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

[Gina]

60s exposure, gamma 1, exposure 120 (half normal)

[ChrisLX200]

Brings it home how bright a full moon is! Internal reflections from the dome are only to be expected - it's actually handling it very well under the circumstances. I tried my colour GPCAM last night and it's amazing how less sensitive the OSC camera is than the mono, we're talking about 4-5x longer exposures needed.

ChrisH

[Gina]

That much?  I've been considering buying a mono camera.  An ASI174MM would give me better coverage as well as more sensitivity.

[ChrisLX200]

That's how it seems - perhaps partly because resolution is better without the Bayer matrix so fainter stars appear sharper and easier to see. I normally use 3 second exposures with the QHY5L-II mono currently installed in my ASC, a 3 second exposure shows very little at all using the colour GPCAM. The mono GPCAM-II is even more sensitive than the mono QHY (and with markedly fewer hot pixels!). I have a colour QHY5L-II as well but I don't use it much. I haven't made any comparative movies but I will try next time out.

ChrisH

[Gina]

I used a QHY5L-II-C in an earlier version but noise was a problem together with hot pixels and lines.  The ASI185 colour camera is vastly better. 

I have another thought - I wonder what an Ha filter would give    With a mono camera, of course.  Might try one of my Atik 460EXs just for fun

Still looking at ZWO cameras to upgrade.  I think I shall go for mono for the much better sensitivity. 

The ASI178MM looks like quite a good bet - very low read noise with an image sensor marginally bigger than the ASI185MC I'm using ATM.  Cost £378 from FLO. 

The ASI174MM seems to suffer from amp glow with long exposure and the read noise is a lot more.  On the plus side, the coverage fits the lens for 180° FOV and bigger pixels will mean higher sensitivity.  £601 for the standard version and £903 cooled.  I imaging the cooled version would fix the amp glow but the read noise is still higher than the ASI178. 

I shall have to decide how much I want that extra bit of coverage at the sides!

[ChrisLX200]

The GPCAM-II mono is good, much lower noise than the QHY5L-II. I use one as my finderscope with a 6mm lens, and I also had a spare 1-1/4" UHC filter which I've stuck on the front and it works well! I do have to increase the exposure time to 5 or 10s though (depends how deep I want to go).

ChrisH

[ChrisLX200]

21 hours ago, Gina said:

I used a QHY5L-II-C in an earlier version but noise was a problem together with hot pixels and lines.  The ASI185 colour camera is vastly better. 

I have another thought - I wonder what an Ha filter would give    With a mono camera, of course.  Might try one of my Atik 460EXs just for fun

Still looking at ZWO cameras to upgrade.  I think I shall go for mono for the much better sensitivity. 

The ASI178MM looks like quite a good bet - very low read noise with an image sensor marginally bigger than the ASI185MC I'm using ATM.  Cost £378 from FLO. 

The ASI174MM seems to suffer from amp glow with long exposure and the read noise is a lot more.  On the plus side, the coverage fits the lens for 180° FOV and bigger pixels will mean higher sensitivity.  £601 for the standard version and £903 cooled.  I imaging the cooled version would fix the amp glow but the read noise is still higher than the ASI178. 

I shall have to decide how much I want that extra bit of coverage at the sides!

I should get my un-cooled ASI174MM delivered tomorrow so I will give that a try after the inevitable new-kit clouds have dispersed. I can't imagine needing a cooled version for anything other than multi-minute exposures on DSOs and I already have that requirement covered   I don't believe the amp glow will be a serious issue, the mono is sensitive enough not to need more than 10secs or so to record very deep - but I will try it up to around 60sec just to see how it performs. I can use on-the-fly dark frame subtraction to remove any glow (I use FireCapture for this job, but SharpCap will also do it - at least, when the bug for extracting the dark frame has been fixed it will!). My real issue will be finding a suitable lens to work with it.

ChrisH

[Gina]

Thank you Chris - I'll be very interested in your findings   I agree with what you say regarding cooling and amp glow.  As for the lens, it's a pity they don't include a fisheye lens with this model like they do with the ASI185 and others - a 2.5mm FL f1.2 would be ideal, I reckon.  Maybe someone has a lens they don't want... if you can find them...

[ChrisLX200]

I have at least a dozen lenses to try out, and some video lenses with auto-iris control. I'm thinking there must be some way of controling that auto-iris without it being attached to a video camera. There are only 4 wires going into the lens, two for the iris motor and the other two - well I don't know yet Maybe an Arduino with a light sensor would do the trick - what do you think?

ChrisH

[Gina]

I have no idea how auto-iris lenses work so I can only guess.  I imaging the camera has a light level detector built in and a voltage (probably DC) is applied to the iris motor the control it to give a constant light level in the camera.  With 4 wires it could be a stepper motor rather than a DC motor.  I can only suggest you Google the lens/camera and see if you can find any info.  How do you know two of the wires control the iris?  I guess it's possible that 2 control the iris and 2 the focus - is it auto-focus?

