First narrowband image

I tried to capture the veil nebula from our backyard, but the noise level was just very bad. So, I tried to take the same images with my Ha, SII and OIII narrowband filters. There are various formulas out there how to combine these, e.g:

R: 0.8*Ha + 0.2*SII
G: OIII
B: 0.85*OIII + 0.15*Ha

another formula that I found:

R: 0.4*Ha + 0.6*SII
G: 0.4*OIII + 0.3*Ha + 0.3*SII
B: OIII

Guess, I'll have to play with these.

I wonder if I should create the 3 color channels in CCDStack with the respective weights and combine them there. Or if I should just stack the individual images and then combine them in Photoshop. I'll try CCDStack first. An email to the CCDStack support mailing list pointed me to File Math or Combine with Pixel Math or Weights.

First, I calibrated all frames. Because I took them over several nights, I used a different strategy:

1. Calibrate all images per night and store the calibrated frames
2. Rotate (if necessary), align, correct and stack all subframes
3. Align all 3 resulting frames and store the aligned frames
4. Now, I can load Individual aligned frames into CCDStack to combine them. E.g. for the first hubble palette, I load the aligned Ha frame and the aligned SII frame. 
5. With pixel math, I multiply the Ha frame by 0.8 and the SII frame by 0.2
6. Combine-Sum the resulting frames for my red image
7. Repeat for the other colors
8. Finally combine the 3 frames to a color image.

Here are the resulting images:

I also tried to just use the individual images for individual colors: OIII=Red, Ha=Green, SII=Blue:

I like the last one the best, it shows lots of fine details in the nebula.

I processed the other image in the same way:

So far so good...

Now, I have to do some more processing:

• there is still a lot of background noise
• need to calibrate both images to make them blend better together
• and then I need to stitch them together

Another imaging automation program: Sequence Generator

By chance I read about Sequence Generator Pro. It's another imaging automation program - for WAY less then the programs that I looked into before. One of the most interesting features for me is that it integrates with PHD guiding. I was always struggling with TSX guiding. The other interesting "feature" is its price: $99!

I downloaded SGPro, installed it, read the helpfile and watched some of the tutorials. It has a very different concept then CCDAP:

• It's based on profiles which describe the system setup (scope, camera, guiding, plate solver, filter wheel...) This is actually very good for as I will image with at least 2 configurations (hyperstar and focal reducer).
• It doesn't integrate with TheSkyX which means that object selection isn't through a planetary software, but the "Frame and Mosaic Wizard" is actually really good.

It's definitively somewhat rough around the edges - many things have to be manually configured or installed. It took me a week to configure and setup everything:

• The frame wizard relies on an external service (which was down for a day). But the good news is that it caches all downloaded data and images, so I can use those later again.
• Automatic focussing: it's a very straightforward process. It took me a while to find the right step size though. I ended up running the focus routine with a step size of 2 and checked how many points were in the critical focus zone (the plateau of the curve).
  I then had to play with each filter to figure out which exposure time to use. I increased the exposure time step-by-step until the focus curve was smooth.
  I had to set "stop guiding during focus routine" - because I'm using an OAG, autoguiding is naturally severely affected if I change the focus too much. The last remaining issue is, that SGPro instructs PHD to select a guide star before the focus routine, then it stops guiding, runs the focus routine and restarts guiding with the previously selected guide star. But now, the guide star isn't in the same location anymore and PHD has to do some crazy guiding to get it back into center. I asked on the mailing list. Jared (one of the developers - they are both crazy active on the mainsequencesoftware mailing list) didn't have an idea how to accommodate for this, but will think about it.
• I used this as an opportunity to start using PHD2 - which works very well. To avoid guiding on hot pixels, I have to use darks. A great advantage of PHD2 over the previous version is that it can re-use darks for subframes and doesn't try to take a new one. I had to set the threshold after which SGPro starts taking images to 0.5 - that's already pretty low for my backyard conditions.
• SGPro uses plate solving for every slew - which is great. Makes it very reliable. Initially, I tried to use Elbrus, but it didn't always work. I then switched to astrometry.net which works great. But now I am relying on an external service - which is bad when I take the scope out. Fortunately, there is a local astrometry.net setup that I can use.
• It was strange that I had to set the "auto meridian flip" bit - I had expected that it is set by default.
• SGPro reads the configured ASCOM devices and offers these directly. That avoids the popup when connecting where you have to choose the ASCOM device. Nice!
• Naming of the images is great!
• I tried mosaics, meridian flips during imaging, multiple targets - all works very well.
• The built-in Image Grader is great for a quick analysis of acquired images.

