mftoet

In the end: brown is dark orange. It’s also called a ‘context colour’. Here’s a YouTube video about brown not being an actual colour.

That are excellent looking images! Nice to see Takahashi filled the gap between the 130 and 180 with this new edition of the Epsilon 160. The dedicated extender that’s in development also makes the 160 more versatile than its brothers. I noticed there are now lock nuts on the collimation bolts of the secondary. The adjustment/suspension of the primary mirror also differs from that of the 180. Good to see there’s an aperture mask on the (oversized) primary mirror. The 130 lacks one and therefore artefacts around bright stars (caused by the mirror clips) can occur.

The colour gradients in your stack are also common with the D810a I use. There's always some green to purple hue. I think this is sensor related. The gradients can be corrected with the light pollution removal tool in AstroPixelProcessor, but sometimes needs several runs and careful placement of the calculation boxes. The issue with the bolts on the secondary mirror also sounds familiar. I think I've just finally managed to get the secondary mirror in the correct rotation opposed to the focuser (and also centred under the focuser). In my case, the dot on secondary has always been just slightly off center causing even worse star images in the corners than on your example image. Yesterday I've imaged with an ASI1600 4/3 format sensor and I no longer detect collimation error. I have to verify with the full frame D810a though. I collimate the primary mirror with the tube pointed straight upwards (to the zenith) and only use the cheshire eyepiece (not the tube with cross hairs). As Mark pointed out, you can screw the 1.25" adapter directly on the ED-corrector. That will make it easier to judge if all circles are perfectly concentric.

That turned out excellent and very deep, just as you wanted.

When I acquired the Epsilon-180ED, the RASA systems weren't released by Celestron. In the late analogue / early digital age, a friend of mine used an Epsilon-160. I fell in love with the crisp stars that telescope produced and promised myself I would acquire one some day. About 10 years later I ordered an Epsilon-180ED including the ridiculous expensive tube rings, base plate en 7x50 finder scope (which in the end I only use for star alignment after switching on the mount). Another thing that I like about the Epsilons (and other fast Newtonians for that matter), are the diffraction spikes. I know, you either like them or you don't. Would I consider acquiring a RASA instead of a fast Newtonian? Maybe, but probably not. A thing that would bother me is that the camera (and cables) must be placed in front of the corrector plate. I can imagine taking proper flats can be challenge with a RASA. So respect for those who manage to produce excellent images with these astrographs!

And thanks again for the nice comments 🙂

Yes, you can, Richard. I suppose a 3D-printer can do the job.

Thanks! The primary mirror of the Epsilon-180 has a diameter of 190 mm and has a mask / edge support with an aperture of 180 mm. A simple but clever solution to avoid undesired diffraction patterns like spikes caused by a turned down edge. (Please don't get upset by the dust on the mirror: this picture was taken just before cleaning...)

Thank you Craig, Olly, Mark and Göran. @gorann: no the browns have nothing to do with light scattering in Earth’s atmosphere. It are genuine colours in these molecular clouds. You can also see the yellows and browns in dust lanes of other galaxies. I don’t know the exact (physical) reason for the colour, but probably a combination of absorption, reflection and ionisation in relation to the ratio between CO and H2 in these regions.

This is my final image of a week of pursuing astrophotography at @ollypenrice's 'Les Granges' in Southern France. Captured during the last two nights. Unfortunately I had to ditch about 2 hours of subs due to focus drift when I was asleep (resting for the trip back home). This is a crop. A larger field of view can be found at https://www.mauricetoet.nl/DeepSky/i-vtgtMB4/A (and a high res of this crop at https://www.mauricetoet.nl/DeepSky/i-KmtWWpX/A Also seen are LDN 1353 & 1357, VdB 7, 8 & 9 and LBN 643 Exposure time: 7 hours, 30 minutes (5 min. subs) | Optics: Takahashi ε-180ED f/2.8 | Camera: Nikon D810a (ISO 400) | Mount: Astro-Physics Mach1 GTO | Guiding: Lacerta MGEN + Vixen 70S | SQM: 21.3 - 21.5 magnitude/arcsec² | Location: Étoile-Saint-Cyrice, France | Date: August 19 & 20, 2020 | Processing: Astro Pixel Processor, PixInsight and Photoshop CC

Just keep adding data and the lovely browns will show up!

