APT + Stellarium Imaging Workflow

I came across an excellent video last week by Matt's Astrophotograpy. Matt's setup and choices for software are much like mine but his experience is vastly greater so I took a lot of notes.

I'm going to post those notes here and alter them as I do more imaging.

Software

Please consult each software's documentation to determine how it is to be configured.

Imaging Control: Astro Photography Tool

Once upon a time I used ImagesPlus camera control, then moved to BYEOS when I switched to a DSLR. My first impression of APT was that it was a mare's nest of capabilities and was too tangled to tame. I tried to like SGP, but the way it functioned seemed counter intuitive. I found NINA interesting but had to give it up when I found it didn't support my SBIG CCD or the QSI I was hoping to buy. Maybe by the time I buy that QSI it will be supported. So I sat down and started learning APT!

Be sure to install version 3.84 or later so you get ASTAP support (see next section).

Plate Solving:

I think you really only need to install ASTAP and its G17 star database. ASTAP seems superior for both near and blind solving compared to the old standards, PS2 and ASPS. And please don't tell me about AstroTortilla. Not to diminish the role it had in bringing plate solving to the masses, I always found it to be slow and unreliable.

Guiding: PHD2

Obviously.

Planetarium: Stellarium

This is a personal preference thing. I like Stellarium; it's pretty and it does what I need. This workflow will make use of Stellarium.

You may want to install version 20.1 instead of 20.2, as the latter requires you to manually connect to the mount.

Stellarium tip: The config.ini file lets you configure Stellarium's defaults. Here are two examples...

Turn off full screen mode, look in the [video] block, and set fullscreen = false

Turn off daytime sky brightness, look in the [landscape] block and set flag_atmosphere = false.

Slewing/Parking/PEC:

Slewing in RA is needed for Polemaster, which will want you to slew your mount several times. This can be done conveniently from within an ASCOM control panel or by using a hand control.

If you would rather slew entirely from within APT, do this:

Start with the mount at counterweight down (CWD) orientation and the RA axis pointed at Polaris. Connect APT to the mount. Copy the values of current RA & Dec to the GoTo fields. To do the requested rotation, usually just subtract one hour from the RA and click the GoTo button. (If the stars turn in the opposite sense of the PoleMaster display arrow, add instead of subtract.) Repeat for the second rotation.

To return to the start orientation, undo the RA changes in one step. DO NOT use the APT park button!

Setup & Initializing

Assemble

Start by assembling the components of your imaging system. This includes making all the data and power cable connections.

If your system is portable, this means rough-aligning your mount to north and balancing it for imaging.

When ready, power it all up: Laptop, Gemini II, imaging camera, dew heaters.

Make the data connection to your laptop. (In my case the data connection must be made after power-up because it could damage the SBIG camera if made too soon.)

Start APT and optional Camera Cooling

Steps marked with an asterisk are required even if not using the cooling aid.

*Launch APT
*APT/Camera / Connect
APT/Camera /Cooling Aid. Check settings and start.
*APT: Tools / ATP Settings / Main. Set image destination folder (optional)

Polar Align

(I use a PoleMaster for polar aligning. I agree with Matt 100%: PoleMaster is the way to do polar alignment.)

 

APT/Gear: Connect Scope (This launches an instance of the GeminiTelescope ASCOM driver.)

Attach PoleMaster to mount, connect USB
Launch PoleMaster software, and connect

Perform slews using one of these methods

ASCOM controller

1. Find the Gemini ASCOM driver icon in the Windows tray area. Right click and choose Show Hand Controller
2. Confirm Speed is "S" and that PEC is checked.
3. Use the hand control RA buttons to perform slews
4. When finished use the tray icon menu to close the hand controller. DO NOT minimize it!

