[Mr Ian David Sharp]

Hi all,

I managed to image 12P last night from Spain. Here is a stack of 20 x 60 secs with an L filter. North is to the left. Image is 18′ x 14′ (0.48 “/pix).

The nucleus is very bright!.

Cheers
Ian.

Attachments:

1. 

   12p_20231116_182724_ids.jpg
   

[Mr Ian David Sharp]

Kevin West wrote:

I don’t know what stretching is.

Ah! then you have to learn about this!

Astronomical deep-sky images contain mostly black (or near black) sky. When you view an image un-stretched astronomical image you see virtually nothing – just a few pin pricks of light from the brightest stars. This is because most of the data is residing near the black-point of the ‘histogram’. But applying a non-linear stretch to the image, the data is spread more evenly across the histogram from the black point to the white point.

See my attached screen shot. The image on the right is a clone of the one on the left but I have applied a histogram stretch to the one on the right. Without this skill you will not be able to see your data properly, nor be able to check the calibration properly.

I feel you have learning curves all over the place! If you would like a Skype or Zoom (or similar) call I could share my screen and take you through a few things? Otherwise there will be a lot of back and forth with messages etc.

You can PM me here if you want to set something up…

Cheers
Ian.

• This reply was modified 12 months ago by Mr Ian David Sharp.
• This reply was modified 12 months ago by Mr Ian David Sharp.

Attachments:

1. 

   stretch.png
   

[Mr Ian David Sharp]

Hi Kevin,

Further to this, as Grant has mentioned, compare your uncalibrated lights to your calibrated lights. See my attached image where I show three heavily stretched images. Top left is uncalibrated – note the gradients and the dust marks. Top right is calibrated – note it looks pretty flat. Bottom is the flat frame with a big stretch.

Not the most dramatic example because my C11 has a pretty flat field over this sensor to start with. But – I must try and get rid of that horrible splodge on the sensor!

Cheers
Ian.

• This reply was modified 12 months ago by Mr Ian David Sharp.

Attachments:

1. 

   calib.png
   

[Mr Ian David Sharp]

Kevin West wrote:

So the image it outputs, is that a calibrated image? Is it possible to tell?
What does the software do to the original uncalibrated lights?

Hi Kevin,

ASTAP does nothing to your uncalibrated lights and it creates calibrated copies with “_cal” on the end of the file names.

If you look at the FITS headers of the calibrated files, you will see something as shown below towards the end of the header. In my test I only selected my master dark and master flat files and you can see resulting CALSTAT = ‘DF’. Also the COMMENT 1 field indicates it was calibrated by ASTAP.

What do you see in the CALSTAT field when you use your flat-darks?

Cheers
Ian.

COMMENT 1 Calibrated by ASTAP. http://www.hnsky.org
PEDESTAL= 5.000000000000E+002 / Value added during calibration or stacking
CALSTAT = ‘DF’
DARK_CNT= 1 / Darks used for luminance.
FLAT_CNT= 1 / Flats used for luminance.

[Mr Ian David Sharp]

Kevin West wrote:

SIMPLE = T / file does conform to FITS standard
Which I know is a bit of a deal breaker as they have to conform. So that’s where I am. Any thoughts please?

Hi Kevin,

I don’t understand the problem. It all looks OK to me. Here, for comparison, is one of my FITs headers after it’s been calibrated. (Captured in SG Pro, calibrated by AA8).

Cheers
Ian.

