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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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Looks like a nice clear sky - rather out of focus!  Still sunlight to the SW but the Milky Way is visible.  Pity the stars are out of focus!

5a088cd21531f_Screenshotfrom2017-11-1218-00-48.thumb.png.4d97fe152e10b678d8919a09e0e46106.png

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I guess that to provide full control over the focus and angle it would need three adjusters as there are three dimensions to adjust.  These could be vertical motion at three points at 120 degrees around the lens.

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Brought rig in and adjusted focus.  Put it back out without casing.  Exposure 10s, gain 240, gamma 20.

5a08909b31470_Screenshotfrom2017-11-1218-17-06.thumb.png.050374f1292fdfb6237d06bf087bee0f.png

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Screenshot from 2017-11-12 18-54-00.   Exposure 20s, gain 240, gamma 1, Camera temperature 3.2°C.

5a0899a2bded4_Screenshotfrom2017-11-1218-54-00.thumb.png.9caf2a3e4c2bf909facb1ef4ffafa640.png

Edited by Gina
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Regarding focus etc. I shall need to redesign the camera to lens holder to allow for three vertical adjuster screws whether manual or remote controlled.  May need springs.

It's looking rather like it may need a new casing :eek:

Edited by Gina

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Here's a diagram showing a possible method of providing manual lens adjustment.  This is a simplified diagram that doesn't show the offset.

5a08d7b53c985_LensSupportDiagram03.thumb.png.26991a39cba0704dbca1cf509a696dd5.png

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Another image.  Screenshot from 2017-11-12 23-16-41.    Exposure 20s, gain 240, gamma 1, Camera temperature 2 .2°C.  Some cloud coming in.  Orion has risen but seems to be in a bit of thin cloud.

5a08de5f22eb3_Screenshotfrom2017-11-1223-16-41.thumb.png.14f0952c5aa7ab24a5e3be78bf326332.png

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Here's an image captured just before dawn this morning.  This is the FITS file cropped in GIMP.  It was the wrong way up so I had to flip vertically, also there's no sign of colour which is puzzling.

Light_20599.thumb.png.670cfc48f8ef6942f78b70e25dde163d.png

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This turned out to be a GIMP problem as the file opens correctly in PixInsight.  While there I cropped the image to just the relevant portion and increased the gamma a bit.  Some problem saving in PNG so I saved in JPG format.  Exposure 30s, gain 240, gamma 1 (but increased in PI) and camera temperature was close to freezing.  When I brought the rig in this morning the camera had a couple of mm of ice on it.  (Rig was uncased.)  Could probably do with some thermal insulation round it.  Focus seems good - if I could retain this I would be satisfied :D  Nice image of Orion about to set though Betelgeuse and Rigel are overexposed and lost colour.

Light_20599.thumb.jpg.5be5de86d0364ea9e81df980b071612c.jpg

Edited by Gina

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Some bright red TPU, a springy filament, will provide the spring for the lens adjuster and also thermal insulation and sealing of the camera top to help with cooling and also stop condensation on the camera window.

5a09ca04cec8b_SpringRing01.png.e0a29999f99c6505f4370917e148bcd7.png

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Soon be ready to assemble the lens adjuster parts with lens and camera and try it out.  Having got the focus so good it seems a shame to take the thing apart but it would only need a touch on the side of the lens and it would be out again.

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Slowly getting there :)  The domeless approach really does seem to be paying off.  Seeing the stars even with the moon in the FOV was never really possible with the dome and however good, the dome always seemed to produce some distortion.

I've decided that trying to keep the present casing is causing more trouble than it's worth.  A new casing is only likely to cost around a fiver plus some time and effort to design but the time and effort to make things fit the present one is just as bad.  I'm not even happy with the way the stepper motor is supported and covered.  Consequently, I'm firstly concentrating on getting the lens adjustments sorted out and this may include some thermal insulation for the camera.  Printed plastic with the air cells contained in it makes a very good insulator and can combine that with the mechanical aspects.

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This will fit over the camera.  Grub screws either side (top & bottom of sensor) will allow adjustment for offset.  The other three holes will be tapped for the lens angle and height adjustment screws.

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This is not proving easy :(  The adjustment for offset doesn't work very well.  I reckon it's going to need another re-think!!

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Going to try a simpler approach - large holes in the three legs of the lens adjuster then washers under the heads of the adjustment bolts.

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Much better :)  Adjusting the offset was easy.  Moving lens in tube by hand was the coarse focus and adjusting all three adjuster screws together provided fine focus.  Individual screws will provide differential focus if required probably by trial and error on the outdoors.  Can't put it outside ATM as it's raining.

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Rain has stopped and I've put rig on the guttering.  Next door have their gazillion power floodlight on but here is the image anyway.

5a0b3ae7a5a1c_Screenshotfrom2017-11-1418-45-58.thumb.png.4410747a3ed6bcd437d0b092d7e32e76.png

Edited by Gina

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Light now off so new image.  Exposure 10s, gain 150, gamma 50, temp 9C.

This image shows the problem with the differential focussing.  To the east the focus is good, in fact better than I've achieved before but to the SW it's way out.  NW seems reasonable though it's a bit difficult to tell.  To bring the rig indoors, tweak a screw setting the put it back out and see if it's any better and repeat until good focus would be very tedious and time consuming.  This is not helped by interaction between the adjuster screws.

5a0b50b74576b_Screenshotfrom2017-11-1420-20-44.thumb.png.700e116efaa314235dd4ed8c3579601e.png

 

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Conclusion from above :- The offset adjustment seems alright now but the lens adjustments are far from it.  One possibility would be to remote control the three lens adjustments.  This would be possible but quite a lot of work.  It should be possible to get the lens perpendicular to the front of the camera but there is still the focussing.  The problem is how to retain perpendicularity whilst changing focus ie. moving the lens up and down.

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Here's a photo of the lens adjustment system.  Even if I got this correctly set, it won't stay that way due to the plastic moving under pressure - it's already bending.  Having the spring in the middle and adjuster screws further out on arms is not going to be satisfactory.  I had set the lens upright by arranging the room lights at the edge of the field in each of the three directions.  Then I adjusted focus by giving the screws the same number of turns.  But by the time I had the rig outside on the guttering the focus had changed.

5a0b624ac6dce_LensAdjuster04.thumb.png.fc4d8c2d791ebb5ebfaa2e8bf4816031.png

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I think I'll go for very small compression springs on each screw and replace the sealing/spring ring with soft plastic foam just for thermal insulation and sealing.

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