Jupiter May 2018

Jupiter has just gone passed opposition which made it perfect for imaging. Also, from my backyard, it was in prime position between the trees, above my neighbours’ house. With so much deep sky imaging, it is easy to overlook the bodies in our solar system, and Jupiter is an ideal candidate for even beginners to have a go at.

One of the challenges to imaging Jupiter, particularly at the minute, is that it is relatively low on the southern horizon in Britain (just above 30 degrees). Combined with it rising at dusk, this means poor seeing caused by temperature currents affecting the atmosphere. Imaging through these disturbances means that the target will appear to go in and out of focus rapidly. This is further exasperated by the magnification of your scope. One way around this is to use ‘lucky imaging’, a system whereby you shoot high FPS (frames per second) video that you then stack using software to reduce noise, as well as reject all but the best frames.

Due to it’s rotation, I limit my videos to 90 seconds at a time so I am typically gathering 3,000 – 5,000 frames per video. With several such videos taken in rapid succession, I typically process around 20,000 frames to stack into my overall image.

Before moving onto Jupiter, I focus using a bahtinov mask on a nearby star (Arcturus works well for me). Once I am focused, then I know that Jupiter will also be well focused, even if it is slipping in and out of apparent focus due to the seeing. Yes, people will argue that stars are hugely further away than Jupiter and so technically they are not in the same focus plane however the actual differences on my scope would be measured in nanometres and so is irrelevant.

I image using Sharpcap as it enables me to gather .ser videos rapidly as well as name them how I wish. This step is important as I want the filenames to contain the universal timestamp of when they were captured as I need this information for later on in WinJupos.

I tend to drive the camera gain quite high to allow the FPS to be as high as possible. This will create noise so it is a balancing act, and also this noise can be mitigated to some degree in stacking as well as post processing.

I ended up with 6 x 90s videos which I then loaded into PIPP for alignment. PIPP allows me to crop the video down to the size needed as well as do some basic pre-processing such as weight each frame by quality. I then loaded the saved videos into Autostakkert!3 for stacking. I know this might look like duplication as I also use Registrax later in the process, however I prefer using Autostakkert!3 as it is 64bit and can use all my machine’s cores.

In Autostakkert!3, I stacked each file, rejecting 90% of the lowest quality frames. The remaining 10% were then automatically stacked and saved as a TIFF file. From here, I loaded it into Registrax for processing. I first of all aligned the RGB as my planetary camera has a RGGB matrix so the videos tend to be green before processing. Once aligned then I moved to wavelet sharpening. This allows details to be drawn out on different wavelet (resolution) layers, along with noise reduction of the same layers, This is a real ‘trial and error’ for me, however this tutorial does a great job at introducing the concept of wavelet sharpening.

Finally, I save the image down and move to Photoshop for saturation and final noise reduction. And the image is complete.

My equipment:

Altair Astro Hypercan 178c
Skywatcher EQ6-r Pro
Skywatcher 130pds using a 2x barlow

Jupiter May 2018

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NGC 7023 Iris Nebula

Finally, some more clear nights with an almost moonless night. After my last successful outing on the Pinwheel Galaxy at the end of April, I was keen to complete at least one more LRGB image before we lose astronomical darkness for the summer. I attempted Iris Nebula last summer but a lack of ability along with inclement weather meant I failed badly on it. It is still early in the season for this nebula as it remains low in the north eastern skies, however this allowed me to complete 3 clear runs without meridian flipping so it was worth the gamble.

I imaged over three nights, gathering 6 hours of luminance and 3 hours total of RGB data. The exposures were all on gain 0, offset 10, captured on my QHY163m using Sequence Generator Pro v3.

Lum: 75 x 300 secs
LRGB: 30 x 120 secs per filter

Again, I used Astro Pixel Processor to stack and calibrate the subs. I really love this program now I have got used to it. Its ability to remove light pollution gradients, in particular, is superb. I really must get around to completing a review and tutorial on how I use it.

The stacked and calibrated subs are then moved across into PixInsight for processing and combining. I wanted to try and bring out the dust lanes around the nebula, as well as keep the star and nebula colour vibrant without over-doing them. I think I have found a balance here – one I am happy with at this stage anyway. I started to use more complex methods of bringing out the dust using wavelets layers however I found I need more practice with these before I am competent in using them so I stuck to my usual masked stretches, a wide range of star, nebula and bright object masks, and then little adjustments until I reached the final image.

I am a lot happier now with my LRGB process, especially given the skies I have to deal with. The use of a CLS CCD filter in addition is, to my mind, a sensible step to take in order to block out unwanted light polluting light frequencies before they ever hit the sensor. Others disagree, but that’s half the fun of imaging.

Unless I have more clear nights very soon, it’ll be on to narrowband emission nebula until August when we get astro darkness returning in the UK and, with that, Andromeda!

The Iris Nebula -NGC 7023

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M101 Pinwheel Galaxy in LRGB

I can’t believe it has been over 2 months since my last post. The weather here in the UK has been terrible; a combination of snow and heavy rain every day since January. I was worried that galaxy season was passing me by and so, when the weather finally broke last week, I was eager to try and capture something worthwhile. With that in mind, I decided to target M101 Pinwheel Galaxy as it is high in the sky but remains an elusive target for me due to being relatively dim (mag 7.8).

This would also give me a chance to finally use LRGB filters on my mono camera; something I have had a go at with little success in the past.

The weather last week was clear overnight three nights out of four so it made life a little easier. I set up on night 1, using drift align to get my polar alignment as close to perfect as possible. Now we are in British Summer Time, it isn’t dark until after 10pm and gets light again around 4am so, especially during the week when I need to get up at 5am for work, I didn’t want to be wasting time setting up each evening. I elected, instead, to leave my equipment in situe for the four days so that I could not only begin imaging as soon as it got dark, but that I could also quickly capture flats the following morning before putting the covers on.

As I mentioned earlier, I am not very experienced in LRGB imaging. I know the theory but have not had much practice. I wanted to use longer exposure times to go as deep as conditions would let me, not just in terms of overall integration, but also to try and capture fainter dust lanes. I ran a couple of test images on each filter to work out a similar exposure outcome in terms of ADU and ended up shooting:

Lum: 20×600″ bin 1×1
Red: 37×183″ bin 2×2
Green: 20×240″ bin 2×2
Blue: 23×440″ bin 2×2

My issues started from this point onwards! The subs all looked good quality and so I began calibrating in Pixinsight. That was when I realised my first schoolboy error: I had cpatured all calibration files in 1×1 binning which meant they were unusable to calibrate the RGB files. I had a dust bunny on the sensor (I really must get around to dealing with that) and so each sub had that on it too so I really needed flats to remove it. Then I had a brainwave – could I create master darks and flats, and then resample them to create synthetic 2×2 binned calibration files? Turns out you can! WIth those sorted, I tried calibrating the lights and then stacking them with limited success in Pixinsight. I have been having real issues recently with this element of the process using Pixinsight and so I bought a licence for Astro Pixel Processing a few weeks back.

For calibrating and stacking, I really like APP. It produces clean, well calibrated light stacks and has the added bonus of an effective light pollution removal tool in post processing that does, in my opinion, a much better job than ABE or DBE in Pininsight.

Once stacked, I moved back into Pixinsight for processing – it is still, for me, the most effective tool for processing light stacks into a final image.

I went through several iterations before settling on this as my final image. I am really pleased with the depth of the image in terms of its sharpness and the ability to bring out the fainter outer lanes in this distant galaxy. I would likt to reshoot this using a longer focal length to make the most use out of my small sensor and pixel size, but I also really like the wider field in this version.

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