catburglar

Here's where it all started- Arp 1 (NGC2857)..I don't think we've seen this one in the thread so far and I wonder why?

Arps 1-6 are in the section "Low surface brightness" . This example looks like a perfectly normal face on spiral galaxy (Type: SA)- most out of place in an atlas of peculiar galaxies. Whilst there's nothing peculiar visually, Arp 1 is a LINER  (Low-Ionisation Narrow Emmision Line Regions) - part of a class of Low luminosity AGN's characterised by lower levels of OII ionisation than typical AGN's.

The two bright galaxies at lower left (NGC2854 & 2856) are unrelated to Arp 1 at just over half the distance (circa 120Mly) and just to complete the long distance leg of the journey- the two PGC galaxies marked on the zoomed in shot are around 10x more distant at 2.2 and 2.9 Gly.

I thought it might be interesting to compare my shot with the one from the catalogue- for anyone that's not sure, mine is on the right 😉 . Whilst the Palomar 200 inch clearly has the edge in resolution, it's still possible to see hints of the condensations in the spiral arms and the prominent bridge between the two spiral arms below the nucleus in my shot with altogether more modest equipment.

You could do this with an app on your tablet connecting to an ASI Air or Stellarmate…or alternatively you could use a laptop/mini pc to control the mount and camera and then  you’ve got a selection of applications you can use- Starlight Live or ASILive or available for SX ccd’s or ASI CMOS cameras. Sharpcap can also do live stacking for any camera supported by ASCOM…but it may only be the paid for version and not the free version. I use Jocular - developed by fellow SGL’er @Martin Meredith. It works a treat with my ASI290mm, and I’m sure would work well with the ASI224MC too but it can also work with lots of other branded cameras by picking up the images from a ‘watched’ folder.

I’m not sure what scope you’d be planning to use, but you’ll probably want to be running at F6 or so to increase the ‘speed’ of the system. So you may benefit from some sort of reducer - but with these small chip cameras you could get away with the 0.5x reducer that screws in to the nosepiece of the camera.

Have a look at the EEVA Observing Reports channel to see the sort of result you may expect to get.

On 26/02/2022 at 08:12, Mike JW said:

You chose a hard one for your first Arp. My first attempt was not worth posting. The low surface brightness of the galaxy really means it is best to wait until there is a transparent night to get the required contrast and then as you did go for at least 30 subs to reduce the noise.

Mike- Thanks for the comment. I think some of my ‘transparency’ issues may have been few on the corrector too- It looked pretty misty when I was packing up, so I’ll have another go next clear and calm night with the dew heater turned up a notch or two 😁.

It was the posts by you and Martin that got me interested in this- even though the images don’t look ‘pretty’ in the conventional sense- it’s a great opportunity to be able to detect and try to understand a little more about what’s in the FoV.

I’d like to have the option of colour primarily for the PN’s and clusters, but also to help delineate the different colours of stellar populations that the interactions between these galaxies often produce…but for now that’s not feasible with my current set up. However there’s lot’s more to find - even with an FoV of less than 0.5 degrees- so I won’t run out of things to observe.

5 minutes ago, Martin Meredith said:

BTW are you using your ASI via Jocular or via the watched folder?

Martin- I’m controlling the camera via jocular…it’s worked perfectly for the three sessions I’ve tried with it… It means I only have two programs running (SkyTools for planning / goto and Jocular for ‘observing’) so there’s less to go wrong during a session.

I was planning on getting an ultrastar, but the introduction of control for ASI cams into jocular made me rethink…I thought I could reduce the EFL of my scope to around 8-900mm which is a good match for the ASI at bin x2.
 

A very blustery night here in North Wales. Gusting winds meant that I was limited to 5sec exposures and even then ended up excluding approx 30% of the images from the stacks.

Arp 6 (NGC 2537)- The Bear Paw...a blue compact dwarf galaxy- type SBm. Regions of star formation 

Arp 337 (M82)- The nearest starburst galaxy at approx 12m light years. Just a hint of the outflows perpendicular to the disk in the stacked image on the left had side of the galaxy. Might try again with a h-alpha filter to see if I can capture these features.

Arp 210 (NGC 1569) - A dwarf galaxy irregular galaxy- with high rates of start formation. 

I removed the filter wheel today because it wasn't going to work but I didn't get the spacing right when i put everything back together and ended up imaging at approx 1 arcsec per pixel. I'll try again to reduce the spacing from the reducer so I can get a slightly wider FoV without introducing coma or vignetting. Jocular couldn't solve some of these fields- but at approx 18arcmin x 12 arcmin that's not surprising.

I recently picked up a copy of the Cambridge Photographic Atlas of Galaxies which has prompted me to get out and step off the beaten track of showpiece galaxies...

Here's my first dwarf galaxy- Arp 268 (Holmberg II) 11M light years away in Ursa Major. It's an iregular galaxy with some prominent star forming regions- most notably to the left of the triangle of bright stars in the centre of the field.

I'd tweaked my setup to see if I could get a filter wheel in the imaging train - which pushed out my spacing and gave even more focal ratio reduction but a bit more coma. In the end I didn't add any colour here because some light clouds/haze started to appear...Perhaps another day.

