All Sky Camera Revisited

[Gina]

I might see if I can arrange some sort of shield to block that light, at least from the lens if not the whole dome.

[Gina]

The light is only just inside the FOV and I think I might be able to exclude it from the lens by tilting the ASC & mast a few degrees.

Edited March 26, 2019 by Gina

[Gina]

Light is off.  Exposure 60s, gain 200, temperature -15°C.

[Gina]

Conclusions from tonight's imaging :-

1. The focus is much improved over last night but could still be better - remote focussing is back on.
2. The image is showing some noise which may be diminished by running the cooling at maximum.  Better focus should improve S/N.
3. A small shield could stop next door's floodlight from shining into the lens - shielding the dome would be more difficult.
4. 60s exposure is showing no elongation of stars.

Edited March 26, 2019 by Gina

[Gina]

Exposure 60s, gain 400, temperature -16°C.

[Dr_Ju_ju]

Don't you just hate neighbours, who are scared of the dark..... and then there are the street lights, but for me, apart from main roads, they switched off between 11~12.

[Gina]

The neighbours are friendly and do turn their floodlight off when they're not using it.  What it needs is for someone to take a long ladder to it and point it more downwards so that it doesn't shine into my property so much.  I plan to broach the subject when I get the opportunity.  It doesn't affect imaging from my observatory as it's behind the roof when it's open.  The orientation of the observatory was planned to avoid the light - the previous neighbours were not so approachable as my present ones.

[Gina]

I could do with that extra stop of aperture I got with the Fujinon fish-eye lens (f1.4 c.f. f2 of the present lens) but I can't be sure that the batch of them that ENS Optical have are not all the same as the one I bought from them.  The fact that they have sold 200 and no other dissatisfied customers does not necessarily mean the rest are fine and I was unlucky.  Without a perfect lens to compare with, other customers could well be satisfied with imperfect ones.  These lenses are not specified as new but the one I bought looked new so I'm wondering if these are seconds.  Probably no point in asking Steve of ENS Optical as I have no doubt he would say these lenses are perfect. 

OTOH I'm not yet getting the best results from my present lens and camera.  Better focus should increase the brightness of stars and I can get a lower temperature in the camera which should reduce the background noise, assuming this is thermal noise.  Previously I was seeing the Milky Way but no sign of it now.  I know it's better in summer but I think I should be able to see it.

Edited March 27, 2019 by Gina

[Gina]

Returning to next door's floodlight for a moment, this image shows the top of their house and the light is in the apex of that white triangle.

[Gina]

The amount of movement required for fine focussing of the lens is of the order a few degrees and therefore a lever may be more appropriate than a spur gear and provides another option.  I'm thinking the focus motor will probably go below the camera and cooling system though to one side may be another option.

I need to redesign the outer casing anyway to accommodate the new dew heater as it is bigger than my current heater.

Quote

The inner diameter of the module is 52mm, the outer is 72mm

The ID of the top of the casing is currently 69mm so I need to gain 3mm diameter or 1.5mm radius.  This is quite possible without going for the bigger dome and the current dome would be better heated as the heating elements would be round the edge.  This diagram shows a transparent view of the top of the outer casing where the dome fits.  To show the scale, the top ring that goes inside the dome is 2mm wide

This shows a modification to accommodate the new dew heater.

Edited March 27, 2019 by Gina

[Gina]

I've knocked up a quick assembly model of the printed parts of the ASC to check clearances and it would seem that there might be room to arrange focus motor control to the lens.  It will depend on how thick the new dew heater module turns out to be.  Might be easiest to have the motor at the side of the camera casing in a sort of "pod" on the outer casing.  I've made the outer casing transparent to show the inner parts.

Edited March 27, 2019 by Gina

[Gina]

Image tonight.  Exposure 60s, gain 100, temperature -13°C.

[Gina]

Managed to catch the ISS.  Took the timing from Clear Outside and set the image capture to continuous 60s exposures just before it was due to appear in the west.

Edited March 27, 2019 by Gina

[Gina]

Heavy dew this morning - current dew heater is definitely not sufficient.

[Gina]

No new dew heater today but had email to say they sent it off this morning so hopefully it may arrive tomorrow.  I might investigate motor focussing this afternoon.  No point in procrastinating - I've achieved all I can with the present setup so I think I'll bring the unit indoors and have a play.

Edited March 28, 2019 by Gina

[Yawning Angel]

Gina, does the evaporated moisture, from the heater, have somewhere to go? When I had delusions that I could build one, I'd thought to blow the hot air from the peltier sink up the dome like a car windscreen de-mist, then vent it out of a side louver vent

[Gina]

Only the outside of the dome can mist up as the inside is desiccated by two 10g bags of silica gel granules.  Dew on the outside simply evaporates off to the atmosphere (or doesn't land on the dome at all).

I too thought of using the heat from the Peltier TEC to warm the dome but found it too difficult.  In fact, with the water cooling the hot side of the TEC is being held close to the ambient temperature inside the observatory scope room.

Edited March 28, 2019 by Gina

[Yawning Angel]

I didn't twig it was the outside...sorry. 

7 minutes ago, Gina said:

found it too difficult

This was where my whole idea stalled ?

 

[Gina]

Many people seem to think an all sky camera is simple but it isn't.  If you want good night views (on a clear night) the requirements are the same as for other imaging rigs, but more difficult in some ways. You need a fast fish-eye lens and an astro camera, preferably cooled.  A big problem is that, unlike "normal" imaging rigs only used in dry weather (except for dew), an ASC is usually fixed and open to all weather.

[Gina]

Nothing done this evening as I've been out but before I went out I designed and printed a cone to fit on the lens focus ring and extend down the side of the camera casing.  A future version could have teeth on the lower edge to engage with a pinion on a little stepper motor.  I have yet to decide whether the motor will be beside the camera casing or below the waterblock.  I'm hoping there will be room for this cone below the dew heater module but I won't know until it arrives and I can try it.

Edited March 28, 2019 by Gina

[Gina]

Dew heater included in assembly assuming it's 2mm thick which leaves a gap of 1mm between dew heater and focus cone.  If the dew heater is 3mm or more there's a problem.  (This drawing is not quite right - some components are skewed slightly but it shows the idea.)

Edited March 28, 2019 by Gina

[Gina]

Dew heater module has arrived and it's good news - the PCB is about 1.5mm thick so no problem.

[Gina]

I'm now trying to work out where the 28BYJ-48 geared stepper motor will go.  It's looking like just below the camera housing.  Between that and the baseplate.

[Gina]

There's a lot of work to do to get to the point of being able to even try the remote focussing and it will not be ready for testing on the stars tonight.  Whether it will be ready for tomorrow night depends on how things go but I'm not holding out much hope.   A couple of the new prints will take several hours.

Here's a photo of the focus cone with ring gear. 

 

[Gina]

The neater way of having the flange used for bolting the outer casing and baseplate parts together on the inside is not very practical so I've changed over to an outer flange which will be much easier though not as pretty.  Here is a model of the new baseplate with stepper motor mounting.  This is 160mm OD.