Gina's DIY All Sky Cam - Complete Redesign

[Gina]

I think it probably would.  I did briefly consider writing V4L2 drivers for cameras I wanted to support.  I sobered up quite quickly though.  And in fact V4L2 is probably lacking a few features you'd want for supporting astro cameras generally.

James

I played with V4L2 a few years ago for capturing weather pics with a webcam and uploading them to my web site.  It wasn't easy to get working.  May be many updetes/upgrades since then though.  eg. 17 versions of Mint since I started using v1

[JamesF]

Yes, I found that and set it up   Then I went to set the capture for single frame or a small number of frames and found the lower limit was 500 frames or 30 seconds.  For a nighttime run, the time limit would be fine as the exposures would be quite long.

You can set your own limit if you wish by entering it in the box.

James

[Gina]

Thanks   Funny, I thought i'd tried it but couldn't have   Now set to take 5 frames with a minute between.

[JamesF]

The behaviour of the input box can be a bit odd.  It seems to try to autocomplete from the list it knows if what you enter is a prefix of something in that list, so you end up having to type in what you want and delete the rest.

James

[Gina]

Ah yes, noticed that - thought it was me

[Gina]

In day imaging mode (with solar film covering sensor) there seems to be a difference in focus between top and bottom of image (north to south).  I shall need to closely inspect a night sky image to see if this is to do with the solar film or whether the sensor is not perpendicular to the light path.  It it turns out to be the latter, I shall try turning an aluminium lens to PCB box on the lathe.  Though I don't know if my lathe is any more accurate than my 3D printer.

[Gina]

I can now capture and save single (or multiple) FITS files, move them into Photoshop via FITS Liberator and process them with curves and levels.  So I can exaggerate the contrast in the clouds

[Gina]

Nearly dark and the camera has switch to night mode.  Here's a saved and processed frame from oaCapture.  Clear clouds with just a small patch of clear sky in the west where Venus can be seen (yes, it IS Venus - I've checked in CdC).

[Gina]

The sky is clearing   A few stars starting to appear and there's still Venus to the west and now Jupiter just south of centre at around 50 degrees inclination.  I have identified the stars Alpha Bootes low in the east and Alpha Auriga higher than and slightly north of Venus in the west.   And The plough is just visible NE of centre

[Gina]

The cloud is back!

[Gina]

One thing I was able to do was to check the difference in focus between north and south on the trees at the edge of view.  The difference was negligible so I think the sensor is pretty much at right angles to the light path.  The resolution is considerably poorer to the south but this is at the very edge of the field and could be due to imperfections in the lens or the acrylic dome.  I can remove the dome to check the latter.  So the black ABS plastic QHY5 housing is fine in that respect.

Another possible reason for making an aluminium housing might be the thermal expansion - I think the thermal expansion of aluminium is less than ABS plastic.  Must see if I can find out...  OTOH temperature control should counteract any temperature effects in any of the components of the optical path and may be a better approach.

Later...  Found the thermal expansion data on this site - ABS = 73.8 and aluminium = 22.2   (10-6 m/(m K))  So it is as I thought, ABS has over 3x the thermal expansion of aluminium.

[Horwig]

Interesting point about the thermal properties, I'd have assumed the other way around, live and learn.

This might be an interesting read:

https://www.sbig.com/site/assets/files/18247/allsky340_manual.pdf

It mentions that the photos are of the prototype, which is black, but that it was changed to white for the production units due to thermal considerations...

Still struggling with my sofware, and now my lathe has thrown a wobbler, just in the middle of making some adaptors.

Huw

[Cath]

This might be an interesting read:

https://www.sbig.com/site/assets/files/18247/allsky340_manual.pdf

When you see the measures they have had to take (image below) to give the user fine enough control over the focus I guess it tells you (along with the posts in this thread) that wide angle focus is only achieved with minute adjustments.

Just goes to show we never stop learning ! .. I do like reminders like this Huw, and I think the older we get the more we need them.

[Horwig]

Yes indeed Cath, that Fujinon that SBIG use is a beast, it's a prime, but with NO focus control, so the idea of moving the focus to the base plate is genius, focus and tilt in one place. But it's not an operational adjustment, it's a setup adjustment, which is interesting.

Huw

[Cath]

But it's not an operational adjustment, it's a setup adjustment, which is interesting.

I guess that means that an all metal construction is suitably stable enough for this application without requiring further adjustments beyond initial setup ?

