Another 1-hour image (only 6 x 10-minute subs) from the early hours of this morning.  This is the North America nebula NGC7000 with the Pelican making a cameo appearance on the right.  This time the mount was dithered so not hot pixels – YAY!!!

I’ve had my suspicions for quite a while now, but for some reason after just over 5 years  it has finally jelled in my last two remaining neurons what the problem has been.

From way back when I was imaging with the original Sky 90 (bought from True Technology) piggy-backed on the C11 – I had this bunch of trailing stars in the corner of the field of view.  It looked like polar rotation (or coma) but it wasn’t dependent on the sub-exposure time (even for very short subs) so polar rotation was written off.  I got a reasonable collimation (overall) according to CCDInspector, but there was always this bunch of annoying stars in the corner.  Then I saw Steve Cannistra had a similar problem which was due to flexure in the camera rotator – I did his fix and the problem stars were still there.

Recently I bought another Sky 90 from an Irish astronomer and this went on to the mini-WASP array as one of the two main imaging scopes.  I was able to collimate the M26C to this scope very quickly, and unlike the other scope I didn’t have to really bolt down the adjusters to the metalwork on the M26C to get good collimation.

So after just over 5 years I finally come to the conclusion that the collimation of the Sky 90 itself is way out!!  Luckily this is the model that has the three collimation adjuster screws on the lens cell.  So the offending Sky 90 has now been removed from the mini-WASP framework and is now sitting on its own tripod ready for yours truly to attempt collimating against a star.  Not done this before for a refractor, so I’ll let you know how I get on, and if the problem goes away.

Even though collimation on the second camera wasn’t too good (again) last night, I still took 6 x 10-minute subs of the North America nebula using both cameras and scopes.  I’ll be looking at the data very shortly.

Well here it is – one hour’s worth of data taken with the two M26C cameras on the New Forest Observatory mini-WASP array.  Still lots to be done before it’s properly tuned in – but I’m pretty close now.  As I was finishing this off at 3:00 a.m. this morning I might well be writing a load of rubbish here – but I’ll carry on all the same.  Note this is just 6 x 10-minute subs from each camera – now try and imagine my usual 8-hours plus with the Sky 90.  I’ve left all the hot pixels in the background as I didn’t have the dither function running last night – but I’ll try to have that going on the second outing.  The collimation for camera 1 (the top half of the image) is spot on – the collimation for camera 2 (the bottom half of the image) is off a little and needs to be tweaked just a bit (lousy stars bottom right hand corner).  However – the field of view is as you can see MASSIVE (there’s M29 sitting at the bottom of the frame, check out the FOV on your favourite planetarium program) – and the M26C cameras really seem to be delivering the goods with only a single hour’s worth of data!!  Well done Terry Platt.

As it looks like it might be clear again tonight I’m off to bed for a couple of hours.

It has been a glorious day all day with clear blue skies – and this time it didn’t fog over as soon as the Sun went down.  So I started the final hard bash at getting the mini-WASP array commissioned at 8:30 p.m. and got it to the state where I can start imaging with both cameras and an overlapping field of view at 1:30 a.m.  I am now doing a 2-framer (in one go) around the Sadr region.  The only thing I haven’t got running is the dither which is a bit annoying, but I can probably work around that with a bit of luck.  So – after 4 years of planning and execution the mini-WASP array is finally all systems go.  Must admit I didn’t think that simply doubling up to two cameras and scopes would be so much trouble.  There’s a very good chance that I won’t go the whole hog and build the 4-camera 4-scope array unless I get VERY used to running these 2 cameras – and somehow I don’t think I am going to get THAT proficient.  Still – mustn’t be greedy, a 4 x 3.33 degree field of view at 3 arcseconds per pixel should be good enough to last me for quite a long time

A number of people have asked me how many stars appear in the Cocoon nebula 3-frame mosaic.  I use a program called Registar to link separate frames together so I can see how they all fit – and Registar will also do a “star count” for the stars in the image (I don’t think it is accurate to the level of a star )  Anyway – Registar says there are 68,200 in this image – always turns out to be a LOT less than you would guess.

As it continues to pour with rain here in the New Forest – thoughts go back to the hot, dry days at the Starmus Festival in Tenerife June this year

As I sit here with a gale roaring outside and the rain pelting down I wonder if I will ever see a clear sky again – and this got me thinking about how I will run the mini-WASP array.

