An Imaging Platform is Born

In the spring of 2017 an anonymous donor (hereafter called 'AD') came forward with an offer to fund what was needed to make the Minnesota Astronomical Society's dark sky site at Cherry Grove a high-end imaging site. Basically the AD was volunteering to fund the purchasing of a new imaging platform. The money would come with a few strings:

• The platform would make use of an existing underutilized mount in the observatory. This mount was a Mathis MI-500, a huge mount capable of carrying 180 pounds of imaging gear. The mount is already outfitted with an Astro-Physics GTOCP4 control box and handset.
• The platform must be easy for beginning imagers to use.
• Purchased telescopes must to be able to fit under the roof. The purchase of large refractors like those installed at the club's other two sites was discouraged along with truss-tube scopes.
• A person or people need to be found who will maintain the platform
• Adequate training must be provided for those wishing to use the platform

Existing Facility

Cherry Grove Observatory (CGO) is a large roll-off roof building located in Goodhue county, Minnesota, about 23 miles northwest of Rochester and 20 miles south of Cannon Falls. While it's not a truly dark site (light green zone), it's far darker than the other club observatories. Horizon glow from the metro area of Minneapolis/St. Paul 60 miles to the north can be seen, as is a growing glow of light in the southeast from Rochester.

Cherry Grove. Warming house at left, observatory on right

The Process

The task of choosing gear for the Imaging Platform was passed to the small committee that oversees CGO. None of the committee members are imagers, and they thought it best to form a task force of imagers to make recommendations for what to purchase. That's when I entered the story.

Recruiting task force members went reasonably well for something like this. Some people agreed to help, others said they weren't really qualified or had other obligations. Five volunteers were quickly selected and I was designated the chairperson, probably because I had advanced some ideas for what might be done in an earlier request for help from the CGO committee.

The early going was hindered by a lack of any idea for what the AD was willing to spend. We quickly settled on a two-tier recommendation for what might be possible at around $10K and $20K.

Guiding Thoughts

Beginners will be using it, many with DSLRs but a few with CCDs or newer cooled CMOS cameras. Astrographs for which no flatteners are needed are simple and convenient. Beginners wouldn't have to be concerned about having the correct spacing rings.

What will people want to image? Probably the objects that image well from dark sites: Diffuse and dark nebulae, but not solar system objects. That suggests a telescope with short focal length and fast optics.


Many objects are small. After diffuse nebulae likely targets will be planetary nebulae, globular clusters, and external galaxies. The way to image them is with a longer focal length scope. Since these tend to have higher surface brightness than many diffuse nebulae optical speed is less of an issue.

Beginners will bring a wide variety of learning skills. Some will be happy to learn how to use software to control the mount and camera while others may be reluctant to use more than the mount's hand control. We should try to accommodate as many people as is reasonable.

Given all of these factors we decided to go with a platform that would provide two imaging astrographs in tandem-one short focal length, the other much longer for those tiny planetaries and galaxies.

As we looked over the available scopes it became clear we the low cost option of about $10K was unrealistic. In fact given the cost of all the accessories, shipping and taxes the higher tier of $20K would be inadequate, too! After a talk with the AD it was decided to go with a budget of between $30K and $35K.

At that point we were ready with our recommendation: A Takahashi FSQ-130ED as the short, fast scope and a Planewave 12.5" CDK. Along with the Tak we decided to get the 0.6X focal reducer and 1.6X tele-extender to provide three focal lengths: 390mm, 650mm, and 1040mm.

Current Status

The club's Board signed off on the purchase and we placed our order with Oceanside Telescopes.

The Tak has arrived and is on the mount for testing. So far it's living up to the Tak reputation: Exceptional optics and build quality. It's a great scope!

Takahashi FSQ-130ED on the Mathis mount (to be remounted when the Planewave arrives)

The Planewave is scheduled to arrive in July.

We hope to have the platform fully functional by autumn -- if this year's run of cloudy nights will ever relent!  I'll post images taken using the platform as they are created.

Modernizing my imaging setup

Yes, I'm finally going to move into the 21st Century by adding software mount control and plate solving! Along the way I'm consolidating all my cabling with both a 12V power hub and powered USB 3 hub.

