Small widefield Rig. TS60/ASI1600M

[MattJenko]

This is my first attempt at a serious review of a small widefield imaging rig I have set up over the last few months. The brief I gave myself was quite simple, but hard. I wanted a small, fast, well corrected refractor with a large, cooled, mono sensor camera with decent resolution for both LRGB and narrowband imaging of large DSOs with a minimum need for mosaics. It was to be portable and have the ability to be mounted on a StarAdventurer, although the last requirement was a bonus, not an essential. It all had to be "affordable", so I budgeted for under £2000. I already had a filterwheel and some 1.25” Baader filters to add to the setup if I could use them.

The refractor first.

I had a look at a LOT of small refractors. The market has a LOT of them. I have had 60mm scopes before, including an AA triplet, but they all disappointed, either mechanically or optically, but I found the specs of the TS Photoline series very appealing and after much agonizing, I purchased the TS60ED Photoline with a good deal more hope than expectation. What attracted me was the small size and weight, the quality reviews of the focuser and the ability to use the Photoline flattener/reducer to give this little scope some serious paper specs: FL 260mm, F-ratio, 4.3. If it works, who could argue with that.

For the camera, there were only 2 real options at my price point. A camera based on the Kodak 8300 chip and the new ASI1600M cmos from ZWO. I did consider some mono DSLRs, but they are expensive and seem more like a tool doing the wrong job than a dedicated astro camera. The reviews of the ASI600 and the specs seemed like it also would be too good to be true with the TS60:

Pixel Scale : 3.01”/pixel
FoV : 3.89 x 2.95 degrees

Massive field of view with almost as good a resolution than the Skywatcher ED80 and Atik 414ex I have had for over a year now...

The clean cooled CMOS chip and USB3 means that I could theoretically get away with shorter subs, so with this in mind as well, the resolution won out over the bigger pixels of the 8300 and I bought one from FLO.

The TS60 scope itself is very sturdy, comes in a lovely soft padded case and has a dual speed 2” RnP focuser which instantly struck me as much better than the previous 2” RnP focuser I had on my 60EDT. The tube rings are nicely done and I used an ADM dovetail to attach it all which ties it all together lovely I also worked with Ian King to get an adaptor made so I could attach my existing Lakeside motorfocuser to it. Worked a treat - many thanks, made accurately in a matter of days all based on my crude measurements and photos! However the most striking thing about this scope is its size. It is tiny!

 

 

The ASI1600 camera is much like other ASI cameras. It is light for what it is (450g) and appears nicely made without being industrial. The case was a simple cardboard and foam affair. Installation of drivers was trivial and it connected fine. The fans are quiet, much quieter than my Atik 414 and a SX694 I owned for a while. They seem to work very well though, cooling to -20 easily, even on the recent warm nights.

The first major issue was that the compression ring in the focuser simply would not hold the reducer and imaging train properly. The compression ring unscrews to reveal an M54 thread, but the adaptor is optional,  so needed to be ordered separately, at additional cost and time.

The next issue was that the ASI has a male T-thread in the 6.5mm configuration. The TS flattener has a male T-thread pointing at the FW, so using the Baader variable spacer, I needed to add in the female/female T-Thread adaptor, which pushed me well past the stated optimal spacing. In addition, with the reducer screwed in, there is precious little back focus and at first I couldn't even get focus because the spacing was too close in, and I started to think the worst of my entire plan. It is stated on the TS site that this configuration should work, so I soldiered on and picked up a Female SX adaptor to remove the need for the 10mm female/female t-adaptor and things worked nicely after that, with enough focus room to perform autofocus routines, one of the keys to how I like to run things. A bonus with the focuser being racked so far in is that there is no room for tilt due to the focuser being over-extended.

One heart stopping moment came in playing with spacing and screwing and unscrewing the camera in all the fiddling about. I ended up tightening the front nosepiece of the ASI as it was almost cold welded on the filterwheel. This caused the camera body to screw further into the nosepiece and as a result, 2 of the desiccant tablets came loose and got crushed and ground against the 2 moving parts in and around the sensor itself, covering everything inside in dust and desiccant bits. I had to fully remove the front to expose the sensor and the crushed tablets and give it a good clean out. Very nervous moments. The tablets are very loose inside and not held securely at all. Something I will need to be very mindful of in future and a warning to others. My flats currently look awesome!

 

SGP connectvity was a breeze using Windows 10 for all the components. EQMod, Lakeside, SX FilterWheel, ASI ASCOM.

For guiding, I use a finder guider, which attaches to the finder bracket included with the TS60 which sits out offset to the side on the tube rings. It requires the bracket to be tightened a lot to prevent any movement, but it holds pretty well although I do need to tighten it every other session. 

Overall  this is a very simple setup and pushes the weight to just over 5kg with the camera and filterwheel. Without the finder, I can get balance with the StarAdventurer and the standard dovetail/counterweight, so this whole rig now fits and balances on my SA, which is very promising indeed. It looks positively tiny on my AzEQ6 and in reality is not balanced as it is too light, even with the 5kg counterweight pressed up to the mount, but I don't think this matters at this weight class!

There has been some debate online about filter sizes for this camera and sensor. My experience is that you can get away with 1.25" filters. In theory, minimum filter size = CCDdiag*(FL-DC)/FL + (DC/f).

With the ASI1600 having a short attachment option of 6.5mm to sensor, this allows the filters to be around 21mm away with the SX Filterwheel, requiring a filter size of 24.6, with a theoretical usable in 1.25” filters of 28mm. My flats show a slight vignetting in the lower left of my images due to the final orientation of the sensor, but it seems to calibrate out fine, and I have no plans to upgrade to 36mm filters. 

