Open clusters with live RGB combination

[Martin Meredith]

Here's a selection of open clusters I've been observing over the last two nights, mainly in the Orion and Cassiopeia regions. All were produced at the scope using StarlightLive's live spectral combination with Baader RGB filters attached to a mono Lodestar X2 camera on an 8" f/4 Newt, mounted in alt-az, using a motorised filter wheel controlled from StarlightLive. I use short subs (5 or 10s) to minimise saturation (to preserve colours), and brightness mapping is linear (again, to preserve colours). Saturation is set to 1 and hue to 0 in StarlightLive i.e., no modifications from the defaults. I've found in the past that these settings produce realistic colours.

I enjoy exploring as many OCs in one session as possible, both to contrast the different types/colours, and because occasionally I find one that stands out. I actually explored as many as 25 over the two sessions but not all are visually appealing. Open clusters look best when there is plenty of space around them and it can be a challenge to find interesting-looking clusters when using a small sensor (at medium focal lengths at least). For instance, M46 (below) fills the view and might not be very interesting if it were not for the planetary nebula. 

Nearby M47 and M50 are similarly uninspiring. However, M67 in Cancer has a lot going on, so much that I'll give it a separate entry later in this thread.

The ones I've tended to go for are either sparse and compact (and close), or dense and faint (and distant); in both cases these occupy 10' or less.
Here's the so-called "37" cluster, NGC 2169 in northern Orion, at a distance of over 3000 light years. This is a young cluster which some catalogues claim has only 3 members! In this case I suppose the orange stars are just convenient interlopers that help make up the number "7". Quite apart from the asterism, there is a great variety of spectral types on offer in this field, from the M type star to the upper left of the cluster to the K at the apex of the "7", the G-type at the left of the "3" and the several blue B types. (OK, so I've been re-reading James Kaler's excellent Stars and their Spectra recently ).

Not far away is a very different kind of cluster, NGC 2141, 13000 LYs away. The cluster is said to have 385 members and is more than 100 times as old as NGC 2169. I have to say that  I really like this kind of 'gritty' cluster. It reminds me a bit of the view of M46 in a small scope.

Unfortunately, I can't fit the Double Cluster into one field. But there are some other double clusters out there. This is the pair NGC 7790 (left) and NGC 7788 a couple of degrees away from Caph in Cassiopeia. Actually, following the line joining the two clusters to the left one comes to Berkeley 58, the three being equally-spaced. These two clusters are reported to be at around the same distance (~9000 LYs).

Another less-balanced pairing I came across is NGC 2194 (right) and Skiff J0614+12.9 in northern Orion, both at a distance of 10-12000 LYs. The bright red stars at the top are artefacts produced due to field rotation between subs (by the time the G and B filters get to be combined, the view has rotated...).

NGC 559 is a small and fairly inconspicuous cluster in Cassiopeia. What I didn't realise was that it is on the edge of a dark nebula (LDN 1325/26), presenting a huge void at the lower left.

I think my favourite 'find' from last night was IC 166. This shows up as a patch of numerous faint red/orange stars not far from Segin (epsilon Cas). At nearly 16000 LYs, this is a very distant cluster lying behind a smattering of much closer stars. I get a real sense of perspective from this shot (perhaps aided by the timewarp look of the slightly elongated foreground stars!).

Thanks for looking

Martin

 

 

 

 

 

[elpajare]

Fantastic shots Martin

Are you explained in other place what scope/camera/software are you used?

Im very interested to know this and I can't find it.

[Martin Meredith]

Thanks elpajare. I'm using a Skywatcher Quattro 8" f/4 carbon tube model with a Starlight Express Lodestar X2 mono, a 7-position motorised filter wheel also from SX, all mounted on a Skywatcher AZ-Eq6 mount (in alt-az mode). Everything is controlled from Paul Shears' excellent  StarlightLive v3.2 software that I've been using now for nearly 3 years (attached a shot from an earlier version). I started out with a colour Lodestar but I prefer the colour rendition from the RGB filtering approach.