APT

Use the add/subtract RA method described earlier

Disconnect and Remove PoleMaster

Sync

Launch Stellarium

Stellarium: If using version 20.2, manually connect the mount (use the telescope control plugin)

Stellarium: left click a suitable sync star, then use CTRL-1 to go to it

APT/Gear: Open Pointcraft

APT/Camera. Verify that exposure time is appropriate (I use 10s with my ccd and L filter)

APT: Shoot
APT/Pointcraft: "<< Scope Pos" to populate approx. position fields
APT/Pointcraft: Solve
APT/Pointcraft: (assuming solve is successful) Sync
Stellarium: Should now show true position of scope. Use CTRL-1 to center star in FOV
APT: Shoot new image to confirm star is now reasonably centered. If it is not, use Pointcraft Aim as described later and then Sync again

Focus

Please refer to APT documentation to learn how to best use the focus aids. I use a Bahtinov mask whenever possible.

APT/Gear/Filter Wheel/Go To Filter: Select filter to focus
APT/Camera/Bulb Seconds: Set appropriate exposure time

Attach Bahtinov mask
Shoot single images or use Live View. If Live View is used, possibly disable Live View Automation (APT:Tools/APT Settings/Main/Live View Automation) to prevent binning
APT/Tools/Bahtinov Aid: Make sure focal length, aperture, and pixel size are correct; turn on Cross mode

Drag Aid window so that focus star is at crosshairs

Recalc as needed if not in Live View mode
Adjust focus until satisfied with focus
Close Bahtinov aid
Remove Bahtinov mask!

Acquire

Obtain and Compose Target

Obtain a Target Object

    Find target in Stellarium, CTRL-1 to it
    APT Pointcraft:  <<Scope Pos
    APT Shoot image
    APT Pointcraft Solve
    APT Pointcraft Aim, click on image to refine center if desired
    APT Pointcraft GoTo++
    When completed you are good to go.

   
Go To Specified Coordinates

    APT Gear Enter coordinates into Center FOV boxes
    APT Pointcraft GoTo++
    When completed you are good to go.

Resume an Old Session

    Find target in Stellarium, CTRL-1 to it
    Open image from previous session
    APT Pointcraft Solve
    APT Pointcraft << Solved
    APT Pointcraft GoTo++
    When completed you are good to go.

Autoguiding

Launch PHD2
Toolbar Connect Icon or simply CTRL-C, connect guide camera and mount
Main Menu/Tools/auto-select star or simply ALT-S
Click SHIFT-toolbar Guide button to calibrate
Let PHD settle

APT/Gear/Guide to connect to PHD2 and configure optional dithering

Acquisition

APT/Camera Select Imaging Plan

APT/Camera Start

Shutdown

APT/Camera/Warming Aid: Warm the camera slowly (optional)

APT/Gear/SHIFT-Guide to disconnect from PHD2

PHD2/Toolbar/Stop button

PHD2/Toolbar/Connections disconnect all

Close PHD2

Find the Gemini ASCOM driver icon in the Windows tray area. Right click and choose Show Hand Controller

ASCOM Hand Control/Park (optional)

APT/Gear/Disconnect Scope

Tray ASCOM icon/Right click, Exit

When warming is complete, APT/Camera/Disconnect

close APT

close Stellarium

Turn off Laptop

Turn off Gemini II

Disconnect USB cables from any devices that may be harmed (Applies to my SBIG ST-8300M)

Disconnect all from power supply

2020 Nebraska Star Party: What Might Have Been

Fans of NSP know it was cancelled for 2020 due to the pandemic. The cancellation may have seemed a bit premature when it was announced on June 12, but to me it was clearly the right thing to do. During the last month the virus has been spreading almost unchecked in some parts of the country. Nebraska itself has seen a mild rebound in the number of positive tests, but not nearly as bad as what is happening elsewhere. Possibly the good people of Nebraska have more sense than those in a few other states and they're not afraid of masks?

The 2019 NSP was a real dud with only one decent night of the five I was there. Mostly it was clouds and rain. There was hope that 2020 would be better. Then came the virus.

What follows is a night by night summary of what the 2020 NSP sky would have been, based on satellite cloud images, North Platte radar, and observations at Valentine. I don't use cloud observations from Valentine because I don't trust their accuracy. (Valentine will sometimes report clear skies when there is high overcast; go to the bottom of this entry to see an example.) I don't doubt some people are staging a private NSP and can provide better estimates, but until they report I'll depend on my estimates.