Modern OSC cameras can generate astonishing or at least unexpected results, can't they @ollypenrice? This is a two panel mosaic of the familiar Veil Nebula Complex in Cygnus. Captured during one night with a Nikon D810a and Tak Epsilon-180. This camera has the same sensor as the QHY367c (i.e. the 36.3 megapixel full frame (36 x 24 mm) Sony IMX094 CMOS sensor with a pixel pitch of 4.87 microns), though not cooled. Even during warm summer nights, dark current is so low, I don't bother using dark frames. That would be quite difficult in practice, because ambient temperature can drop from 22 to 12 degrees Celsius during the night. AstroPixelProcessor did an excellent job making the mosaic. The image was rather difficult to process due to the many stars in the field of view! They obscure the nebulous features. The yellowish glow to the right of NGC 6960 (the Western part of the Veil Nebula a.k.a. the Witch's Broom) with bright star 52 Cygni is not a colour gradient but actual dust or nebulas. The same is true for the tornado shaped grey 'smudge' in the lower right corner. Exposure time: 6 hours, 25 minutes (5 min. subs) | Optics: Takahashi ε-180ED f/2.8 | Camera: Nikon D810a (ISO 400) | Mount: Astro-Physics Mach1 GTO | Guiding: Lacerta MGEN + Vixen 70S SQM: 21.3 - 21.5 magnitude/arcsec² | Location: Étoile-Saint-Cyrice, France | Date: August 18, 2020 | Processing: Astro Pixel Processor , PixInsight and Photoshop CC

Always. If possible, I always keep an eye out for the darkest site possible and plan during new moon weeks. Not only because of astronomy but also because my family and I like the peace and quite (away from crowded places like we’re used to living in a city).

Yes, it’s always a pleasure to enjoy the Milky Way in full splendour at Olly’s Les Granges and having mr. Penrice around - though at proper distance - with his great sense of humour.

Thanks. @gorann: I just returned home to 52 °N, but I see you're almost at 60 °N. Time to book a trip to Namibia 😉 (Well, after the pandemic, that is.)

This field of view with lots of ancient yellow stars can be found in the hart of the Milky Way between the more familiar Messier objects M16/M17 and M8/M20 (and probably therefore often overlooked). IC 1284 is the circulair pink nebula just above the center. Attached to it on the lower left is IC 1283. Together they are also catalogued as Sharpless 2-37. The two blue reflection nebulas to the lower left of Sh2-37 are Van den Bergh (VdB) 118 and 119. The the dark clouds on the right side are Barnard 92 and 93. Exposure time: 3 hours, 10 minutes (5 min. subs) | Optics: Takahashi ε-180ED f/2.8 | Camera: Nikon D810a (ISO 400) | Mount: Astro-Physics Mach1 GTO | Guiding: Lacerta MGEN + Vixen 70S SQM: 21.3 - 21.5 magnitude/arcsec² | Location: Étoile-Saint-Cyrice, France | Date: August 14 & 19, 2020 | Processing: Astro Pixel Processor, PixInsingt and Photoshop CC

I use a Bahtinov mask and focus on a bright star while manually adjusting the focuser and look at the spikes at the live display of the camera.

Thank you for your replies. @tooth_dr: try your D800E on your Epsilon. DSLRs can do a fantastic job with fast optics, especially on a dark site. @Tom OD (and others mentioning the 3D-look of the browns): no magic was used to enhance the browns. I think the most important step was to carefully correct the background for colour gradients using AstroPixelProcessor's 'Remove Light Pollution' tool. Usually I run several preview iterations (calculations) and keep placing new boxes in the image that look to be 'nebula free' patches of background sky if neccesary. I don't bother about the yellow and red boxes showing up after the calculation. Sometimes I remove them, sometimes I don't. It depends on the result judged by the eye. To make it easier to judge if the colour gradients are properly corrected, I apply a maximum DDP preview stretch during this process. I don't think you can make it perfect with so many dust in the field that differs in brightness, but I find that this tool in APP gives better results than PixInsight's DBE. In the end, I don't process my images for scientific purposes, but to make a picture that's pleasant to the eye. Another thing that helps giving the browns (or any colour for that matter) a vivid look, is to adjust the saturation slider in APP and/or the vibrance slider in Photoshop's Camera RAW convertor. And then there is 'Match colour' in Photoshop and slight s-curve transformations on the a and b channels in Photoshop's 'Lab colour mode'. Here's the RAW stack in APP (DDP stretched) to show you what was my starting point.

I like sweets (ask @ollypenrice), especially chocolate. A lot of chocolate coloured molecular clouds can be found in the wonderful constellation Cepheus. This is the area of LDN 1228 (on the left) and LBN 552. Shown here is the full field of view and a crop that zooms in on LDN 1228 and LBN 552 to show the dark dust clouds in more detail. Captured during two nights (August 14 and 15) from the dark site of Olly's 'Les Granges' in Étoile-Saint-Cyrice. Total integration time: 6 hours, 10 minutes (74x 300s subs) | Optics: Takahashi Epsilon-180ED f/2.8 | Camera: Nikon D810a (ISO 400) | Mount: Astro-Physics Mach1 GTO3 guided with a Lacerta MGEN and Vixen 70S guidescope | SQM: 21.4 - 21.5 magnitude/arcsec² Data reduction and gradient removal / background correction in AstroPixelProcessor using 30 flats and 200 bias frames. I don't use dark frames but apply (excessive) dithering. Post processing in Adobe Photoshop and PixInsight.

Just saw this post on my iPhone and the image already looks outstanding, Tom! Will have a good look at it on my computer.

Thank you! @HunterHarling: yes, that’s the exceptional image of Marcel I referred to in the opening post.

