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New RASA 11, Ursa Major I Dwarf galaxy hunt not very successful


symmetal

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First time last week to use the new RASA 11 for an extended period. Thought I'd try the ASI6200MM full frame camera with a luminance filter for deep sky hunting. Very happy with the star shapes out to the corners though the vignetting is quite severe. I think the 48mm adapter on the RASA 11, the largest one supplied, is a bit restrictive for full frame. Unable to get good flats despite several methods which all produced different results, none of which worked properly. On one occasion I forgot the A2 Huion flat panel was on top the scope and moved it to the home position. Panel lands on concrete, corner first which took a chunk out of the perspex and a crack across the panel face. 😬 Panel still working though and the crack is outside the viewed area.

I thought I'd try for Ursa Major I Dwarf, apparantly the third dimmest galaxy known. According to McConnachie's Properties of Dwarf Galaxies in the Local Group (2012) it has an apparent magnitude of 14.4 and a radius containing half the galaxy's light of 11.3 arcmin. The mean surface brightness within this area is 28.8 mag/arcsec^2.

Here's around 3.5 hours of 60 sec exposures with no moon and I was disappointed with the result. Not even any IFN. Annotation checks showed nothing but a couple of galaxies near the edge. Must be a contender for the most boring picture ever. :icon_mrgreen: I've marked approximately where the galaxy should be. I've uploaded the APP stack here if anyone wants a go at revealing anything. You'll have to deal with the odd gradients though due to poor flat calibration. It's 240MB big. No visual images of the galaxy exist AFAIK not even from Hubble. At the moment that's still true. 😊

Ursa Major I Lum.fits

The SQM reading was 21.4 and I was swamping the read noise by 5 by the sky background noise at around 10s exposure but I'd be wasting over half the imaging time just downloading and get TB of data, so used 60s as a compromise accepting all the blown brighter stars.

132745205_UrsaMajorIRASA11Lum.thumb.png.07874f7111f485d3b18685f70a1d6efc.png

139575330_UrsaMajorIannotated.png.930c46d44076c6fff0bc9ea6fac14458.png

I did start with a couple of hours on NGC147 to see if I could resolve the star streams that @wimvb was looking for, but the Moon was too close to show anything.

The ASI2600MC is showing rather misshapen stars due to the spacing not being correct. I've ordered a set of 10 M48 stainless steel spacing rings from 0.1mm to 1mm via AliExpress which should be here soon. Spacing is very critical.

Alan

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21 minutes ago, symmetal said:

First time last week to use the new RASA 11 for an extended period. Thought I'd try the ASI6200MM full frame camera with a luminance filter for deep sky hunting. Very happy with the star shapes out to the corners though the vignetting is quite severe. I think the 48mm adapter on the RASA 11, the largest one supplied, is a bit restrictive for full frame. Unable to get good flats despite several methods which all produced different results, none of which worked properly. On one occasion I forgot the A2 Huion flat panel was on top the scope and moved it to the home position. Panel lands on concrete, corner first which took a chunk out of the perspex and a crack across the panel face. 😬 Panel still working though and the crack is outside the viewed area.

I thought I'd try for Ursa Major I Dwarf, apparantly the third dimmest galaxy known. According to McConnachie's Properties of Dwarf Galaxies in the Local Group (2012) it has an apparent magnitude of 14.4 and a radius containing half the galaxy's light of 11.3 arcmin. The mean surface brightness within this area is 28.8 mag/arcsec^2.

Here's around 3.5 hours of 60 sec exposures with no moon and I was disappointed with the result. Not even any IFN. Annotation checks showed nothing but a couple of galaxies near the edge. Must be a contender for the most boring picture ever. :icon_mrgreen: I've marked approximately where the galaxy should be. I've uploaded the APP stack here if anyone wants a go at revealing anything. You'll have to deal with the odd gradients though due to poor flat calibration. It's 240MB big. No visual images of the galaxy exist AFAIK not even from Hubble. At the moment that's still true. 😊

Ursa Major I Lum.fits 239.85 MB · 0 downloads

The SQM reading was 21.4 and I was swamping the read noise by 5 by the sky background noise at around 10s exposure but I'd be wasting over half the imaging time just downloading and get TB of data, so used 60s as a compromise accepting all the blown brighter stars.

