Can the output from the STX Guider camera be binned?

Hi,
I am doing long focal length deep sky imaging (C14 Edge HD) with the SBIG 16803, FW7 filter wheel and the STX Guider.

I don't have a rotator and as you may recall, have the camera bolted directly to the adaptor which is screwed onto the Baffle Lock Nut. In order to give the correct set back distance I use fine spacers. Incidentally Colin & Doug, I have this beautifully dialled in now and it is sensitive to within 0.1mm and the Noctua fan continues to give me perfectly round stars right across the field of view, even to the corners, which as you noted Doug, is well beyond the 42mm image circle guaranteed by Celestron. It has been up to 23C in the observatory at night, but the power output has not exceeded 75% so far, so I have not had to resort to water cooling, although the may change later in our summer.

However, my biggest issue and the reason for this post is finding guide stars, as I am sure you appreciate. I am basically using Sequence Generator Pro and PHD2 Guiding. For some objects, it can be difficult to find a suitable guide star and where I am normally using an exposure duration of 6 secs, I have had it up to 8 sec to try and get a high enough SNR for the star in PHD2. I have had occasions where PHD has lost the star, which can be annoying. I have also had to frame the object I am imaging differently on each side of the meridian, such that in each case there is a guide star to guide on. This means I have to crop and reduce my already small FOV.

I thought perhaps I could resort to binning the guide camera's output, but I cannot find anyway of doing that.

Can you advise on the general problem of locating guide stars and secondly, can you suggest a way I can bin the guide camera's output especially using SGPro and PHD2 Guiding?

Thanks & regards,
Niall

 

Thanks Colin,

I had found it when I went looking hard enough. But thanks for the confirmation of the validity of this approach. In fact after I set it up, it helped a lot. The SNR ratio was considerably better and the performance was good, despite the poor seeing. In steady moments it performed as well as the unbinned scenario.

 

On the subject of camera cooling, of course, as soon as I said I haven't had to use the water cooling, we had a warm spell. In fact in the early part of last evening the ambient temperature was 26C and at that the cooler ran out of capacity with the power draw getting up to 100%. Once the ambient temperature dropped below 25C it was fine, but this prompted me to commission the water cooling system which I did today.

Here is the set up. You can see the feed and return tubes and the 12V power supply running down to the pump. I looped it via a hanger on the OTA handles, so the tubes wouldn’t be directly dragging on the camera.





It worked like a charm.

Here is the SGPro output. At left on the focus control you can see the ambient temperature. The camera parameters are at lower right.



Notice the ambient temperature in the dome, when I took this screenshot was 34C. The peltier cooler was easily achieving -20C, with the power draw at 52%. The water temperature in the bucket at that time was ~ 25C.
In the meantime the ambient temperature has climbed to 35C and the water temperature has naturally risen to ~ 30C, so the power has crept up to 58%. Of course as the heat is being dumped into the water, its temperature will rise, theoretically to above the ambient temperature, so the heat can be lost from the large surface area of the metal bucket to the environment and probably with some evaporative cooling. The higher the ambient temperature the more work the cooler has to do to reject the heat from the camera and the more heat is being removed to the water. A certain equilibrium will eventually be achieved.
In fact I am now looking at the ambient temperature and it has reached 36C, but the power draw has stabilised at 58%, whilst the water temperature has risen to ~ 35C..
This is most satisfactory. Of course I don't expect these temperatures at night and the power draw will be much less.

Can I leave this connected up or does it need to be disconnected and drained from time to time? If so how often? Do I need tube clamps to ensure the tubes don't come off the spigots on the camera? When I remove the camera I will need to disconnect the tubes to unscrew the camera. Can I periodically remove the tubes without impacting the efficacy of the spigot connection over time. I notice the spigots are well designed with a circumferential flange which is sharpish.

Thanks for your help in getting to this point.

 

Hi Niall

Have some experience running water cooled medical imaging cameras over the years and there are a couple of tips I can pass on.

Yes, you do need pipe clamps, in very hot ambient conditions the thin-wall piping will soften and stretch and eventually the tail joints may leak and there is always the risk that a pipe may become detached while the pump is running and allow water to spray on the equipment below.

Each time you pull the pipe off the tails the sharp barbs on the tails will cut and damage the inner wall of the pipes and together with the natural stretching of the pipe material you should never reattach a pipe once it has been pulled off, these are designed for one-time assembly only.
The normal procedure would be to cut off and shorten the end of the pipe that had been previously attached to the tail by a few cm, enough to reach an un-stretched piece of pipe, then reconnected the pipe to the tails using fresh, undamaged piping.

