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New FSQ106, maintenance


Have obtained a new-to-me FSQ106EDIII. After some false starts I have the adapters from OPT and Texas Nautical. Built another bracket to attach the EZFocus motor.

While testing the focuser for slippage the wall wart died. Very hot, no voltage. Replaced it with a cable to the old 12V power supply, seems to be working now.

Odd issue – while running the VCurves and ACP Focus Offset script, I notice that the focus position seems to be consistently changing. If I run multiple focus runs in a row, as quickly as possible, the resulting position seems to shift by about 35-40 focuser tics. This shift is probably roughly the size of the crtical focus zone.

So, when Focus Offsets runs, it seems like the focus position of each filter is off by n*35 tics. When HAlpha comes up with an offset of 189 tics, it may actually be off by 140 tics!

I don’t know what is causing this shift. The scope certainly doesn’t shift temperature that fast. I thought maybe the focuser was slipping, but measuring the position of the camera with a dial caliper shows to slippage. I ran the focuser back and forth 5 times (1000 pulses each way) and it ended up back at the correct position each time.

I did find that the backlash was off; I changed from 200 to 500 pulses. I will re-run the Focus Offset script again.


Updated ACP to 8.1, including updating the web system.Cleaned up the web menu system a bit, added a couple of items (AstroCalc).

Updated FM to

Bias Frame Stability

In the course of chasing down a weird problem, a couple of issues came up in discussions with other people.

Does the Bias Master frame change at different temperatures?

I.e., do I need separate Bias Masters at each temperature, or does one master work at all temperatures? Maxim is clearly set up to use different temperatures.

I generated Bias Masters at several temperatures from 0C down to -13.5C. This was as low as I could go, since Arizona is still too warm for the camera to get any cooler. Forty subs were taken directly in Maxim and converted to the Bias Master in Maxim using the SD Mask combine of 40 subs. The subs were taken after the new temperature set point appeared to be stable (roughly 20-30 seconds after the set point was reached). I ran a couple of them twice to see how much variation might be seen from run to run. Also, I have a couple of older masters (1-2 years old) at -15C and -20C.

For each master I measured the median intensity at the center of the image using Maxim’s Information tool with the biggest aperture available (20 pixels).


It seems clear that the recently built masters are the same out to -13.5C. The colder ones are likely too old, which is why they are different. I would not expect some dramatic shift from -13.5C to -15C.

Is it necessary to wait some period of time for the CCD cooling to stabilize?

In discussions with Joe Mize (he has had a number of interesting points!), he pointed out that he waits a couple of hours for the CCD to stabilize before taking Bias frames (he calls this “cold soaking”).

As a typical impatient person, I generally set the cooling target, set up the AutoSave sequence to take the desired Bias and Dark frames, then start the imaging. The Bias subs are taken first, for no particular reason. As the temperature approaches the set point the temperature typically oscillates a bit around the set point as the system control settles. This usually happens for 15-30 seconds. Once the cooling target appears to be stable I start the AutoSave acquisition.

Now Joe indicates I need to wait a couple of hours:(

So, I did a couple of runs. Run 1: I set the cooling point to -10C, waited as usual for the temperature to settle, and took a set of 40 Bias subs. These were combined into a master in Maxim’s Set Calibration tool using SD Mask median combination. I then used the Graph Information tool to draw a horizontal line in the exact center of the image.

After 30 minutes I took another set of 40 subs and created another master. I repeated this process at 1 hour and 1.5 hours. The following animated gif flips among the resultant graphs. The red text at the upper right indicates the elapsed time before creating the master.


It appears that the initial master is in fact somewhat lower than the subsequent graphs by 32 counts (about 1.5%). After 30 minutes the graphs seem to be relatively consistent. So, it looks like I do in fact need to wait perhaps 30 minutes.

Run 2: I turned the system off for about three hours, then repeated the test. This time I created a master every 5 minutes in order to get a better estimate of when it has stabilized.


I should have changed the label at the top; 1 is the first master, 2 is after 5 minutes, 3 is after 10 minutes, etc. It looks like by 10-15 minutes the masters have equilibrated.There is less of a shift (15 counts, or 0.75%); perhaps the system didn’t completely warm up from the previous test.