132745205_UrsaMajorIRASA11Lum.thumb.png.07874f7111f485d3b18685f70a1d6efc.png

139575330_UrsaMajorIannotated.png.930c46d44076c6fff0bc9ea6fac14458.png

I did start with a couple of hours on NGC147 to see if I could resolve the star streams that @wimvb was looking for, but the Moon was too close to show anything.

The ASI2600MC is showing rather misshapen stars due to the spacing not being correct. I've ordered a set of 10 M48 stainless steel spacing rings from 0.1mm to 1mm via AliExpress which should be here soon. Spacing is very critical.

Alan

Hello,

Can you you send me the link to those spacers, am after some ideally in M54 size, but M48 would work….

Thanks 

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41 minutes ago, Stuart1971 said:

Hello,

Can you you send me the link to those spacers, am after some ideally in M54 size, but M48 would work….

Thanks 

M48 Spacer set at £17.09. They also do a M54 Spacer set at £19.29, free shipping to UK. Actually there are 9 in the set with 0.15mm included and no 0.7 or 0.9mm which is better.

I had previously ordered an M54 adapter from them which wasn't available in the UK, and was impressed with the service. Shipped the same day, and they keep you very up to date with emails on its shipping progress and it only took 10 days with free shipping. 

Alan

Edited by symmetal
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Taking a quick look on the file just out of curiosity and to my eye it looks like you do have IFN, but it appears to be at the edge of your flat calibration artifacts (the ring).

2022-12-04T19_03_37.png.bed7796a1e911e4bf5b3c7ac63ce6eb9.png

Right in the middle of the the bright flat ring are wispy somethings that i believe would be IFN. Its in pretty much the worst location from a gradient removal perspective but i think its workable with some careful gradient work.

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Did not find the galaxy, but IFN pops up in a cropped field of view with a very heavy stretch so safe to say the exposure is already quite deep and the galaxy is seriously elusive:

Symmetal-rasa-bkg-missinggalaxy.thumb.jpg.19406724401ad0d8f34f8c67998cb581.jpg

By the way, there is loads and loads of IFN and background galaxy stuff in the image for just 3.5 hours. In case you decide to sacrifice a couple more nights to it you'll get a killer IFN image out of it for sure, even if the galaxy stays hidden somewhere. Cropped feature from middle of the flat calibration ring artifact thingy (was easier to process the flaws out when cropped):

Symmetal-rasa-bkg-16-j.thumb.jpg.444a3089b25d86bc48c8a1d2f426088f.jpg

Never had a chance to play with a full frame RASA 11 shot so this was an experience, thank you for sharing!

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@ONIKKINEN Wow, thanks for processing that and showing the IFN. I was using Startools which I think has trouble stretching without a feature to focus on as it ends up stretching the noise. I'll have to try something else. I have AstroArt 8 and APP as well as PS. I used to use AA mainly for calibration but use APP now although it does take much longer to calibrate. I'm restacking now without flat calibration which might be easier to fix as the vignetting looks a standard shape falloff. 

I'm wondering as to whether the flats illumination is reflecting off the shiny red rim of the camera causing the bright ring that dominates the flat calib version. I'll try 3D printing a black cover to fit over the camera to hopefully improve that. PLA+ isn't available in matt finish, only PLA, which is too weak to work with, so I'll have to spray paint the PLA+ gloss version.

I'll post the no flat calibration version when it's done which you may have more success with.

