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Astro Projects

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All Sky Camera Mark 7

Gina

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This is my latest generation of all sky cameras and based on the ASI178MM followed by ASI185MC CMOS astro camera and a Fujinon fish-eye lens of 1.4mm focal length.  Although rated at f1.8, this lens lets a lot more light through than this would imply.  Image capture is provided by a Raspberry Pi 3 in conjunction with INDI software.  This is used with KStars/Ekos client software running on a Linux Mint desktop indoors.  Communication is via Wi-Fi.  The Mark 6 ASC has proved inadequate after being in use for some time. 

This blog will describe the problems of the Mark 6 and report my progress in developing this new version.

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Now printing my third attempt at a lens support that fits :D  First was a little too small, second a lot too loose so now on the third which is just 0.2mm bigger in both the camera and lens fittings than the first.  Fingers crossed.

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The print is a nice tight fit on the camera but too tight on the lens so increasing the lens tube by 0.2mm diameter which should be about right.

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New print is fine though the lens is a little tight in the tube but the offset isn't enough.  I reckon it needs twice as much so I'll change the design and print again.  I've increased the offset by another 0.7mm giving 1.2mm altogether.  If this is too much I can turn the support on the camera to reduce the Y offset and add a bit of X offset, which doesn't matter as there's plenty of room in the X direction.  In fact there is already some X offset which I could reduce by turning the support tube in the right direction.

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Edited by Gina

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I could do with a finer method of adjusting the focus than just by moving the lens in its support tube.  The screw adapter wouldn't engage with the offset, hardly surprising.  I'll do some more thinking :D

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I opened the window and did my best to focus on the moon.  Then put the camera on the pipe and hung it on the guttering.  The FOV seems alright though can't be sure until it's in it proper position on the observatory.  Here's a screenshot from SharpCap.  Out of focus unfortunately.  I've cropped the image in the X axis only.  Bright lights cause reflections in the lens, it seems.  This is without a dome.  Think I'll bring it in and try focussing on the moon again.  The sky has almost cleared now.

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Edited by Gina

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Well, that's better :)  This is with 5s exposure, gain on Auto and showing 240, gamma on 50 and brightness on 1.  No camera cooling and no dew heater.  Image capture with SharpCap and this is just a screenshot of the Preview.

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Edited by Gina

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The sky is now pretty much covered in clouds :(  And waiting for the moon to set but it looks like I would have to wait until nearly 1am :D

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Just realised what's wrong with these images - they're reversed - east is to the right!!  Very strange!

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Left the ASC running overnight capturing PNG images with SharpCap, continuing after the moon had set.  These were 10s exposures at one per minute to keep the number down a bit with gain on Auto, gamma on 25.  As before, this is just the camera and lens mounted on aluminium pipe and hung on the guttering.  A couple of things are evident.  The lens is not straight (focus is fine top right but out at bottom left of image) and the camera needs cooling to reduce noise.  Surprisingly there was no sign of dew but maybe there was heat coming from the camera.

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This morning the sun is out but with a bit of cloud to the east.  Again running SharpCap and this image was taken with gain set to 0 and Auto Exposure giving 0.4ms gamma 25. I believe this shows that this arrangement could by used for daytime imaging as well as night.  Unfortunately, not with the RPi and INDI driver though as that only goes down to 1ms exposure.

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All this needs thinking about but the easiest option is to stick with the RPi and INDI and only use this ASC for lower light situations.  I guess it might be possible to use the one ASC for all light levels but it would need different software unless or until INDI match their minimum exposure to that of the camera.  It really does seem strange!  I'll have another go at trying to register with the indiserver forum - tried before but it didn't work.

I have an RPi camera with fish-eye lens attached, on order with deliver on a very slow boat from China, that might do me for daytime imaging.  I also have a couple of acrylic domes on order to look at and consider, due to arrive next month.

Edited by Gina

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Brought the rig back indoors and can see why the focus was wrong - the lens support wasn't properly on the camera - it was up a bit on one side.  Daft duffer! :D

Clear sky forecast for tonight until around midnight but the moon doesn't set until nearly 2am tomorrow so no chance of seeing any stars tonight!  The moon is 78% full, so very bright.