So, it looks like I should let the system cool for 15-30 minutes before starting the Bias frames.

I might expect the same effect when taking darks. However I expect the issue to be less noticeable since the subs are typically 15 minutes or so; the first sub might be off but subsequent subs should be equilibrated. There might be an effect if doing short subs like 1 minute.

Another Measure

I was reading an interesting article Signal to Noise: Part 3 – Measuring your Camera by Craig Stark. I thought it would be fun to go through the exercise of measuring the various characteristics of my STF8300M.

One of the checks is this very topic – how long does it take your camera to cool to a stable temperature? His approach is to turn on the cooler, then start taking 1 minute dark frames. He expects to see a pattern in the beginning followed by a steady state dark median after some time.

In my case, the camera reached the target within 1 minute! Only the first dark showed any significant difference while the camera cooled.


Dueling Air Conditioners

I installed a small 8000 BTU window air conditioner in the dome several years ago to keep the dome cool during the summer. I am concerned about the dome getting so hot in our 115 degree heat that the electronics will be damaged (computer, power controller, mount, …).

As described in an earlier entry, I built an Arduino based temperature probe and wrote a little program ACCycle to turn the air conditioner on and off.


This has been working OK, but the AC is clearly unable to keep up. As the image above shows, no air conditioning would generate the red line. The orange line shows the typical response to the single unit coming on; it lowers the temperature in the dome by 5-10 degrees, but otherwise follows the ambient.

So, I bought a second 8000 BTU unit. This one is a portable unit with the big hose that exhausts out the window. The blue data shows the result of both units turning on – the temperature immediately lowers back to the target 85 degrees.

Not So Simple

First, it is clear that the two units together work very well. Now, instead of seeing the dome temperature follow the outside temperature (but a few degrees cooler) I can see the AC units kicking in and bringing the temperature back down to 87. I have it set to start cooling at 90, stop at 87. In the image below the dome temperature (blue line) rises steadily in the morning. About 8:30 it hits the upper limit of 90, at which point the two units kick on. They quickly cool back below 87, at which time they shut off. The units cycle until about noon; at that point the heat is enough that the units stay on steadily until about 5:00 PM, when it starts cycling again.


But –  I am encountering power problems, which I have never had to think about before.

Surge Protector Limit

To start, my Power Controller is plugged into a big surge protector, which in turn is plugged into the wall. When the two AC units are turned on, the power exceeds the surge protector limit. The surge protector shuts off, including power to the computer and everything. I have to reboot the system and start everything again. Doesn’t happen every time, so I am apparently close to the limit of the surge protector.

Power Controller Problem

So, my next step is to plug the power controller directly into the wall, bypassing the surge protector. In addition, the controller has an “A” and “B” side, each allowing 15 amps. I had been running both AC units from one power cord on the “B” side. Now I plug one AC into the “A” side and the other into the “B” side.

Well, it is better, but every so often ACCycle turns the AC on but they don’t actually turn on! I think the surge through the Power Controller is problematic somehow. I have trouble reproducing the problem, but is seems to happen a couple of times a day. Unfortunately, it can end up in a state where the AC is off, but ACCycle thinks it is on. Thus, the dome keeps heating up.

Shadow AC

Next approach – get around having both units turning on simultaneously.

One approach would be to put the two units on separate ports in the Power Controller and have ACCycle control both units. However, I don’t have any extra ports in the Power Controller. I could buy another controller:(

Instead, I put one unit on a manual timer on the wall socket. This timer will turn on the AC at 9:30 in the morning and turn off at 7:30 at night, after sundown. At this time of year there aren’t any days where cooling isn’t needed, so this is reasonable.

Now ACCycle only controls the second unit. It only kicks in when the first unit cannot handle the load. Both units don’t necessarily run, and they don’t kick on at the same time. In the image below the first unit started at 9:00 AM. It was a cooler day (only reached 101) so the second unit wasn’t needed until late in the day about 4:30 PM. It kicked in briefly when the temperature got above 90 and quickly brought it under 85, at which point it wasn’t needed any more.


