Thoughts on which imaging rigs to concentrate on

[Gina]

Phew...  That was a bit of a detour but something else learnt on the way   Now to the rest of the INDIlib installation - using these instructions.

Oh dear - "Huston - we have a problem..."

 

[Gina]

There's a problem further up too

[Gina]

Clear sky tonight so I'm imaging the Heart & Soul Nebulae.  Currently capturing 60s Ha subs.

[Gina]

Another 60s sub in Ha this time slightly cropped and gamma stretched to bring out the fainter data.  I plan to take 100 Ha subs if conditions permit followed by OIII and SII subs as and when we get clear sky.

[Gina]

Now capturing OIII subs and these are very much fainter, making me wonder if I should increase the exposure.  OTOH if I do the stars will saturate more and become bigger making the combining of different wavelengths more difficult.  I think it's more the overall accumulated time that counts rather than individual subs as long as the noise is low - which it is.  Random noise accumulates as the square root of the number of subs whereas the signal is directly proportional.  So the more subs the better the resultant signal to noise ratio.

Here is one OIII 60s sub histogram stretched to show the nebulae.

[Starlight 1]

Stars are not as little in olll is the seeing not as good ?.

[Gina]

I think it's more likely to be the much greater histogram stretch applied.

[Gina]

Still clear but the Heart & Soul are about to go behind an obstuction for an hour or so, so I'm moving over to the NAN area and capturing SII.

Edited October 26, 2016 by Gina

[Gina]

No good - the fog has rolled in now so packing up for tonight.

[Gina]

This thread has become somewhat mixed up with both the imaging and the RPi software setting up and I think the RPi stuff ought to be in a separate thread.

[Gina]

I have posted the new thread but cannot get any further with it without help from a more learned member...

[Gina]

Gave up on that and just copied the backup image I took of the ASC micro SD card to a new card.  The software wanted is the same except for the cooling and dew heaters (cooling is built into camera and may or may not want a dew heater control).  So next job is to work out layout and size of box to take all the bits.

[Gina]

Since the facility is available I've decided to provide a switched dew heater supply, same as the ASC, though I might as well use Line A (GPIO5) rather than Line B (GPIO6) as this will be the only Astroberry Board driver control wanted.  There is sufficient room on the HAT and I'm currently adding the extra components.

[Gina]

This is the new power distribution and RPi control/capture circuit.

[Gina]

Working on the design for the construction of a frame to hold the RPi with HAT plus all the power distribution bits.

 

Edited October 30, 2016 by Gina

[Gina]

Well, there's good news and bad news!  The good news is that I sorted out the mounting and that is fine.  The bad news is that the RPi software doesn't work

I thought copying the card image from the working ASC system to a new card and putting that in another RPi would work but it doesn't1

[Gina]

Beautiful day here today - sunny and warm and forecast is good for tonight after dark too   Seems the main imaging rig will be put back to the windoze setup - can't see much hope of sorting out the RPi   Might go for a walk and get some fresh air   gets a bit boring and gives one a headache!!!!!!!!

Edited October 31, 2016 by Gina

[Gina]

Sky is mainly  clear - a few contrails and odd bits of cloud on the horizon but looking reasonable so far.  Rig is set up with Arduino focuser, back out on EQ8 mount and connected up to Win7 laptop.  Lens manually focussed on far tree and focus ring clamped for remote focussing.  Too bright for stars yet but everything set up ready

[Gina]

Imaging the Heart and Soul Nebulae - currently capturing in Ha with 60s subs with gain of 500 and sensor temperature of -25°C (it's a mild night).

[Gina]

Having captured a fair number of Ha subs of H&S before I decided to just take 40 odd tonight and go over to OIII which will need a lot more data anyway as the OIII nebulosity is very faint.  Here is a 60s sub in OIII with other parameters as for Ha but with considerable histogram stretching in Photoshop.

[Gina]

There is so little data in these 60s frames that I have decided to try increasing the exposure and see what I can do with the inevitable bigger stars later in the processing.  This is already a 3nm filter which is the narrowest available so no optical way of reducing the strength of the stars.

[Gina]

Here is a 120s sub also histogram stretched in Ps but this does show data and the stars aren't too bad.

[Gina]

On the processing front, I am still organising my data.  One slight disadvantage of the ASI1000MM-Cool is that it needs darks and presumably bias frames for calibration as well as flats whereas the CCD cameras only need flats.  At least a library of darks and biases can be used and now I have removed the dust from inside my camera sensor chamber the dust bunnies have gone and I can use one set of flats for each optical setup.  Once calibration sets of subs have been used once there is a master file that can be used in future processing - one file rather than dozens of subframes.  So the subframe data can be dumped as no longer required.

In view of the problems I've had with mobile dust in the sensor chamber I think all lights and flats prior to fixing the problem should probably be dumped and new data obtained.  I think bad data is worse than no data.

The data parameters fall into these categories.

1. Optical setup - eg. scope or camera lens focal length.  This determines which master flat to use.
2. Filter.  With the dust bunny problem solved one flat can be used for all filters.  Doesn't apply to darks or biases, of course.
3. Exposure.  A separate master dark and bias is needed for each different exposure.
4. Gain.  Same as exposure.
5. Sensor temperature.  A separate master dark is needed for each temperature as the noise depends on temperature.

Libraries of calibration data can be categorised by type and the dependences.

1. Bias.  Depends on temperature only.
2. Dark.  Depends on exposure and temperature.
3. Flat.  Depends on optics but not on other parameters.

That describes the problem - many permutations!

[Gina]

Now to look at the database fields and interconnectivity plus the parameters of each field.

I'm thinking the following fields.

1. Optical rig - Not sure about MN190 as it would produce oversampling with this camera for DSOs.  Esprit and the various lenses.  Only affects flats.
2. Filter - not needed for this database as can be combined with DSO ID.
3. Exposure - Probably 30s, 60s and 120s but I may add more if required.
4. Gain - I seem to use 500 except for galaxies in RGB but have used 440.
5. Temperature - I shall keep to -20°C, -25°C and -30°C as near as I can, using the lowest of those achievable depending on ambient temperature.

This already makes for rather a lot of permutations!  A multidimensional database   No wonder I've been having a problem getting my head round all this!

Since the optical rig only affects the flats and not other calibration files I think I can separate it out.   But flats still need calibration frames themselves - these could be taken in the same session as the flats and used to calibrate the master flat then discarded.

Next stage will be to work out how to organise all the calibration files.  Not tonight though

[Gina]

Still getting decent imaging data and with this target it will be a few hours before a meridian flip would be required so I think I'll leave it capturing OIII subs for a while and see what I've got in the morning.  No rain in the forecast just mist or fog and cloud, of course.

Here's the latest OIII 120s sub, histogram stretched.