The "No EQ" DSO Challenge!

[The Admiral]

As you say Neil, there is certainly a lot going on. If one Googles 'Rosette' images the amount of nebula that is revealed in long exposure Ha images is staggering. For example, 'Christmas Park' at http://deepskycolors.com/deepspace.html, or here http://www.caelumobservatory.com/gallery/rosetteabtp.shtml.

Ian

[Stub Mandrel]

That's chap's got an Ha filter and he's going to use it!

[Filroden]

58 minutes ago, The Admiral said:

For example, 'Christmas Park' at http://deepskycolors.com/deepspace.html,

Wow, those images are high contrast! I feel like someone stretched my eyes until I could see into UV and IR!!

[Stub Mandrel]

It's interesting, my photo is obviously not in they same class, but if you look at the light clouds in it they are pretty well correlated to his red clouds, even if there is a lot less detail. I've redone the pic reversing the effort I put in to 'de-redding' the background.

Edited January 25, 2017 by Stub Mandrel

[The Admiral]

That's true* Neil, and I'm not convinced that the Cone cannot be made out in your image either. At least, with an eye of faith. There is a dark 'blob' where it should be!

Ian

*Sorry, I didn't specifically mean the comparison of class

Edited January 25, 2017 by The Admiral

[Stub Mandrel]

32 minutes ago, The Admiral said:

There is a dark 'blob' where it should be!

About three pixels across!

[The Admiral]

That it may be, but....

Ian

[Filroden]

I think we're taking the "size isn't everything" to extremes! Guess we could call it the cone nebula?

[Stub Mandrel]

:-)

That's pretty much where I thought it was. It's a bit like the tiny 'antenna' on the horsehead's nose, I was able to process it hard enough to get it to show, but the rest of the image was totally destroyed in the process!

The rosette will be my next target.

[Nigel G]

I had a go at the cone neb, had issues throughout the session, focus was bad, had to re focus 3 times, and it had shifted quite a bit. Tracking wasn't to good either. My mount tracks best to the west I have discovered.

I took around 80 x 45s and had to dump 50% then used only 60% of the remaining subs, need to start again on this one, get a fresh bunch of subs.

This is only around 25x45s Modified 1200d + CLS filter, 150p, DSS & ST. Very noisy due to lack of subs so large amounts of processing.

Nige.

[Filroden]

1 hour ago, Nigel G said:

My mount tracks best to the west I have discovered.

Have you tried switching your balance for the other side of the meridian?

What is causing the focus to change? Is it just chNgng temperature?

As you say, your image suffers for noise because of the lack of subs but its unmistakably the Cone/Christmas Tree. The colours look so good with the modded camera! 

It fits the frame really well so a worthy target to try again another night without the focusing issues! 

[The Admiral]

On 26/01/2017 at 16:42, Nigel G said:

Tracking wasn't to good either. My mount tracks best to the west I have discovered.

This is only around 25x45s Modified 1200d + CLS filter, 150p, DSS & ST. Very noisy due to lack of subs so large amounts of processing.

Well I think you've squeezed out a decent image there Nige, considering the distinct lack of data. Certainly very identifiable. It'll be interesting to see what a decent number of subs with your modded camera will produce.

I've also found that my mount micro-tracks better towards the west than the south. I put it down to the fact that towards the west both altitude and azimuth are increasing steadily and both drives are working continuously, but towards the south the altitude isn't changing much so that drive seems to less frequently operate (bearing in mind it's a stepper type motor so the drive will make discrete jumps), and I find that it seems to play catch-up with consequent streaking whilst it does. I also wonder whether the grease gets a lot stiffer in this very cold weather. Who knows. I've also found that the macro-tracking (i.e. keeping the object centred) has not been at its best of late (when I've been imaging towards the south), even though I've tried to keep the 2 alignment stars well either side of south and separated by approx. 90°. Certainly I wouldn't say the tracking is consistent, but I'm not really sure what causes it.

Ian

EDIT. I meant towards the East, not the West. Doh!

Edited January 27, 2017 by The Admiral

[Nigel G]

Not sure what caused the focus to keep shifting, don't think it was the temperature, it has gone out so much the focuser must have been moving in slowly, I checked the screws on the focuser which were ok, I have nipped them up a fraction anyway.

I can't balance my scope and camera, its always top heavy, the dove tail is to short, to add counter weight to the bottom of the scope will add to much weight.

Hopefully I'll have a better session next clear night.

Nige.

[rotatux]

I also had another session yesterday at dinner time. It gets more and more confirmed that the SLT tracks better (to east at least) when back heavy: I can steadily achieve good keep rates up to 20-25 seconds (30s seems impossible). Maybe it was designed for refractors / cassegrains type scopes -- focal plane and eyepiece/optics at the back, since I got it with a MAK.