Iris Nebula NGC 7023

Click to enlarge

Click to enlarge

Common Name: Iris Nebula
Formal Name: NGC 7023
Date: 6/23/2015
Constellation: Cepheus
Location: Casa Grande
Hardware: Takahashi Sky90 on Paramount, SBig ST2000XM Camera/Filter Wheel

unguided exposures

Temperature: -0C
Bin Mode: 1×1
Images: (x) x 15 minute Red exposures
(x) x 15 minute Green
(x) x 15 minute Blue
Total Time = x hours
Sky Flat fields 
Processing: This version uses only RGB exposures (Synthetic Lum by integrating RGB).
Reduced in Maxim, Aligned/Stacked/Processed in PixInsight
Notes: The Iris Nebula, also NGC 7023 and Caldwell 4, is a bright reflection nebula and Caldwell object in the constellation Cepheus. NGC 7023 is actually the cluster within the nebula, LBN 487, and the nebula is lit by a magnitude +7 star, SAO 19158. It shines at magnitude +6.8. It is located near the Mira-type variable star T Cephei, and near the bright magnitude +3.23 variable star Beta Cephei (Alphirk). It lies 1,300 light-years away and is six light-years across.. (Wikipedia)

Arduino Shutter Control is Implemented

I have gotten my replacement for the Foster Systems shutter control operational. Go to this page for more information.

Basically, I have had too many problems dealing with Foster’s shutter control. The Rotation system works well enough, but I have constantly had problems with the shutter system. In particular, the software always had problems (the hardware seems to be robust).

Cooling the Observatory

I am starting to get more concerned about the temperature in the Dome during the day. It gets crazy HOT here in AZ.

Step 1 – installed a tarp over the western wall where the sun is hottest. The tarp attaches to the top of the wall (a few inches above the top edge, leaving room for the dome lower shutter to go over), then slants out a couple of feet to the ground. Attached the bottom to the ground with stakes, with big bricks on top to keep the wind from pulling up the stakes. The tarp appears to drop the wall temperature 5-6 degrees, and blocks the UV.

Step 2 – I decided to insulate and drywall the observatory. I should have done this in the very beginning, of course, but didn’t realize just how hot it was going to be. I had expected the window air conditioner to be able to handle the heat:(

Removed all the equipment except the telescopes. Put giant plastic garbage bags ove the telescopes and the mount. Pulled the pegboard off the walls, installed insulation both above and below the floor. Did this part at night so it was somewhat cooler – only 90 degrees:) Then put drywall on the walls, both above and below floor.

I installed a Vernier sensor device (LabPro) and the associated software on the observatory computer so I could monitor the temperature. I am measuring the temperature on top of the electronics cabinet, about a foot below the mount. There is clearly a strong temperature gradient from the floor to the dome. The window air conditioner is situated just above the floor, so the cooling mostly wants to sit on the floor and sink below it. I have a small fan below the air conditioner to help blow the cool air up into the room. This helps a bit.

Here is a temperature graph from before the insulation project:


You can see the overnight temperature of 73 rises quickly at sunrise. A little after 10AM the air conditioner was turned on, with the temperature about 92. The temperature drops to 87, about 5 degrees. It the continues to climb, although at a slower rate. The temperature peaked at 4 PM; the AC was turned off about 10:30 PM. Notice the squiggles aroun 9-10 PM; this is when the AC “cycles”, where it just blows for awhile, then actually cools awhile, then goes back to just running the fan. You might think this is oscillating around the AC setpoint, which is 72. However, the temperature does not seem to be close to that setpoint. I see this pattern show up every so often.

Her is today’s data, with the insulation installed.


At 10 AM the AC cut in and dropped the temperature a couple of degrees, after which the temperature continues to climb. The cycling of the AC is very evident.

At 1:30 PM, I went out and moved the computer cabinet and repositioned the small fan. I had cleverly positioned the cabinet so it “blocked” part of the AC vent, forcing cool air to flow through the cabinet (the cabinet has screen doors for air flow). I moved the cabinet so the AC vent was unobstructed. I also repositioned the small fan so it was blowing more upward from below the AC; it had gotten knocked to the side a bit.

