Gina's DIY All Sky Camera - Mark 4 - with ZWO ASI185MC

[Gina]

Designing and printing parts to use the Fujinon lens ATM but if I find a more suitable prime lens I'll change to that.

[Gina]

52 minutes ago, ChrisLX200 said:

Depends whether you go for a C or CS mount lens, the latter mostly cover 1/3" sensors whereas the C-Mount lenses tend to cover 1/2" (12.7mm) sensors. Either will fit your camera, the C-Mount would need an extra 5mm spacer. C-Mount also _tend_ to be of better optical quality as this format is often used for machine vision devices but, as in all things, there is considerable variation. For 1/3" sensors a 1.8mm CS lens gives you 180deg coverage with a circular fish-eye FOV - and a total waste of time I would have thought for your ASI185 because you can get all there is to see onto the 1/3" sensor! A 2.1mm f/l lens gives you a 150deg FOV and is a good compromise as it cuts off much of the useless horizon area. The rectangular shape of the ASI185 sensor doesn't lend itself well to AllSky camera use because inevitably there would be [a lot of] waste pixels if you wanted to cover the whole sky, a much better prospect though if you were willing to accept a smaller FOV as you'll take advantage of the extra resolution. Stock Optics is a useful source of lenses, and Bern @ Modern Astronomy stocks some really nice lenses (though none are automatic iris models).

ChrisH

Thanks Chris   I go and have a look on Bern's site

[Gina]

No joy there.  Only 3 lenses and all to suit the QHYL-II.

[Gina]

I'm going to try the ZWO lens on the sky and see what I get.  Now printing an adapter to attach to a bracket on my test pole/pipe - a 2m length of 32mm aluminium tube with a bracket to hang on the gutter of the bungalow with the pipe through a window.  I used this when developing my earlier ASC.  A test through the window shows that the sky is plenty dark enough already for the camera to cope with the f1.2 lens

[Gina]

Here's a pic of the clouds with the moon trying to break through.

[Gina]

Just captured a 40m AVI showing a number of stars before thick cloud returned.  Using 10s frames I couldn't see any sign of noise - bit different from the QHY5L-II-C I used before

[Gina]

I'm going for the quickest build option which means the ZWO 2.5mm FL prime lens.  Last night's run with a few holes in the cloud showed that 10s frames resulted in no noticeable noise so I don't think I'll need darks.  This option rather than the zoom lens not only means I should be able to get this done quite quickly but also make most use of the camera's pixels - best option for stars and The Milky Way.  In slower time I can redo the Mark 3 version with QHY5L-II-C camera and Fujinon zoom lens and use this for the full 180° coverage for cloudwatch both night and day.

[Gina]

I'm just wondering if I could get away without a dome by sealing the casing to the outside of the lens because the dome produces slight distortion of the image and changes the focus slightly.  Last night's run was with bare lens - no dome.

[pete_l]

You could .... but.

The lens will inevitably get dirty: rain, dust, birds
When the dirt is on the dome, it's a long way from the lens / sensor, so each individual particle won't obscure much of the light that hits each pixel on the sensor.

With a naked lens, each particle of dust will create a shadow on the image,. You'll have to clean it much more frequently.

One solution I have considered is to have a motorised "hatch" that opens in front of the lens every few minutes when you want to sample the sky. Obv. that doesn't work if you want a continuous live view. But for cloud monitoring, it's enough to get an inage every 5 minutes AND it protects the camera from direct sunlight.

[Gina]

Yes, I thought of having a motorised cover for the lens originally for taking darks but now I don't think I need that.  The camera has a shutter so I imagine it's quite safe in sunlight if switched off.  Anyway, the supplied lens is intended for ASC use so the camera must but alright in direct sunlight.  I might possibly be able to find a better quality dome but I may try my present dome and see how well it works.  Of course, if anyone has a suggestion for where I can get a high quality dome I'm "all ears"

[Gina]

I decided to print a very simple basic case to start with.  This will take the dome and the USB plug will go through a hole in the case with a TPE printed square grommet to seal it.  TPE is a rubbery 3D filament which I have already used for the motor gear for my moon phase clock very successfully.  For testing the case will be attached to a plug to fit the bracket on my test pipe with gutter bracket to hold it with the ASC well above the eaves.

[Gina]

Here's a photo of the ASC on the test pole.

[ChrisLX200]

I meant to say - This was my source for the dome used here: http://www.scsastro.co.uk/catalogue/orion-allsky-camera-replacement-acrylic-dome-5857.htm?term=dome  These are made for use in AllSky cameras (hence not cheap).

ChrisH

[Gina]

Thanks Chris - I'll order one   Only a tenth of the cost of the camera and lens (neglecting carriage) so not that bad and I want a really good one   The one I'm using now can then go on the cloudwatcher ASC when I get round to doing it

[Gina]

Ordered it    I see they are in Wellington which is just a dozen miles from here so I might pop over to their shop sometime.

[Gina]

These photos show the grommet/seal between USB plug and the case.

[Gina]

Now have the ASC outdoors, hooked on the guttering.  Here's a screenshot of AMCap with exposure of 500μs and still light outside.  There is some red sky to the west.  This is as shown above with the acrylic dome.  The mast at the edge just south of east carries my weather station wind instruments.

[Gina]

20m later and the exposure increased to 10ms.

[Gina]

With no sign of a break in the cloud cover I have brought the ASC back inside and packed up for the night.  One thing I observed was that there was considerable dew on the pole but none on the dome.  Seems the camera produced enough heat to stop condensation on the dome

[Gina]

Further work on this project will have to wait until there are some clear night skies.  No point in making a bracket for attaching it to the permanent mast until I know whether it will want a dew heater.  I need at least a few breaks in the cloud.

[Gina]

Some clear patches of sky this evening - I wonlder if that will contilue until after dark   This camera and lens combo easily copes with this light level with about 120μs - well above the minimum

[Gina]

Improving ATM

[Gina]

Another image.

[Gina]

And another.

[Gina]