Gina

Most of the clouds have gone away

Another capture.

Much better

So far so good - Orion is pretty clear

I don't know how long Orion is going to be visible - there's cloud about.

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.

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

Here's a screenshot of a 60s sub at gain of 600 and -30C of Orion - just risen in the SE - ground in the image.

Image histogram stretched in GIMP.

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

There are dust bunnies but I suspect this image may be exaggerating them.

Focused on the far tree and also moved up into the sky to see what dust bunnies appear - just a few faint ones so vastly better than last time (see image above).

Fingers crossed for tonight I've brought the imaging rig indoors and given it a good going over with my rocket blower - there was quite a lot of dust on the filters - now there's a lot less. I also added the Astrodon 5nm Ha filter into the last free hole. So I now have Ha5, Ha3, OIII3, SII3 and Luminance IR/UV cut, in positions 5 1 2 3 4

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

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

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

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.

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.

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...

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.

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.

Case extension printed. Photo shortly...

Top support added to camera and RPi attached.

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.

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