Please note that all times are approximate. The time of total darkness each night is now five hours six minutes, extending from about 11:17 P.M. to 4:23 A.M. I'll take this as five hours and rate each evening on a five-star basis; one star awarded per hour of possible imaging. A perfect night would look like (⭐⭐⭐⭐⭐). Because I usually arrive on Sunday and depart Friday morning I'm only going to report on five evenings. How many stars will NSP 2020 earn of the possible 25?

Sunday, July 19 (No Stars)

Daytime: High 87° with dew point around 61° most of the day.

Overnight was cloudy from dusk to about 4:15 A.M. with thunderstorms and rain around 11 P.M. and again at about 12:15.

Monday, July 20 (⭐⭐⭐)

Daytime: High 88° with dew point again around 61° most of the day. Thunderstorms with rain from about 8 until 9 P.M.

Overnight: Overcast until about 12:30 A.M., then clearing with occasional clouds until about 4 AM. About three hours of imaging were possible.

Tuesday, July 21 (No Stars)

Daytime: High 84° with dew point around 59° or 60° most of the day.

Overnight: Blowoff from thunderstorms in southeastern Wyoming spread overhead between 9 and 10 PM. Clearing began around 4:30 A.M. No precipitation was indicated by radar.

Wednesday, July 22 (⭐⭐)

Daytime: High 92° with a 69° dew point (heat index a very sticky 97°). At 9 P.M. (20m before sunset), it's 83° with dew point temperature 69°, winds are 14mph, and cloud cover is about 50%.

Overnight: A poor quality night, with broken high clouds most of the hours of darkness. Occasional wind gusts around 21mph, and heavy dew from dew point temperatures between 71° and 69°. "Clearer" periods from 11:30 P.M. to 1 A.M. and 2:00 to 3:00. Probably some light frames could be gathered during these short holes? If not, then it's a zero stars night.

Thursday, July 23 (No Stars)

Daytime: An even more unpleasant day (96° with a 67° dew point at 4 P.M., heat index 100°), but without the relief of the Wednesday air-conditioned high school.

Overnight: Persistent scattered clouds until a little past midnight, then cirrus from a thunderstorm passing to the south. Winds gusting up to 32mph until 3 A.M. Dew point temperatures around 69 all night. I think the clouds and wind would have essentially caused this evening to be useless for imaging. Visual observers would do better, but the scopes would have been bouncy and the transparency poor for much of the evening.

Friday, July 24 (No Stars)

If you would have hung around for Friday, ugh. The day was miserably hot and humid with a high of 99° and dew point of 70° most of the day. And then there were the thunderstorms and clouds to ruin the evening. A complete loss.

Saturday, July 25 (No Stars)

Well, wow. Hot, miserable day, then storms and clouds again. This completes one week of what might have been NSP 2020.

Summary

There were only 5 hours of imaging out of 25 possible:

Sun 😡😡😡😡😡
Mon 😡😡⭐⭐⭐
Tue 😡😡😡😡😡
Wed ⭐😡😡⭐😡
Thu 😡😡😡😡😡
Fri 😡😡😡😡😡
Sat 😡😡😡😡😡

It's even worse if you include the two additional washouts of Friday and Saturday: 5 good hours out of 35 possible, the equivalent of one good night in a week. It was a very good year to stay home; the virus didn't deprive you of much.

I hope to make it to NSP 2021! It has to be better than NSP 2019 and NSP 2020!

----------------------

Here's an example of problems with cloud reporting. This is not unique to Valentine, but is a consequence of how cloud observations are made in this era of automation by devices called ceilometers. A quote from an abstract for a 2016 study of ceilometer errors indicates the problem:

The limited areal coverage of ceilometers results in error when skies are heterogeneous, but these errors are small compared to those caused by the limited vertical range: observations of clear sky or few clouds are often in error as the instrument cannot detect the presence of upper-level clouds. [My emphasis.]