At present I’ve got a usable FoV of about 0.4 deg x 0.24 deg - but if I can sort out the tilt I think I’ll get a bit more width because the left side of the FoV shows minimal vignetting out to the edge and a few flats should hopefully sort it out. 
 

I could also reduce the spacing a little to bring it closer to 800mm fl, but I’ll still lose FoV and I won’t gain much from the increased sampling rate. 
 

I think what I have is quite usable if I can’t get it any better- so I’m nearly ready for galaxy season.

Been tinkering with my EEVA setup over the last few weeks- between storms.- trying out an F3.3 reducer with the ASI290 mini (bin x2) in a 10inch LX200. Current spacing seems to give a focal length of about 750mm instead of the native 2500mm and a sampling rate of 1.6 arcsec per pixel.I got a couple of hours tonight to get the backspacing and focus sorted...although I've still got a little bit of work to do on collimation and sorting out some tilt (vignetting/coma is a little excentric- more pronounced towards the lower right (although cropped in this image).

I chose to look at the Eskimo as a first target because it was well placed away from some local light pollution. I might look to add in a filter wheel to get some colour in the mix, but might have to sacrifice the zero image shift microfocuser or the backspacing will be too long.

2 minutes ago, stargazermanc said:

So you think the second image is the more accurate back focus distance?

I think so:

The C8 has a specified focal length of 2032mm so for a 0.63 reducer you'd expect to be somewhere around 2032*0.63=1280mm

The specs of the camera are 3.76micron pixels and 23.5mm x 17.5mm dimension for the imaging chip.

From the platesolved image (rearranging the formula pixel_scale=pixel_size*206.265/focal_length) gives focal_length=3.76*206.265/0.603=1286mm.

So that's pretty close to the target EFL.

I platesolved the middle image at 109.5mm spacing- it works out at 0.603 arcsec per pixel and an effective focal length of 1286mm which is almost exactly on spec for a 2032mm fl and 0.63 reducer- which should give an effective focal length of 1280.

Still not sure what's causing the dodgy star shapes.

I’ve just platesolved the images on astrometry.net:

the first image at 105mm spacing has a pixel scale of 0.596arcsec per pixel- which gives an effective focal length of around 1301mm.

the last image at 129mm has a scale of 0.638 arcsec per pixel which gives an effective focal length of 1215mm.

So the first one is closest to the spec of 0.63 reduction factor.

The other thing that’s odd with those images is that the coma appears to be pointing in the same direction (almost horizontally) across the entire image- if it was simply a spacing issue I’d expect the coma to be more radially symmetrical. But I’m sorry I don’t know what else might explain it. Could it be tilt- it's certainly much worse on the left side of the frame?

The optimum sampling frequency depends on your local seeing conditions…For seeing at 2” then you’d want to sample somewhere around 2/1.6= 1.25 arcsec per pixel and about 2.5 arcsec per pixel if you’ve got 4” seeing. 
 

I’d probably aim for the latter because with a relatively small aperture you want to maximise your SNR so you can see faint things and @ 2.5 arcsec per pixel your system is approx 4x faster than at 1.25. 

Field rotation (which is the issue for alt-az imaging) is independent of focal length. For any given ‘acceptable’ amount of field rotation the max exposure time increases as the object moves away from the N-S meridian and reduces as it gains altitude…There’s a table in the book Astrophotography on the go that does the calculations for observers at different latitudes…the take home is that in the UK you should be able to get 30sec exposures without appreciable field rotation in any direction below about 60degrees in altitude and 15second exposures up to about 80degrees.

I’d agree with Martin- the scope/camera combo will be significantly under sampled at about 4arcsec per pixel…so you might be better off looking at a smaller pixel CMOS camera like the ASI178 (probably bin x2) or the 183 if you want a larger FoV or the 290 which is about 1.5arcsec per pixel unbinned 

The OP asked 3 questions:

Has anyone done a side by side comparison of standard vs premium sob at the same aperture? I haven’t, but I’m pretty sure I know the answers to the other two questions (I would say that wouldn’t I 😁)

Is the cost premium worth it in respect of optical performance? For some yes and for some no…It’s a personal value judgement that each of us would make…Those that have made it will most likely not regret having done so because in addition to any optical performance gain they’ve probably also got a scope with much improved mechanics that makes the ownership and observing experience much more enjoyable- what’s not to like about that?

Are the optical differences immediately obvious? Probably not ‘at first glance’ but I’d suggest it depends on a number of factors beyond the scope optics- object type, seeing conditions, light pollution and observer skill and experience. But I’m sure there will be differences most likely towards the threshold of visibility because the law of diminishing returns applies in optics manufacturing as well…so that’ll be subtle planetary features at high magnification or perhaps low contrast DSO’s…

So in practice I think this boils down to how much am I prepared to spend? If I’m prepared to spend on premium optics I’ll almost certainly be able to justify it to myself and if I’m not then I can be satisfied that I’m not missing out on too much…
 

I’d like to dip my toes in the water of the the former group, but I’m comfortable with being in the latter.

