All Sky Camera

[Gina]

I've now searched SGL for the thread I was convinced I'd written on this several time now without success so I'm starting again.  I'm sure I didn't dream it!   I'm also sure I'm not going senile!!!  The dreaded lurgy is sapping my energy both physically and mentally but I believe I can still function albeit at a lower level than usual

Now I'm going to search my Pictures library and see what I can find for this project.

[JamesF]

I know you started posting images (I think from the Lodestar?) with a short focal length lens.  Is that the thread you were thinking of?

James

[Gina]

Yes, a fair collection of photos   Here are a few to start off with

One of my daytime images just after sunset.  As can be seen the software used for capturing is PHD2.

I think this is the latest version of the hardware, showing the outer casing and plastic dome.  The latter was purchased from Amazon as a casing for CCTV cameras.  The inner grey plastic shield comes out leaving a full 180 x 360 degree clear dome.

The basic components are a Fujinon wide angle lens and QHY5 camera.  I took the circuit board out of the case of the camera as the original casing wasn't suitable.  A black 3D printed plastic housing connects the lens to the camers board with provision for a shutter with Baader solar filter for daylight use which is moved out of the way for nighttime use.

[Gina]

One thing I spent a lot of time on was finding something to turn the shutter blade that would be reliable enough to ensure that the camera sensor would be protected from direct sunlight in daytime.  The latest system uses a solenoid recycled from an old video recorder.  This moves a 3D printed lever with a gear tooth rack on the end which in turn engages with a quadrant gear to turn the shaft of the shutter.

These pics show the principle.

Have to say that I'm not completely satisfied with this and I might have a rethink.

[Gina]

The mechanism is held between two plates which in turn fit into a clip together framework - all 3D printed ABS plastic.  The framework fits inside a cylindrical outer casing with plastic dome on the top and cone shaped attachment to a mounting pipe on the bottom.

[Davey-T]

There you go.

Dave

http://stargazerslounge.com/topic/121275-diy-all-sky-cam/page-17#entry2385473

[JamesF]

I was sure there was a QHY5 involved somewhere too, but as it wasn't in your signature I thought I must have been mistaken

There was a discussion a few months back on the ASI camera Yahoo group about all sky cameras.  The chap from ZWO seemed to think that it wouldn't be necessary to protect the sensor from the Sun.  I have to admit hat I'm sceptical, but perhaps it's worth considering.  I don't know how we'd go about deciding though.

James

[Gina]

The plastic dome needed some alterations for use with the All Sky Camera project.  In the end I removed most of the bottom of the base to allow the lens to go through.  The outer housing was designed to fit the dome base. 

[Gina]

There you go.

Dave

http://stargazerslounge.com/topic/121275-diy-all-sky-cam/page-17#entry2385473

Ah yes - thank you   I see now why I couldn't find it - not my thread   I did do a general search though which didn't pick it up

So I needed to start my own thread anyway then

[Gina]

I was sure there was a QHY5 involved somewhere too, but as it wasn't in your signature I thought I must have been mistaken

There was a discussion a few months back on the ASI camera Yahoo group about all sky cameras.  The chap from ZWO seemed to think that it wouldn't be necessary to protect the sensor from the Sun.  I have to admit hat I'm sceptical, but perhaps it's worth considering.  I don't know how we'd go about deciding though.

James

I guess the QHY5 isn't in my signature because last time I updated it I wasn't using the QHY5.  Sorry about that

Those ZWO cameras aren't cheap1   I'm not sure I'd want to risk it with one of those.  It would save an awful lot of bother if the sensor were safe in magnified sunlight.  I guess we need someone with either very deep pockets and a sense of adventure or someone with more money than sense   Now if ZWO would guarantee that their sensors were safe without solar protection we would be onto a winner.  I gather the ZWO cameras are somewhat more sensitive than a QHY5 so would make for a much better All Sky Camera for use in day and night times.

Were they talking about OSC cameras or mono?

[JamesF]

I'm not sure which it was.  I've tried to find the original posting, but it's defeated me for the moment.  I'll give it another try later.

