Home > Uncategorized > Adventures in Dual-Scope Imaging

Adventures in Dual-Scope Imaging

Since I get so few clear nights each year, I decided to take a different approach to my wide-field imaging: two scopes, two cameras, one mount. This way I can capture twice the image data every clear night. I knew going in that it might just be twice the trouble too.

So what equipment to use? I mean, we’re looking at thousands of dollars to pull something like this off, so I need to save money wherever I can, but I’d be wasting my time with poor equipment. Half as many great raw images are better than twice as many crappy ones. So I started with what I had already and bought used where I could. I also sold my STL-11000M and filters to fund the project. That camera produced amazing widefields with the FSQ-106ED (which I did not sell), but I’m choosing to go deeper rather than wider with this setup. I feel more than a twinge of regret selling the STL, but the bank account is finite. And besides, this will be an adventure, right?

To keep weight down and alignment simple, I decided that this would be a short focal length setup for widefield imaging. Because my sky is very light polluted, I focus almost exclusively on narrowband imaging when doing widefields. Let’s start with the cameras and filters then. I already have an ST-8300 with seven-position filter wheel and the full set of basic Baader LRGB, Ha, SII, and OIII filters. Ideally I would have gotten another ST-8300 used, or even an STF-8300 with similar filters. However, a good deal popped up on a QSI 583wsg with 3 nm narrowband filters, so I jumped on that. Because the sensors are the same, the final images should have the same image scale. But because the filters and camera electronics are different, I won’t be able to combine images from both cameras into the same channel. Based on the filters I had, the SBIG is used for RGB (for star color) and H-alpha. The QSI will take the SII and OIII channels.

On to the scopes. I recently purchased a William Optics Star 71, and I was pleased with its price-performance ratio. In my dream setup, perhaps I’d use two FSQ 85s, but buying another Star 71 wasn’t going to break the bank. The Star 71 is about six pounds, and it’s a fast f/4.9 with a flat field. There are very few options available for side-by-side mounts that can be aligned, but I ended up with the ADM VSBS-MiniMax. It was a frustrating experience to combine an existing VSBS I purchased used with the MiniMax; in hindsight I wish I’d just purchased the complete package. The SBS mount is also very heavy at about ten pounds, which means I’ll be pushing the limits of my CGEM.

Finally, guiding. I really didn’t want to add a third scope to the setup, so I utilized the guide port on the QSI. I purchased the QHY5L-II-M for this, and despite the cost overruns for my new system now approaching Pentagon contractor levels, I am amazed at the performance of that little camera. (Note to readers considering the combination of the QSI with the QHY: I can verify that if you purchase the “CS adapter” with the QHY5L, it will be at focus with the QSI guide port.)

So there we have it, two scopes, two cameras with filters, on one mount.
Dual Star 71s

Now the real fun begins. Without going into the details, I suffered a comedy of errors and challenges that took many clear nights to resolve. Aligning the two scopes. Putting a filter in the wrong slot. A glitchy USB cable. Realizing that the QSI has the sensor oriented 180 degrees from the way I thought it was. Good times.

One area where I thought I was going to have a lot of trouble was with software. Amazingly, this was one place where things worked well right away. Using the QSI driver for CCDSoft, I was able to open up two instances of the software: one to control the QSI and one to control the SBIG. The two instances independently controlled the cameras without issue. To avoid too much traffic on the USB cable, I stagger the images by a minute or so for good measure.

So now that it’s summer nebula season, where are all of my images? Shouldn’t I be producing twice the images in this beautiful weather we’ve had? Well dear reader, I should have mentioned at the beginning that this story does not have a happy ending (at least not for now). As soon as I got all of the kinks worked out of the system, I was able to take a couple of nights worth of exposures on the Veil Nebula. This is a perfect first target for these scopes. The second morning, I woke to the sound of a few raindrops. I jumped out of bed and ran out to the scopes. Thank goodness, it had just started drizzling, so I was able to get everything inside quickly. I toweled off the outside of the cameras and scopes, and I got some lens tissues to wipe off the objectives. Some of the water wouldn’t wipe off the lenses, though. Looking closer, the water had wicked up between the doublet lens elements. I’ve never had this happen before, but apparently there is a space where water can enter between the lenses on the Star 71. I put several silica packs in both ends of the telescopes, I tried the warmth of a light bulb, but it still took over a week for them to dry out. And you know what was left behind: a film. Between the lens elements. I was heartbroken.

The film

I spoke with William Yang at William Optics, and he’s been kind enough to have the scopes disassembled, cleaned, and reassembled for me. I really appreciate that kind of service from a vendor. This has to be done in Taiwan however, so right now I’m waiting for my scopes to return.

Wouldn’t you know it, no sooner do I ship my scopes off to WO than the skies clear for five straight nights. Right now, I can’t bring myself to process the Veil Nebula data yet. I’m trying to ignore the beautiful, clear nights and focus instead on working on the second edition of The Deep-sky Imaging Primer instead. Hopefully, my scopes will be back soon, and I can continue the adventures.

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