I’ve used a TV 8-24 zoom and the one original version of the Nirvana’s in 4, 7 & 16mm FL. Other than the FoV there wasn’t much to choose in terms of image quality or viewing comfort.

The zoom was very convenient- much more so than the fixed FL eyepieces. In a tracking scope I didn’t miss the FoV and sold the Nirvana’s. I now rarely use the zoom however- preferring the Baader and Fujiyama orthoscopics for critical lunar and double star observing.

I’m not sure if you misunderstood my earlier post or if I’m confused by your references to Ekos and the disappearing panel.

Going back to you’re original question - I don’t think oaCapture supports DSLR’s…oaCapture is designed for rapid frame rate image capture using the video for Linux (V4L) driver model whereas Ekos uses the indi drivers which for DSLR’s are based on the gphoto library…

So just because your Nikon is supported in Ekos doesn’t mean it will work in oaCapture…there may be a way to get it working, but I gave up with my old Canon…

The floating / disappearing panel allows you to start the indi server and automatically connect to a camera (and any other device supported by indi) , but it won’t do anything to help with oaCapture - if that’s still what you are trying to do.

You can make the folder on the usb drive using your windows machine and then plug it in to the stellarmate and then just tell Ekos to store them on the usb drive… you don’t need to use the terminal.

If you do want to do it on the stellarmate you can do it using the  built in file manager application or the terminal…

I don’t have a Stellarmate to check- but if you plug in the usb drive, open a terminal and type df -h and press enter that should list all of the drives and should show where the usb drive is attached…there’ll be a line that starts something like  /dev/sda… the last part of that line tells you where the usb drive is in the folder structure…in my case it /media/astroberry/Sandisk …(Note Sandisk is the volume label I gave to the disk in windows)

To create a folder called pics on the drive I would type:

mkdir /media/astroberry/Sandisk/pics

note- it’s case sensitive.

I think the floating tab that Elp refers to is shown when you connect to the pi from a web browser if you use a VNC viewer application to connect to the pi then you don’t see it.
 

Ekos does allow you to automatically load the indi drivers when you start the indi server, but I think you have to start the indi server from the Ekos dialog…but I’ve not got access to my pi setup at present, so I may be missing something.

I’m not sure that DSLR’s use the same drivers in oaCapture which is based around V4L rather than gphoto that the indi DSLR drivers use. 
 

You may be able to get it to work, but I couldn’t get a canon DSLR working when it was fine in Ekos…

Does your OAG have a T-thread? You could get an SCT-T mount visual back, or alternatively a 2inch visual back like this: https://www.firstlightoptics.com/adapters/baader-click-lock-2-for-celestron-meade-sct.html

I’ve not done a comparison of 130mm vs 150mm aperture but I don’t think you’ll notice a big difference in light grasp between them.

If I was in your position I think I’d definitely go for the 8 inch Evo. 

I started meteor detection using the article from popastro- as a guide. The loft  mounted yagi gave good detection of echoes from Graves (I’m located in North Wales) and I didn’t have too many problems with interference.

I did also get detection software working on a raspberry pi using echoes meter or detection software (https://sourceforge.net/projects/echoes/)

I haven’t been running it for a little while, but you should have some fun getting it up and running.

I’ve used Meade and Celestron SCT’s and Maks over a number of years (although never done a side by side test). I don’t think there’s much to choose between the optics…The electronics of the Celestron mount seem to be more favoured, although I’ve not had any problems with my Meade kit either…but I note you intend to use a manual -push to- mount, so the electronics are not a factor…

I’ve had each size of ETX at one time or another- the optics have always been great…Your ETX125 would make a great WL solar scope with a front mounted filter rather than a Herschel wedge.

My current 90mm OTA, mounted on and SW Heritage Virtuoso tabletop mount and with a Baader Astrosolar film from mounted filter is my white lite solar setup. Ready in 2mins, with no cool-down issues and good enough (although not perfect) tracking simply by eyeballing where north is.

I always found the goto accuracy a bit temperamental on the ETX’s (I had the older generation- I’ve no experience with the newer observer models), but you could probably align it at night and then park it and move it indoors. As long as you eyeball the home position reasonably you’d probably get tracking as good as the heritage when you unpark it in daylight.

I mostly use SkyTools4 visual (https://www.skyhound.com/skytools_visual.html) - it’s got the ability to create lists of objects you want to observe -e.g Hershel 400, or all planetary nebulae brighter than mag 15 etc. In a list like this, not all will be visible on any given night, but you can then create a plan that filters the list to those likely to be visible given your location, scope, the moon phase, and the time period you wish to observe…It’s got great charts for star hopping, but can also control a GoTo/push to scope if you get the real time add on..In which case you also get the ability to use a SkyTour mode, which turns the plan into an interactive observing session…It also allows you to log observations, find dates/times of events e.g GRS transits or shadow transits at Jupiter. It’s only available as a windows app, but I run it on a PCstick and RDP/VNC from an iPad or chromebook. It’s relatively expensive at $140, but it does the lot for me…