SIMPLE = T / file does conform to FITS standard
BITPIX = 16
NAXIS = 2
NAXIS1 = 2750
NAXIS2 = 2200
BZERO = 32768.0
BSCALE = 1.0
CRPIX1 = 1375.999999978
CRPIX2 = 1100.999999981
CTYPE1 = ‘RA—TAN’
CTYPE2 = ‘DEC–TAN’
OBJECT = ‘CF PEG ‘ / Object name
DATE-LOC= ‘2023-10-08T21:50:30.3930000’ / Local observation date
DATE-OBS= ‘2023-10-08T19:50:30.3930000’ / UTC observation date
IMAGETYP= ‘LIGHT ‘ / Type of frame
CREATOR = ‘Sequence Generator Pro v4.2.0.1158’ / Capture software
INSTRUME= ‘Starlight Xpress H694’ / Instrument name
ROWORDER= ‘BOTTOM-UP’
OBSERVER= ‘Ian Sharp’ / Observer name
SITENAME= ‘PixelSkies’ / Observatory name
SITEELEV= 850 / Elevation of the imaging site in meters
SITELAT = ’37 44 23.000′ / Latitude of the imaging site in degrees
SITELONG= ‘-0 38 38.000’ / Longitude of the imaging site in degrees
FOCUSER = ‘PegasusAstro ProdigyMF’ / Focuser name
FOCPOS = 5489 / Absolute focuser position
FOCTEMP = 19.48 / Focuser temperature
FWHEEL = ‘Starlight Xpress Filter Wheels’ / Filter Wheel name
FILTER = ‘L ‘ / Filter name
EXPOSURE= 60 / Exposure time in seconds
CCD-TEMP= -10.2 / Camera cooler temperature
SET-TEMP= -10 / Camera cooler target temperature
XBINNING= 1 / Camera X Bin
CCDXBIN = 1 / Camera X Bin
YBINNING= 1 / Camera Y Bin
CCDYBIN = 1 / Camera Y Bin
XPIXSZ = 4.5390625 / Pixel Width in microns (with binning)
YPIXSZ = 4.5390625 / Pixel Height in microns (with binning)
STRSZ1x1= 6 / SGPro minimum star size filter
READOUTM= ‘Standard Readout Mode’ / Camera readout mode
TELESCOP= ’10Micron Mount’ / Telescope name
RA = 325.297497442515 / Object Right Ascension in degrees
DEC = 26.2268339926879 / Object Declination in degrees
CRVAL1 = 325.2979715357
CRVAL2 = 26.20068031717
OBJCTRA = ’21 41 11.399′ / Object Right Ascension in hms
OBJCTDEC= ‘+26 13 36.602’ / Object Declination in degrees
PIERSIDE= ‘West ‘ / Side of Pier the objective is on
AIRMASS = 1.04170531837155 / Average airmass
OBJCTALT= 73.8212777777778 / Altitude of the object
CENTALT = 73.8212777777778 / Altitude of the object
FOCALLEN= 1956 / The focal length of the telescope in mm
FLIPPED = F / Is image flipped
ANGLE = 267.83 / Image angle
SCALE = 0.472905 / Image scale (arcsec / pixel)
PIXSCALE= 0.472905 / Image scale (arcsec / pixel)
AOCDEW = 10.3 / Dew Point in degrees C
AOCHUM = 75 / Humidity in %
AOCRAIN = 0 / Rain Rate in mm/hr
AOCSKYT = -28.5 / Sky Temperature in degrees C
AOCAMBT = 18.7 / Ambient Temperature in degrees C
AOCWIND = 12.5833333333333 / Wind Speed in m/s
EGAIN = 0.3 / Electrons Per ADU
STAR = ‘CF PEG’
PROCESS = ‘DK+FLAT’
CALSTAT = ‘BDF’
EQUINOX = 2000.0
CD1_1 = 4.981204779451E-006
CD1_2 = -0.0001310849482926
CD2_1 = -0.0001310385252376
CD2_2 = -4.948753747364E-006
CDELT1 = -0.0001311331670384
CDELT2 = 0.0001311783283646
CROTA1 = 0.0
CROTA2 = -87.83051432587
AVISUMIN= -33.0
AVISUMAX= 467.0
AVISUTYP= 0.0
END

[Mr Ian David Sharp]

Grant Privett wrote:

I thought it was the case that when Windows Defender objected to something you could bypass it by choosing the other option (which isn’t highlighted and doesn’t say “bypass” 🙂 ).

Ah, I know the one you mean now – the one where you have to go into an option and choose “Run anyway”. Yes, that often happens.
Ian.

