Friday, January 31, 2014

Back to the SX H694

So, after much trying and experimenting, I finally sent my ML 11002 camera back to FLI - they want to take a look and hopefully adjust it to avoid those vertical stripes.

For me, that means going back to the SX H694 camera. Had to:

  • Set the operating temperature to -10 (had it set to -20 for the FLI camera)
  • Redo the Flat calibration for the flip-flat
  • Set readout noise and gain
  • Set pixel size and chip dimensions
The good thing is that I can use the Super Reducer without any problems - the distortion was only in the out regions of the much larger 11002 chip. The smaller H694 chips doesn't show any curvature or such.

Trying to image some smaller nebula and also M82 with its supernova.

Tuesday, January 28, 2014

Rosette Nebula in Narrowband

I used the same workflow that I used yesterday for the Tadpole Nebula to add OIII and SII data to my Ha Rosette image:
The Rosette Nebula is an emission nebula with a diameter of 130 light years. The gravitational forces on the inside are so strong that they pull gas from the nebula into the center where they form stars. These stars excite the atoms of the nebula itself which makes them emit light. The distance from earth to the nebula is 5,200 light years.

This is a 19hour exposure composed of 20xHa, 19xOIII and 19xSII (each 20 minutes).


I played more with the coloring. First I used the workflow from Bob Franke to enhance the colors:

Then I used Richard Crisp's Synthetic Coloring:

I think I prefer the first one.

Monday, January 27, 2014

Tadpole Nebula in Narrowband

With the help of Bob Franke's CCD-BandAid tool, I could correct my images from the Tadpole Nebula. I then used the tutorial from Ken Crawford on how to combine narrowband images in Photoshop:

The Tadpole Nebula (IC 410) is an emission nebula around an open star cluster (NGC 1893). The "tadpoles" are clumps of gas and dust from the formation of the cluster. Inside them, new stars are born. The tails from the "tadpoles" are caused by the solar wind of the stars of NGC 1893 (that's why the point away from the star cluster).
It's clearly missing some SII data. But nevertheless, I'm pretty happy with it. I'm so in love with my new scope!!!

Don't need to rotate meridian flipped subs in CCDStack

I always made sure that I rotate all images from the "other side of the meridian flip" in CCDStack by 180 degrees. Today, I forgot that ... and CCDStack aligned them perfectly well. It just rotated them by itself. Doooohhh! That will save me some time!

Wednesday, January 22, 2014

Trying out the TOA-645 Super Reducer

While I am trying to figure out if and what's wrong with my image acquisition, I wanted to try the Super Reducer for the TOA-130 scope.

One of the main advantages of this reducer over others is that it has the exact same backfocus of the .67 field flattener. I.e. I don't need different adapters. I exchanged the field flattener with the reducer. The only other thing I had to do was to rotate the OAG as it was pointing sidewards now.

When taking the first images I noticed (of course) that the scope was completely out of focus. I had to move the focuser in a lot (from 7500 to 1000). But then the autofocusing routing of SGPro worked flawlessly.

Next I connected PHD and tried to use it with the same calibration parameters. It resulted in the same accuracy of <0.4 pixels - which means 0.4" accuracy!

Finally, I had to enter the different pixel scale in SGPro to get plate solving to work.

My first try was a 20 min exposure of the Rosetta Nebula:

and compare it with subframes that I took for my first light picture:

First you notice the larger field-of-view. Let's compare details:
Dust lane without reducer:

Dust lane with reducer:

The difference in SNR is so evident - great!

Now, let's look into the corner if the image is flat:

Hmmmm, that doesn't look flat at all! But wasn't the reducer supposed to have the same backfocus? Asked on the UncensoredTAKGroup...

Sunday, January 19, 2014

Vertical stripes on images

I have seen a couple of times vertical stripes on short exposure images with the FLI camera. But last night when I took images of the Tadpole Nebula, I could see them on 20 min exposures (with an SII filter):

And what's worse, they didn't go away in the stacked image, but got even more accentuated:

And that even though I dithered the images. Sent a question to the fli_imaging_systems Yahoo! group.

I also processed the images with DeepSkyStacker and Pixinsight (finally had a real reason to try it out). With the same result. I then acquired the images with other programs (TheSkyX and FLIGrab) - they looked exactly the same.

So, it's not the acquisition and neither the stacking process.

Richard Crisp is suspecting that the stripes are FPN (Fixed Pattern Noise). Which should be eliminated by correct flats. But somehow they aren't. He recommended that I a) take more flat frames (20), and b) go up to 2/3 of full well. My camera testing report stated that saturation is 52266.1e- (with my gain of 0.81 that's almost exactly 64000ADU), so he recommends that I take my flats at 43000ADU.