These changes caused a) an immediate drop in temperature of about 7 degrees, and b) cessation of the cycling of the AC. I wonder if the cycling is removed by the small fan more efficiently moving the cool air away from whatever sensor the AC uses to measure the temperature.

Clearly the insulation project has not resulted in a room that can be controlled at a steady temperature by the AC. The dome is a major heat source which the AC cannot overcome.

Wall Temperatures

I took my little Infrared temperature measuring gun and checked the various wall temperatures, inside and out.


This was done about 1:30PM, so the East wall has started cooling from its high and the West wall has started heating in direct sun.

The interior wall gradient is pronounced, with temperatures going from 93 near the upper floor up to 112 on the interior dome surface.

The tarp is doing some good, lowering the temperature several degrees (and blocking UV). The metal door is absorbing a lot of heat.

The Celestron scope measured 101, while the Paramount measured 93.

More Drift Issue

The previous refractor model was disappointing. I decided to run a separate model for the Edge 11 while I tried to figure out what to do next.

Well, the model came out terrible. Around 300 points, and the RMS was around 43 after supermodel. 20 as bins, elongated in EW direction. So, I went out and tried to find something loose, and what do you know – the front strap on the Homeyer cradle is not attached! The strap is not in the back slot on the cradle. Scary – I don’t know if there is a real risk of the Edge actually falling out of the cradle, but that is certainly scary looking.

Fixed the cradle, also made sure screws were all tight on the 8300. Ran a new model, and it came out great. 7.6 as RMS, 5 as bins, nicely centered points, etc. Now I need to re-run the refractor model, since the loose strap should also mess up the refractor. I have hopes that I may finally get a good model on the refractor;)

Notes – I seem to be having problems when AAG_TPointMapper selects points near 355+ degrees in the North, and 180 deg in the South. The SkyX scriptor throws an error, something about bad syncing near the meridian? Prob need to select Az values asymmetric so 180 isn’t selected?

Of course, I have ordered the Celestron OAG for the refractor. I intend to run this with the Starfish, since I don’t expect I will ever get the 10 min unguided exposures I am hoping for. This will change the balance of the scope, so I will need to re-run the models. I also ordered a Star Analyser 200 for the Edge. So, I will install the SA200 in the 8300 filter wheel, get the OAG installed, and then start again. Of course, when I tried to install the OAG today I discovered they did not include the correct adaptors. There is supposed to be a male 48 and male 42; instead, there are 2 male 48s. OPT will have Celestron send the M42.





Narrowband exposures during full moon?

Common “knowledge” says that one can do narrowband exposures (HAlpha, Oiii) during full moons. I don’t know why that should be OK, since the Moon is scattering HAlpha light from the Sun as well as the usual RGB.

So, I did some exposures during full Moon, and some during no Moon. Here are the results. These are single raw images, with a Screen Transfer function applied in Pixinsight so we can see the image.

Click on an image to see the full image.

HAlpha with Full Moon

HAlpha with Full Moon

HAlpha with No Moon

HAlpha with No Moon

The Full Moon image in HAlpha has a lot of extra blur/nebulosity, while the image without the moon shows significantly better detail and contrast.

OIII with Full Moon

OIII with Full Moon

Not much shows up in the OIII images; apparently the California Nebula doesn’t emit much in the OIII range. The full moon version has a serious gradient, could be a function of where it was in the sky. The No Moon version has better contrast around the two stars.

Conclusion: it looks to me like the Full Moon still has a significant impact on the narrow band images.

OIII with no Moon

OIII with no Moon

STi is well

Well, the STi went to SBig, where they found it is just fine. Something else is wrong. I will have to try some different cables? Ports?

I implemented the 3 port expansion plug for the autoguider cables. Found a 6 conductor phone jack extender which has one male plug that goes into the mount autoguider port, and has 3 female jacks. Each of the cameras (ST2000XM, STF8300M, and STi) can be plugged into the jacks at the same time. Now, when I want to switch guider cameras I do not have to go out and reconnect the guider cables.