Fine Focus

For any astro-imager, focus is always a primary concern. When doing deep sky it has to be spot on to get those tack sharp stars that we love to see. Fortunately for DSO imagers, there are aids such as a Bathinov mask that can help ensure you are on the mark.

Bahtinov Mask

 In planetary imaging it is a little more challenging. We also need to be in perfect focus to capture the subtle details, but a Bathinov mask isn't going to work on a non-point light source. Trying to move the scope to a bright star to focus first before centering the planet also seems to fall short. What one is left with is manually fiddling with the focus knob while watching a feature of the planet to get it as sharp as possible. For example, a Jovian moon or the Cassini division are often good targets to pay attention to in this effort.

Unfortunately the planetary imager is confronted with another problem: the high magnification utilized to get the planet's disk to a suitable size. This means that the slightest touch causes the planet to wildly dance in (and sometime exit from) the field. The result is an iterative set of focus-recenter-evaluate attempts until you feel it is as good as you can get (or your patience is gone and you settle for "close enough"). When rebuilding the OTA for my 10" Cyrus¹ Newtonian I even invested in a nice JMI focuser with a feather touch micro-focuser, but it still didn't solve the fallout of a human hand touching the scope.

I finally came to accept that investing in a motorized focuser was going to be necessary to solve the problem. Based on the positive experience Dale Ghent had with MoonLite focusers for HALO, I opted to order from them. It takes a bit of time to go through all the various options but I eventually balanced my desire for bells & whistles with my budget to get a Crayford 2" focuser with their universal adapter and stepper motor for about $700. To my surprise and delight they had the unit to me within about a week.

Next came replacing the existing JMI with this snazzy unit. If you look at their universal adapter, it is "a plate with multiple many different 4 bolt hole patterns for Newts over the years, Meade, GSO, Orion, Celestron, etc." 

 

However, none of them aligned with the existing holes I had placed into the tube when installing the JMI focuser. So it became a tedious process of securing the plate with a couple of openings that did align and then trying to accurately measure where the new hole had to be drilled to accommodate where the opening was on the plate. After a couple of hours the plate was finally secured and motorized focuser attached. 

 

Installed MoonLite Focuser

As you can see from the picture above, this is a substantial unit. It occurred to me that this would probably alter the scope's balance once I added in the Barlow, camera, and possibly an Atmospheric Dispersion Corrector (ADC). In the past the scope had always been a little "rear heavy" when imaging, requiring placement of a magnetic weight along a shelf bracket that runs along the front half of the tube. I opted to install a similar bracket along the back half of the scope, and indeed it was needed to achieve balance when I did a dry run.

A couple weeks later with Jupiter and Saturn getting a reasonable (if not great) altitude in the pre-dawn skies, I gave the MoonLite unit a test run. I did not purchase a separate hand controller to operate the focuser but instead attached it to the laptop using the provided USB cable. The unit also has to be powered - so yet another cord dangling from the focuser that I tried to tuck alongside the scope to avoid any tension or vibration it might cause.

The interface is pretty intuitive, allowing you to move in or out by orders of magnitude. Once Saturn was centered it was easy to display the planet in the video capture software and have the MoonLite Single Focuser app on top so that I could watch the planet as I commanded the focuser to adjust its position. During the process there was minimal movement of the planet and no risk of knocking it out of the field. I ended up getting what I felt was as good a focus as I could achieve and was happy with the result after I processed the video captures the next day (below). 

While the swapping out of the original JMI for the MoonLite ended up being a little challenging in the installation stage, I'm very happy (and blessed) that I could do it because the results are what I was looking for - a far less painful and far more accurate focusing experience. Like so many other hobbies, amateur astronomy (especially when coupled with photography) is an investment. It seems to be a continuous process of identifying what might improve our ability to see or photograph the heavens and then budgeting to make that next upgrade.
 

¹ I call it the "Cyrus" telescope because the optics were made by Charles Cyrus, a friend and excellent ATM from back in my days with the Baltimore Astronomical Society. After Charlie's passing his instrument made its way to me and I have enjoyed it for a couple of decades now, most recently redoing the OTA that houses the mirror.

Second First Light

Compared to half a century ago we pretty much live in an astronomical COTS time. The vast majority of amateurs peer through equipment that is massed produced. Attending a BAS star party back in the 70s and 80s, one would find a fair number of the telescopes were fashioned by their owner. They ground the mirrors and constructed the mounts, displaying a range of frugality and craftsmanship in their implementation. Many clearly had taken "shop" as part of their secondary education and were comfortable turning out custom parts for their scopes. 

