Avocette

After Markarian's Chain and the Coma Galaxy Cluster, I thought I would have a go at capturing a similar group of galaxies in Virgo including M58, M59, M60, M87,M89 and M90. The image includes plenty of NGC galaxies as well especially noteworthy perhaps the 'Siamese' Twins NGC 4567 and 4568. 

The image is the result of a stack of the best 16 of 20x240 seconds captures on my astromodified Canon EOS 550D (stacked in APP, non-linear processing in StarTools1.7). The scope is a SharpStar 61EDPH II with matching FR/FF operating at 275mm and f4.5 with no filter, mounted on AZGTi with ZWO mini scope and ASI120MC-S guide camera. All controlled by KStars/Ekos/Indi (astroberry).   Flats have corrected for the 'DSLR mirror shading' along the bottom edge of the image, but, of course, not an interesting diffraction spike on rho Virginis which is just at this edge.

The following is an edited screenshot from SkySafari 6 Pro which may help to direct attention to the NGC objects.

The next image is a zoom in of 27 and rho Virginis from the original image.

3 hours ago, kirkster501 said:

Very nice.  Nice colours and framing.  I think you have slightly over-clipped the black point - to reduce noise or to eliminate a gradient?  A bit of noise is OK.

I just downloaded the image and at least in GIMP the histogram doesn’t show any black level clipping from my perspective (well the 0 brightness pixel count is 191 out of a total of 3724225).

Thanks! I had assumed that it was due to the position of the closed up mirror, also emphasised because in this image, the magn 4.3 bright star rho Virginis is just at the bottom edge of the image, and shows a bright diffraction spike due to the mirror straight edge I presume. My scope is f4.5 so that ties up with your explanation.

The fact is I’m struggling with Flats so your suggestion makes me more keen to sort them out. I have made them in the past using a white image on my iPad screen with SharpCap Pro. But more recently I bought a 30x30 cm square LED panel intended for room lighting, not special purpose, and it’s rather bright and since then I seem to have lost the plot. I know Flats are important for dust doughnuts and suchlike but I was guessing it couldn’t do anything for the ‘shadow’ as you describe.

I tried shooting Flats with Ekos but the KStars Fits Viewer histogram confused me and I gave up..... for the moment anyway.

I’ll put in some serious effort and have another go with Flats and Dark Flats.

4 hours ago, alacant said:

Lovely shot. There are certainly many non stellar light sources. Well done.

Please note that you cannot use StarTools to advantage with anything other than linear data. By pre-processing, you removed a lot of its power. Starting from a linear stack, you'll probably find e.g. StarTools' Wipe module does a far better job on gradients than app, and with the unique advantage of retaining your data in a linear form throughout.

Cheers

So far I have found the StarTools Wipe module less effective than the APP tool for light pollution and gradient removal. APP’s tool requires much manual intervention. For this image I carefully drew 80 or so pixel boxes of various sizes in places where my eyes thought there was no specific stars, galaxies or nebulosity. I agree that once you’ve done something of that nature StarTools can no longer track the noise for definitive removal, but for this kind of image I think it didn’t do a bad job! If Ivo reads this and disagrees, I’ll stand corrected!

I have found that my 550D doesn’t have fully even illumination and there is a strip at the bottom of every image (i.e. top of the sensor) which has a different contrast and brightness from the rest. So in the image above I couldn’t correct it, and ended up cropping. I’ll make a new posting on the subject.

@alacantSo I followed through after you pointed me in the direction of the galaxy cluster. Here is my capture from last night using a 61mm 275mm FL scope and astromodified Canon EOS 550D with no filter 36x240 seconds. APP for stacking and to get rid of gradients and light pollution and StarTools1.7 for finishing.

Great image and thanks for adding the Coma Cluster to my imaging list!