The only missing thing (for me) are dusk/dawn flats. It was very convenient with CCDAP to just setup the scope, rough align it and then start the CCDAP flat routine. It would wait until it's dark/bright enough and run through all the filters, dither and adjust exposure times. I wish SGPro would implement this as well.

CalStar 2013

After I had such a great experience at GSSP, I want to attend CalStar 2013 (Oct 3 - 6).

I want to image with the f6.3 setup, but also with the hyperstar lens (f2). I will have 9.5 hours of imaging time (20:10 - 5:40. For images with the focal reducer I'll need 6.5 hours (10x10min Lum + 10x7.5min RGB), for the hyperstar lens, I'll need 1.5h (10x3min Lum + 10x2min RGB). So, in two nights I can capture 3 images with the focal reducer and in the other 2 nights, I can capture 9 images with the hyperstar lens (each night 2 different filters - taking flats for one filter in the evening and the other filter in the morning). I will definitively need to get my automation nailed for this - otherwise, I'll stand at my scope the entire night...

Some Objects:

f6.3:

• M74/NGC628 (imaging time: 21:00 - 6:10)
• NGC7331 (need to do at beginning of night!) (imaging time: 20:10 - 4:10)
• NGC6946 (Fireworks Galaxy) (need to do at beginning of night) (imaging time 20:10 - 4:10)
• NGC1579 (Trifid of the North) (imaging time 22:57 - 5:40)
• IC5146 (Cocoon Nebula) (imaging time 20:10 - 3:41)

f2: (rotate to 114 degrees)

• Gamma Cygni Nebula - one image - (too low at end of the night) (transit: 20:29)
• IC1340 (Veil Nebula) - mosaic of 6 too low at the end of the night? (transit: 20:50)
• M31 (Andromeda) - mosaic of 4 images (or three if I rotate the camera) - take multiple exposures and HDR (transit: 0:47)
• IC11 (Pacman Nebula) - one image - (transit: 1:01) 
• IC63/IC59 - one image - (transit 1:07)
• M33 (Triangulum Galaxy) - one image (1:42)
• IC 1795 - mosaic of 4 (transit; 2:34)
• M45 Pleiades - one image - (need to start late as they are low in the evening) (transit: 3:53)
• NGC 1499 - mosaic of 6 (3 with rotated camera)- (transit: 4:11)

This would mean 25 images - need to get it down to 9 images: M31(3), IC11(1), IC63/IC59(1), M33(1), NGC 1499 (3)

---

I did not find the time to work thoroughly with the Hyperstar lens (focusing, guiding, exposure times, flats...) So, I'll just take some images with the f6.3 setup. Maybe some other time.

Weird optical artifact - caused by OAG

Yesterday, when I took flats, I noticed a weird artifact:

I've spent the last couple of weeks mostly with the new mount and didn't take any flats, so I don't know what change this caused. My first thought was that maybe the filter wheel isn't lined up correctly. But I checked it, and nothing was wrong. So, I checked all elements of my optical train starting from the back:

1. Vent
I recently installed the cooling enhancer from Starlight Xpress to make sure that I can cool the CCD camera down to -10 Celsius - even when it's very warm outside. I turned it off and took another flat:

Clearly that wasn't it.

2. CCD Camera

Next, I rotated the CCD camera by 90 degrees to check if it's the cause of this:

If it were the CCD camera, the artifact would have stayed in the same corner. So, next:

3. Filter wheel + OAG

I turned the CCD camera back and turnd the filter wheel + OAG:

Aha! It's the filter wheel or the OAG!