I've resisted this move until now because it sounds really complicated and my imaging laptop wasn't up to running Astrotortilla. But the long winter gave me plenty of time and I've got a new laptop, too. And I have the motivation of doing something similar for the new imaging setup at the Minnesota Astronomical Society's Cherry Grove Observatory. (More about that in a coming post.)

What's New

• Power: My old wet lead-acid batteries have been replaced by smaller sealed AGM batteries, giving me a total of about 108Ah in the field (assuming an 80% discharge). This should be enough for four summer nights of imaging. The batteries can be connected in parallel.
• Software: BackyardEOS and PHD2 are now joined with StellariumScope, Stellarium, and Astrotortilla. ASCOM for everything, which permits me to do away with the cable from the guide camera to the mount! TeamViewer for remote monitoring and control.
• Cabling: A RIGRunner power hub and separate powered USB3 hub have been added. This means I only need to run one power cable to the mount, and one USB cable. All the cables now join securely using Anderson Powerpole connectors. A small DROK DC step down converter now acts as the power supply for my DSLR. This attaches to the power hub. 
• "Remote Control" via TeamViewer requires a wireless router for those times when the internet is available. I can control everything from my Android tablet.

ASCOM isn't nearly as difficult to implement as I had thought. Install the correct platform and drivers and you're good.

On the other hand, Astrotortilla has been a minor nightmare. The main problem has been the field of view that has to be specified. It really has to bracket* the FOV of your images. I have it solving now nice and fast, and working in conjunction with BYEOS and my mount.

*After running a lot of test cases I'm not so sure this is true. It seems like solving success mainly requires that the long axis of your image is slightly larger than the actual FOV. The short axis can be almost anything greater than zero and smaller than the long axis.

Almost 100%

Last night was just before full moon, which made it perfect for taking the "new" imaging system out and giving it a trial run. What makes it new? Here's a quick recap:

• New batteries connected in parallel
• A new DIY power hub and powered USB3 hub riding piggyback on the telescope along with the finder and autoguider
• A new laptop
• StellariumScope and Stellarium running the mount
• The latest version of PHD2
• Astrotortilla (AT) integrated with BYEOS
• ASCOM control of the mount and autoguider
• TeamViewer on the laptop to allow remote access to the desktop
• A Wireless router to allow connectivity for the remote access

Amazingly almost everything worked! Although AT was able to control the imaging camera correctly, no images were being passed to it by BYEOS (which did have its server mode on). I suspect some sort of interference between AT and Stellarium, so next time I will change my workflow.

I was able to take a first check of the router's range by carrying my tablet about 120m distant. I could still control the imaging laptop using it, and even snapped off a few pictures. I couldn't really walk any farther without adding obstructions to the signal, but given the imaging site was in a depression and not line-of-sight, I think 120m was a good start. It's almost got to be better at the Nebraska star party, where it will be broadcasting from atop a rise.

Remote Control of Imaging Laptop

It's still snowing here-15 inches last Saturday and Sunday, 2 to 4 more inches tomorrow. Naturally my thoughts have turned to Summer warmth. And where is the best summer warmth found? The Nebraska star party, of course!

Along with that warmth comes mosquitoes. They start coming out at dusk and can be pests the entire night. Your only options are hope for a good breeze, DEET up, or seek shelter. Breezes are not reliable, and DEET doesn't deter Nebraska mosquitoes from buzzing around your head. So option 3 is the most reliable, but how do you monitor your laptop while you're sitting in a vehicle or tent?

With TeamViewer you say! And you're correct, it's the remote access software of choice for many people in astrophotography. It's easy to use, powerful, and free for personal use. But it does come with one catch. As typically used it requires internet access. What do you do if you don't have that?

Conveniently, TeamViewer does permit a no-internet mode of operation. After you install it on your imaging laptop start the application and go to the menu's Extras / Options  dialog. Under "Network settings" change the Incoming LAN Connections to "accept exclusively," click OK and you're done!

(TeamViewer will now assume you're connecting to a LAN and will use the laptop's assigned IP address as "Your ID" on its main screen. Any other devices on the same router will now be able to connect with your laptop, even if the router isn't on the internet.)

Without the internet you need to set up some form of communication. I tried several methods to control my imaging laptop with my phone or tablet.