Saludos

Martin

[elpajare]

Thanks for your complete explanation. 

We are using the same scope.

Clusters pictures with RGB combination are a little more colorful than ones taken wit my color camera ( ATIK Infinity). I like it.

[Stu]

Wonderful post Martin, and excellent descriptions of all the objects. Is this a new development in terms of kit i.e. using the filter wheel? The results are amazing!

I don't think I've ever viewed M46, it is not well placed from my house so I'll have to give it a go!

[Martin Meredith]

Thanks Stu. Not so new, but what has really made the difference is switching from a manual to a USB filter wheel since I don't have to get up to change filters, and the change is really smooth and fast. With the manual there was always the chance of knocking the scope, although the software is quite forgiving... Its also fascinating to watch the image building up as the 3 filters are layered on top of each other. There's a moment when the final filter is applied and the cluster bursts into colour. And you never know with some of the less well-known clusters what you're going to get. 

M46 is one of my favourites in binoculars or a small scope where it really glitters. I think that's why I like the very faint clusters from the camera as they remind me of the visual experience.

Martin

[RobertI]

Really fine captures Martin, some interesting finds and great use of the colour filter wheel. You are demonstrating once again the power of EAA to the amatuer, even on open clusters, which have always been regarded as looking better visually than using EAA. Who would have thought the humble Lodestar would be producing 'realtime' colour images of that quality?

i'm wondering if the larger chipped Ultrastar plus a smaller scope might be a good combination for clusters, and might find more clusters which fit into the FOV? The colour version might also work well as sensitivity not required?

Would you use your mount in Eq mode for longer exposures (eg: of 30 seconds or more for galaxies and faint nebulae) or do you use Al-Az mode for all your EAA?

1 hour ago, Stu said:

Wonderful post Martin, and excellent descriptions of all the objects. Is this a new development in terms of kit i.e. using the filter wheel? The results are amazing!

I don't think I've ever viewed M46, it is not well placed from my house so I'll have to give it a go!

Stu, the use of the colour filterwheel for EAA has been growing in popularity and now seems to be an accepted form of EAA, at least there haven't been any major arguments about it recently that I have seen! I also have a colour USB filterwheel and Lodestar combo and was starting to get some nice results at the scope, but then house & job moves got in the way, but I will be hoping to to do increasingly more this year and posting the results here. Without wishing to derail the thread,  I see you have an AZEQ5 - how have you found it? i've been considering one but not many people have them yet. 

[Martin Meredith]

Thanks Rob.

So far I've always used my mount in alt-az mode because I setup before each session either at the front (south-facing) or back (north), and find it more convenient. I'd love to build an observatory one day but in the shorter term my plans are to start taking the scope a few tens of kms to darker skies. But on the question of exposure length, I can manage 30-60s at this FL (800mm) depending on which part of the sky I'm pointing at. I tend not to go above 30 as I prefer the more immediate approach, using stacking to reduce noise.

I think the range of clusters available to the Ultrastar would be marginally more with my scope but with a small scope/small pixel camera would be definitely worthwhile. Or a DLSR.

Even so, there's a lot that will fit with plenty of space around them. Here's a plot showing cluster diameter versus magnitude to give some idea how much there is out there of a given size. 

These are the only clusters with a magnitude specified in the Dias corpus, but there are an additional 1600+ that are listed (e.g. Berkeley, Collinder, Ruprecht, ...) and their mean diameter is about 15'. Indeed, 1200+ have diameters under 10'.

With modern star catalogues it will be possible to estimate an integrated magnitude for these 1600 cases. It's just a matter of doing some kind of weighted sum of magnitudes for all stars within the specified radius. Of course, they will not all be true members, but that isn't important as what we're interested in is the overall effect (unless there are a few very bright foreground interlopers that bias the estimate). 

