IC 2599 is also known as Gum 31 and more poetically, the Gabriella Mistral Nebula, which is named for the 1945 Chilean winner of the Nobel prize in literature. IC 2599 is said to resemble Gabriella Mistral but it takes a photograph of her and a bit of imagination to see her profile along the edge of the nebula. NGC 3324 is the open cluster above IC 2599 and it lies at a distance of about 9100 ly. The region covered in this image is located just to the northwest of the main structure of the Eta Carinae nebula. IC 2599 lies a bit closer than NGC 244 at a distance of about 7500 ly. This is a complex region rich in hydrogen emission nebula that shows itself as the magenta colored clouds in this RGB image. Doubly ionized Oxygen (OIII in spectroscopic notation) emissions show up as a blue/teal-colored glow and interstellar dust shows up in orange/brown colors. The "wall" surrounding IC 2599 contains a lot of interesting details so be sure to zoom in and look around.
I started this imaging session as I commissioned my new refractor in Chile during mid April. I wanted a target in the Milk Way near to the southern pole to test tracking and a few other things related to the telescope operation. Frankly, I picked this object on a whim after spotting it online somewhere (maybe Telescopius?). Once I saw how interesting this region is, I committed to finishing an image. I wound up taking a LOT more data in L+RGB+ Ha than what I included in this image. I started the processing with just the RGB data and the result looked so good that I left the L and Ha data unused. This image only represents just shy of 18 of the 30+ hours of data that I gathered. With my larger scopes, I’m used to gathering gobs of data in order to gather enough usable data to create an image. Clearly, that’s going to be less of an issue with this scope, which means that if I’m careful, I should be able to image many more objects per unit time.
While I’m at it, let me back up a little to tell the story about this scope and why I have it in Chile. Back in 2018, I had an opportunity to buy an Astro-Physics 130GTX refractor and I jumped at it; although at the time, I had no idea what I was going to do with it. I was perfectly happy with my Edge 14 but I had a notion that I'd use the refractor as a portable system. Time went by and I put my name on the list to get in line to buy one of the first Mach2 mounts. I figured that it would be a great mount for the refractor. When my number came up, I bought the mount and set to work getting it all up and running. The first thing that became apparent was that this was NOT going to be a portable system! It was way bigger and heavier than I expected. After working with C14s, AP1600 mounts, and other large gear, I had this stupid notion that a "little" 5" refractor was going to be small and light. Boy was I wrong! Configured for imaging, a 5” refractor like this isn’t all that small and it weighs way more than I’d be willing to deal with on a regular basis.
I half-heartidly worked on the “refractor” project while I assembled my new Planewave 20" telescope. One of the problems along the way is that I was having trouble getting parts. I had the 20" built, configured, and installed in Chile, while I waited on a focusing motor for the refractor. The perfect focus motor for this system was made by Starlight Instruments but the untimely death of the founder (I believe from Covid) stopped shipments. The owner’s wife was rumored to be restarting the business so I never cancelled the order but I eventually had to order an alternative focus motor for Optec. The Optec focuser worked through the Starlight fine focus knob on the scope, which created a slippage issue due to the weight of the camera package. So, it basically didn't work at all. While I was pondering what to do about it, I worked on other projects and one day about 18 months after my order, the belt-drive focuser from Starlight showed up, unannounced in the mail! Bingo...that set the project back into high-gear. I was finally able to get the scope set up and running well enough that I could finally try it under the stars and that’s where my first two trial images (the Cocoon Nebula and M45) were taken.
I’ll mention that I did order the F/4.5 reducer with this scope but it was the original version that AP now says is not optimized for small sensors. I was not happy with the field performance so I went back to using the F6.8 field flattener. As you can see, the imaging quality with the field flattener is superb.
I had an idea that I would just keep the refractor in Bend and use it during the summer when the weather and seeing were often spectacular. It only took me a week or so to realize that that plan was terrible. I hated running the scope at my airplane hangar because I had to spend the whole night out there and I just couldn’t get enough sleep. I also realized that the proliferation of security lights at the airport had past the point of no return. It had become just too bright out there to be workable. So, I needed a new plan. That’s about the time that Vincent at Obstech mentioned that they were about to open a new building dedicated just to smaller scopes. The rent would be about 2/3 of what I pay for the 20” and that sounded like the perfect solution to handle this new scope—so I signed up.
One of the things that I really like about this scope is the Mach2 mount. In my view, this is the very best mount that Astro-Physics has ever made. It is easy to PA align (with virtually no flexure) and the encoders are properly implemented as digital setting circles. The mount always “knows” where it is pointed—no matter how you move it. It is also super smooth and very quiet. I’ve been seeing guide errors of well under 0.2” and FWHM values approaching 1.5” when the seeing is good. Frankly, that’s better than what I get with the 20” on its L500 mount! After using a Pole Master to set the polar alignment, I confirmed that it will indeed go for at least 5 minutes unguided and still produce round, pin-point stars. AP has improved their sky modeling code considerably since I last used it with my AP1600 mount. It is now MUCH faster and I was able to do a 180-point model in less than a couple of hours (still 4x slower than with the L500 mount!). I tend to get slightly tighter stars with gentle guiding so I still use active guiding with an Optec Sagitta OAG. Overall, the performance of the Mach2 is really superb! Now if they would just redesign the 1600 to have the same features and performance! The only problems that I encountered with the Mach2 were software glitches related to operation in the S. Hemisphere. Many thanks to Marty Velente who dropped what he was doing to help me work through some fixes to get things running. A+ support Marty!!
I’ve attached an image of the scope in the observatory. Setting it up was fairly straightforward. Adjusting the correct back working distance and minimizing sensor tilt were the biggest challenges. The camera is equipped with an Octopi tilt adjuster. I originally bought the first version from Keith and when I explained to him that the kinematics were a mess and then told him how to fix it, he did…AND, he sent me the new version! The V2 Octopi is now really fantastic. It allows adjusting both sensor spacing and tilt using orthogonal adjustment screws. Before shipping the scope to Chile, I used a micrometer to set the nominal tilt to zero. Once at the observatory, I fine-tuned the tilt (which was pretty easy) and then used 1 mm spacers to set the nominal back-focal distance to the sensor. I just used the FWHMEccentricity support tools in PI to determine the sensor tilt. By looking at the astigmatism, I established that the spacing was long and when I reduced it, I achieved what at the time, appeared to be acceptable performance across the field. In hindsight, I’ve realized that I wasn’t picky enough. I still have just a little astigmatism that elongates the stars in the extreme corners but BXT easily corrects it. The next time I go down there, I know how to dial it down to near zero. I left a shorter extender tube with the scope so I could even have the techs do it but it’s one of those things that I’d ultimately rather do myself.
Processing this data emphasized to me another reason that refractors are so popular. Wow….it was really straightforward to get everything registered and I didn’t see a lot of the unexplainable artifacts that I often see in galaxy images from my larger scopes. This is only a minor crop of the full frame for the purpose of composition. Because of all of the detail in this image, the high quality, full resolution jpeg image came out at nearly 60MB! So, I had to resample this image to be a smaller image and I couldn’t save it at the highest possible jpeg quality to make it a more useable 10MB. Still the quality is pretty close to what I see on my monitor using the original monster images. In case anyone cares: Just understand that resampling the image changes the pixel scale reported by AB. The actual pixel scale for this system is about 0.89"/px.
I really like being able to image a larger field and I think that I’m going to have a lot of fun with this scope! As usual, feel free to let me know what you think. Hopefully it looks as good on your monitor as it does on mine.
- John
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