The hourly report for Valentine, NE on July 24 at 5:52 P.M. CDT. indicates CLR (i.e., clear) sky at 5:52 P.M. CDT.

A satellite image of Cherry county and Valentine taken four minutes later at 5:56 P.M. shows the sky is at least half covered with high clouds.

The position of the Valentine weather station is just south of the letters KVTN, at Valentine Municipal Airport.

Unfortunately it is often the case that clouds causing considerable extinction are completely missed by weather reports. This is partly by intent, as high clouds are not of importance to aviators.

The lesson here is: Don't assume the sky is clear because a station report says it is. It may in fact be unsuitable for imaging.

Astro Projects for a Shutdown

It's fairly evident that shelter-in-place is here to stay for quite a while. The state continues to feel that it will not be able to prevent a blowup from happening sometime around mid summer, at which time the hospitals may be seriously beyond their capacity. They are working to increase capacity so that when the crunch comes no one will have to go without any medical care they need. Will they succeed? We probably won't know until June or July.

That means it's likely to be solo astronomy until August. What's a person to do from a bright sky-site?

I have several projects I can work on:

1. Mirrors. I believe I have the supplies on hand for the polishing and figuring of several mirrors (one each of 6", 8", and 10")
2. Meteors. I can always set up my meteor detection system and start collecting data. More problematic is analyzing that data, but I may be able to program a sloppy workaround for having to visually inspect hundreds of images. 
3. Daytime Observing. Night observing is difficult here as the light pollution is awful, and in the last few years trees have grown to take away even more of my sky. Rather than fight that, it might make more sense to move to daytime observing. Targets include the Sun, planets, and brighter stars. An interesting question is daytime visibility in terms of star magnitude and angular separation from the Sun.

Getting Real in the Year of the Coronavirus

Old business first. Last time I looked at the idea that a 100W solar panel would be more than adequate for replacing the energy spent in a previous night of imaging. What needs to be realized about this idea is the uncertainties that come into play with it. Here are a few:

• I rarely image for an entire night as assumed. In fact, I can recall doing so on only two occasions. Usually either fatigue sets in or the sky goes cloudy and you lose a couple of hours.  
• Getting four or five consecutive nights clear all night is not something that happens often. In my experience the rule is maybe half the nights of a star party are clear.
• Some imaging sites are quite dry (like Nebraska) and active dew control isn't needed for the first several hours. This eliminates one of the larger power requirements.
• Starting with a fully charged laptop (which is almost always the case) greatly reduces its power consumption. 

In other words the estimates I made for required energy were probably overestimates. So I feel safe in saying that the panel in consideration will be adequate. It's not going to be able to run an air conditioner or refrigerator, but it will be fine for imaging.

---------------------

Now let's get to the topic of the moment, if not the decade, COVID-19. As I write we know that this virus is relatively contagious, spreading across the country, and tough on older people. Active cases are showing up in Minnesota and Nebraska, and doubtless will appear in South Dakota in the coming days. [Update: The day after posting this South Dakota reported 5 cases with one fatality.] Right now the cases are being contained through quarantine; what the situation will be by mid July and the Nebraska star party it's impossible to know. A safe guess is that the virus will be widespread by then and that most group activities will be suspended; NSP may not even happen. Another consideration is that my wife and I are both in our 60s and stand a significant chance of requiring medical assistance should we become ill with the virus. Because of that my current thinking is trying to avoid the illness at least until the end of the year and the release of a possible vaccine. Even without the creation of an effective vaccine it's hoped that doctors will learn how to better treat the illness.

Avoiding getting sick relies on some simple fundamentals:

1. Avoid people who may be infected. Given the asymptomatic spread of the virus this means avoiding pretty much everyone. Especially to be avoided are being in close quarters with many people, such as might happen on a cruise ship or commercial airplane.
2. Wash one's hands thoroughly and often
3. Avoid touching one's face

This is what we will be doing for the next year and hoping to catch some luck. Barring a minor miracle I won't be at NSP this year or any other star parties. My back yard will be safe enough I hope, so I'll try to do some astronomy from there!