I’ve not made any modifications to my AZGTi which is mounted on a SW Star Adventurer EQ wedge. I have a 25cm long piece of 12mm studding as a counterweight bar, with 1kg of large washers at the end, I suppose the effect is of a 1kg weight acting at about 20cm from the axis. The RA axis doesn’t rotate smoothly enough to allow me to find an actual balance between the counterweight and scope/camera load (61ED, DSLR, ZWO mini guide scope and ASI120MC). Here is a practical guide graph from a session this week. 

This is the KStars/Ekos/Indi internal guider analysis graph using the multi-star option. The red line is the total RMS guiding error, although I think much of this comes from the Dec axis. The horizontal pale blue lines show the HFR measurements for the 18x240 second images. Guiding sometimes restarts after dithering and you can see peaks above 3 arcsecs. My assumption for the moment is that it may be worthwhile playing with the details of the guiding parameters but that there may be some stiction/friction in the axes. I am reluctant to open the mount up with such results which give me acceptable images with my 275mm focal length refractor.

1 hour ago, Dazzyt66 said:

I’ve just been using vpn/browser access to set it all up via my Mac. Just a dry run with Ekos left to do (I’m going to use it in client/server mode so I do all the big stuff on the Mac) and then  I just need a clear night to try it out...

The BIG advantage of running everything on the RPi4 is that you only monitor and control the actions from your Mac or PC. This means that at any moment if the WiFi link goes down (it does occasionally happen) the RPi4 carries on regardless, carrying out the jobs it has in its list, and you can just reset the Mac or PC and you’re back connected. In my case I run two astro systems a few metres apart. I have modified the astroberry hotspot SSID names to be able to distinguish between them (AstroberryBlue and AstroberryRed). I set each one up - Polar Align, Focus on a bright star, move to target, ‘capture and solve’ with slew to target to get precisely lined up, and then a test image or two before committing to an hour or two of captures for each kit in turn. Then I monitor from indoors, hopping back and forwards between each WiFi network from time to time to see how things are going. If I feel like doing a bit of live stacking, I use VNC Viewer File Transfer to download some image files from the RPis and run ‘live stacking from folder’ in Sharpcap Pro on my laptop.

I used to do this a lot six months ago because I was running KStars by default in ‘reduced resources mode’ which meant my images were not debayered. However I learnt that an RPi4 is perfectly powerful enough to do the debayering as well and the Fits Viewer auto stretch is much improved these days, so I get a good idea of the incoming images directly without further processing on the laptop.

Well - I may never know exactly what I did to sort this out, but it’s working now! I did link into the AZGTi via WiFi using SyncScan Pro and made some changes to the ‘hibernation’ settings, without apparent impact. However I turned the RPi etc on again today with cable connection to the AZGTi and yippee!

The Indi EQMOD driver is still reporting firmware 3.14...... but I may just live with that. Hopefully Dec guiding will still work (clear skies tonight).

I’m running v3.20 which was necessary to get the Dec guiding to work when I was using WiFi connection. Interestingly (and confusingly) the firmware echoed back to the RPi from the mount is 3.14......

I have been running my AZGTi successfully via WiFi from my Astroberry RPi. However after a couple of hiccups recently I thought to try a solid cable connection. So I'm now the owner of a Lynx Astro EQDirect RJ12 cable. First attempts have not been great - slewing a few degrees from the NCP to Dubhe in the Plough, sends the scope on a long movement until it's pointing at the ground! I am searching for information on the home and park positions and hoping there's something obvious I've got wrong in the settings. Anyone got any suggestions?

41 minutes ago, herne said:

Thanks.  Yeh I appreciate it's the mount to align rather than the scope however something I don't understand - I see people doing an initial rough (or even accurate) polar alignment using the polar scope built into their EQ mount, then a much more accurate polar alignment using their guide scope + camera which is attached to their main scope using Sharpcap (for example).  So why not just attach a polar scope to the main scope?

I appreciate there would be an alignment issue between polar scope / main scope, but there would be for finder scope / main scope too though.  Noob questions I know but I feel like I'm missing something 🤔.