Thank you for all your nice comments. It’s a joy to work with fast optics (although collimation comes very critical).

This is my second and last image from my stay at @ollypenrice's 'Les Granges' last week. I didn't spent as much capturing time on it as I did on the Cocoon Nebula (which was actually the only subject on my agenda for that week), but fast optics help a lot to get a good S/N-ratio in a mere 4 hours of acquisition time. I could have added another 7 hours if I hadn't break down my equipment on the evening of the last night. The skies of course cleared when the equipment was packed in the car (NEVER trust the weather forecast...). This is the Seahorse Nebula (B150) east of the Fireworks Galaxy (NGC 6946) and open cluster NGC 6939. On the far left a red wisp of the Flying Bat Nebula (Sh2-129) can be seen. I hope to continue photographing splendid object in the Cepheus area next year. Acquisitions details can be found on my website. After a night of deep sky astrophotography and some visual observing, a very old crescent moon came to say good morning. I've always loved the ashen light of a young or old moon. A 1 second exposure with the Epsilon-180ED was all it took to capture it.

During my current stay with friends at Olly's 'Les Granges' in Southern France (where the skies are much darker than at home in the Netherlands) my friends and I had a clear spell from August 23 to 26 and - inspired by the images of Fabian Neyer and Marcel Drechsler - I decided to go deep on the Cocoon Nebula. Captured with a Takahashi ε-180ED and Nikon D810a. Total integration time is 21 hours and 10 minutes of which 8 hours and 10 minutes through a 3.5 nm Hα filter (during the period the moon was above the horizon). The Hα layer gives an incredible debt to this field of view. The Hα signal was blend in by mixing it 50% (layer in 'lighten' mode) with the red channel in Photoshop.

In fact, currently I am at Olly's 'Les Granges' (since yesterday). There are several reasons why I've gone back to DSLR from CCD. To be more accurate: I've gone back to a digital camera with a CFA sensor. I've been pursuing astrophotography for about 20 years. My route went from a 35mm SLR (Olympus OM-1) > 645 medium format camera (Mamiya 645) > QHY8 OSC CCD-camera > SBIG ST-8300 mono CCD-camera > Atik 11000 mono CCD-camera > Canon 5D Mark II DSLR > Nikon D810a DSLR. Here's why I prefer using a DSLR (in random order): 1) a DSLR is more versatile than a dedicated CCD or CMOS astro-camera (mono or colour). Important to note is that in all those years of astrophotography I also like to pursue landscape and macro photography and since recent years also time-lapse and nightscape photography. I can (and do) use my current DSLR for daylight photography all the time, including taking family pictures and such (like I did in my early years with a 35mm SLR). Or how about photographing a lunar eclipse? Not very convenient when you (only) have a mono camera. So I spend about € 2500 on a 'secondhand' (demo-model) D810a, giving me the pleasure of doing all sort of kind of photography. 2) My time under dark, clear skies is very limited. Maybe about 10 to 20 nights a year if the weather cooperates. I want to spend that time as productive as possible, so my equipment needs to be as reliable as possible. Do we think computers are reliable? I don't think so. Do I need to mention Windows updates and driver issues? I guess not. I dare say Olly would totally agree with me on this. In fact, he calls himself a stone-aged astrophotographer keeping things the least automated as possible (manual filters wheels, manual meridian flips, manual focuser). Being a mobile astrophotographer my experience is that matters can go worse when you need to setup and break down your equipment every session. Therefore I don't use a computer/laptop in the field, but operate my DSLR with the standalone Lacerta MGEN. Focusing is done on a bright star by inspecting the spikes of a Bahtinov mask on the LCD screen of the DSLR. When you have an observatory (in your back garden or on a remote site), you don't have to worry (as much) about connectors and such getting damaged. You can tidily permanently bundle the cables. You continually optimise your setup and therefore it becomes reliable. If I would have an observatory, I would totally opt for a mono camera for deep sky work but still would like to have a DSLR besides for travels and other kind of photography. 3) As clarified above, I started astrophotography with a 35mm SLR. Back then guiding was doing done by eye keeping a star on the cross hairs of a guiding eyepiece making slight corrections with the handbox. Declare me nuts, but I liked that way of astrophotography in the style of E.E. Barnard. It gave the satisfaction that is was you that provided that crisp image without guiding errors and aeroplane trails (you would shield the aperture during the exposure when an aeroplane was about to enter the field of view). The current way I pursue astrophotography best approaches the way I did it in the early days. By using a DSLR I see and experience more of the beautiful starry sky than I did during the period I was using a laptop to operate the camera. 4) Dew issues. Probably bad luck, but I have owned two CCD camera where dew would form on the window in front of the sensor during the course of an imaging session. Current DSLRs perform very well, so cooling is not necessary. The D810a (and other high-end DSLRs) doesn't need dark frames (low dark current, no amp glow). However it is important or at least preferable to dither between subs. 5) Power consumption. A cooled CCD and a laptop drain a relatively large amount of current. I can operate my setup in the field without having to worry my battery will run flat. I don't need a large battery in the first place.