Good luck to you in the coming year, it's going to be a difficult one for all of us!

Another Imagining Year Ends; Solar Panel Recharging of Batteries.

Bye-bye, 2019

Winter has fallen onto the region with a loud thud. Snow depth is now seven inches and the temperatures are near normal (for the next week, anyway). For a warm weather person like myself this essentially means outdoor astronomy is in hibernation until spring.

It remains possible that I may use the imaging platform at Cherry Grove, but I can't say I'm in the mood for that at the moment. So let's see what else there is to do.

I have some mirrors that are in polishing/figuring stage, so I could get back into those.

There's always the task of learning image processing software, but if things continue on like they have the last two years with awful weather there's no rush.

I could do some programming and try to quantify the meteor reflection data I collected a couple of years ago. But instead, let's have...

More Power Fun!

One thing that intrigues me is solar power for recharging batteries at remote sites. A few years ago when I priced this out solar panels were too expensive compared to buying batteries. But with the continuing decline in panel prices it's time to reassess.

The first step is to determine my power needs. This is the product of my imaging setup's power requirement and the number of hours spent imaging in a typical evening. The first is something I've measured; my current setup (mount, laptop already charged, dew heaters set higher than usual at 50%, CCD with cooling at 70%, autoguide camera) setup draws about 3A. That means I can image with about 40W of power.

Next we need to know how many hours this power will be needed in an evening of imaging. Let's consider the cases of an equinox and summer solstice at 45N latitude, and for each imaging through either nautical, astronomical twilight, or full darkness.

Summer solstice: full dark 3:20, astronomical twilight and darker, 5:31; nautical twilight and darker, 7:10; civil twilight and darker, 8:25; sunlight, 15:35.

Equinox: full dark, 8:31; astronomical twilight and darker, 9:42; nautical twilight and darker, 10:57; civil twilight and darker, 11:50; sunlight, 12:11.

Let's say you image during astronomical darkness and start up about a half an hour before that for polar aligning, target acquisition, and letting things settle. Depending on the time during the summer you will be using power for about 6 hours (solstice) or 10 hours (equinox).

Multiply the above hours by 3 amps and you get 18Ah (solstice) or 30Ah (equinox). These are what you need to put back into the battery after an all night imaging session. (In terms of energy in watt hours, these are about 216 and 360 watt hours.


[Digression: My primary battery is 50Ah. Draining that by 18Ah is only 36%; a 30Ah draining is 60%. By August 1 this has changed to a drain of 22Ah or a 44% drain.]

At this point it's tempting to say a 100W solar panel can bring a battery back up to full charge in only a few hours. Can it? There are a few wrinkles to consider that can reduce that 100W:

• Clouds: Cirrus are no problem, but typical fair weather cumulus can drip power by anywhere from 8 to 20% [ref]. Total overcast drops power by 50 to 75%.
• Heat: Higher temperatures are doubly bad. Panels become less efficient as the temperature rises, and AGM batteries are better off being charged at lower voltage. For typical NE afternoon temperatures (37C or 95F) this leads to a panel efficiency drop of about 2.5% and an increase of about 6% in battery charging time.
• Resistance losses can be minimized by using wires that are heavy enough for their lengths. In my possible system this means using 12AGW throughout and keeping the runs reasonably short, and should not be a factor.
• Charge controller efficiency. MPPT controllers generally have an efficiency in the area of 95%.
• Panel orientation isn't a big factor so long as you can keep the panel face reasonably perpendicular to the sun. This means turning it hourly and using some kind of adjustable altitude brace.

In the worst case it's a hot, overcast day (which are rather mutually exclusive) and we multiply 100W times 0.5 for overcast x (0.975x0.94) for a 95F day x 1.0 for resistance loss (none) x 0.95 for controller loss x 0.86 for being 30 degrees off perpendicular all day. In other words, that 100W becomes 37W. 37W times total daylight time minus two hours is about 500 watt hours (solstice) or 370 (equinox).