James

[JamesF]

This looks rather neat: http://www.skyinspector.co.uk/AllSky-Camera(2587059).htm

James

[Gina]

This looks rather neat: http://www.skyinspector.co.uk/AllSky-Camera(2587059).htm

James

Interesting   The exact same lens model as I'm using.  The lens is directly mounted on the camera with no provision for solar protection in the daytime.  The videos clearly show that he used a colour camera and the videos include daylight either at the beginning or end or both so one must assume that the camera was exposed to the rising or setting sun.  The article shows the camera mounted on the gable end of a garage roof - I hardly think it would be removed or even covered up in sunshine. 

I think it would be a pretty safe conclusion that the ASI120MC camera is safe from destruction/damage by magnified sunlight

I was considering buying an ASI120 camera for planetary imaging some time in the future but I think one would be more useful as an all sky camera.  When my funds recover I might just get one.  Seems the colour version is fine for all sky and gives a nicer result.

Those videos show a much better result than I have achieved with the QHY5

[Gina]

Been playing with the shutter control linkage and I'm far from satisfied.  The construction precision required seems to be at about the limit of the 3D printer.  It may be possible to adjust the printer settings to get good enough prints but I still have to drive the solenoid with a power transistor of FET.  I'm wondering whether to use a servo though that wouldn't have the failsafe feature.

[Gina]

I've redesigned the solenoid lever.  The previous one was too flimsy and broke when I tried to use it.  I think this system may be workable after all.  If it is it will save me redesigning and reprinting the body framework.  One thing I have done since I last worked on this project it to very carefully calibrate my 3D printer.

[Gina]

Matching quadrant gear and axle.

[ollypenrice]

The Robots, as I call them (the group running robotic scopes from my place) have just installed one of these. It has rather curtailed my style. I used to like going up onto the house roof at night, declaring independence, announcing my new set of postage stamps, making indiscrete references to Joan of Arc and hurling abuse at passing enemy aircraft. (Surprising how many there are.) I now have to do this from within the observatory to avoid detection...

lly

[Gina]

Problem printing the quadrant gear and axle   Although the SketchUp model is correct, the printer insists on printing a hole where the axle should be in the quadrant gear.  This results in no connection between the axle and the gear when printed out.  The axle itself is quite strong and perfectly adequate in itself.  I've had sillies like this with 3D printing before.  This is quite incomprehensible - the only answer seems to be to use a separate axle with a hole through the gear.  Computers are magic and so are 3D printers    Well, actually I guess it is the computer

I can either print out an axle or find a piece of 3mm SS rod.

[Gina]

I'll leave that for now and concentrate on powering the solenoid.  I'll get my bench PSU out shortly and see what voltage and current it requires.  Meanwhile, I'll think about the circuit.  I though I'd already produced a rough design but I can't find it.

[Gina]

Here is a design for the solenoid control circuit.  Component values will depend on experiments with the LDRs and solenoid.  (When I've found the LDRs I bought a while back )  I may add positive feedback to make the circuit switch rather than analogue.

[Gina]

In fact this might work though with gradually changing light level the MOSFET will be only partly ON producing heating.  Whether this matters will depend on the current drawn by the solenoid and the power rating of the MOSFET.  I have power MOSFETs with TO220 style case.  OTOH some positive feedback to make a Schmitt trigger would be better.

[Gina]

This might work   Schmitt trigger circuit using MOSFETs.

[Gina]

Been working on the solenoid shutter mechanism.  Initially finding difficulty in getting it free enough.  The solenoid draws 0.7A at 13.8v which is a quite a lot I think and it starts to get hot after a while.  Of course, it will take a lot more current to pull in than to hold so I could use an electrolytic capacitor fed through a resistor so that it gets a pulse of high current when actuated which would die away once pulled in.

I've got the mechanism working and on test it needs 12.5v to pull in but will hold on 2v so I'll try using a pulse for pull in and then hold at much lower current.

[Davey-T]

I'm sure there must be a better way than having the solenoid drawing power continuously, got something in my head, keep doodling but can't get it on paper

Dave

[Gina]

Well the point is to have a mechanism that will close the shutter if the power fails, for safety, to stop full focussed sunlight falling on the image sensor.  Anyway, once operated it only needs 2v and 200mA to keep the shutter open.