I was feeling quite dejected with the poor result I got for all that expense, but you have shown that it gives good results if you process it properly. 😊

Bright stars near the edge of full frame are a bit flarey, but not like the horrible asymmetric flares I was getting all over with the RASA 8.

Alan

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4 minutes ago, symmetal said:

@ONIKKINEN I'm wondering as to whether the flats illumination is reflecting off the shiny red rim of the camera causing the bright ring that dominates the flat calib version. I'll try 3D printing a black cover to fit over the camera to hopefully improve that. PLA+ isn't available in matt finish, only PLA, which is too weak to work with, so I'll have to spray paint the PLA+ gloss version.

Hmm, maybe, but not qualified to say as have not owned a RASA type scope before. But the aberration itself looks familiar as failed newtonian flats also looked like that but its been a number of years since mine failed so bad as to cause that as i have fixed most of the issues. But when i was taking flats the next day or used previous flats they looked like that with a bright ring and some weird things going on on some of the corners. Is it possible something mechanical has failed like mirror locks, focusers etc? Probably not as the RASA11 is not exactly entry level kit and one would hope its mechanically stable.

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Unlike Cass II (And XXX), UMa I dSph consists only of individual stars, no dust or fuzzy patch. The scattered stars give it the absurdly low surface brightness of 28.8 Mag/arcsec2. Even with a RASA you will need many hours to drown the sky brightness if it is at 21.4 Mag/arcsec2. But fortunately, the stars that make up the dwarf satellite are easier to image.

https://www.astrobin.com/0gvm5z/B/

My guess is that they are in your image. I'll have a look.

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Now I know why I've been struggling to find a reference image to help me look round Alans original image. It seems that Wim's earlier work is the reference!

Certainly looks like something of it has been captured in the stretched/cropped rendition.

What a great project to undertake. There are no failures in such endeavours, just great scenery :)

Edited by Paul M
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Odd with so much vignetting. I do not get that with my RASA 8s and ASI2600. In any case, if you do not want that may subs to stack, why not set the gain to 0 and take longer exposures? (assuming you use gain 100 now)

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@wimvb Oops, I forgot you have already imaged this galaxy, and I commented too. :redface:. Your colour image seems to make it easier to pick out the fainter stars. Where did you get the information detailing the invidual known stars?.

Here's the stack without flat calibration. There's 380 ADU difference between the centre and the corners.

Ursa Major I no flats.fits

4 minutes ago, gorann said:

Odd with so much vignetting. I do not get that with my RASA 8s and ASI2600. In any case, if you do not want that may subs to stack, why not set the gain to 0 and take longer exposures? (assuming you use gain 100 now)

If you crop it to APS-C size I suppose the vignetting isn't too bad. Using gain 0 I'd lose the HCG lower read noise, though with long enough exposures that won't matter. Gain 0 is also still higher than unity gain so you don't throw away any photons. It's worth considering for luminance at least. Thanks.

Alan

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PS. I now did like @ONIKKINEN and cropped out a bit and stretched it (in PS). There is definitively some IFN around. It also suggested to me that you could use longer exposures. No problem with burned out star cores, if that is your worry. Those could easily be fixed in processing since you have so much halo with colour info that you could use for star colour. In RGB I go for 2-3 min subs and gain 100 for most objects.

Cheers, Göran

Ursa Major I Lum GN copy.jpg

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I guess I was doing it that hard way. I plate solve one of @ONIKKINEN processings in ASTAP (for no particular reason) and started identifying stars from Wim's reference.

Looks like I can stop now :)  By the way Wim, how did you get the positions/overlay for this objects members?

image.png.c956c131856e5dbc9e4de8db1d819444.png

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33 minutes ago, symmetal said:

Where did you get the information detailing the invidual known stars?.

