On one of three clear nights in February, I managed to capture this amazing image:
Just three hours of RGB data has captured a host of bright and many faint galaxies. Some of the faintest detected are very red indicating a huge distance away from us. PGC2299122 and PGC2299019 are estimated to be 3.8 Billion light years away!
Making the most of my improved guiding I have been using the big 250mm Newt to image some classic galaxies:
This is a combination of several partial sessions that I had to stop for one reason or another. 10hrs split as 4hrs of Red, 2 hrs of Green and Ha, and only 1hr of Blue! I’ve no idea how many frames were rejected – I left that to the WBB scripts.
I’d like to make the Holmberg IX dwarf galaxy a bit more prominent if I can (I have some Ha there but it’s very faint).
RBG 30s sub @ 0 Gain
For once my guiding was sub 0.5 arc-sec and conditions were great all night (even with gusts of wind) so I was able to capture all the data in one session🥳. This is 3hrs or RGB and 4hrs of Ha. On this occasion I used unity gain for RGB and 200 for Ha, I’ve decided that with so few good nights it makes sense and the noise isn’t excessive. I combined the Red channel as 80%Ha+20% Red to emphasize the disruption. This is probably my best galaxy to date. Only my processing skills limit what my kit can produce.
In comparison here is a wide field image I took last year using my 150mm newt. There’s a lot wrong with the image but it shows the progress I am making.
Broadband imaging is already tricky in the suburbs but I perhaps didn’t help myself by trying to image this lovely galaxy with an almost full moon chasing it across the sky and haze. But still, for 4 hrs of data this RGBHa image is okay. The star field is aggressively clipped to remove the psychedelic rainbow mottling which I think is just pure moonlight.
For the rest of January, I had two more nights where I attempted to capture this target, luckily no moon glow just LP. So here is take 2, this time about 1 hr each of RGB and only 40mins of Ha. But you can easily see the improvement from by the better seeing and lack of moon – more fine details in the galaxy and lots of smaller galaxies sprinkled throughout the image.
Captured while waiting for M1 to clear some trees. This is an ideal target for a quick imaging session. 1.5hrs of RGB imaged with the ASI1600 on my 250mm Newtonian. Simple stacking a processing in Pixinsight. On this occasion I used a combined dark-flat with the flat frames This seems to work well.
I first imaged this supernova remnant back in 2005 using a modified web-cam.
I tried again is 2012 with a DSLR:
I was very pleased with the results then but my recent efforts (Dec 2021) are significantly better as they should be given all the high-tech I have thrown at it:
It still needs more signal to get a decent SNR but the results so far are excellent given this is 1.5hrs RGB, 1hr for Ha and S2 and 2hrs for O3. By coincidence we have the same orientation for each image so a direct comparison is easy.
1 month later (6th Jan. 2022) with an additional 4.5 NB data and 45 minutes of RGB I was able to produce this version which uses only SHO data for the Crab nebula itself:
The narrowband light emitted by the nebula images very differently showing that the Crab has lots of very complex structure:
This is a tricky target from my back yard, I only have about a 50-minute window between some trees to capture this. Imaged on a windy night the stars are not a great shape but I can live with that. This an Ha only image cropped and focused on the horsehead itself:
And here is the full frame:
Imaged using the ASI1600 on the OO250mm Newt, just 22 x 120sec Ha. Accidentally imaged at 0 gain! It’s tricky to get more data at this focal length due to the small window of opportunity so I’ll likely go portable for the classic a wider view with my short focal length refractor.
This is the bright 7-Sisters star cluster in Taurus visible high in the winter northern skies. This is a target that has been long on my list of failures – results have previously been poor with not having the right focal length and not taking enough sub-frames. It’s a broadband object so it is also at the mercy of light pollution.
Whilst the stars are bright the reflection nebula surrounding this cluster is quite faint and easily swamped. Bringing out the reflection nebula without saturating the stars requires choosing an exposure length that does not clip the stars and then take lots of exposures.
I decided that it was a good target for my un-modded, uncooled Canon 550D, matched to my 70mm APO refractor to give me a good level of detail with some surround star field for context. The result above took 479 x30sec exposures (4hrs). It was processed in Pixinsight and finished off in Paintshop Pro as a full frame resized to 30%. If I took another 4 or 8 hrs(!) I might be happy to display this at native resolution.
