All Sky Camera Revisited

[Gina]

Strange!!  It's gone green!! ?

[Peter Drew]

Doing its bit to save the planet?   ?

[Gina]

Increased exposure to 1ms.

[Gina]

And of course - rain tonight so no stars!

[Gina]

Have to say I'm not happy with the Fujinon zoom lens nor really with the other Fujinon lens.  The zoom lens is poor quality and awkward to control whilst the bigger fixed focal length lens has no facility for focussing, making this difficult and it cannot be used with the ASI 120MC-S camera for daytime use as the minimum camera sensitivity is too high and any sun in the FOV causes whiteout.  The ASI 178MC with smaller pixels and half the minimum exposure will cope with the f1.8 lens in daylight.  Unfortunately, even with the new month and input of funds into my bank account I can't afford a new lens and ASI 178MC camera as well as pay the bills so I shall have to put up with the zoom lens somehow.

I now have the two servo motors I ordered and these are very much better then the tiny micro server motors though considerably bigger.  The ASC will need quite a large casing.  I have to arrange mechanical coupling from servo motor to the little levers on the zoom lens and also sort out how to operate the servos from the RPi.  If I can't drive the servos directly from the RPi I could use an Arduino Nano between them so using servo motors is certainly possible.

For use with the ASI 120MC-S camera the lens focal length has to be 1.4mm or less to cover the amount of sky I want (though still not all of it).  There are 1.55mm focal length lenses available but these don't cover the sky with the small image sensor in the ASI 120.  For those with buildings and trees restricting their view of the sky these lenses would be adequate.

Edited March 1, 2019 by Gina

[Gina]

I've been doing more searching of the internet and it seems nobody has achieved what I desire in an ASC at any price.  Even the Oculus ASC at around £750 doesn't achieve full sky coverage.  Seems there is no fisheye lens at any price that will do what I want though the Fujinon DF1.4HB-L1 that I was using before,comes closest, in combination with the ASI 178 camera.  That lens is several hundred UK pounds new though used ones are available much cheaper, as I said above.  Of course, getting both nighttime and daytime decent images out of the same ASC is asking a lot.  One solution to this would be to have two ASCs.  The daytime one would still want a super wide angle fisheye lens but clouds don't need high resolution.

Edited March 1, 2019 by Gina

[RadekK]

21 hours ago, Gina said:

Back to the "Economy" version...  I have found RPi GPIO lines for PWM0 and PWM1 which I assume will drive two small server motors using a 1K resistor to protect the RPi.  Then I went on to see if I could find out how to drive servos via PWM with INDI and drew a blank.  I'm sure this is quite simple but Google couldn't find it.  @RadekK maybe you have the answer as an INDI expert, please.  Now I'll go back to the WiFi problem...

I'm not aware of an INDI driver for RPi PWMs. What you can do is control servos with a simple python script. Take a look at this simple example used for bahtinov mask on/off

[Gina]

Thanks.  That looks like a neater way to do it than using an intermediate Arduino.  Found tutorial on using Python with INDI.

[Gina]

In view of the way the prime Fujinon fisheye lens seems to be getting scarcer and more expensive as time goes on I have decided to buy a used one from ENS optical as linked to above.  Not an OTT price for an astro item, I guess.  I have an ASI 178MM camera I can use with it and upgrade to the colour version later on when/if funds permit.  The zoom lens and ASI 120MC-S should be adequate for daytime.  Alternatively, I could team up the prime lens with the ASI 120 for nighttime to get the star colours.  It's all "still in the melting pot".

[Gina]

I shall concentrate on the "Economy" version for the moment - I've no idea of how long delivery of the big Fujinon fixed focus lens will take, only that they say it's been sent.  OTOH most of the design ideas I'm working on will apply to both versions.  From testing the ASI 120MC-S camera and darks I've concluded that the passive cooler is inadequate as the camera temperature needs to be well below freezing to reduce noise sufficiently and I shall be going for water cooling (not as complicated as it sounds - just think of the flexible tubing for the water as cable carrying water rather than electricity).

Having decided on the cooling system, the next question is the mounting.  Whilst there are advantages in mounting the ASC on the apex of the roof such as just needing to be screwed to the barge boards there are serious problems with where the water cooling reservoir is mounted.  Also, with the rolling roof the power cable has to loop down, with a possibility of catching on something and is subject to flexing every time the roof is opened or closed.  The alternative is a mast (1¾" OD aluminium tube - very stiff and strong) attached to the observatory main framework with a strong bracket to bring it out clear of the rolling roof.  The bottom can go in the ground.  I think the mast mounting wins.

[Gina]

I think the next design decision is whether to put all the electronics in the ASC housing.  The advantage of having it inside the ASC casing is that it reduces the number of wires going into the sealed ASC casing plus the heat generated can help with dew heating (that's dew on the outside of the dome - the air inside is desiccated).  The disadvantage is that the ASC would want shielding from the summer sun to stop it overheating and also it would make the housing a lot bigger.  Silicone sealant can be used for sealing the wires where they go through the casing so I don't think that would be a problem.  Overall, I think I would prefer to have the temperature inside the ASC controllable rather than leaving it up to "the elements".

I think that's another decision made ?

[Gina]

Commercial ASCs do not have remote focus from what I can find and I think the focus should remain good once set up.  If I can do away with remote focussing I can save 4 wires from the controller to the ASC.  If I want to use the ASI 120MC-S and Fujinon zoom lens for daytime imaging it will need the aperture control.  This can also be used to take darks as the aperture completely closes.  The disadvantage is the need to include a servo motor within the ASC casing.