& @Paul M, Strasbourg, the Vizier catalogues. It takes a bit of detective work, and clouds help 😁

Edited by wimvb
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Btw, Alan, if you want to go for the really faint stuff, and pixel scale isn't your first concern, you could experiment with bin 2x2 at 0 gain. Full well is four times higher, while read noise is only two times higher. In this mode, you may be able to capture faint signal while keeping the stars under control. Mind you, the pixel scale will be 2.5"/pixel (now 1.25"/pixel), and the fainter stars may look a bit blocky. But the file size will only be 1/4 and downloading will be faster. Definitely something to consider if you need long integration times.

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41 minutes ago, wimvb said:

Btw, Alan, if you want to go for the really faint stuff, and pixel scale isn't your first concern, you could experiment with bin 2x2 at 0 gain. Full well is four times higher, while read noise is only two times higher. In this mode, you may be able to capture faint signal while keeping the stars under control. Mind you, the pixel scale will be 2.5"/pixel (now 1.25"/pixel), and the fainter stars may look a bit blocky. But the file size will only be 1/4 and downloading will be faster. Definitely something to consider if you need long integration times.

That's a good point. The 6200 download times are twice that of the 2600. The image I posted was reduced to 50% in PS anyway to make it look 'better' so I could do it in the camera and speed things up. PS uses bilinear interpretation rather than just combining pixels so that may make a noticeable difference. There are a few green hours on some days expected this week although the Moon is full. I can do comparison tests on different gains and binning though. 🙂

Alan

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4 hours ago, ONIKKINEN said:

Hmm, maybe, but not qualified to say as have not owned a RASA type scope before. But the aberration itself looks familiar as failed newtonian flats also looked like that but its been a number of years since mine failed so bad as to cause that as i have fixed most of the issues. But when i was taking flats the next day or used previous flats they looked like that with a bright ring and some weird things going on on some of the corners. Is it possible something mechanical has failed like mirror locks, focusers etc? Probably not as the RASA11 is not exactly entry level kit and one would hope its mechanically stable.

The RASA does seem very stable optical wise. I was concerned that mirror flop might give focus/tilt problems like the first RASA 11 version, after a flip, but that has been fixed with the V2. All corner stars still round and in focus, a re-focus ending up in the same position after a flip. Unlike the V1 there are also no mirror locks on the V2 as they aren't needed which is great. There is a slight image shift when the focuser changes direction of about 10 pixels but the focus itself doesn't appear to be affected.

2 hours ago, gorann said:

PS2. As I understand it you will not lose anything from using gain 0 instead of gain 100. You just have to stretch much more in processing.

Yes, you're right Göran, the gain is applied either at the camera or later in processing. Apart from increased read noise at gain 0, but that gets swamped pretty quickly anyway so won't really be an issue, particularly if I bin 2x2 in the camera.

Thanks for your processing showing the IFN like @ONIKKINEN has done too. Must improve my processing. 😁

Alan

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I forgot to congratulate you on now having a set up that is virtually unbeatable when it comes to collecting photons from faint objects!

If I get the math right it will collect as much as my dual-RASA8 rig with ASI2600 since you combine your RASA11 with the ASI6200. (using a RASA11 with an ASI2600 would be a waste of photons).

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I have the RASA 11 as well, which I use with a full frame ASI2400MC Pro.

I don't use the Celestron image train, but have the Baader UFC. On the one hand this is much wider than M48 and removes vignetting, but on the other hand I use the UFC filter changer with 2" filters, which adds back quite strong vignetting, despite being very close to the camera!  I find that mostly my flats correct everything (I use an Aurora flat panel). Sometimes it's not so good with the IDAS NBZ filter, particularly when the moon is out and gradients are around. 

Great that your stars are good. Mine were OK to start with, but not good enough. I use an (expensive!) Octopi tilt / backspace adapter to manage fine adjustments to tilt and backspacing. Having used a Hyperstar previously, I sort of knew I would need this so actually bought it at the same time as the RASA.