This will be a problem with the Ha and SII flats. They already take 150 and 350 seconds to get up to 22000ADU. That would double the exposure time :-( Not only does it then take WAY long to get these (20 * 700 seconds = almost 4 hours!) but I also need to start taking darks for the flats. The only way to do this are dusk flats. Will try that out tomorrow morning.


I took 20 sky flats with CCDAutopilot. Exposure time ranged from 6.4 to 11.4 seconds. But the result was exactly the same. Richard Crips checked all my subs (lights, flats, darks, bias) for me - but he couldn't find anything either.

Next suspicion is the connection to my laptop. Right now, I run the USB cable from the camera to the USB switch on the mount. From there I run it to another USB switch and then through an (active) 15 feet USB cable to my laptop. I put my laptop next to the scope and connected the scope directly to the laptop.
... same result :-(


So, at this point, I know that I get these vertical stripes on my lights, but not in my flats. So, the issue is most likely with image acquisition. When I investigated last night, I found another issue: when acquiring bias frames they don't show any signal at all! Not sure it's related, but it's another indication that there is something wrong with acquiring or transferring the image.
  1. either capturing the photons in the camera
    Could be that the camera itself has an issue. I took some bias frames right after I received the camera which showed signal. So, at some point this worked. This indicates that this issue was recently introduced.
  2. transferring the images from the camera to the computer
    I tried various USB cables and connecting the camera directly to the computer. So, it could be that my laptop's USB port isn't working well.

I did more experiments and am convinced that this is an issue with the chip/camera itself. I took several flats last night with increasing exposure time (starting from 0.1 sec). And the vertical stripes are visible in the lower exposures, but they disappear in higher exposures when the signal gets stronger.

0.1 seconds:

2 seconds

40 seconds:

The lines are easily visible in the 0.1 sec exposure, less in the 2 sec and almost disappear in the 40 second exposure. Just to check that this is not an issues with stretching the image, I subtracted 44.000 from the 40 second exposure (it had a mean ADU of 45000, the 0.1 second exposure had a mean ADU of 1,800). But even then the stripes are not there:

Also, all these flats were acquired with the luminance filter, i.e. it's not related to the wavelength, but apparently purely to the signal strength.


After some more research, I found more references on the web about this issue with the 11002 chip, e.g.
CCDBand-Aid repairs vertical bars in Kodak KAI-11000M images or Files Not Being Calibrated Correctly. Bob Franke even developed CCD Band-Aid - a program to eliminate these vertical bands. I tried it but initially got an error message ("1x1 Phase is not an integer.") I selected a different image and now CCD-BandAid detected a phase of 23 (it handily saves this in its .ini file, so you have to run the analysis only once). I then tried to correct one of my subexposures:

Original Image:

Corrected Image:

I wanted to find out if and what CCD-BandAid corrected and created a diff of both files:

So, this only difference between the files are these vertical stripes. So, CCD-BandAid seems to have identified the phase correctly, but apparently didn't apply the correct amplitude?

I also contacted FLI to ask them for advice. They told me to send the camera in, but also cautioned me that it might not be possible to eliminate these vertical stripes 100% hardware-wise.


I was finally able to use CCD-BandAdi correctly and created narrowband images of the Tadpole Nebula and the Rosette Nebula. But I finally sent the camera back to FLI to correct the chip.

Wednesday, January 15, 2014

Polar alignment, guiding accuracy, flatness with the new scope

With the Celestron EDGE scope, I was fighting a lot with guiding and flatness of the image (which was related to collimation). With the TOA-130 scope, I expected that flatness wasn't an issue anymore - though the large image area was concerning. But with the much larger and heavier scope, guiding could become a problem. And finally, with the much larger imaging field, I expected that I'd have to pay much more attention to my polar alignment, so that I won't introduce field rotation.

But none of these worries seem be justified:

  1. Guiding
    My guiding error is constantly <0.5 pixels (on the Lodestar) - mostly < 0.4. That's less then 1".
  2. Flatness of the image
    Here is the CCDInspector analysis for some of my images:

    3% tilt is pretty good. But it's weird that the image is tilted to one side. Here is another curvature plot from images that were taken on the other side of the mount:

    It seems as if my imaging train is somewhat susceptible to tilting. But again only a little bit. The image itself doesn't show any curvature in the edges!
  3. And finally polar alignment (and also flatness) of the image. Here are magnifications from the 4 corners of my image of the Rosette Nebula:

    What can I say? Round, pointy stars all around. No elongation into the corners (flatness) and no elongation around the center (field rotation)
Very, very good. I can now setup my scope. Do a quick polar alignment with the RAPAS - and off I go!

Monday, January 13, 2014

First Light: Rosette Nebula in Ha

Because of the full'ish moon and our light pollution, I did my first light image in Ha. A great object was the Rosette Nebula. And I'm very happy for this first try:
(click on image for full-size image)
14 x 20min Ha

This image is just a little DDP stretched, but not more processed. I'm sure that there are some more details that I could get out. But for a first image, I'm very pleased!