I first had a quick try at M1 before it got out of my view, but could not frame it adequately -- I just can't remember what optical direction gives each command arrow, apart the axis, so with 5s framing subs I can't manage to correctly shift the subject in the image, given no reference stars and subject deeply burried in LP. Gave up this time on this one.

Than had a first test at cone nebula too, about 25-40 x 20s subs. Will process later to check what comes.

During few past days I had a process at my first rosette test. It's interesting because with only 14 x 30s subs (at <30% keep rate!) it shows some color differenciation in the nebula just out of sensor. I want to show you and get thoughts here about a matter on star colors, but no more Internet at home (I'm switching providers which will take a few days) so no more B-V color calibration and posting will have to wait.

Anyway, given what I already got I decided to have a true go at it yesterday. So now there's also ~120x20s of Rosette waiting for a processing of mine (will take longer).

[rotatux]

16 hours ago, Nigel G said:

I can't balance my scope and camera, its always top heavy, the dove tail is to short, to add counter weight to the bottom of the scope will add to much weight.

If you can't add weight at the back, you could try removing some at the top: attach a few (helium) balloons to the finder, for example.

Er, I admit it could look like a joke but it might work...

[rotatux]

A good surprise, I already got back my Internet at home, so here the image I talked about.

It's 7 good + 7 average lights x 30s x 2500iso and 30 NG darks (from another subject in the same session) usual Alt-Az train + my new TS UHC filter. Ignore the noise...

This is without any color calibration, direct colormap from the sensor. Usually I get really weird star colors and a B-V calibration is required. But with the new filter I think the colors are already very good. I had a doubt when seeing those very red stars but I checked their B-V index and the color is plain justified (there's one at 2.30 !).

Just the stars of the cluster are cyan when they should be pale blue, and the brighest of the cluster should be orange rather than white (or whatever). Means there's too much green ? I can't believe it, where would it come from and why only those stars.

I also perceive a noticeable color transition from red around to blue or grey in the center, which I think is nice, if not physically real. A thing I rarely notice in most other shots.

However I find the stars are too saturated at 30s x 2500iso, that's why I only did 20s for the real session. I just tried a quick BV but not good, most stars are good but the nebula turns all red, loosing the center blue/grey. I hope the big stack will turn better.

Edited January 27, 2017 by rotatux
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[The Admiral]

That's pretty reasonable for only 7 minutes exposure Fabien. Looking forward to your 120 x 20s set. The transition from red to blue is, I think too, unreal, and your B-V calibration is probably giving you nearer to the truth. A lot of images one sees with red/blue are of course NB images with colour mapping. I wonder also whether you really need ISO2500, as you are reducing the DR significantly I feel. I used 1600 on my Rosette, and have used 400 on M42 and M45 where I wanted to retain as much information in the bright areas/stars.

Ian

[Filroden]

The Rosette is incredibly bright in red. I believe it has increasing amounts of OIII as you move towards its heart, so the colour goes from a purer red fringe, to a weaker red/orange as you move towards the centre. There are very few examples of emission/reflection nebula that show strong green/blue from OIII - the core of M42 being one of them.

Given the short number of subs it's hard to tell too much about colour balance. However, my instinct tells me the colour balance is towards the cool/blue and probably needs to be be warmer/redder. As you say, 12 Mon is a K0 III star so should be yellow/orange in colour. When I enlarge your image, I can see this star does have a different colour to the other bright stars in the core but the blue cast is masking it at the moment.

I'm sure once you've processed the big stack it will be much easier to process and work on the colour calibration. I find that once the basics fall into place (for me that's removing gradients and calibrating the colour) it becomes much easier to get a pleasing result.

[The Admiral]

I can understand why mounts do better when the 'scope isn't perfectly balanced, but I've never quite understood why it matters whether it is front heavy or back heavy, for Alt-Az mounts at least. The gears will either be pushing up or pulling down according to the balance situation, but either way they will be under constant load and not give rise to backlash. So why is there this perceived difference?

Ian

[mxgallagher]

Having been inspired by what I've seen here, and eventually getting a clear night. I dusted off the t-ring adapter for the 250 goto dob and had a stab at m31

Just over 7mins worth of 10s subs at 3200iso on an eos 70d

Not edited much, just had a quick play with the levels in gimp

[rotatux]

13 hours ago, mxgallagher said:

Not edited much, just had a quick play with the levels in gimp

I feel there's a lot more detail than what appears, so it's a good shot ! And the same time the core is quite saturated... Typical of my own historic stretches with Gimp levels You could try using Color->Curves rather than ->Levels so that you can avoid to stretch the brighest parts and only affect low brightness parts.