I find the RASA 11 picks up dust within minutes. Shooting broadband (which I mostly focus on, and I think the RASA is best at) I very rarely go above 1.5 hours of data (mostly 30 second exposures, which already saturate bright stars).  It's a brilliant tool for our limited clear sky time!

PS I also slewed to zero position with my panel on top - fortunately I noticed in time and caught it!

some of my stuff here if you're interested - https://www.astrobin.com/users/Fegato/

Edited by Fegato
added astrobin link
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@Fegato Thanks for your information about your RASA11. Most helpful. I thought the Celestron M48 fitting would lead to full-frame vignetting. I'll take a look at the Baader UFC system. If my flat frames worked I wouldn't have been too worried. My A4 Huion panel was fine with the RASA8 but the A2 one may not have such even illumination. I'll try it rotated 180 degrees and see if the flats problem rotates with it. I'll get an Aurora or similar if that's the case.

I was surprised that the 6200 gave good stars on first try while the 2600 didn't. It looks like the spacing needs to be within 0.1mm or so. My current smallest spacer is 0.3mm but that causes issues in the other direction if used. I found the filter drawer on the 6200 ended up under my cable routing so I thought I'd just rotate the camera 180 degrees. Not good as poor corner stars resulted. Put it back again and all good so I've had to change the cable routing. Looks like the good stars was mainly luck. :D

I assume you use the HCG mode on at gain 140 for your camera. I may try 0 gain for luminance as I mentioned above just to avoid spending more time downloading than imaging. 🙂

You have a great collection of images on your site. 😀

Alan

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Thanks!  

Yes I use gain 140. I tried zero gain briefly, but the exposure time penalty didn't seem worth it to me given how limited the clear skies are here (I have worked out a range of median ADU values to swamp read noise, ranging x3 to x10, and use that to determine reasonable exposures, although the light gathering is so fast that I often exceed x10 by a long way).

I did use an A3 Huion panel with my 8 Edge, but decided to go for the Aurora with the RASA. You can get dark filters for it which allow for flexibility on flat exposures. I think many people have found that a flat exposure measured in seconds is preferable to the very very short exposures you get with a bright panel.

Note that with the Baader UFC you can get a vari-lock extendable adapter which covers 15-20mm, which is very useful for sorting out back focus distance, although in some ways it's a bit cumbersome, as you rotate the camera behind it as you move it. The critical focus zone is measured in microns - even tighter for you with your smaller pixels. I have my vari-lock fixed now, and just adjust the Octopi if I need to. I don't rotate the camera at all - too much risk of introducing tilt. If I need more width, I shoot 2 panels - it's so fast, that's the best thing to do!  

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I calibrated with two flats, one as before and one with the Huion panel rotated 180. They are very different so the panel looks to be the culprit. As the panel is stood vertically against the dew shield they are not looking at the same panel area, hence not looking similar, but just rotated.

427452141_Flatpaneloriginalorientation0_5s.png.22f5fca90c11c0ff4848fd0914f1ba67.png

1668334980_Flatpanelrotated1800_5s.png.5887293bdaa5b4b7a612e3b297a4d394.png 

I see that EL panels are cheaper on ebay compared to the Aurora ones. Aurora 315mm circular panel with mains inverter is £249 from Widescreen Centre, while an A2 panel from ebay with mains inverter is £160. Is it worth going for the cheaper one, or do you think the Aurora ones are selected for more even illumination?

@Fegato Thanks for the extra info. I used 3 sheets of 0.9ND filter on the light panel totaling 9 stops which allowed 0.5s flats exposure, but they were similar to the results with no ND filter and 0.5mS exposures. I think the earlier CMOS cameras had issues with short exposures, compared to the newer ones.

I agree that it's not worth rotating the camera. Luckily, if I remove the camera and put it back in the same orientation even if having to loosen off the Celestron adapter plate to position it accurately, it does give the same results each time which is good. So adding thin spacers to get the right star shapes for the 2600 shouldn't be a problem, I hope.

Alan

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