Connections required assuming no remote focussing :-

1. USB cable.
2. Peltier TEC - 2 wires.
3. Dew heater - 2 wires.
4. Servo motor - 3 wires.

No. of wires required is not 7 as some may be combined - a common ground for instance.  The servo motor needs ground, +6v and signal, TEC & dew heater need the +12v line as the electronics is ATM but I could change it.  If I keep the +12v line that makes 6 wires otherwise 5.  I could use a 6 way round cable or a sealed plug and socket.

[Gina]

These are the connectors I have in mind for the ASC - they seem to be sealed - I already have 4 pin and 2 pin types.

Multi Contact Multi-Pin Connector Chassis Socket or Plug Microphone Aviation x1 

[AngryDonkey]

Just looking at similar plugs ?. Got these from AliExpress:

https://www.aliexpress.com/store/product/Multi-Socket-Plug-5A-Waterproof-IP67-Automotive-Electrical-Connector-M20-Round-9-Pin-Connector/3619191_32891816934.html

they also do a waterproof USB connector if you are thinking of having a plug on the camera housing:

https://www.aliexpress.com/store/product/Factory-IP67-USB3-0-Metal-Shielded-Plug-Mount-Socket-Waterproof-Cover-Electrical-Waterproof-Car-Audio-Vertical/3619191_32859744235.html

[AngryDonkey]

On 02/03/2019 at 03:06, Gina said:

I've been doing more searching of the internet and it seems nobody has achieved what I desire in an ASC at any price.  Even the Oculus ASC at around £750 doesn't achieve full sky coverage.  Seems there is no fisheye lens at any price that will do what I want though the Fujinon DF1.4HB-L1 that I was using before,comes closest, in combination with the ASI 178 camera.  That lens is several hundred UK pounds new though used ones are available much cheaper, as I said above.  Of course, getting both nighttime and daytime decent images out of the same ASC is asking a lot.  One solution to this would be to have two ASCs.  The daytime one would still want a super wide angle fisheye lens but clouds don't need high resolution.

You've probably seen this already but it looks like the Fujinon 1.4 combined with the ASI178 does achieve 180:

https://www.astropage.nl/weather/

The ASI178MC does also provide pretty good daytime images too so you wouldn't need a second one.

[Gina]

Yes, I have used the Fujinon 1.4mm lens with the ASI 178MM and did get full coverage.  When funds permit, I'm planning to buy an ASI 178MC camera.

[Gina]

The (used) Fujinon 1.4mm lens arrived in the post this morning.  It's supposed to be used but looks brand new ?  Hooray!!  I really didn't want to mess about with the Fujinon zoom lens, I've played about with that in the past and didn't like it.  Controlling those little levers was very difficult and never really worked well. 

I have checked my funds again and realised I had money in a saver account so transferred some of that to my current account and now have sufficient funds for the ASI 178MC camera which I've ordered from FLO.  I guess I knew I was going to take that route eventually as I've done nothing towards designing controls for the zoom lens.  Only trouble is the camera is not in stock and will take a week or so to arrive.  Meanwhile I can use the ASI 178MM and get everything working with that.

Edited March 6, 2019 by Gina

[Gina]

I have two clear acrylic domes I could use (more if you count damaged ones).  The one I've been using is 3" (75mm) and an ideal size but it has slight damage near the edge on one side.  I also have a 4" (100mm) brand new, unused one so the question is whether to put up with some smearing of the image (it could be oriented towards the NW where the trees prevent a horizontal view of the sky) or go for the pristine big one that is a lot bigger than needed.  A third alternative would be to buy another 3" dome but that's more money and I've already spent too much!  I guess smeary trees are no real problem, as long as the good part covers most of the visible sky, it's good enough.

[Gina]

I'm thinking of 3D printing the outer casing in PMMA filament (acrylic) so that I can see the state of the bags of colour-changing desiccant beads (orange dry - green wet) without opening the casing.  This won't be glass clear but translucent though still showing the colour of what's inside.

[Gina]

Been trying to use a fixed focus with the new Fujinon 1.4mm lens.  I cut some thin card to put in between the size adapter and the camera body.  That wasn't enough so tried two layers which was too much so cut a piece of paper to replace the second card  and that seems about right.  I can get very fine adjustment by how tight I have the adapter.  Here are some photos with the rig pointing out of the window towards the village.  Firstly full frame then zoomed right in to the highest magnification in the KStars FITS Viewer.  The final image is with the 3" dome over the lens.

Edited March 6, 2019 by Gina

[Gina]

Here it is through an open window.  Those aren't starts in the sky, they'r hot pixels.  20s exposure with gain at 0, camera temperature 26C with no cooling.

[Gina]

Clear sky tonight but I've been out to WI and just got back.  Not quite ready for testing the water cooling outdoors as I still need to print some casing parts but I can put the camera and lens out out the mast (as long as I'm very careful).  No clear night skies forecast for at least a week after tonight!

[JamesF]

Was forecast to be clear here, too, but our delivery of holes in the cloud cover appears to be somewhat late

James

[Gina]

20s exposure - gain 300 - gamma 40 - temperature 12°C.

20s exposure - gain 200 - gamma 50 = temperature 10°C.

[Gina]

7°C other settings the same.  Cropped image.

Same image adjusted in GIMP with Curves.

Edited March 7, 2019 by Gina