If you feel like it, you could also try 16+-bit aware imaging software, starting with Gimp 2.9 since you are a Gimp user -- though I have yet to try it myself. This will help recovering faint details.

[Filroden]

13 hours ago, mxgallagher said:

Having been inspired by what I've seen here, and eventually getting a clear night. I dusted off the t-ring adapter for the 250 goto dob and had a stab at m31

Just over 7mins worth of 10s subs at 3200iso on an eos 70d

Not edited much, just had a quick play with the levels in gimp

I'd be proud of that with 7m of data! You have a colour cast which I think could be corrected by slightly raising blue in levels or pulling back on red a little. However, with some careful stretching using lots of small curves adjustments rather than levels (so you can pin the highlights) and I think you'll be amazed. There is a lot of fine detail leading into the core.

You've probably picked a very difficult target for your field of view. M31 has an incredibly bright core and the fainter detail extends quite far. You may be better finding a bright target that will fit more within your field of view. M42 is a good target, especially at 10s subs as it also has a bright core. The Flame Nebula might also be good, but the nearby bright star can cause a lot of flare. The Pacman Nebula would fit nicely I think but is better with a camera with a very good red response (I don't know if the 70d is similar to the 60d but you'd get something, but not everything).

[rotatux]

Just to not let unfollowed my horrible Alnitak shot proviously shown, this is my 2nd try at Alnitak and its nebula friends. Much better I hope, though still not on the par.

Capture: 101 good of 123 lights x 25s x 2500iso, 30 NG darks, Olympus E-PM1 with Skywatcher 130PDS on Celestron Nexstar SLT, TS-UHC filter.

Thanks to much more subs, there's much more detail.

However I had difficulty with color calibration: I had to revert to the semi-manual version, the full automatic gave green stars rather than blue. Again I suspect the UHC filter to be the cause, just as if it was ripping out some information essential to the calibration But I've no idea what yet. On my calibrated displays this results in white/grey rather than blue stars, including Alnitak itself (and some nebula too), but I'm happy I eventually managed to avoid getting green stars.

Gives me a headache: On one hand the filter would allow me up to at least 30s subs (if not limited by mount accuracy) and catch many targets, while without it I am limited to 8-10s subs by light pollution and unable to catch Rosette or Horse Head. On the other hand the filter seriously reduces Regim's ability to auto-calibrate colors. And I love good (correctly) colored stars...

Edited January 30, 2017 by rotatux
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[Filroden]

6 minutes ago, rotatux said:

I had to revert to the semi-manual version, the full automatic gave green stars rather than blue. Again I suspect the UHC filter to be the cause, just as if it was ripping out some information essential to the calibration

UHC filters remove most of the green/yellow wavelengths (see the image below for an example). This probably affects calibration, particularly of the yellow stars. You may first have to manually rebalance the image and then run a more automated calibration.

 

[rotatux]

On 27/1/2017 at 22:22, The Admiral said:

That's pretty reasonable for only 7 minutes exposure Fabien. Looking forward to your 120 x 20s set. The transition from red to blue is, I think too, unreal, and your B-V calibration is probably giving you nearer to the truth. A lot of images one sees with red/blue are of course NB images with colour mapping.

Thanks. I hoped some shots I've seen had real colors rather than mapped, but maybe not after all. As Ken reminds us, the Rosette is very bright in red. Just wonder then why the sensor captured 2 different colors.

On 27/1/2017 at 22:22, The Admiral said:

I wonder also whether you really need ISO2500, as you are reducing the DR significantly I feel. I used 1600 on my Rosette, and have used 400 on M42 and M45 where I wanted to retain as much information in the bright areas/stars.

That's a matter of camera. Actually I've tested 800, 1000, 1250, and 1600. With only 12-bits depth and 30% quantum efficiency (taken from sensorgen), most if not all deep sky (not clusters) subjects' data just happens to be below the minimum first value above zero with short exposures. Said otherwise, lower ISOs just don't give me enough data to stretch within my exposure limits. So I need to amplify more than all of you 14-bits sensors owners, and 2500 is my camera's maximum of analog amplification (3200 and above is digital). Would be different if my mount accepted to do 40-50s subs

Good news is my read noise is about the same at every iso, so I prefer to always use the same ISO level and vary the length and number of subs. Bad news is my noise is quite high so I need about 80-100 subs to tame it.

BTW don't be fooled by the DR such as indicated at sensorgen.info, it's for a single shot: If you consider stacking removes the noise, you get full DR for any analog-scaled ISO from a sensor-only point of view; What matters then is to avoid saturation of your subject wanted parts (you may saturate some subs for HDR to get faint parts), and hence match the subject brightness range to your camera by adapting the exposure. It's good if you have the choice to adapt the exposure, to lower ISO in addition to varying sub length, I don't think I have that choice.