Martin

[Stu]

2 hours ago, RobertI said:

Stu, the use of the colour filterwheel for EAA has been growing in popularity and now seems to be an accepted form of EAA, at least there haven't been any major arguments about it recently that I have seen! I also have a colour USB filterwheel and Lodestar combo and was starting to get some nice results at the scope, but then house & job moves got in the way, but I will be hoping to to do increasingly more this year and posting the results here. Without wishing to derail the thread,  I see you have an AZEQ5 - how have you found it? i've been considering one but not many people have them yet. 

Thanks Robert. Thank goodness is all I can say regarding the lack of arguments! Any form of the art of EAA is welcomed at SGL, let's just enjoy it and benefit from the amazing images!

Regarding the AZEQ5, I confess I've not really had the chance to use it much at all. Having had an AZEQ6 previously, it has both positive and negatives in comparison.

It definitely feels built to a cost and weight. Some of the fittings feel a lot less substantial than the 6, and the tripod is shorter and has thinner diameter lower legs. That said, its quoted load capacity is 10kg less so it is to be expected.

The design of the mount seems very well thought out, although it took me a while to work out some elements, like tightening the clutch on the alt axis, but it all works well.

The benefit of the 'diet' is that the mount is much more manageable than the 6. I made the change mainly because I have a fairly dodgy back, and wanted something I could more easily handle and potentially take out into the field. The 6, for me, was very much something I left permanently setup at home, but now I don't have a big 6" ED frac I don't need the load capacity and the 5 is much more suitable for my needs.

[Martin Meredith]

Due to collimation sensitivity I tend to leave my scope mounted and carry the mount + scope + one of the 5kg weights as a unit (only for very short distances mind!). The Az-Eq6 is quite a heavy beast and I can imagine in a few years I may not be quite so willing to lug it around like this, so it is interesting to hear about your experiences with the 5. I have a feeling that it would handle my 8" scope. There's something to be said for downsizing in EAA where short exposures are the norm.

Martin

[RobertI]

6 hours ago, Martin Meredith said:

Even so, there's a lot that will fit with plenty of space around them. Here's a plot showing cluster diameter versus magnitude to give some idea how much there is out there of a given size. 

 

That graph certainly proves the point, seems to be plenty out there of small size. I've never really considered chasing this kind of object before (ie: small faint OCs) so something else to add to my ever growing list.

Its encouraging to hear that you do your EAA in Altaz mode, I have been thinking about this (see below).

 

6 hours ago, Stu said:

Thanks Robert. Thank goodness is all I can say regarding the lack of arguments! Any form of the art of EAA is welcomed at SGL, let's just enjoy it and benefit from the amazing images!

Regarding the AZEQ5, I confess I've not really had the chance to use it much at all. Having had an AZEQ6 previously, it has both positive and negatives in comparison.

It definitely feels built to a cost and weight. Some of the fittings feel a lot less substantial than the 6, and the tripod is shorter and has thinner diameter lower legs. That said, its quoted load capacity is 10kg less so it is to be expected.

The design of the mount seems very well thought out, although it took me a while to work out some elements, like tightening the clutch on the alt axis, but it all works well.

The benefit of the 'diet' is that the mount is much more manageable than the 6. I made the change mainly because I have a fairly dodgy back, and wanted something I could more easily handle and potentially take out into the field. The 6, for me, was very much something I left permanently setup at home, but now I don't have a big 6" ED frac I don't need the load capacity and the 5 is much more suitable for my needs.

Thanks for the info Stu. My main interest in theAZEQ5 is that quick setup time is key to me. Although polar aligning my CG5 only takes me a few minutes, the goto alignment process can add another 15 minutes especially if things go wrong, which they frequently seem to! I was thinking that an Altaz plus Starsense could knock 20 minutes off setup time which is definitely worth having on a precious work evening. I don't have far to move it (garage to patio, maybe 20 feet) so perhaps an AZEQ6 isn't out if the question for me, although £400 more than the AZEQ5 there seem to be plenty of used examples coming up. 

Sorry to derail the the thread Martin....