Skyward 200 Astrograph: Fifteen Hours on the Heart
When I wrote about wrestling the Skyward 200 to life last summer, I ended by saying we needed some clear skies to do some testing. My friend Vasu, who helped me assemble that first prototype, took that very seriously. This fall he has been putting the Skyward 200 Astrograph through its paces, and the results speak for themselves.
The Heart of the Heart
The image above is the core of the Heart Nebula, IC 1805, about 7,500 light years away in Cassiopeia. Vasu shot it in narrowband using sulphur, hydrogen and oxygen filters, then mapped those three gases to red, green and blue. This is the "SHO" or Hubble palette, and it is why the image glows in gold and blue instead of the deep red you would see in a regular colour photo of this nebula. He even made sure to include WeBo 1, a small and faint planetary nebula, in the framing.
When he posted it in our Discord the reactions were pretty much all capital letters. I felt the same way.
The Rig
Here is the equipment Vasu used:
Telescope: Ten Telescopes Skyward 200 f/4 Astrograph (800mm focal length) with the Ten Telescopes 3D printed focuser
Camera: ZWO ASI1600MM-Pro
Filters: ZWO narrowband and RGB in a 7-position 1.25" ZWO filter wheel
Focuser motor: ZWO EAF
Coma corrector: Explore Scientific HRCC
Mount: EQ5
Dew and cooling: Ten Telescopes PWM controller running the OTA fan and the primary and secondary dew heaters
The EQ5 and the Skyward 200 spent the whole winter set up outside under a cover, which is a good test of a printed telescope in its own right.
For final collimation Vasu used a tri-Bahtinov mask. A Bahtinov mask creates a diffraction pattern around a centred bright star that makes it easy to see when you are in perfect focus. The three zone version goes a step further and lets you check collimation across three regions of the mirror at the same time. I never thought I would redesign a telescope around a specific Bahtinov mask, but this spring I changed the Astrograph's spider to work with one. It was worth it.
Here is how it works. The mask is split into three sections, and each one lines up with a region of the mirror that is adjusted by one of the three collimation knobs. With caps covering two of the sections, only one third of the mirror makes the pattern, so you turn the matching knob until those spikes line up. Then you take the caps off. When all three sets of spikes line up together, the scope is collimated.
The Focuser
Vasu's focuser is one of ours, the Ten Telescopes 2 Inch Focuser. The body is 3D printed and the drawtube is CNC machined aluminum. I'll be honest, it was as much work to design and test as the rest of the telescope. I went through about seven variations before I was happy with it.
Why go to all that trouble? A fast f/4 telescope like the Skyward 200 Astrograph has a very small zone of perfect focus, only about 0.04mm deep. Move the camera more than that and your stars start to bloat. On top of that, focus drifts as the telescope cools down through the night, and each filter comes to focus at a slightly different point. Nobody wants to stand outside refocusing every hour.
That is where the ZWO EAF (Electronic Automatic Focuser) comes in. It is a small motor that turns the focuser for you. Pair it with a computer running NINA, or with a ZWO ASIAIR, and the software takes a series of test images, measures how sharp the stars are and moves the focuser to the best spot. It can repeat this automatically when the temperature changes or when the filter wheel switches filters. That is how Vasu could let the Skyward 200 collect data all night without babysitting it.
For autofocus to work, the focuser has to be stiff, smooth and repeatable. If it sags or slips under the weight of the camera, the software chases a moving target. Ours is a Crayford style focuser running on linear rails, and the machined aluminum drawtube keeps the camera, filter wheel and coma corrector square to the telescope. The Astrograph itself is also designed with extra stiffness and printed in a stiffer filament, so the whole imaging train holds its shape through the night. I first tested the focuser with an EAF in May 2025, and by June Vasu was reporting back that it was working well. It took a few small changes to the EAF mounting bracket to get it to attach, but once it was on, it just worked.
For people focusing by hand, I designed a planetary gear reducer that prints in place, with all the gears coming off the printer together as one piece. My first version was 12:1, which was great for fine focus but painfully slow for getting close. The latest version is 9:1, and racking through focus now feels just right.
I have four more of the aluminum drawtubes ready to go, and they will be going into other scopes in the near future. I have also moved the focuser to more common, easier to source rails to bring the cost down.
A couple of build tips if you print your own: use 50% infill for the focuser parts because there is real load on them to create the Crayford friction, print the planetary gears with a 0.2mm nozzle if you can, and break in the gearset by spinning it with a drill.
The focuser files are free on GitHub, and there is a build video on our YouTube channel.
Nineteen Hours of Data
Vasu captured about 19 hours of data over several nights, in 5 minute exposures (subs). He takes his flats on the twilight sky, which is a simple way to calibrate out dust and uneven illumination without any extra equipment.
Quality Over Quantity
When it came time to stack the data in PixInsight, Vasu raised the minimum weight threshold from the default of 5% to 50%. In plain terms, any sub that wasn't close to the quality of his best frames was thrown out. About 20% of the subs were rejected, leaving 14 hours and 10 minutes of SHO data and 49 minutes of RGB for star colour. That is roughly 15 hours in the final image.
Throwing away four hours of data is not easy to do, but it shows in the result.
Two Hours on the Leo Triplet
Not every target needs a week of clear nights. In September Vasu processed some data he had sitting around on the Leo Triplet, three galaxies in the constellation Leo. It is only 2 hours in total, 1 hour of luminance and 1 hour towards RGB. He pointed out a slight artifact from the spider and a reflection in the middle, but he was surprised at the result for just 2 hours. So was I.
The Pac-Man Nebula
Vasu's latest target is the Pac-Man Nebula, NGC 281 in Cassiopeia. He got 7.5 hours of data on it in his first night with the Skyward 200, then went back for more the next night. The Moon didn't make it easy. One night his automation shot oxygen before sulphur instead of waiting for the Moon to set.
Here is the finished image, about 14 hours in the HSO palette. This time hydrogen is mapped to red, sulphur to green and oxygen to blue, which is why it looks so different from the gold and blue of the Heart.
In Vasu's words, "these scopes are no joke." I couldn't agree more.
Nice work Vasu. Great to see the Skyward 200 putting out these quality images. A tribute to all the hard work and design of this great scope. Kudos to Bryan.