[Mr Ian David Sharp]

Kevin West wrote:

A few first impression comments about the suggestions. Working my way through them.

ASTAP intiates a Windows Defender warning.

Calibration Intro Tutorial for Tycho Tracker seems to suggest it’s for moving targets.

I have installed AstroImageJ, found the DP button but there is no option to process flat darks.
So I have found various tutorials but I’m getting the impression they are for CCDs which do use bias frames I believe.

Trying not to be too negative but I think I need something with very basic tutorials that walks you through it.

Kevin

Hi Kevin,

I run ASTAP on 3 different PC’s and I’ve never seen a Windows Defender warning. ASTAP does deal with flat-darks as far as I can see but, as I said, I use PixInsight to create my master calibration files.

Tycho Tracker handles both static and moving targets, but I’m not sure it deals with flat-darks – I might be wrong.

I think you’re right about AstroImageJ – why not experiment with Bias frames and see what you get?

Lastly, I’ve found this calibration tool which looks interesting:

https://astrohobby.ca/my-software/calights/

Cheers
Ian.

[Mr Ian David Sharp]

Hi Kevin,

There are quite a few choices for software packages that will calibrate your images, and some will calibrate and perform the photometry. Did I see somewhere that you are learning to use the AAVSO VPhot software? I don’t believe that has calibration facilities? It’s amazing on the calibration side of things.

I, personally, use AstroArt 8 (AA8) for my photometry and this is because it can be scripted and controlled by my Python programs. AA8 also performs the calibration. I prefer to use PixInsight to produce my calibration master files, but that’s only because I’m well versed in PI and it has an incredible set of calibration processes. AA8 would do the job too.

Having said all this, I’ve recently been using the excellent Tycho Tracker program to do photometry. This also copes with calibration. I would recommend looking at this and there are lots of very good videos on YouTube by the author of the Tycho software and he is very responsive with questions. There is a small one off cost for the Pro version but it is well worth a look.

Other than that, there is Maxim DL which is widely used for calibration and photometry. Also AstroImageJ (free) is incredible but takes a bit of learning.

You could use the free DeepSkyStacker for calibration.

I know lots of people swear by Siril which I believe is free.

A few links:

https://www.tycho-tracker.com/
https://siril.org/
https://www.astro.louisville.edu/software/astroimagej/
http://deepskystacker.free.fr/english/index.html

Cheers
Ian.

[Mr Ian David Sharp]

Kevin West wrote:

Just to clarify
My flats taken with a light pad and T-shirt required exposures of 2.3 sec to get the histogram max
between 1/3 and 1/2 of max ADU count.
That means I need to take a set of darks at the same exposure (all other things as you say replicated, temp gain etc.)

Hi Kevin,

Yes, that’s correct – you need darks to match your flats (and darks to match your lights of course!). My exposures vary from about 2 to 8 seconds with my CCD based system with my LED screen.

Cheers
Ian.

[Mr Ian David Sharp]

There looks to be some fine advice from the manufacturers of SBIG cameras:

https://diffractionlimited.com/calibrating-cmos-images/

Cheers
Ian.

[Mr Ian David Sharp]

Hi Kevin,

The first thing to bear in mind is that bias signal always needs to be subtracted during calibration. However, the thing to also remember is that *all* images contain the bias signal and this includes your darks and flats.

The traditional CCD workflow is to take separate bias, dark, and flat frames, then explicitly subtract the bias from darks, flats, and
lights. This works well with CCD’s because they are very well behaved in terms of their linearity.

CMOS cameras, however, have certain non-linearities with short exposures and dark frames (amp glow). (a lot of new CCD cameras seem to have all but eliminated amp glow).

To calibrate CMOS images, we don’t need to take separate bias frames, but rather keep the bias in the darks and flats and the bias subtraction is done when calibrating the flats with dark flats and the lights with their darks. So, it is not that bias is not used, but rather how it is ultimately subtracted.