The HEQ5-Pro continues to be an excellent mount for this scope. Basically, its sub-arcsecond tracking accuracy with this load means it’s rare to lose a frame due to mount errors.
Earlier this year purchased a ZWO ASI1600mm Pro + 36mm 7-position filter-wheel complete with the LRGBNB filter set.
The ZWO filters represent very good value and I have had a lot of fun with them. However, of the set the Oiii is not the best performer, it produces distracting halos around bright stars and rings around dimmer ones.
I have learnt a technique to reduce the impact of halos during image processing but it is better not to have them in the first place if they can be avoided. Its asking a lot of budget filters so I had a look around, prepared to spend a lot more. But I noticed that the Baader filters had recently been updated with improved anti-reflection halo reducing layers (even claiming halo free). At £143 from FLO they are a similar cost to the ZWO filters when bought individually. I decided to give the Baader filter a trial to see how it lived up to the claim.
I fitted both the Baader and ZWO Oiii filters to the filter wheel for a side-by-side comparison. The optical train was ASI1600mm Pro, Filter-wheel, Lacerta KomakorrF4, Orion Optics 250mm F4.8 Newtonian. Autofocusing between filter changes was done with a ZWO EAF.
The camera gain was set @ 139, sub-frames were 120s. I took 34 subs with the ZWO Oiii and selected the best 10 frames to stack. I took over 100 frames with the Baader. Using the same quality selection criteria I had 38 frames, from which I took the first 10 for stacking for this comparison. I used the N.I.N.A autofocus routine with each filter change. All subs were taken during the same one-night session. Conditions during the night varied but because I restarted a few times, the conditions evened out for the two filters.
To conduct the test, I chose a new target for me but one with a reasonably bright star in the ROI. I chose the Bubble Nebula. Below are the stacked images with automatic stretch applied:
ZWO 7nm Oiii Narrow Band Filter
The ZWO filter gives us a very obvious halo around the bright star.
Baader 6.5nm Narrow Band OIII Filter – CMOS Optimised
The Baader filter also has a halo but it is very faint. Additionally, the star appears better defined suggesting less scatter overall. The fainter stars appear brighter than in the ZWO image. (More testing would be needed under stricter conditions to verify this).
Finally for comparison here is a closeup of the ZWO Ha subs (80 minutes integration). There is no halo apparent.
Conclusion
The new Baader 6.5nm Oiii filter offers a significant improvement in halos over the ZWO 7nm. There are still halos present in my particular setup, but the Baader halo is over 4 times fainter that the ZWO.
There is also the suggestion of less light being scattered, giving brighter stars and better definition in distributed objects like galaxies and nebula.
The Baader Oiii filter wins over the ZWO.
This is was my first image of the 2021 season after a long break. It’s the result of two nights of roughly 1hr total for LRGB, 2hrs Ha and 5hrs Oiii.
I’ve been practicing with methods to combine the images…
LRGB subs were 30sec @ gain 0, Ha and Oiii susb were 120sec @ gain 200. ASi1600mm pro and filter set, scope was the OO250 newt. Even at 30 seconds and 0 gain I still manage to clip some stars.
This is the Wizard Nebula. I’m told it is supposed to look like a wizard in a pointed hat and gown with open arms. I imaged this over two nights under very bad weather conditions and a bright moon.
I attempted and abandoned some S2 – the signal was weak and too many subs were trashed. At the end of the two days I applied more than my usual rigor to the frame selection process and ended up with just 100mins each of Ha and O3.
Stacking just the best subs didn’t change the star sizes but the fainter ones were sharper, over-all contrast, range and noise was improved (so spending the time up-front to select good frames is really worth it). O3 was still weak but I decided not to push it too hard. I applied the halo reduction technique for the O3 described here it works surprisingly well.
I’ve combined the signals as R=Ha, G= 0.3*Ha +0.7*O3, B= O3. The central blue area of the nebula was enhanced using an O3 range mask and just increasing the blue saturation a little. This was quite tricky to process and easy to overdo.
After imaging this nebula, I’ve purchased a replacement O3 filter. For future narrow-band projects I’ll be swapping out the notorious-for-halos ZWO 7nm O3 filter for the Baader 6.5nm (new for 2021) O3 filter that is supposed to have much improved antireflection and halo reduction coatings. I plan to do a side-by-side comparison in a mini-review just to see if the Baader filter is worth it in my setup.