Conclusion: Even in an unlikely worst-case situation a 100W panel + MPPT controller should be able to do nightly recharges adequate for imaging using my setup.

Back From the 2019 Nebraska Star Party

I was at the 2019 Nebraska Star Party for Sunday through Thursday nights and it could have gone better.

It's been a wet year in Nebraska and that means the usual mosquito herd is larger than normal. The first night, Sunday, there was only a modest breeze that faded around sunset; the herd emerged and immediately zeroed in on me. My bug spray was unable to hold them off and I was forced to retreat to a screened enclosure after obtaining only a polar alignment. No imaging.

Monday night had a partly cloudy hour, but Tuesday through Thursday Nights were all cloudy with episodes of rain. So for me NSP 2019 was a bust. At best I would have gotten one solid night had I been able to endure the biting.

I have a feeling that as the trend of increasing rainfall continues (thank you, global warming) this will be the case more and more often. That means it's time to adapt.

My thought is that if I can work from a screened enclosure I can manage even on those really buggy nights. This means I need an enclosure and a way to control my imaging rig from a distance of maybe 20 feet or so.

At present I control everything using a single USB cable from laptop to imaging rig. According to standards this limits me to about 16 feet between laptop and rig. Subtracting 6 feet for drops to and from the ground and I'm left with about 10 horizontal feet of separation, so I need to extend my USB. This can be done using powered USB repeaters, but that would mean added connections and power lines. the simpler way is to use an Ethernet extender like this:

This passes USB between two boxes via up to 60m of Cat5 or Cat6 Ethernet cable, with only the box on the rig requiring external power. Some serendipity: The required power is 12V DC and uses the same connector I'm already using with my USB hub on the rig. And the on-rig box acts as a powered four-port USB hub. The only drawback is that this is strictly USB 2, so if I add a USB 3 device I'm in trouble. This is available on Amazon for under US$60.

Focusing is not pleasant when you're being bitten, so a motorized focuser is needed. Unfortunately the only motorized focusers for an AT-65EDQ cost close to $1000 when all is said and done. This is a very nice little scope, but I'm not sure I want to spend that kind of money on it. A much less pricey option is a JMI Motofocus, but they have stopped making them for the AT65 and I could find no vendor who has one in stock.

Luckily some years ago I was given an Orion version of the Motofocus. It wasn't designed for the AT-65, but it was close. All I needed to do was add a small piece of aluminum sheet to it and buy a couple of longer bolts.  I made a nice long phone cord so that it can be used over a much greater distance than the coiled handset cord it came with.

The piece of aluminum (silver rectangle in the above image) is epoxied to the Orion-provided mounting bracket to extend it the required distance. The longer screws and small stacks of washers provide the needed offset to keep things square and allow the larger focus knob to rotate freely. Note that there is no clutch on this so while the motor is attached there is no manual focusing. If you need manual, just undo the two outermost screws on the bracket and replace the motor with the AT65's fine focus knob.

The last operation is one I can't really do much about: polar aligning. This will still require standing at the scope and adjusting azimuth and altitude by hand. Nothing is perfect :)


The final adaptation is a freestanding screened area that's large enough for setting up a small table and chair. I went with this one from Coleman:

This is available from multiple vendors for a wide range of prices. The footprint is a spacious 10'x10', so I'll even have room for a little lie-down while imaging. Despite this being floorless, it gets good comments about keeping the bugs out. We shall see. One thing, though--don't imagine that this is adequate as a sun or rain shelter. I purchased mine from Kohls.

So I'm now set for the mosquitoes. Unfortunately there's nothing I can do about clouds and rain, but that's always been the case.

DIY Sky Brightness Meter; Coleman Outdoor Compact Table; Lapdome; First light with Losmandy G11G

I've been tinkering with a microprocessor called an Elegoo Uno processor, and as a part of that I came across something called Phidgets. This is a collection of clever sensors and devices that can be controlled by laptops and mobile devices.

