Imaging NGC 7000 and IC 5070 using Optolong L-eNhance EOS clip in filter

I have bitten the bullet and gone ahead with the purchase of an EOS Optolong L-enHance clip in filter for my DSLR. This was against advice from people at various astronomy retail outlets and also on various Facebook forums. Essentially, they felt I should wait until I upgraded my image train to a specific astro cam and filter wheel arrangement and then go for the Optolong L-eXtreme or some such other filter. 

But, I can't afford to upgrade my image train at the moment, nor for the foreseeable future and anyway, I like imaging with my DSLR. 😕

Recently, finding a cloudless night has been about as rare as finding golden hen's teeth. But one did occur a few nights ago and so I went out into the back garden for an imaging session. 

Now I was facing some constraints!

• a 60% waning moon rising at 1 am
• my first try at using a clip in filter with my newly astro-modded DSLR
• a limited sky view - I can only image from NW to NE skies from my garden; or directly overhead towards the zenith. The steep hilly garden to the south with its tall woodland trees block southern sky views. 

I decided to try for an emission nebula - NGC 7000, The North American Nebula. I've given details further down the post. A bonus would be capturing IC 5070, The Pelican Nebula. 

Wanting a widefield view and after my disaster missing Rho Ophiuchi last session (because I used my Zenithstar 61ii), I opted for my samyang 135mm lens. So, equipment on the night was as follows: 

• Samyang 135 mm lens
• Canon 800D astro-modded DSLR
• Optolong L-eNhance clip in filter 
• Skywatcher EQM-35-Pro mount
• ASIair mini
• RVO 32mm F/4 guide scope with ZWO 120mm mini camera
• Red dot finder scope 
• Celestron Lithium Pro battery pack 
• Two dew heater straps
• Two power banks 
• Skywatcher right angled Polar viewer and MSM green pen laser 

So here is the night's images - the same image - wide view and cropped in. Shooting details shown between the images. Remember that Blogger has a 100mb upload capacity and so I have had to reduce the quality of the images somewhat to get them to load up to this post. 

Shooting details: ISO 1600, F/2.8, 300" x 25 with 10 of each calibration frame

Post editing details: Stacked in Siril; background extraction and denoise in GraXpert; colour calibration, deconvolution in Siril; finishing stretches, sharpening and colour balancing etc in Affinity Photo

So, two questions - how did the night set up go; and, how did the post editing workflow progress? 

The night went smoothly. Actually one of the smoothest night set-ups I have had.  From getting out the tripod to finally shooting on the target took just 40 minutes; not my normal 60 or so! Result! 

I was worried that using the clip in filter would cause me some focusing issues but I whacked ISO to 12,600 and then found the brightest star I could find in the sky. Using Live View and my zoom in buttons, I was able to see the star clearly and get sharp focusing straight away. I used a strip of masking tape to then secure the focus position on the lens. 

Because I couldn't see Polaris (due to scaffolding up the side of the house - recent huge flat roof leak - long story - let's not go there 😱) I had to rely on 'All sky align' mode on the ASIair mini. It worked perfectly! Five minute long exposures are the longest I have ever done and BIG result? Guiding was spot on perfect, most of the night it was below 1.0. Seriously, on a stiff to balance EQM-35-Pro - amazing! 

Time spent a few weeks ago working on my imaging train also paid off. I have sorted my cabling and arranged it so that surplus cables are bundled neatly and stored on the imaging rig - reducing the cable rig weight. My son-in-law kindly 3D printed off some tripod powerbank holder clips which helped as well. I will do another post about this at a later date. 

Upshot? I managed to image for around 2 and 1/4 hrs before clouds started to close in. Ideally I would like to try and get three hours worth of images. Maybe I will try and add more images on the clear night - although I am also being tugged by the desire to go off and get some milky way landscape images! 

I am, in all truthfulness, always pleasantly surprised when I manage to get the ASIair working as it should. Initially, things didn't look very promising but then things settled down. 

Ok, what about post editing then?