[Gina]

Hmm...  I wonder

Thank you Huw - that is extremely interesting and promotes several thoughts   I'll have to re-read it and note down things as I go through it but ATM I have the following thoughts :-

1. Interesting that they find it necessary to adjust the tilt even with a machined enclosure which ought to provide a sensor orientation that is perpendicular to the light path.
2. I feel the focussing arrangement is rather crude and I do wonder if the focus really does stay put with varying temperature etc.
3. Darks are very critical of temperature - I knew this of course but hadn't considered it in this application.
4. SBIG use a non-cooled camera
5. SBIG use a CCD camera rather than CMOS though I'm not sure the distinction is as great as it used to be.
6. Their lens top is above the dome centre of radius but not at the top - different from both yours and mine.  I need to test this as I think I'm getting distortion from the dome.

A few things surprise me but I guess they are trying to keep costs down.  I like to keep my costs down but this doesn't include my time and that makes a difference.

1. I think remote focus is a great boon - I've tried manual focus setup and don't rate it!  With knobs on
2. I reckon my idea of temperature control is better than their idea of the user taking darks quite often.
3. The darks variation with temperature and the uncooled sensor have triggered another thought - why not cool the sensor - I've done it with DSLRs

Having an Arduino on board increases the options considerably

I now have quite a lot to think about

And to James I would like to suggest reading the SBIG manual too for ideas to improve oaCapture and/or for add-ons to it   Please

[Gina]

Yes indeed Cath, that Fujinon that SBIG use is a beast, it's a prime, but with NO focus control, so the idea of moving the focus to the base plate is genius, focus and tilt in one place. But it's not an operational adjustment, it's a setup adjustment, which is interesting.

Huw

I considered changing the lens to sensor distance as an alternative to using the lens' own focus lever but concluded that the ultra fine adjustment required was beyond my fabrication capabilities.  I thought ordinary screw threads would be far too coarse and SBIG comment on this in their manual.  I think setting up their ASC for focus would be extremely tricky even with their bigger pixels.

My thoughts for this sort of focussing would be to use fine thread screws with a large gear reduction from a stepper motor.

[Gina]

I've just brought the assembly indoors and partly stripped it down and the lens was quite hot from the full sun in a clear sky.  I think I shall change my casing.  Currently I have a black ABS tube from the light grey box up to the dome.  I'm thinking I should use white ABS instead.  I want a shorter tube too - the lens top is too near the distorting bottom part of the dome.

Also on the subject of temperature... I think it's counter productive to have the dew heater in the lower square box where it can heat the camera chamber and hence the sensor.  I put it there because I happened to have a 10W 68 ohm ceramic resistor which is too big to go in the dome section.  I'm going to change this either for two or three smaller resistors or nichrome wire, just below the dome.

[Cath]

I have the craziest urge to ask a question

[Gina]

Please feel free   Ask your question.

[Gina]

I have opened up the camera chamber to see what's behind the image sensor.  There are several components on the other side of the PCB immediately behind the sensor so it seems Peltier cooling of the sensor is out   It might be possible to cool the air in the chamber but I think it would be quite difficult without risking dust getting on the sensor.  Other than heating (and making the noise worse) I can't see any way of keeping the sensor temperature constant ATM.

I can have the dew heater higher up though and maybe control it's heat output.

[Gina]

I tried nichrome wire in heat shrink sleeving but with what I have it takes up too much room.  So I'm going for several resistors in series - probably 4 or 5 22 ohm half watt metal film type.

The white ABS filament jammed in the printer so I've gone for light blue which works fine and I've made and fitted a replacement dome tube.  The lens is now several millimetres higher in the dome (or more correctly the dome is lower compared with the lens).

[Gina]

I've re-read the SBIG AllSky-340 manual and I seem to have pretty much covered all comments relevant to us.  I have already mentioned that the camera they use is 640x480 pixels of 7.4 microns and isn't cooled.  No doubt pretty sensitive in spite of that but with the whole AllSky-340 costing $2,495 as quoted by SBIG I must say I'm rather amazed at the low resolution.  OTOH the main purpose of the ASC is to watch for clouds for AP remote imaging use so I guess it's quite sufficient but then so would a cheaper lens like the Fujinon most of us are using - and the latter has a focus control saving all that messing with screws needing adjustment to 1/25th of a revolution!

My overall thoughts are that this is rather an odd beast.  It's huge, it's expensive and very difficicult to set up, but they've put great thought into the software.  It certainly has some interesting features but "curate's egg" comes to mind.

Reading the SBIG manual has certainly got me thinking and has given me some ideas for improving my All Sky Camera.  However, it has also made me reconsider the real purpose.  For me there are two purposes - provide warning of incoming cloud for AP and seeing/publishing nice clear images of the sky.  The latter leads on to ultra widefield astro images and maybe capturing meteor trails.  An extension of my astronomical activities into new fields

[Horwig]

An extension of my astronomical activities into new fields

Wherever will you find the time Gina?

H

[Gina]

I really don't know Huw   I was pondering over that only this morning - thinking I really need to consider my priorities...  Trouble is, my body just can't keep up with my brain!!!