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Onto the electronics then...  Of the available INDI drivers, the Astroberry Focuser seems to be the only one that drives stepper motors so I shall probably use this for the cover motor to start with.  It's not ideal but will do until I manage to write my own INDI drivers.  Another possibility would be to use an Arduino Nano to drive the motor and control that with the Astroberry Board which has four ON/OFF controls.  I will already be using this to switch the cooler and dew heater and the another line could operate the cover.  OFF = Closed and ON = Open.  It should be relatively easy to edit the code for the Astroberry Board to show the correct labels.

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Readjusted the focus using the far horizon.  Put back out on guttering and captured image.  With the angle of the pole and hence ASC, the coverage is not horizontal showing the field in the foreground.  The shed at about 8 o'clock is my observatory.  The moon is just above it and rising.   The second image is with the bottom end of the pole positioned away from the window a bit.

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Edited by Gina

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Looking dark outside now but it isn't really :D  Some lights coming on though - mainly house lights and the odd car.  Second image shows more lights including some distant street lights, the red lights in the tree at 7 o'clock are on the Stockland Hill TV and radio transmitting mast.  A few stars showing.

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Edited by Gina

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Next door have switched on their flood light :(  When I had a dome this caused such reflections in the dome that no stars could be seen.  Without the dome there are still reflections in the lens but not as bad.  Next time I see either of them I'll try to remember to mention that their light interferes with my astronomy and get them to switch it off when they don't need it.  I might add a little screen to shade my ASC in that direction for when the light is on.  It would be easier to keep the light off the lens than a great big dome.

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I can't dictate when my neighbours have their ultra-powerful floodlight on though I know I can complain if their light impinges on my property but I want to get on with them and not have friction of any sort.  That is more important to me than a good view from my ASC.  When I built my observatory the neighbours then were not very friendly and rather than brew up a storm I built the observatory to protect my imaging equipment - telescopes or lenses - from that light. 

I could arrange that my ASC also has some sort of protection from the light.  There are two ways I could shade the ASC from the light - arrange a shade attached to the ASC or position it in a shadow area.  The former method would be easier.  It can be a permanent feature as there are trees behind their house and I don't need the view.  When I had the dome on I was considering protecting it from other lights much further away but without the dome those are no problem.

The two images below show the present night-time situation and the daytime view.  The light is near the apex of the roof on the white building at about 4 o'clock in the daytime view.

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Lens has now misted up.  It didn't mist up at all last night and I captured images every minute all night but tonight it has misted up already.  So a dew heater is definitely needed as I expected.  I have already planned for this in the form of six 10ohm resistors from the set I used before with the dome.  These will sit between the lens support and the conical underside of the lens.  I shall probably improve heat transfer to the lens with thermal paste.  6x10ohms totals 300ohms which when running off 13.8 volts will dissipate just over half a watt.  Just have to see if this is enough.

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I've been reading up on the INDI protocols and how to write and modify INDI drivers.  I think I can probably take code snippets from the Astroberry Focuser board driver and incorporate them into the Astroberry Board driver such that turning LINE A ON (will be labelled "Open Cover") will send the appropriate number of steps to the stepper motor to open the cover.  Once that has been done the driver can report OK to the client software.  The associated light would show yellow while the operation is being carried out and go green once the client receives OK from the driver.  A similar process would occur when the "Close Cover" button is clicked but closing the cover. 

I would like some sort of feedback from the cover mechanism to confirm that the action has indeed happened.  Physically this could be achieved with a microswitch or Hall sensor and magnet.  This would feed a digital signal into the GPIO of the RPi.  I would need to add code to detect these inputs viz. cover open or cover closed.  I'm gradually getting my head round the way INDI works and the associated code.  The control protocol is a version of XML but the working code is written in C++ with which I'm familiar.  (Arduino code is C++).

The alternative to quite a lot of INDI driver coding would be to use an Arduino and just a slightly modified Astroberry Board (labels only) and feed a digital signal to the Arduino - logic "1" for Open and logic "0" for Close.  But with this system there would be no feedback.  It is a far less satisfactory solution in many respects.  I don't like "bodged" solutions!  If I can get my aging head round INDI driver development, there are all manner of possibilities :)

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