If the mount is polar aligned, then the main telescope, guidescope or finder scope are all polar aligned. The mount is simply reversing the rotation of the earth from all perspectives! Of course you would like the telescope to be aligned close to the polar axis and likewise the guidescope and finderscope, but if not, the mount is still aligned. You can polar align using your DSLR but it’s more convenient with an astro camera which might be your guidescope camera. 

You could indeed add a polarscope to your AZGTi but you’d need a lot of precision mechanical skills, and the cost would not be trivial. However you have already got the makings of an electronic polarscope - with the help of some software on a laptop or a Raspberry Pi. Astroberry.io (open source - no cost) software package on an inexpensive RPi4 has transformed the precision of my AZGTi polar alignment, and also GoTos using plate solving.

48 minutes ago, wimvb said:

Personally, I would get the RPi with Astroberry or INDI/Ekos, and a Pegasus Power box, and just strap one on top of the other. Both seem to be good at what they are designed for.

I did just that about a year ago and find the combination great. I sandwich a TP-link 7 port USB3.0 hub between the two units. This is powered from one of the Powerbox 12V outputs, and it provides a 2.1A USB socket to power the RPi4. The current supplied is perfectly adequate since the RPi4 USB ports drive relatively low power to the directly connected devices (the TP-link unit and an SSD). 

22 hours ago, dave_tucker said:

My day job is as a Software Engineer and I was wondering how I might put those skills to use on the Uk's famous cloudy nights.
I've been playing with KStars/Ekos and INDI and it's awesome, but it's unclear to me (from the website at least) how to contribute my time (Ikarus will gladly take my money though lol).
So I'm wondering if any of the maintainers hang out here and might be kind enough to point me in the right direction... or if there are other popular projects that might need a helping hand.

I’ve been an avid user (rather than a developer) of KStars/Ekos/Indi with a Raspberry Pi  3+ and since they were launched in summer 2019, RPi 4s. I monitor, update and occasionally ask questions on the forum at www.indilib.org where the are certainly developers posting news and answering queries. I suggest you offer your skills over there where I’m sure you would be welcomed.

Here’s a photo from which you can perhaps see my balance arrangements. The SW ED80 has its rings at the rearmost position (some boltheads prevent them actually touching the focuser casting). Then the dovetail is held also at its rearmost position. For the 61EDPH II I replaced the ludicrously short supplied red dovetail with a SW 21cm green one which leaves plenty of length for adjustment. The clamshell wide ‘ring’ is again close to the back end of its range of movement.

Where is the balance point of your fully loaded telescope/guidescope/cameras combination? If it’s not within the length of the present dovetail, perhaps you could turn it backwards, at least as a test, before ordering the rings and new dovetail? 

I have just completed a very quick (but careful) dismantling and reassembly of my SkyMax150 Pro, taken some measurements, taken some photos and blown away a very few dust motes from the optics. The primary mirror diameter   (measurement K in Magnus’s nomenclature) was 163mm overall and around 160mm if I discount the ground edge which is chamfered at about 45°. The Primary Mirror Retaining Ring (J) is 47mm. The Secondary Baffle Skirt is 52mm (H) at the wide end, and has a depth of 43mm (C&I). 

The metal tube is 2.2mm thickness and 178mm internal diameter. In my scope, this means that the eight screws, which attach the Corrector Plate Rim and the Rear Cell, distort the circular profiles when tightened appropriately.

My scope at least ten years old and possibly somewhat older. It has the ‘Black Diamond’ paint job and the 2” visual back but with a 66mm thread rather than the SCT compatible rear thread of more recent manufacture.

Here are a few photos for the curious!

@Captain MagentaDuring these stormy days I was thinking of having a look inside my SkyMax 150 and just wondered if you had yet found a moment to dismantle and reassemble yours? I bought mine second hand seven years ago and became convinced that ‘someone had had it apart’ probably for cleaning, when I noticed evidence of clear glue fixing the secondary baffle to the surface of the secondary mirror. I suppose cleaning the secondary mirror is more simple if the baffle is first removed. I have held back until now but have an urge to open it up to look more closely at the condition of the mirrors, even if I don’t attempt to clean them if they seem in good enough condition.

