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Gina's DIY All Sky Cam - Complete Redesign


Gina

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Another shot after adjusting the zoom and focus.  Changing the zoom changes the focus which then need readjusting.  Manual focussing is all very well wnen the laptop is a foot or so from the camera but will not be easy with the camera outside.

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I seem to have changed the zoom a bit too far so I'll move it back a little.

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Zoom now about right.  Here are two captures - 15s and 5s in PHD2.  The blob RH bottom is the moon.  Got the focus as close as I can but it's rather difficult even with the screen nearby.  I'm thinking I might add remote focussing - it would make things so much easier :D

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Unfortunately the wider the angle the more precise the focus needs to be.  Even with a 7:1 reduction ratio on the gearing, the focus knob only needs turning a few degrees to lose focus and I'm not sure I've got best focus now.

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Been looking into remote focussing.  I've used stepper motors for this in the past and this is a well known solution but I'm not sure whether I can fit one into the case.  The alternative is a servo motor and this will fit in as shown in the photo below.  My only doubt is whether these will have enough power so I shall print a quadrant pinion to fit the shaft and drive the focus spur gear and try it.  Having found (and marked) the approximate focus position, the remote focussing will only need to move the focus by a small amount and the 180 degree range of the servo will be sufficient.  In fact, one of the supplied actuator levers and a wire link would probably be adequate.

Photo showing servo motor - blue body and white shaft, bottom left.

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Further research on servos has shown that I was wrong in how they work and what they require to control them.  I was under the impression that simply controlling the voltage on the control wire would turn the output shaft but it needs pulse width control.  This would require either an Arduino or something like a 555 timer - more complication than I would like.  OTOH they are certainly up to the job - a lot more powerful than I thought.

The above shifts the balance back in favour of manual control :D  I found the 25mm OD focussing knob and 7:1 gear reduction, too coarse for adequate focus control so I'll print a bigger knob (I now have the 3D printer working properly again having cleaned the nozzle by soaking it for several hours in acetone).  I might be able to increase the gear ratio a bit but the pitch circle of the pinion is already down to 11mm diameter.

I guess I can mount the ASC on the NW corner of the warm room and place the laptop on the warm room roof for focussing.

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I'm putting the ASC near the SW corner of the warm room as the position requiring least offset from the body of the observatory. 

Previously I had a pole attached to the NW corner of the warm room with the brackets bringing the pole all of 3" out to miss the roof when open.  3D printed brackets proved inadequate to take the bending moment of the considerably overhung pole - one bracket at the bottom and the other just below half way up leaving the top with camera blowing about in the wind!

The new arrangement will have an aluminium pole be attached to the roof running rail support post and take the ASC up above the roof when open.  This position also means the shortest practical distance from main power supply and laptop (or I might use a separate computer to run the ASC due to lack of USB2 ports on the main laptop (just one USB2 and one USB3 and while USB3 is supposed to be downwards compatible I haven't found it is :().

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Gina, As you know I am a big fan of servos! Why not do the conversion Like I have done with a stepper motor in place of the dc Motor? I can say with confidence that the accuracy and control is superb. If you prefer, you can still use PWM to control the original dc motor with a nice little board from technobots, I used these on one of my large guidescopes to move the position of the guidecam via simple resistor pots.Boyd

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Mounted and working :)  Not dark enough for stars yet but enough to open the shutter.  Now to go out and set up the laptop on the roof and see if I can get the focus better.  Or wait until I can see some stars...

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Some stars showing and I've been out, put the laptop on the roof, climbed the steps and adjusted the focus :)  It was a bit out but that bigger knob was great - I was able to fine focus on a star almost overhead.  Here is a screenshot via TeamViewer.  West is at the top.

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And here is a 4s image captured in PHD2 unbinned, saved on laptop, transferred to desktop via TeamViewer, processed in Photoshop with curves and levels and saved in PNG format.  I cropped the LHS a little.

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And a 15s exposure.  Used GradientXterminator to counter a bad left to right gradient.  Cropped a bit of the LHS, applied levels and saved in PNG format.

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Well... Basically the ASC seems to be working but there's this serious brightness gradient which, if uncorrected, makes image processing difficult.  I have been processing captures frames individually but in the future I shall want to collect frames automatically and publish them on the web or produce time-lapse videos.

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This gradient does not occur in my previous design of all sky camera so I'm now examining what the difference may be.  It's as if light is getting in but the only light is the LED on the QHY5 and that has not changed.

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I think I may have it :D  The light side is the same side as the dew heater - maybe it's heat not light...  I'll disconnect the dew heater at the supply end and see it that cures it.

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No not that - dew heater now OFF - disconnected! :(  Should have cooled off by now too. 

Here's latest screenshot.  Moon is now well up and starting to drown everything out!

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Having slept on it, I'm no nearer solving the gradient problem.  Still there with the dew heater off - in fact later images showed dew on the dome lit by the moon.  I'm stumped! :(  Anyone any ideas, please :)

On the plus side the shutter works as expected and the manual focussing works well :)  I'll collect some dark subs when we get a nice dark night with no moon - can be cloudy too.  The enclosure may not be light tight enough for 15s darks if the moon is out.

Don't know why but I seemed to be capturing fewer stars last night than with the previous design and using the same camera, lens and software - PHD2 and 15s.  I guess the sky may not have been so clear.

My feeling is that the QHY5 is just barely sensitive enough for this application.  I think I shall have to look into alternative software - a longer maximum exposure time might be helpful.  Maybe I should start a thread devoted to that just as Huw has with cameras.

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So nobody has any idea of what could be causing the gradient then? :(

I've connected the dew heater again since that wasn't it.  It's clouded right over now so I doubt we'll see any stars tonight :(  I coould capture some darks though, when it gets dark enough.  ATM there's lots of stray light getting under the shutter - this screenshot shows the stray light causing shadows on the sensor from the fine gold wires round the edge :D

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Does the gradient rotate with the camera?  I'm wondering if this is light that is getting in through the lens and bouncing around inside the camera body.  Or perhaps it's from the LED and bouncing around the camera body.

In "pre-Gina" guise the QHY5 sensor has a black foam insert around it.  From one of your earlier pictures I believe you removed that?  Perhaps it's necessary for blocking stray light?

James

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I'll try rotating the camera (the whole unit and pole) later when it's dark enough to use a long exposure - it doesn't show at short exposures.

Yes, I did remove the black foam from around the sensor but that was before the earlier images where the gradient doesn't show so I think we can rule that out.  Good thought though :)

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I'm now running SharpCap rather than PHD2 to see if there's any difference.  The max exposure time is greater with SharpCap.  Here's a screenshot.  I haven't climbed up to check but I think the dark splodge on the right of the image is down to a bird :(  Christened already :grin:  Two or three stars out now and lots of cloud.

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