If you use PixInsight and the excellent WBPP (Weighted Batch Pre Processing) script, then all the settings are nicely set up for you. You just need to feed it with your darks, flats and flat-darks (yes, take dark frames to match the exposure of your flats as well as your lights). The only time that PixInsight needs Bias frames is in the situation where you have not taken dark frames to match your light frames. In this situation, the bias frames are used to scale your darks to match. So, for example, if you have 300s darks in your library and you have taken some 360s lights, the program will scale the 300s master dark to produces a scaled-dark. This is not ideal but works very well.

In summary, take darks for all the exposures and temperature combinations you are likely to use. Take flats for all of your filters and also take flat-darks to match the flat exposures. I’m assuming here that you have chosen your Gain and Offset values. These must be kept the same for all lights and calibration frames.

Adam Block explains all in great depth here: https://www.youtube.com/watch?v=WzEpygFGbN0

Hope that helps!
Ian.

[Mr Ian David Sharp]

Hi Kevin,

Section 3.3.10 in the AAVSO CCD/CMOS Photometry guide is very informative with regards to the Gain and Offset settings in CMOS cameras:

https://www.aavso.org/sites/default/files/publications_files/ccd_photometry_guide/CCDPhotometryGuide.pdf

Once you choose a gain and offset, just stick with it for all lights and calibration files.

With regards to temperature, just go with a value that your camera can cool to reliably. I use both -10C and -20C with my CCD. I use -10 in the Summer months when I find the camera can’t cope with -20. I have a QHY268C CMOS camera which I image with and I find that it can’t get down reliably cooler than -15C, so I tend to stick with -10.

Binning – I use both 1×1 and 2×2 for fainter targets.

Cheers
Ian.

[Mr Ian David Sharp]

Hi Kevin,

I forgot to mention that I used an Alnitak Flip-Flap on my 104mm refractor setup at PixelSkies in Spain. See photos and details here:

http://www.astro-sharp.com/2021/10/23/my-new-remote-setup-in-spain/

This was brilliant because I could control it remotely. I have recently replaced the OTA with a C11 and now I have to ask the folks there to place a light panel on to the C11 when I need to refresh my flats (which is not very often).

Cheers
Ian.

[Mr Ian David Sharp]

Hi Kevin,

For what size OTA?

I use LED flat panels for my kit (is that what you mean by a pad?). I have an A3 size panel which covers my C11 ok. I have a smaller Pegasus Astro Flatmaster panel which covers my refractors and is dimmable and USB controllable. There are lots of choices of LED Flat panels out there now.

These look nice: https://www.widescreen-centre.co.uk/aurora-flatfield-panels.html

Cheers
Ian.

[Mr Ian David Sharp]

Hi all,

It looks to be slowly dimming again. I got Vmag = 11.62 and Bmag = 12.42 last night. See attached.

Cheers
Ian.

Attachments:

1. 

   V426-Sge-20231019.png
   

[Mr Ian David Sharp]

Thanks for the info Gary,

I managed a decent set of R, V and B last night from Spain. V mag was coming out at around 14.6 with R at about 14.2.

All uploaded into the dB.

Cheers
Ian.

[Mr Ian David Sharp]

Hi all,

I got some nice results last night in B and V – 10 images of each. I get 11.43 in V and 12.16 in B and it looks to be brightening from David and Gary’s recent points. See attached.

Cheers
Ian.

Attachments:

1. 

   V426-SGE.jpg
   

[Mr Ian David Sharp]

Thanks for the heads up David,

I’ve set up a run from Spain in B and V tonight…

Cheers
Ian.

[Mr Ian David Sharp]

Hi all,

My B mag. measurements from last night suggest a bit of a rise in the past few days. Hope to check this again tonight.

Attachments:

1. 

   T-Crb-20230920-ids.jpg
   

2. 

   20230920_T-CRB_B_PixelSkies-C11_IDS_plot_points.png
   

[Mr Ian David Sharp]

Wow! Just been watching Brad Schaefer’s presentation. This is so exciting! Now I understand why the call for B-band photometry.

Marvellous!

Ian.

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