Another reason for the choice of camera was the possibility of using significantly shorter exposure times, using many more subs. This would work with the non guided SA and also in getting the best out of the few gaps in the clouds we seem to have in the UK these days. I have found that 30 secs works wonders for star images.

Imaging

Getting the spacing right proved tricky and it is still not perfect. The slight vignetting from the filters might be making the problem worse, but just as the edges start to flatten, the center starts bulging, so it seems that a full flat field across the entire ASI1600 sensor might be tricky with this particular setup, but it is close and gives a better overall result than anything else I have.

Crucially though, there appears to be minimal bloating on the Blue end of things, which means that Lum exposures can really be pushed hard, something which was a limiting factor in my ED80 work and something I was starting to hit up against as my imaging skills increased and has been a major factor in me wanting to upgrade. This was also the killer for ALL the other small doublets and budget triplets I have tried. This was very good news indeed.

A few tweaks to things like platesolving configuration etc took up a little time, but without too much fuss, I have been up and imaging. 

Something else very noticeable is the download speed of the ASI using USB3 compared to by CCD images over USB2. Awesome. The slowest part is the rendering on screen in the various applications, the images download in microseconds. 32M in the blink of an eye. I admit to having an Alienware laptop with SSD, so a high end laptop, but all the same, this is marvellous and just adds to the whole feel like this is a serious bit of kit. With short exposures, this makes some operations much faster. 

Cooling seems to work effortlessly. As mentioned , the fans are significantly quieter than my Atik 414, which is a noisy little thing, and also much quieter than an SX694 I had for a few months, which I am sure is great news for my neighbours. It cools down to -20 easily and could probably go further, even in these summer months, although I don't believe the fan usage value displayed within SGP is correct, which seems to remain very low, even on initial cooling, but it runs cold and quiet, so I am not bothered

I tried out the Coathanger to start with as it is easy to find, has bright stars and a decent starfield, with some nebulosity in the background. I tested some different exposure times, all at the default unity gain, and found that 30sec exposures with the RGB filters results in just about non saturated stars and a decent dusting of nebula. At 30secs, it is easy to bang out multiple subs for stacking to increase the overall dynamic range and it also makes guiding much less crucial, especially at 3”/pixel. Getting decent RGB star data at 30s means I would be able to push Lum exposures safe in the knowledge I can unsaturate stars using the colour data in processing.

Ironing out the kinks on the Coathanger, I wanted to really push the rig, so decided on a bit of a summer icon. The North American Nebula. With my field of view, I can also include the Pelican without the need for mosaics, which is a huge reason for the choice of hardware, so I duly gave this a go.

For the Lum detail, I went for 5 min subs at unity gain. This results in a 50% saturation for the nebula and obviously saturated the stars. These I recovered using much shorter RGB subs, 30 seconds each. Imaging time is 1 hour for each RGB channel, so 120 subs for each!

Processing is more of a challenge, purely in the processing power required. I have to now not only calibrate/register/stack more images, they are bigger as well. All processing functions take longer and an image needs more care, as a PixInsight function over a small region might not be applicable to the whole, so masking is key in my new world. Processing these images is a whole different skill than the 414ex images I have been used to.

I have also tried some narrowband during the recent full moon cycle. I managed 5 min Ha exposures at 95% Moon and am extremely pleased with the results. 5 mins narrowband is a huge boon for my UK imaging, as my previous 20 min NB subs were never reliable and a devil to get enough good ones for a proper image. 5 min subs are much, much easier to knock out and I managed just under 100 in under 2 sessions. A simple stretch shows the results of stacking that number. It is remarkably noise free. The image only has a flat applied to the subs, which was taken with a different filter

From this image you can see that the corners show the curvature, but for now this is more than acceptable for me. I know that this would not be the case for everyone, and maybe I will get frustrated with it in time and try and see if I can improve it.  There also appears to be the amp glow mentioned in other threads about this camera on the right hand side. I will be doing further investigation into this as I am sure it could be calibrated out and there are rumours that a driver upgrade can help with this too. We shall see.

There comes a point though, when one just wants to see what your equipment can do as opposed to concentrating on what it can't do.

 

All in all, I think I have achieved my goal, although I went slightly over budget when I add in all the adaptors, connectors and postage etc. I don't mind though, because now I have the ability to capture enormous fields of view at a resolution similar to my ED80/414ex combo at a much faster rate and I have a high quality setup which without all the knowledge gained on this site and others, would have cost me significantly more, for something delivering significantly less.

Hope this was of interest and of use to some of you as I am keen to try and give a little back of what has been given to me.

Matt

[RobertI]

Fantastic detailed review Matt, that's a beautiful compact setup and a great little scope.

[Chris]

really great review Matt, the scope and camera seem amazing! I'm pleased your hard work and taking a chance paid off with great results, lovely images! Do you even need guiding with this focal length combined with relatively short subs and 3"/pixel?

[pete_l]

A superb review, thank you.

It's clear, well written, detailed, talks about the minuses as well as the pluses, goes into technical detail.

If the magazines carried content of this quality this I might start buying them again

 

[rl]

Great review, really useful. I'm tempted by the TS60 myself...this may tip me over the edge...

RL

[MattJenko]

Thanks all. I would feel totally comfortable recommending this to people who wanted a step up from decent "beginner" AP kit, or even a starting kit for those with deeper pockets.

Chris - I think I could do shorter, unguided subs by pushing the gain as well and 30seconds should be easily doable on my StarAdventurer as well. I am planning on doing all manner of tests, but the problem is that the desire to actually use the setup rather than play with the setup is just too great!

This is the kind of thing I have been day-dreaming of doing for a long time now! A mere 2 panel mosaic of the heart and soul. Currently only Ha, shot last few full moon days and simply stitched in PixInsight to make sure I got the framing right