One of the sensors is a light detector. It's capable of measuring light down to 188 microlux, which just happens to match the value you would expect to measure for a nearly perfect dark sky site. That suggests it might be the basis for a night sky brightness measuring device. Fortunately it's built to report visual brightness and not full spectrum which can include a strong IR component.  The Phidget sensor is made up of two sensors; the second is IR and is used to correct the first.

The actual semiconductor sensors sits in a well with beveled sides within a plastic case. Rather than expose this to stray light I placed it in a PVC tube as shown in the picture and diagram below. This shield tube is probably too long, which means I'm blocking out some of the light cone entering the sensor compared to what it was normalized to receive.

Version 1: Long light shield

Version 1: Long Light shield

The length of the version 1 light shield was based on an incorrect calculation. Correcting the error gave a light shield length of 60mm, or about half of the Version 1 length. A few minutes of sawing gets us to Version 2, which is decidedly smaller in appearance:

Version 2 closed

Version 2 open

At this reduced length the shield is not much more than a way to keep the two caps together. In fact, it doesn't act as a shield at all; it's completely outside of the sensor's field of vision.

There are two black objects on top of Version 2. The smaller one is a combination temperature and humidity sensor; the larger is the hub used to communicate with my laptop via USB. The USB connection provides the power needed by the devices.

Thus far only Version 1 has been tested.The conditions were clear sky with a first quarter moon. (The sensor was pointed straight up and did not include the Moon in its field of view.) The reported light value was 2 millilux or about 2000 microlux. Is this a reasonable value?

It now gets a little complicated. First we need to correct for the oversized light shield. This introduces a factor of about 1.67 (a very uncertain value determined from indoor testing) so the measurement is now about 3330 microlux.

The site I was testing at was not Bortle 1, so the natural sky contributed some signal.  Assuming the site was at midpoint of Bortle 4, it was at about 520 microlux.

Next we have to add on the contribution of the first quarter moon, which takes a site from Bortle 1 to Bortle 5. A Bortle 5 sky at m = 19.7 has a value of about 1560 microlux, so the moon adds about 1370 microlux

In other words the sky starts at 520, to which we add 1370 from the moon for a total of about 1900 microlux.

Is 1900 close enough to 3340 to call it worth working on further? Yes, definitely, given the uncertainties in the numbers. If it had blown up or started a fire I'd say that it should be set aside, but this did neither.

I will continue to tinker with it, including rewriting the sample polling program to take time averages and log them. In addition to more local testing I'll also take this to this year's Nebraska Star Party, where the sky is Bortle 1 😃

__________________________

New Stuff:

1) My old field table finally fell apart after 15 years of service and has been replaced with a Coleman Outdoor Compact Table.

It seems sturdy enough and I like the solidity of the aluminum tabletop, but time will tell how well it holds up. So far the only negative I can say about it is the carrying bag; it's several times larger than it needs to be and allows the contents to flop around inside.

2) You know how when you try to make something you get the feeling that it's just not coming together and that you might be wasting your time? That sums up my attempt to make a portable light box for my laptop. I have thrown in the towel and puchased a LapDome. I haven't used this in the field yet, but it looks like it should be a great way to keep laptop light from interfering with visual observers without make the laptop difficult to use.

It seems really well made and should help with dew control, too. I kind of wish that it had side openings for cables in addition to the rear opening; my laptop has only side ports and none at the back.

One improvement I may make is to cut a board to fit the inside bottom to keep the laptop's air intakes happy.

-----------------------------

Lastly, the same night I was tinkering with the light sensor and watching people try to get first light with the Cherry Grove Observatory Planewave 12.5" CDK I also got some time with my new mount. It worked great! The following image is little more than a simple trial: 14x60s luminance frames and 15 dark frames. First, the full frame, reduced in size. Click to see it at 31% of the original scale:

Obviously an AT-65EDQ doesn't give the best pixel scale for an object like M51.

Here is a crop to the target so you can see it a little better. Click the image to see it full scale.

Not bad for total exposure time of 14 minutes! (Camera = SBIG ST-8300M)

Luminance is nice, but I can't wait to try out the other three Astrodon filters.😀