It was always my original intention that the mini-WASP array would be a “parallel imager” – that is each scope and camera would image the same object so that the total imaging time would be effectively the time you image that evening multiplied by the number of imaging cameras.  I then got field of view fever and thought I’d rather have the cameras having an overlapping field of view (along one edge) so that I can form a mosaic in just one imaging session.  The main negative thing about this approach is that by overlapping images you are effectively throwing away the pixels in the overlap region of one camera – with my 10 Megapixel SXVR-M26C cameras this is likely to amount to 1 Megapixel – almost the size of my first imaging camera!!  This is not too clever.  You also don’t get the “time gain” if you work this way, and seeing the very few good days we’ve had for imaging these last few months I am beginning to think that time gain is much more important than field of view gain.  There’s also another reason why it might be a good idea to image just one object with multiple cameras.  At present I have two scopes and imaging cameras – when it comes to adding the 3rd scope and camera it would be difficult to bolt its field of view onto the other 2 cameras – but of course it is no problem at all to use the third scope to once again image the same object as the other 2 scopes.

So – the way my thinking is going at present is that I will double up my effective imaging time on the single camera/scope field of view of 3.33 x 2.22 degrees, rather than sacrifice the imaging time for a massive 4 x 3.33 degree field of view.  The full 4 camera mini-WASP array would of course offer the possibility of a massive 6 x 4 degree field of view at a very respectable sampling of 3 arcseconds per pixel.  When I finally get to fitting all 4 imagers to the mini-WASP I might just possibly use it in the large field of view mode to capture those few very big objects (or groups of objects) that require it – it really is very tempting to play with a 6 x 4 degree high resolution deep-sky imager

Hooray – September – and some decent long evenings after what has been a very long wait.

So what can we spend our time on this month to make all the effort of maintaining an interest in this hobby worthwhile?

Well, I particularly like imaging in the north, mainly because this isn’t done too much.  And what about going for the most northerly Caldwell object?  Caldwell 1, otherwise known as NGC188 – a nice large open cluster in Cepheus.

NGC188 lies around 4,800 light years away and shines at a magnitude of 7.1 (O’Meara) with an apparent diameter of 15 arc minutes – so fairly large.  There isn’t much up this high in the northern wastes so NGC188 is a bit of a gem out there all on its own.  It does quite well even in the large field of view of the Sky 90, and the large FOV does accentuate the barren surroundings of Caldwell 1 – something that once again gives the image a little bit of impact.

As with clusters in general, I recommend 3-5 minute sub-exposures and as close to 100 as you can get for a nice low-noise image.

NGC188 is one of my favourite open clusters, and as it doesn’t seem to get much imaging time, why not give it a try this year?

Until October – clear, dark skies to you all

Tom How spent a night over the Bank Holiday weekend at the NFO where he had a good play with the mini-WASP array – I was attempting (half satisfactorily) to polar align the Hyperstar III in the south dome.  Meanwhile Tom in the North dome was collecting some quite nice Heart nebula data from Camera 1 of the two camera system.  This image shows about an hour’s worth of data collected using the Sky 90 with IDAS filter and an SXVF-M26C 10 Megapixel one-shot colour camera.  The camera has not yet been collimated which explains the star shape changes across the FOV.  However – the camera response is much as I have seen previously with the M25C (bigger pixels) and so it proves as I had anticipated, that I will not see any reduction in sensitivity with the smaller M26C pixels as I am working at a pretty short focal length.  So – a step up from 6 Megapixels to 10 Megapixels and then times 2 for two cameras – this mini-WASP array will be producing some amazing data when it is all tuned up.

So what more needs to be done before we can see the full power of the mini-WASP array?  Not a great deal really:

1)  Properly focus train and collimate both cameras.

2)  Align cameras for slight overlap so that I can take a 4 x 3.33 degree field of view in one go.

3)  Take some new flats with a properly collimated system.

4)  Focus train for the H-alpha, H-beta, SII and OIII filters.

And that should be  it for a while

Here are a few pictures from the day – I still can’t believe how lucky we were with the weather.  Had a few drops of rain first thing in the morning just to put the scarers on us – then cleared up beautifully for the rest of the day