it down a bit.
11.  Here is the field that drove me crazy when I was trying to figure this out. I’ve seen a bunch of long strings with several variables entered here. I have the detailed string figured out now, but in the beginning, the more variables I added to make it “faster” the more it just didn’t solve at all. The Sigma setting is the most important and tells Astrotortilla what to recognize as a star. The lower the number, the more stars it will detect. When I’m imaging away from the Milky Way, I have success with this setting at 70. When I’m shooting DSO’s inside the Milky Way, I might have to turn this up to 125-150. Otherwise it detects too many stars and takes several minutes for the each solve.

This will get your objects in the field of view if your GoTo is off, as mine is. What I’ve found is that another variable is required to have things perfectly centered. I talk about this down the page, in the advanced setup. Another number that may need some tweaking is the exposure time and ISO. Exposure length has it’s own field on the main window. To adjust the ISO, click on the Setup button in the Camera Section. There’s no good rule for this. A dark site might only require a couple seconds at ISO1600. I have the most success for my home sky conditions at 15 seconds/ISO800.

Now that it’s configured, follow the steps below to actually use it. My slews are as much as 10 degrees off, and Astrotortilla puts the object dead center within about 3 minutes. This is much more effective than manually searching the skies with the handset.

1. Open your planetarium application of choice and slew to a target (assuming you’ve already gone through your alignment).
2. Open your imaging software if not already opened.
3. Connect your mount from the drop down in Astrotortilla.
4. Check the boxes to Sync, Reslew and Repeat
5. Set your exposure length and hit the Capture & Solve button
6. Let it do it’s work. Keep an eye on the status bar to see how well it’s working.

Tips if you’re not solving:

• Don’t assume that going high on the ISO will give you a better result. The name of this game is star detection, which works better with more contrast. In my light polluted skies, I use a 15-20 second exposure at ISO800 and solve almost every time, anywhere in the sky, even when a poor slew has me shooting into tree branches.
• Look at the status bar when the image is solving and pay attention to the number of stars detected. If you’re over 100, raise the Sigma number. If you’re below 15, lower the sigma number. I find the application to work best, and solve fastest in the 20-40 star range, but don’t obsess over it. After a while, you’ll know what number will work best in each part of the sky. You can also set a max detect on the starts and an option to sort the stars by brightness. Scroll down for more advanced options.

Advanced Configuration for the Custom Settings Field.

OK, so you have the basic settings configured in Astrotortilla now, and you’re getting some success. This section will talk about the custom settings field option by option and the strings to get things in the center of the field and do it a little bit quicker. These aren’t required for the application to work, but I think they’re necessary for it to be effective and really hands-off. There are several even more advanced settings and capabilities of Astrotortilla, but all I don’t use them, and honestly don’t understand all of them. The only thing I use the application for at this point is to center the object I want to image.

–sigma 70 –no plots -N none -H 1.55 -L 1.14 –r –objs 60: This is the string that I use, and I’ll usually solve an image in under 10 seconds. Let’s examine what each of these options are.

–sigma 70 :  This option sets the level at which Astrotortilla detects a star over noise. The higher the number, the more discerning the app is and the fewer stars will be detected. In general, a number from 50-100 should be successful. This option is the primary driver for solving, and is dependent on your skies. I have severe light pollution (and use a CLS filter). 70 is the number that works for me. I will occasionally raise the number to 100 or 125 if I am shooting inside a milky way band. I’ve seen recommendations to leave this at 70 and adjust exposure time and ISO if you’re having issues solving, but I have more luck changing the sigma number.

–no plots –N none : From what I understand, the presence of these fields prevents the application from saving annotated images and creating new FITs files respectively. I don’t need these, because I’m just trying to center up an object. I leave these in to speed things up just a touch.

-H 1.55 -L 1.14 : These are the high and low options for your FOV. They seem redundant to me, but having correct fields in here has helped me get objects centered. I think the scale min and scale max options are for BYE or other imaging software, and the High and Low used in the options string is for Astrotortilla. Without this entry, Astrotortilla said it solved, but the object was always about 10 arc-minutes to the bottom left of the center point on the screen. People say you can round these, and some say to go way over and under your actual FOV. As you can see here, I’m pretty much exactly on my FOV numbers and this is what given me the most success. If you round, I would keep the rounding equidistant from the midpoint.

–r : This configuration option sorts the stars by brightness (contrast measurement against the background) so the brightest starts are used to solve the image first.

–objs 60 : This limits the number of objects that are used to solve. It seems a bit backwards, but oddly the more stars detected, the less success I have and the longer it takes I find the most success in the 40-60 object range, as long as they are sorted using the previously mentioned –r option.

As with everything, these are the options I use, and what is most effective for me.  I’m not sitting under your skies with your camera or scope, but I hope the explanations of the options will help you get this incredibly useful application working effectively and efficiently. Let me know if you have any questions and I’ll try to find an answer.

Clear Skies – KA