It’s been a week since my last post and it’s been the busiest 7 days of 2021 so far; hence the slight delay in this post being published.
As some readers my already know, I’ve decided to create a Facebook page and a YouTube channel to accompany this blog. If some keen-eyed viewers had already spotted, I’ve also done a little re-brand to tie everything together. Going forward, these outlets will allow me to produce videos as well as written content, also they’ll allow me to do livestreams of my imaging sessions if I have a partially good night. But that’s for the future…
Back to the present…
With a string of clear nights this past week, I’ve been out capturing some more data on the Horsehead & Flame Nebula. However, with the moon at nearly 100%, I’m afraid to say it was to no avail. I had to reduce my exposure time to 4 minutes, just to stop the captured frames from being over exposed. That isn’t such a big deal breaker as I take fresh calibration frames each night. However, when compared with my first stack of only an hour, the new version that consists of 4 hours 40 minutes is really no better off, if anything it’s actually worse! I’ll try again when the weather’s clear and there’s no moon in the sky. I just hope it’s still around by then! If not, I’ll just want to wait another 9 months!
Previous to this week, I did have one clear night that was only meant to be a testing and configuration night. It didn’t start out as an imaging session, but it quickly became one when I found a target that I’ve always wanted to image.
As I mentioned in my previous post, I stripped down my declination axis and re-adjusted both the worm-gear and the motor positions…AGAIN. I had previously re-aligned the motors back in October of last year when I was first having problems with backlash, but I didn’t touch the worm gear. Turns out this is where my problem was hiding.
As I had previously thought that the backlash was being caused by the gear system being too loose, I had moved the motors tighter together. It turns out my declination worm gear was actually too tight; so tight in fact, that under the pressure of the motor, it wasn’t turning fluidly. The massive ‘kicks’ that I mentioned in my previous post was actually the wormgear overcoming the static-friction. This resulted in the sudden large movements that were plaguing my images, causing me to discard over 50% of my images.
So this time, when I took the declination motor off, I adjusted the worm gear so it was as loose as possible, with large amounts of rocking between the worm and the main axis gear. Then, I slowly tightened everything up; only by 1/8th of a turn of the adjustment hex bolts before checking the wormgear axel again. Slowly but surely, it got to the point where there was no rocking between the teeth, and I could easily rotate the axis with my fingers rather than a set of pliers. With everything tightened down, I replaced the motor and cleaned everything up inside. It was running a lot smoother when just slewing about through EQMod, but I needed a clear night to re-calibrate PHD2.
Fortunately, one came around on the 18th February, but of course it’s always accompanied by the moon! This night however was only 41% illuminated, so it was tolerable enough to image. After re-calibrating my mount in PHD2, I also ran the Periodic Error Correction (PEC) within EQMOD for 5 worm cycles; around 40 minutes or so. This generated curve is meant to counteract any tracking imperfections within the RA axis, so PHD2 shouldn’t have to work as hard to correct any errors. That’s the theory anyway!
When this was enabled and my mount was guiding, my total RMS error was between 0.5″ and 0.8″, which is fantastic! So much better than it was before! Also, within the 40 minute period of recording the PEC curve I only had 2 kicks, and that was only due to the wind. So it looks like I have sorted my declination problems once and for all. Hopefully now I shouldn’t be wasting valuable image time with streaky stars.
After that, I was just slewing around the sky, checking everything was running smoothly and guiding correctly, when I stumbled across NGC 2237/Caldwell 49, better known as The Rosette Nebula.
This stunning Hydrogen Alpha target lies in the constellation Monoceros around 5,200 light years away from earth. The physical nebula is calculated to be around 130 light years in diameter, which from our location in the Milky Way gives an apparent view of five times the size of the full Moon. If only our eyes could see it, what a sight to behold!
The stars that form the open cluster at its core (NGC 2244) are formed from the nebulas stellar material, with the young blue stars emitting UV radiation as well as strong solar wind. This causes the hydrogen gas to emit the vivid red colour and all the dust at the core of the nebula to be cleared, leaving the hole in the middle.
When the first test image came in, I was utterly blown away! So I loaded up my imaging sequence preset and snapped away until I lost it behind my neighbours garage at 11:46PM, culminating in 23 exposures.
When I loaded everything up in Deep Sky Stacker, I was utterly amazed at how few subs I had to remove from the stack. I captured 23 light frames, and I could happily stack 20 of them. However, this only gave me only 1 hour 40 minutes, so I wasn’t expecting much in the output file. Again though, I was amazed at how much detail was in the final image. This allowed me to stretch the 32/bit TIFF file to its limits while still keeping the dark background sky!
To say it was only mean to be a quick test shot while battling a 41% moon, I was blown away by this target, and will definitely have to revisit it again from a dark sky location when we’re able to safely.
I know I keep saying that I want to spend more time on single targets, and then seemingly moving on, but I really do want to sink some serious hours into stunning target in and around Orion. I wonder if a new dual narrowband filter is in order sometime soon!
Unfortunately though, the clear weather seems to have passed for now with the clouds starting to roll back in this week. Hopefully by the next clear night though, it will be a new moon and I’ll be able to re-take my 4 hours or so that I captured on the Horsehead. I’m really disappointed that it didn’t turn out… I’ll have another go at stacking the three nights, it but I’m not holding out much hope when looking at the individual frames.
Well, that’s it for this week, and I hope you that you’ve had better luck that I have the past few nights. Till next time!