I am still using Siril version 1.2.6.  I know there is a new, really whoopy new version out but I haven't bothered to download it yet because I am still trying to understand the basics on this simpler version. Small steps and learning to walk before you run and all that! 

However, I am really pleased with these images. The full resolution ones show marked improvements in my post editing skills? So why the sudden leap forward? Well, I have managed to better understand GHS stretches in Siril. I have altered my workflow slightly to do more stretching in affinity photo as well. I better understand how to reduce star intensity and luminosity using JR Ritson Macros for affinity photo (thanks James). For the first time, one of my DSO photos has some 3D depth and structure to it. 

At long last! 

I know there are still many issues not addressed - especially colour saturation and blowing out some of the detail in core areas - but small steps as I said before. I am a 'slow' learner. Persistent, curious, determined, resilient - but 'slow'! 😁😂

So, what about the filter? 

A game changer in my view. Wow. Noticeable effect immediately from my bortle 5 back garden. I won't bother doing a review of the filter as there are many already on the net - try these if you are interested: 

https://astrobackyard.com/optolong-l-enhance-filter/

What are my initial impressions? 

It is easy to insert. The springy arms on the clip can be adjusted, and unlike my optolong L-pro, this filter doesn't fall out as soon as you move the camera! It seems to work well with an astro-modded DSLR. I used auto white balance for a change and got no odd colour casts. However, I need to play about with colour balance in the DSLR and see what happens on future imaging sessions. I think for the first time, I have gained some good contrast and colour saturation in one of my images. It certainly reduced the normal light pollution colour casts that I normally get. I read on many forums that if I was going to use it, longer exposures was the way to go with some people recommending between 5 - 8 minutes each. Given the longest I have ever imaged before now is three minutes - this is a game changer for me! A Bahtinov mask helps you get really sharp pinpoint stars and focus and of all the calibrations frames, the flats are the most important I suspect as they will correct any vignetting caused by the filter (although I couldn't see any on the finished Siril results image.) 

And finally, what do we need to know about the two images above? 

NGC 7000 The North American Nebula is magnitude +4.00, an emission nebula in the constellation Cygnus and close to the bright star Deneb. The nebula covers an area x10 the size of the full moon and was first discovered by William Herschel in October 1786, from Slough! When light pollution was obviously not an issue! 

It is a huge interstellar cloud of ionised hydrogen and the shape we see from earth is caused by a band of interstellar dust that lies between it and our planet - this dust absorbs the light of stars and the nebula itself and somehow causes this shape to materialise to our vision.  Can tell I'm no astrophysicist can't you! 😁

The portion of the nebula that represents Mexico and central America is known as the Cygnus Wall and is an area of concentrated star formation. 

From us to the nebula is around 2,500 light years. 

So why do we see red? The hydrogen alpha area shine because their hydrogen gas has been ionised by UV radiation from a nearby hot star. For a long time it was thought that this was due to the proximity of Deneb, but not so! Its surface temperature is only 8500K. A star with at least a surface temperature of 35,000K is required. Deneb is not hot enough and too far away from the middle of the nebula complex.

So, where is the UV coming from? There is a star off the 'Florida' coast area of the nebula which may be a contender. It appears small and dim from Earth because it is behind the nebula but it is closer than Deneb and its surface temperature is 40,000K. Ideal! 

And IC 5070 The Pelican Nebula? 

Tricky to discern but I have circled it above. You will need a little imagination here! Early astronomers thought the nebulous gas emissions resembled a pelican! Nope! Me neither but hey there we go! 

Anyway, it is an area of very intense mixed star formation and gas cloud formation and is highly studied by modern astronomers today. Light from energetic young stars are slowly transforming cold gases to hot ones, so causing an ionised front to slowly advance outwards. 

IC 5070 is divided from NGC 7000 by a dark dust molecular cloud area. 

Still can't see the Pelican? Look for a dark dust cloud eye and then a long bill. The bright front of ionised gas curves away forming the head and the neck. 

Nope, me neither! And normally, as a geographer, I am really good at this 'spatial awareness' malarkey!