One of those individuals was Charlie Cyrus who built a 10" Dobsonian. I will always remember the first time I peered through the instrument at M13 - I was blown away at how well it resolved the stars compared to my 6" telescope. When looking at the planets it always provided crisp views that spoke of the hours he had poured into sculpting the glass to his standards. Charlie was the epitome of an ATM.

When Charlie passed his good friend and fellow BAS member Dr. Richard Pembroke became the steward of his telescope. Richard was a passionate, respected amateur astronomer and well connected to the community of observers. As he contemplated downsizing in retirement he asked if I was interested in having Charlie's telescope. I immediately said yes even as I pondered how I could explain to my wife that I had another telescope in the garage. 

For about 15 years I used the Cyrus scope as often as I could. Its additional aperture allowed me to track down multiple additional Herschel 400 objects and pick out more details among Jupiter's clouds and Mars' surface. It accompanied me to many Stellafane visits and Tuckahoe star parties, creating memories along the way. But time and use took its toll, and eventually the wooden Dobsonian mount became too feeble to properly support the optical tube assembly (OTA). I could almost hear Charlie saying, "OK Jim, it's your turn now to use some ATM skills to restore it!" 

And so I set off on what would turn out to be a multi-year endeavor to give Charlie's scope continued life observing the heavens. I elected to replace the Parks tube that housed the mirrors since the focuser (which Charlie had made) was no longer usable with too much slop. Lacking machine shop skills, and no friends with that talent, I calculated that a sturdy "Sonotube" would be best since it was a material I could work with. I ordered a long, sturdy tube - thicker than a Sonotube to ensure support - and cut it to size. This was like pulling the thread that unzips the seam, because now the machined mirror cell had to be adapted to the new tube, or a new one made. It seemed that I would clear one hurdle and then have yet another technical challenge to address. But finally the new OTA emerged under my hands. 

One of my primary objectives was to have the scope on a mount where tracking was feasible. My grand scheme was a Dobsonian tube cradle that could have a mounting plate affixed to it, permitting the OTA to move from Dobsonian rocker box to my Orion GEM, offering the best of both worlds. I made several attempts at it before finally facing the fact that it was not going to work - the Cyrus OTA was just too heavy. 

Growing tired of having the OTA but no mount, I elected to contract the task of creating a Dob mount. I coordinated with a shop out in California about a year ago and ordered one of their products, hoping that I could add a Losmandy mounting plate to the tube cradle to permit me to attach it to my sturdier CGX-L GEM that I had acquired. I had hoped to have it by the Mars opposition last October, but that deadline came and went. Maybe by the Grand Conjunction in December, but that, too, came and went. Finally I received it in April and assembled the new Dob for the Cyrus scope.

The mount seemed adequate and I believed it would work out as I placed the OTA into its cradle. One issue I noticed quickly was that even though I had added additional felt liner, the tube would still slip down under its own weight. But that felt like a problem that could be fixed. With the Moon almost full it served as a convenient target to verify if the optical train was properly configured. I found that the mirror needed to be set back down the tube in order to achieve focus, but again, a task that was very doable. 

Almost there! Or so I thought. The next free weekend I set about repositioning the mirror and adding additional felt when I noticed that the laminate on one of the wooden altitude bearings was separating. Indeed, the entire thing was coming loose and breaking. I couldn't believe it and contacted the vendor. Long story short, there would be no resolution from this person, and given the delays in receiving it I was not about to ship it back and have another year pass waiting and hoping for this individual to make it right. One benefit of my heart attack has been making it clear to me that every day counts.

Laminate Separation

I decided to take off the Friday before the July 4th holiday and dedicate that 4 day weekend to making a tube cradle with an attached Losmandy plate that could support the OTA on the sturdier mount I had purchased - no more excuses! In some regards it reminded me of software development in terms of the life cycle - design, create, test, remediate defects you uncover during testing and try again. Finally, in the pre-dawn hours of July 5th, I got a true "first light" for my Cyrus scope restoration by imaging Jupiter for an hour. The detail it provided, along with the exciting prospect of having this wonderful instrument back, made it all worth while!

 

And now the refinement process has to happen, steps to take to make the telescope easier to use (because a telescope that requires a lot of effort to set up for a session does not see as much starlight). Inspired by some photos of HAL member Victor Sanchez's setup, I used last weekend to craft a "dolly" so that the entire rig can be rolled in and out of the garage. Next up will be adding a dovetail to attach a finder scope and hopefully a paint job to make it look a little more polished. The biggest lesson in this journey has been a better appreciation and respect for the talent, effort, and ingenuity that an ATM puts forth into their telescope - truly a labor of love from which I have benefited greatly. Thank you Charlie for leaving behind such a gift - I'm proud to be its steward and hope I'll pass it to another generation of stargazers one day!