If you buy the ZWO ASI533MC version, a number of spacers come with it to make replacing a Canon DSLR very simple. The pixel size is not very different from the Canon although the sensor size is just 11mm square so a somewhat reduced FOV.

Just watched a Youtube video which does a comparison although I didn’t figure if there were any conclusions......

5 hours ago, david_taurus83 said:

It would be easier to get an AZGTi and use the SA wedge and counterweight bar with the AZ in EQ mode.

Exactly right.... I had planned to buy a Star Adventurer for a small grab & go rig, but then realised how much I would miss GoTo. And then with a RPi4 and Astroberry you can have back-friendly polar alignment and full platesolving.

The RPi 400 is a keyboard ‘hiding’ the RPi4 4GB, so you’ll need to think about mounting it and preventing ingress of damp.....

.....and for the purpose you propose, an RPi4 2GB in a flirc case, would do the astroberry job nicely!

On 03/01/2021 at 17:24, Gfamily said:

I haven't tried using my AZ GTi in equatorial mode (and if I did, I would initially use my existing SW Wedge), so this is simply reporting what others have suggested. 

HTH 

The luxury of being able to test with an SW wedge is unusual at the moment with supply shortages! I use such a wedge with good results.

Where angels fear to.......

I think you should hang on to the 200p Dobsonian until you are sure that whatever you choose to replace it with really is as good and as easy to handle! Your Dob has the significant advantage that it is very quick to settle to thermal equilibrium although it is a bit bulky and awkward. But everything is relative!

As my ‘signature’ shows I presently have a number of telescopes of various types. Not listed are the ones that I have bought and subsequently sold over the last ten years beginning with a 200p Dob, then a 250p Dob and ultimately a 300p Flextube Dob. Also the mounts I have owned and sold include a EQ3 equipped with motors and a EQ5 Pro GoTo. 

I live in Switzerland in a semi-urban semi-rural place with Bortle 5 skies (according to Clearoutside.com). However, in reality I have four yellow streetlamps which shine into the garden, so maintaining dark adaption of my eyes is almost impossible. Combining this with the physical struggle to carry my 300p Dob from its basement storage position into the garden, finally ‘clicked’ with me 18 months ago and I sold it to a much younger enthusiast. During the lockdown and continuing pandemic, my wife has been very tolerant and encouraged me to keep my favoured astro equipment in a corner of the lounge ready to carry out into the garden whenever clear skies are forecast. So I now mostly use my refractor on the GoTo mount, controlled by open source software on a Raspberry Pi (like the ASIair but DIY) and I mix a bit of EAA (Electronically Assisted Astronomy) at the time of observation with storing the captured images for later processing, more like Astrophotography. So an astro-camera has replaced my eye at the eyepiece, and I observe and control on an iPad or laptop at the telescope in reasonable weather or indoors when it’s colder. I keep the stored images for later examination and processing on cloudy nights.

During the Mars opposition and Jupiter and Saturn sessions earlier in the year, I mounted my SkyMax 150 on the EQ/AZ5 GoTo. I have to say that this combination really was at my weight limit for ‘grab & go’. The instant images were initially disappointing due to the turbulence in the atmosphere and the thermal currents inside the Maksutov, but two minute video captures provided good material for subsequent processing to tease out the detail.

Final word on ‘GoTo’. If you have a fixed mount (such as on a pier) and therefore precise alignment, then GoTo can be pretty accurate for visual observing. But with grab and go, levelling the mount and polar aligning with a conventional polarscope on an EQ mount can be tedious and back breaking. However, with an astro camera connected to some open source software, polar alignment and platesolving compensate for any small alignment errors, and GoTo really is GoTo! In the case of my SkyMax, I use a guidescope and camera to carry out the polar alignment and the GoTo functions to find the target although afterwards the mount simply tracks without auto guiding corrections.