4. OAG

Just because it's easier, I pull out the OAG:

Gone! So, it is the OAG. Maybe I can push it back in:

half in:

Good! 3/4 in:

Yei! And once more, all the way in:

OK, I know how to fix this. But where did this suddenly come from???

Non-parfocal filters and OAG

I wanted to start using the Astronomik OIII and SII filter. And then I realized that I can't use them with my off-axis guider. Stupid me - never thought or realized that!

... guess, I should try to sell the Astronomik filters and get Baader filters instead.

No more reflections

I tried out the brand new Celestron focal reducer. And behold: no more reflections!!! Of course, I can't be sure anymore if I don't have any tilt anymore. But because the Celestron t-adapter get screwed in, it's way less likely.

Now, I have to try to sell the Lepus reducer ...

Mach1 GTO from Astro-Physics - Guiding

I spend some time on the PHD parameters to improve guiding. With the default values of PHD, I can get my combined RMS error easily below 1 arcsec. Doesn't sound like much, but with the CGEM that was already a struggle. Good.

After some more optimization, I ended up with graphs like this one:

RMS error: 0.56 arcsec (peak 1.39)

RA RMS error: 0.12 arcsec (peak 0.3) 

DEC RMS error: 0.16 arcsec (peak 1.06)

And very often I got graphs like this one:

Something is clearly wrong with DEC guiding...

I asked on the ap-gto mailing list and received a number of good suggestions:

• Calibration isn't correct which leads to an overcorrection in DEC
• Lower aggressiveness, so that PHD does not overcorrect
• Make sure that the guide stars are not distorted
• Make sure that the OAG is pushed in as the stars in the outer areas might be too dim
• One user has the exact same setup that I have - except that he does not use a focal reducer. He sent me his settings:
  RA Aggressiveness: 60
  RA Hysteresis: 10
  Max Dec Duration: 75
  Min Motion: 0.70
  Calibration Steps: 125msec
  Auto/Resist Switching
  Extreme dithering and Settled at < 0.5
  3 - 4 sec guiding exposure.
  I could remove my focal reducer and try these out.

Last night I tried these out:

• Lowered my calibration step size - now PHD needs 20+ steps for a calibration run
• Played with aggressiveness
• Checked if the OAG is still parfocal, pushed the OAG all in

But with the same results. I then updated PHD to the latest version and even installed PHD2 (alpha) to check if this is some PHD bug. But same result.

I then tried out some things:

First, I took an 5 min image of the Eagle Nebula unguided. Here is a magnified version:

The stars are elongated mostly in RA direction.

The same image with PHD guiding - DEC set to auto:

Now the stars are mostly elongated in DEC direction - RA seems to be fixed.

Now with PHD guiding - DEC guiding off:

Very round stars.

The with DEC only North:

Also, very round stars.

So, RA guiding really seems to be good, but the DEC=auto guiding is a problem. Now, in PHD2, there are more possibilities for DEC guiding (identity, resist switch, lowpass, lowpass2, hysteresis). I played with those, but couldn't improve DEC guiding. And then I read in the release notes, that in the current version of PHD2, calibration only works with DEC=auto. So, I had to run all these experiments again. But it got very late again and I went to bed...

I wanted to make sure that my scope is not out of balance. The Mach1 is quite sticky, so balancing isn't easy. So, I removed my OTA from the scope and balanced it on a pencil. I noted that point on the OTA and made sure that this point is in the middle of the dovetail saddle.

Next, I removed the focal reducer, so that I could try out the parameters (above) that I received. Here is the result:

Another idea that came from the ap-gto mailing list was that the DEC gears might be meshed too tightly. This pointed me to checking my cables that are now routed through the mount - maybe they are getting stuck somewhere. I just moved them out of the mount and tried again:

Hmmm, still no luck. Well, the good news is that I can move the cables back inside, but I should take a closer look on the DEC gear...

I followed the instructions on how to remesh the gears. Tried again ... same result :-(

Now, I'm sending an email to tech support at astro physics...