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Gina

Gina's All Sky Camera Mark 6 with Fujinon 1.4mm Fisheye Lens

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The Mark 5 was alright up to a point but didn't cover the whole sky and was atrociously difficult to get in focus.  I now have a new lens which is already showing promise.  I have yet to test the focussing aspect but at least the full image fits onto the sensor in the ASI178MM camera.  I shall have to design and print new supporting brackets and at least part of a new enclosure.

Here is a photo of the ASC uncased but including all parts.  The only connection required is 12v power - data communication is by WiFi.

Mark 6 with Fujinon 1.4mm Lens 01.JPG

Edited by Gina
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Won't be tonight I'm afraid - it's raining  :clouds2:

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Have designed and now printing the modified top support bracket which centres the camera in the case and hold the RPi.

Top Support 01.png

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The case will want to be 70mm taller and I have designed an extra piece to fit between the two halves of the Mark 5 casing.

Case Extension 01.png

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Top support added to camera and RPi attached.

Top Support 02.png

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Case extension printed.  Photo shortly...

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Here is the ASC in it's new case (well partly new).  Looking at the photo I think the lens wants to go further into the dome.  The light rays from low down enter the lens near its edge and rays from high up near its centre.  I think ideally the distance from lens to dome want to be as near the same as possible.  With the little fisheye lens I was using before it made sense to place the objective at the focal point of the dome but this new lens is very much bigger.

ASC 01.JPG

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This is close but I've had second thoughts.  Maybe it's more important that the light rays pass through the dome at right angles to avoid distortion, the distance mattering less.  That brings us back to the original position.

ASC 02.JPG

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I think this is the more logical position.  But the proof will come when I can test it on the stars - whenever that might be...

ASC 03.JPG

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I've printed a new case extension to match the exact extra required.  Here are some photos.  First two of the whole thing from different angles to show the lens, dome and dew heater resistors.  The third a close-up of the top, level with the edge of the lens objective glass.  I think that to get the dome material at right angles to the light path the lens needs to be lower or, more realistically, the dome higher - the heater resistors need to be below the FOV.

ASC 04.JPGASC 05.JPGASC 06.JPG

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Done some measuring.  This dome is a genuine replacement part for a commercial ASC costing several hundred pounds so I presume of high quality.  Assuming the dome is a hemisphere plus an extension to the rim I can calculate the centre of the hemisphere from the radius of the rim circle and the depth of the dome at the centre.

The ID at rim level is 95mm inside the dome and the depth to base level is 51mm.  Hence the radius is 47.5mm and the centre of the hemisphere is 51 - 47.5 = 3.5mm above base level.  So I reckon the edge of the lens objective glass wants to be placed 3.5mm above the base of the dome, which is 1.5mm above the top of the rim. 

The dome needs securing to the case with either clips or a ring holding the rim which with the specified FOV of the lens being 185° will encroach slightly on the FOV.  OTOH even 180° FOV will include trees and buildings to the north and west and I don't actually need 180° FOV.  I'm thinking a 3D printed rim will be the best way of holding the dome.

Here is a close up photo of the dome with a steel rule beside it to show where the curvature ends.  Looks like the main curvature ends about 5mm from the base but it doesn't reach vertical as would be expected if the dome were really part of a sphere.  This agrees with the measurements in that the dome is not quite a full hemisphere.

Dome 01.JPG

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Here's a cross-section of the dome, case parts and top of lens in SketchUp.

Dome 02.JPG

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Have designed and now printing the new dome securing rings.  Inner and outer rings.

Dome Inner Ring 01.JPGDome Outer Ring 01.JPG

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The dome rings fit perfectly :)  I'll post a photo or two shortly.

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All assembled and focused manually to the best of my ability and then some ie. a lot of luck.  I need the C-CS adapter so that I have finer focus.  Here is the very first image of this version hung on the guttering.  Not orientated - just poked out there to test :D

Screenshot from 2017-01-18 17-47-58.png

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All assembled and focused manually to the best of my ability and then some ie. a lot of luck.  I need the C-CS adapter so that I have finer focus.  Here is the very first image of this version hung on the guttering.  Not orientated - just poked out there to test :D

Screenshot from 2017-01-18 17-47-58.png

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This lens is certainly much better than the little 2.5mm ZWO fisheye.  Seems faster :)  This is 10s exposure with gain of 350 and Gamma at 10.

Screenshot from 2017-01-18 18-53-44.png

Edited by Gina
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This lens looks seriously sharp and fast, how do you think it compares to the old Fuji zoom lens?

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Now that the sky has cleared considerably I can see that this lens gives nice even illumination across the whole image - the little ZWO lens had a serious variation.  There is a problem with the LHS of this image - roughly north - which appears to be image tilt.  I shall investigate.

There is something wrong with the RPi control of both dew heaters and cooling - neither are working.  Just something not connected I would think.  The camera is running at +12C with an ambient of about -2C and there's no dew heating other than the heat being produced by the electronics and camera.  So far no sign of dew.  Yes, I do have the dome on :D

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Nice project Gina!

I also want to make an all sky cam with a ZWO cam.

Where did you buy the dome?

Are you willing to share the files for your 3D printed parts? 

Which kind of filament do you use?

 

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