I had thought of doing a kind of auto-iris control with my Fujinon lens.  I had in mind measuring the light level with a CDS cell (resistance varies with light level) and producing a transfer curve/graph such that a stepper motor controls the iris to maintain a constant amount of light going into the camera.  But this would be extremely difficult and need much experimentation.

What I have calculated is that a 2.5mm FL lens will give 180° FOV just fitting inside the vertical axis.  There would be a lot of pixels wasted in the horizontal axis.  In this case a lens covering 1/3" would be fine.  You may want a C or CS to 2" M42/75 thread to fit the lens to the camera - I don't know if this is included though - it might be.

[Gina]

I'm hoping we might get some clear sky tonight but it isn't all that likely - it's just clouded up after a mainly sunny day with just a few cumulus clouds around.  I have 3D printed an adapter to attach a Baader 36mm unmounted Ha filter to the lens and will try that with my ASI185MC camera.  I might be able to counteract the just past full moon.  Initial testing has shown multiple reflections within the filter plus there's the problem of change of focus.  The filter really wants to go between the lens and the camera sensor, of course.

I've mounted the Hα filter onto the lens and put the ASC outdoors supported on the guttering.

[Gina]

[ChrisLX200]

You are probably right Gina - 4 wires for a stepper motor. Thinking about it now, I have seen such tiny stepper motors (with linear drive) being sold for camera use. The default position (with no power or camera connection) is for the iris to be fully closed. It must be spring-loaded or something because if you snap the power off whilst it is wide open the iris shuts - there's no time for a drive motor to close it. Neither have I seen it in any other position than fully closed when disconnected. That was actually a disappointment when I was experimenting with it because if the default were wide-open I could have used it at night. It only needs crude control really - a setting to hold it wide open, maybe one to close it (only useful for daytime use), and perhaps one in between (if that were possible, I'm uncertain if 'fully closed' really means that or if it's at a high f-number). The exposure times can then be adjusted to suit. The ability to close it while powered up is really just to protect the sensor during the daytime.

I will look at some camera specs - I suspect there's more chance of finding useful info there than the lenses - all lenses must work the same otherwise they would not be interchangeable.

ChrisH

[Gina]

Here's a screenshot of the TeamViewer image from my imaging laptop.  Exposure 60s - Standard Gain - Gamma 16.  Getting near the limit of the camera here - beginning to see some noise and hot pixels.

[ChrisLX200]

OK, fallen at the first hurdle...!  The 4 pin allocations are:

For EIAJ Video auto-iris lens  1) Power  2) not used  3) iris signals  4) GND

For EIAJ DC auto-iris lens  1) Control -  2) Control +  3) Drive +  4) Drive -

ChrisH

[Gina]

Oooohh errrr

[Gina]

Exposure 2m - Gain half - Gamma 16.

[Gina]

[ChrisLX200]

Found this: http://forum.arduino.cc/index.php?topic=76958.0

Sorry, I'm dumping on your thread Gina, I'll open a new one when I have something useful to say about it

 

Your images - that's with a Ha filter on a colour sensor? Doesn't look hopeful if 120s gets you that

ChrisH

[Gina]

That's alright Chris

Using an Ha filter with a colour camera is obviously nuts I'll admit.  I'm not even sure it's an Ha filter - it could be SII - they look exactly the same.  Slightly different red colour looking through them and I chose the lighter one.  I've now swapped for the other filter and will see what that gives.

[Gina]

No noticeable difference.  But I have to conclude that a narrowband filter is useless with an non-cooled colour CMOS camera.  On a day when I'm not going out, I might arrange to use an Atik 460EX mono CCD camera - maybe tomorrow.

[Gina]

Filter and adapter remove and lens refocussed.  Exposure on automatic giving 4s - gain on automatic 240 - gamma set to 20.  Bare camera and lens - no dome.

 

[Gina]

Exposure upped to 10s.  North is to the right at 3 o'clock.

[Gina]

Clouded up now

[ChrisLX200]

Yes - I can see Polaris is the star peeping out the cloud nearest the Chimney

 

I now know more about the DC auto-iris lens and how it works. It's a trivial task to open fully or close the iris under Arduino control - simply apply 5v to the motor drive (through a current limiting resistor) and it opens! An intermediate setting is much more tricky though - the other pair of wires control a 'damper' circuit which acts as a feedback on the servo motor, it prevents oscillations at intermediate positions and allows the servo to overcome friction (which is a variable). It can be done with a PWM output though, but I'm not sure the additional effort is worthwhile. Just being able to open/shut the iris is the essential thing and that is so simple

ChrisH