If you are into RV’s or aquatics etc you might like to look at installing inexpensive in-line quick disconnected water pipe couplings, these will save you needing to touch the pipe tails at all when removing the camera.
Plastic in-line quick-disconnect couplings simply use a sprung bayonet system of push-and-turn to uncouple the pipe and the reverse to reconnect. The low pressure plastic versions only weigh a few tens of grams and can be placed anywhere in the pipe run.

There are many manufacturers making these all over the world and an example local to me can can be found here:

https://www.coleparmer.co.uk/p/masterflex-quick-disconnect-fittings/81465

There are two types of quick-disconnect couplings, self-sealing and open.
The self-sealing ones have an internal valve that closes and seals both sides of the coupler when de-coupled to stop fluid leaking out and air leaking in. These are the easiest to use as it saves having to drain the camera exchanger when removing the camera, plus they help to prevent air-locks forming in the pipes and heat exchanger. The open types are just a simple coupler and when decoupled allow fluid to drain away and air to enter the system.

Even in the dark of the observatory algae, or even more dangerous organisms, will establish themselves in the pipes and will grow anywhere there is warmth. This is particularly troublesome inside the camera heat exchanger and can block the exchanger over time.
To counter this, change the water regularly and add an eggcup full of pure bleach to the water bucket every six weeks, run the pump for an hour or two then empty the bucket and fill with clean un-bleached water.
The bleach will kill algae spores and other bacteria and keep the system clean.
Don’t be tempted to add too much bleach though as too strong a mix may harden the rubber seals used in the pump.

If you don’t have easy regular access to the observatory to clean the system then instead of bleach you can add baby-care feeding-bottle sterilising solution to the water each time you exchange or top-up the water in the bucket.
More expensive than bleach but not so aggressive against rubbers and plastics in the pump it can be used full time.

If water evaporation is rapid and the water is hard then mineral deposits may build up through the entire system over time. If you notice mineral deposition forming inside the pipes or leaving ring crusts inside the bucket then you may need to flush the system with a weak de-scaler from time to time, Doug or Bill may be able to advise a safe chemical for that.
Years ago we used to use White Vinegar for de-scaling open water-air coolers, which is just a weak acetic acid, and run that through the system once a year for a couple of hours then flush and refill with clean water.

William.

 

Thanks William,
I greatly appreciate this advice. I had already bought 2 valves and two quick connect fittings, with the intention of attaching them to the camera. This will allow me to isolate the water within the camera and then disconnect the hoses. They are the open type so I will look around for the self sealing type that you recommended locally.
I didn't realise that fitting the hose to the spigots is a single use function. I will cut off the small section of hose and then attach another piece with hose clamps, then to the valve then to the quick connect fittings. The only downside is how to secure these fittings to avoid them swinging around when I don't require the water cooling.
My water is tank rain water so as soft as it comes.
I will take your advice and change the water regularly. Because my water has never been chlorinated algae can quickly get a hold if there is any light, so it might pay to clean with bleach more frequently than every 6 weeks. Do you see any issue with adding a small amount of bleach to hold a low chlorine level like 2 ppm as you would have in a pool?
Cheers, Niall

 

Thanks Colin. I doubt scale will be an issue but algae will. What do you think of maintaining a low level of chlorine in the water as I suggested to William?

 

Hi Niall.

Re: The single-use pipe tails, it's not that the tails are single-use, rather it is the type of pipe used.

Soft natural rubber piping doesn't take a permanent stretch in the same way that PVC does so soft rubber hoses can be pulled off the tails several times before the inner wall of the pipe becomes deeply scored and once removed from the tail then natural rubber returns to the original size.

Once PVC pipe has been on the tail for a while it permanently deforms and weakens and loses it "grip" and every time you pull it off the tail the inner wall tears a little more.

The downside of natural rubber is that it degrades much faster than PVC and after a while it sheds fine rubber particles into the circulating water which has to be filtered otherwise there is a risk of blocking the heat exchanger. PVC is fine for this job and if you can find the self-sealing quick-release fittings locally that would solve the issue for you.

The in-line plastic quick-release fittings are very light weight and if you keep the hose length short between the camera heat exchanger and the coupling then they can be secured with Velcro pads and straps to the back of the camera.

A low concentration of pure bleach permanently added to the water should be fine, as long as it is low, as unlike pool pumps most submersible pond and fountain pumps don't use chlorine resistant plastics or valve seals and after long exposure to high levels of chlorine the seals and valves stiffen and may leak or cease to function.

William.