All Sky Camera Revisited

[Gina]

Looks like here we go again!!  With a new design of ASC casing.  Must say, I'm not really happy with the idea of setting the focus manually and relying on it not changing over many months of use.  I don't want to have to keep taking it down and removing the dome to reset the focus so remote focussing seems to be on the agenda again!!  Groan!  The main imaging lenses needed a 6" quadrant gear (lever) with a stepper motor with small pinion engaging it.  I would rather not have to enclose a 6" lever within the ASC casing!  The problem is getting reduction gearing without too much backlash.   I shall have to get thinking...

Another thought is an external cover for the dome to use when not using the camera.  Although it's quite capable of daytime imaging and can produce some rather nice pictures of the clouds scudding across the sky, I don't want much of this and mostly the ASC is not used in daytime.  Nor is it used when it's raining.  A cover would keep the sun off in the daytime and insect and bird droppings at any time.  It should lengthen the life of the dome and reduce cleaning.

ATM the electronics is in the observatory rather than within the ASC casing but if I add remote focussing and remote dome cover control that's a lot more wires between electronics and ASC and it would make sense to have the electronics in the ASC casing.

[DaveL59]

ah the "fun" never stops hey Gina 😉

I'm surprised focus has shifted that much though, but then you heavily cool yours where mine just have to cope with the norms of exterior temps plus however hot it gets inside the casing. So far neither have shown much focus drift but then again if I needed to tweak them the domes can be removed fairly easily. Perhaps they're holding a little better being bare board with the lens in a holder directly mounted to the board compared to your ASC unit?

I've yet to have issues with droppings on the dome but then I'm not located next to a pond, there's really only a large oak nearby where the birdies gather 🙂 

[Gina]

Actually, I've been very lucky with lack of droppings on the dome.  Not had a bird dropping so far and I guess fly droppings have been washed off by the rain or are so small and out of focus that they don't show.  I didn't notice anything when I washed the dome.

[Gina]

The most important change will be in the dome sealing.  This will be a 3D printed ring which will sit on the small flange on the dome and clamp it to the body of the ASC with a rubber sealing ring.  This means a change to the part the dome sits down onto.

This is the current arrangement of the sealed part of the ASC.  The dome is outlined in red to make it show better.  The conical shaped section will need to have a wide, flat top to take the clamping ring.  I shall split the clear blue part into two to make in printable without support material.

[Gina]

Two possibilities for the screws that hold the ring to clamp the dome.  Tapped holes in a solid lump of PLA or a flange with nuts and bolts.  I think one problem with the old arrangement is that the wind could blow rain up the cone and under the dome.  This flange would stop that.  Also, since there is a possibility of needing to remove the dome more than once in the future, metal nuts are more suitable than threaded plastic!

Edited September 2, 2020 by Gina

[Gina]

Found the ideal rubber ring for sealing the dome.  Have to buy 10 off when I only need 1 but no matter! 

Nitrile Rubber O-Rings 95mm OD 85mm ID 5mm Width, Metric Buna-N Sealing Gasket, Pack of 10

[Gina]

Oops re-read the description and those are not UV resistant so have cancelled order and ordered a couple of these instead.  These ARE UV resistant.  More expensive but better for the job.  Ordered one and a spare so 2 off.

Silicone O-Ring, 90mm OD, 85.2mm ID, 2.4mm Width, VMQ Seal Rings Gasket, Red

[Gina]

New camera housing and dome flange.

This part goes on top and covers the top of the camera for thermal insulation and also carries the dew heater.  Plus it holds the O ring in position.

Edited September 2, 2020 by Gina

[Gina]

The three new parts have now been "sliced" and ready for 3D printing tomorrow.  I've ordered a new dome as the old one has silicone sealant on it which I can't get off and this would spoil the seal with the O ring.

[Gina]

This small redesign only allows for the new dome mounting and not remote focussing or remote controlled cover.  The aim is to get the ASC working again ASAP.  I can work on a major change with remote focussing and dome cover in easy time without the pressure of wanting the ASC in use.

[Gina]

Printing is going well, the O rings and new dome have arrived.

[DaveL59]

sounds good Gina and the O-ring will mean future maintenance will be easier too 🙂 

[Jonk]

I’ve been watching this with interest.

Rather than focus the lens by turning it with a stepper / gear combination, could you move the camera / sensor pcb up and down, in the same way as a telescope focuser?

I found there’s too much play in the lens thread and a slight tilt makes the difference.

A fixed lens and moveable sensor board might be better.

I know you’ve kept the pcb in the aluminium body, but I tried this and too much condensation was formed.

I plan to remove the sensor board and use a smaller tec nearer the sensor, with the whole board adjustable vertically.

I wondered if you considered this or tried similar?

[Gina]

I have certainly considered taking the sensor etc. out of the casing but the lens to sensor distance has to be accurate to microns!!  In the past I have used fixed focus lenses in my ASCs but using the mounting thread for focussing was far too coarse.  The lens I'm using now has a focus ring and focuses using a very fine thread.  This is a lot better but still needs just a few degrees rotation to take the focus from good to dreadful.

I have a few ideas for finer focussing.  I can get rid of backlash with a spring but have to be careful to avoid plastic creep.  One idea is a lever and cam.  Another is a threaded rod and nut moving the lever.

[Gina]

I'm considering using manual focus but using a shaft brought out through a gland so that I can refocus without taking the dome off and also providing very fine control.

[DaveL59]

15 hours ago, Gina said:

I'm considering using manual focus but using a shaft brought out through a gland so that I can refocus without taking the dome off and also providing very fine control.

Hope a wee birdie doesn't think "oh a nice perch to rest on" and shift the focus 😉 

[Gina]

Hmm - I see what you mean!!

[Jonk]

Just make a lever detachable, using a simple thread.

Or, a screw head on the outside face to adjust focus.

[DaveL59]

a couple of my eyeball type CCTV cameras are done that way for zoom and focus, very handy for making the odd tweak with just a small screwdriver. No issues with moisture so could be the simplest solution.

[Gina]

I have now stripped the ASC right down - needed if only using the O ring to seal the dome.  The wet is evident everywhere, even the copper waterblock has gone green!  But the cause is known and can be fixed.  Focus is a different matter, even manual focus.

[Jonk]

It must be condensation. You either need ventilation, or purge with argon and then seal.

[Gina]

No, I used silicone sealant which failed and the rain got in.  The new plan is O ring sealing.

[Gina]

For even manual focussing I shall need a re-design.  Whether I can do it with the current size dome etc. remains to be seen.

One possibility is to buy a bigger dome and O ring, such as a 4.5 Inch Clear Acrylic Dome for use in all sky cameras.  This would provide more room to get a focussing mechanism in and also with the centre of curvature being near the bottom (as opposed to being 18mm above in the case of the present 3.5" dome) the mechanism would not need to be totally inside the dome. It would mean spending another £25 on parts but I guess this is a small price compared with the overall cost of the ASC and particularly with astronomy in general.  I'll work on the design and see.

Edited September 9, 2020 by Gina

[Gina]

I've ordered the 4.5" dome and corresponding O ring.  Decided there was no need to give myself a harder job for the sake of a few quid!!

Edited September 9, 2020 by Gina

[Gina]

Stage 1 - Camera, lens and dome.  The top of the camera is going to have to be slightly above the centre of curvature to allow 180° FoV.  Hopefully, this won't be enough to cause distortion and elongated stars.  The smaller top part of the lens rotates to focus.