• Use the laptop as an access point, then have the controlling device connect to it. I couldn't get TeamViewer to work with this configuration.
• Use my tablet as an access point. Unfortunately my particular tablet couldn't do this.
• Use my phone as an access point. This worked, but turning on the capability required phone service to verify that it was allowed.  Since I don't have service at the Nebraska Star Party, this won't do for now. At other sites with service (like the Iowa Star Party) it may be the best option.
• Use a wireless router. This works perfectly. You don't need an expensive router for this, but there are a couple of considerations: the wi-fi bands used must be compatible with your devices; It should be reasonably waterproof on top to deal with dew, and you might want to look at the voltage requirement. I settled on the ASUS  RT-N12 ($20 from Amazon) that accepts 12V DC and can be powered directly from my batteries. The ASUS is found to consume a scant 2.3W which means it draws a tiny 0.2A.

The theoretical range of the ASUS is 500m, which would provide this coverage around my usual campsite (atop a very low rise) at NSP [CORRECTION: the red circle denotes a distance of 250m around the campsite, not 500m]:

ASUS Theoretical Range at NSP

Will it really be this good? I hope to do a little survey once I have it set up. if it allows me to see my laptop from Dob Row I'll be really pleased. If not, I'm quite confident it will easily reach my tent (maybe 3 to 5m away) and allow me to sit in mosquito-free comfort while imaging!

New Batteries; Nice Try, Fleet Farm, but You Can Do Better

My 50Ah batteries have arrived, both purchased from Battery Superstore though Amazon. Delivery was promised by April 4-9, but they got here March 31-The day after placing the order! Both were double-boxed, arrived in perfect shape, and were fully charged. Amazing!

They're smaller than I had imagined, and should fit easily into the Group 24 boxes that will arrive tomorrow.

Today and Tomorrow are snow days-another 4 to 10 inches of the stuff are due to arrive, followed by another week of well below normal temperatures. It's a good time to get the battery boxes wired up with their Anderson Powerpole connectors. But first I'm going to get my new imaging laptop loaded up with  the software I need to image- BackyardEOS, ImagesPlus, and Astrotortilla. Yes, I'm actually going to join the 21st Century and start using plate solving as part of acquisition!

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I did a few more battery capacity tests, staring with a Duracell Powerpack 600 28Ah portable power supply I'd been given years ago.  The nice thing about this is it has some bells and whistles built into it-radio, light, and inverter. The previous owner said it has been allowed to go dead at least once, so I wasn't terribly hopeful; in fact I was ready to send it off for recycling. It tested out well enough, though: 253 minutes, 15.7Ah. That's about 56% of the stated capacity, which is quite a bit better than either of my old wet lead-acid batteries were able to provide.

I also tested my old 7Ah power supply. I replaced the battery in it several years ago, and it has been used only a few times since then to run a small camping fan when it gets really hot.

After a full charge (or so I thought) it kept the inverter going only 40 minutes during which it produced 2.58Ah. Not very good! I recharged it and let it sit on the charger overnight, then tried it again. The second performance was much better, 71 minutes and 4.42Ah. That's about 63% of the 7Ah capacity. In its capacity as a fan battery it needs to provide only a fraction of an amp, so it will probably do better.

The way the 7Ah battery rebounded after a first draining makes me wonder if I should retest the Duracell. Maybe I'll do that tomorrow.

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I've had a personal boycott going with Mills Fleet Farm since the Sandy Hook shooting in December of 2012. MFF sells assault-style rifles and large clips, and also handguns. I won't shop in a any store that sells weapons like that, so my money is now going to stores like Menards, Home Depot, and Ace Hardware.

MFF recently decided to stop advertising their weapon offerings, but it isn't changing what it sells. Changing advertising is a good, but essentially meaningless public relations gesture. It's time they do better: get rid of guns designed to kill people, Fleet Farm.

A Tale of Three Batteries

I recently complete my piggyback power and USB distributor that should allow me to image using only two cables running to the mount. (I'll have more about that after it's been field tested.) I'm standardizing power connections using Anderson Powerpole connectors, and the plan is to use all my batteries connected in parallel. This means adding Powerpole connectors to all of the battery boxes, which got me thinking about the batteries themselves.

The old batteries are 6 and 7 years old, and there was little doubt they were starting to show their age. Both are the wet lead-acid type, which is a little messy and a tad bit risky to haul around. They're also heavy, each being rather large (Form 27) and weighing about 55 pounds.  I could justify replacing them with nice new AGM sealed batteries if they proved to be in poor shape, which raised the question of how to test a battery's capacity.

Both batteries have reserve capacity (RC) values of 175 and were advertised as being deep-cycle. I can't attest to their deep-cycle ability, but they served me through several Iowa Star Parties and four Nebraska Star parties.

RC is the number of minutes a battery at 80°F can provide 25A before it is fully discharged (it's open circuit voltage falls to 10.5V). RC is not the same as amp hours, and certainly not the same as usable amp hours.

To see why, let's pretend we can convert RC to Ah directly:

Amp hour capacity = amps provided • elapsed hours =  25A • (RC  / 60) =  0.417 • RC

An RC of 175 gives a capacity of 72.9 Ah. Seem easy, doesn't it? The catch is that you almost never want to drain a battery that far-it will gradually decrease the battery's capacity. If you only discharge it about 80% you probably won't notice any loss of capacity until you're well past 200 discharges. 200 discharges is a lot of nights out imaging! So that 72.9Ah is really more like 58Ah. Sorry!

(Much of the literature about deep cycle batteries is written for solar power users who discharge their batteries nightly. In their case a maximum discharge of only 50% or less is needed if the batteries are to be economical.)

But wait, it gets more complicated! Astrophotography seldom requires anything like 25A. (For example, my setup for imaging with a DSLR requires only about 3 to 4A; it jumps to about 6A when using my CCD) Batteries are more efficient at providing power when the current is lower, meaning that the "real" Ah capacity in that case is higher. My batteries also have a stated alternate RC value of 200 based on 23A draw, which gives a full drain capacity of 23A • (200 / 60) =  76.7Ah. Two amps less and you get 3.8 more Ah. Great!

We're not done yet, though. What you're powering also will come into play. As the battery is drained its voltage falls, and as that happens voltage converters and inverters may have to work harder to provide regulated power. Some devices (Kendrick dew controllers, for example) may shut off. So draining a battery by 80% may not work for you.

Possibly the "best" way to determine how a battery will perform is to test it yourself. I recently found a nice way of doing this that employs a simple AC electric clock, AC lamp, and an inverter with a low voltage alarm. An inline DC power meter can be useful, too, but it's not necessary.

I used a 40W bulb to better match my typical current demand. (The calculation is easiest if we use amps = power / volts, so in this case 40W / 12V = 3.33A.) The inverter and clock draw power, too, so  My inline meter suggested that inverter, bulb and clock used about 43 watts and would draw about 3.6A initially. My inverter is programmed to sound an alarm when the loaded voltage drops to 11V; in reality it appeared to cut off at 11.2V

As a reality check I tested my relatively new and well cared for 35Ah AGM battery. I was unable to find an RC value for it that I could trust, so I took values from its spec sheet and (with the help of a spreadsheet) interpolated a capacity of 31.65Ah at a drain of 3.6A.

The battery powered the inverter for 399 minutes, and the meter reported 28.5Ah were provided, but a closer look at current and voltage measurements suggests this should be adjusted by a factor of about 0.93--so 28.5 becomes 26.5. given the uncertainties, I'll use that as the output of the battery. 26.5 is 83% of the estimated 31.65Ah capacity.

Even though all of these numbers are fairly approximate, I think it's safe to conclude that the relatively healthy 35Ah battery was able to provide something like 80% of its capacity before the voltage fell low enough to shut down the inverter. Given that, the test can be repeated with the other batteries; if they are  in perfect shape they could be expected to each deliver about 80% of their 73Ah, which is 58Ah. This is very likely an underestimate because we drain at a much lower amperage than 25A.

Battery One, which is seven years old and was once allowed to go dead, provided power for only 213 minutes. That means it provided only about 3.6A • 213 minutes • (1 hour / 60 minutes) = 13Ah. Awful!

Battery Two, which is six years old and was better maintained, provided power for much longer and ended up delivering 26.5Ah, which is still less than half of what a new battery its size could be expected to provide. It should be replaced, too.

The options are 50Ah batteries, $100 ($2/Ah), 30 pounds, or 75Ah, $140, ($1.90/Ah). I think I'll go with the 50Ah ones! Time to place an order!