StarTools

I took a number of images last night because it was my first clear night for many days. I avoided the region of the full moon but the images do have quite a bit of background light. Despite this I am happy that they show some detail. My problem is still a lack of real familiarity with ST. I have done a AD, wipe, AD but still not managed to understand how to proceed further. There is some vignetting in the images as well. Can the moonlight effect be reduced?

Lawrence Harris

FWIW, I am still hoping to better understand how to use ST and then feel ready to register.

Hi Lawrence,

If you would be able to share your stack with us, we would be able to assist you better. Much depends on the characteristics of the data...

Thanks,

I am posting to Dropbox; the file is a fits of ~70Mb. It is a 'master' from six 30 sec images with *no* calbrations. Taken under full moon (to test) using an f2 Celestron 11" Edge, I am in the early stages of imaging at f2 and consider myself a starter with ST. Some of the images are not bad after basic AD+wipe+vig. With other software I would not know where to start!

I will try to get Dropbox available for the forum.

https://www.dropbox.com/s/rq034ze8a1dcw ... 6.fit?dl=0

Lawrence Harris

Hi Lawrence,

I just had a look at the data.
It's very challenging indeed, especially with the lack of proper calibration (e.g. flats). As you already alluded to, this should be your main focus going forward.

I had to give Wipe an extreme workout and ended up with this;

Before looking at the workflow, I should mention that this one is very image-specific. I had a fair bit of trouble colour balancing the data as well. What software did you use to stack? Any filters used?

Workflow as follows;

--- Auto Develop
To see what we got. It's *a lot* of stray light and heavy vignetting.
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside ROI Influence] set to [15 %]
--- Bin
Parameter [Scale] set to [(scale/noise reduction 50.00%)/(400.00%)/(+2.00 bits)]
--- Crop
Crop away stacking artefacts (bottom especially).
Parameter [X1] set to [20 pixels]
Parameter [Y1] set to [13 pixels]
Parameter [X2] set to [1492 pixels (-24)]
Parameter [Y2] set to [994 pixels (-14)]
--- Wipe
Masked out M81, started with Vignetting preset. Cranked precision and aggressiveness way up.
Parameter [Mode] set to [Correct Color & Brightness]
Parameter [UNKNOWN] set to [Yes]
Parameter [Precision] set to [2048 x 2048 pixels]
Parameter [Dark Anomaly Filter] set to [5 pixels]
Parameter [Drop Off Point] set to [0 %]
Parameter [Corner Aggressiveness] set to [100 %]
Parameter [Aggressiveness] set to [99 %]
--- Auto Develop
RoI over M81.
Parameter [Ignore Fine Detail <] set to [4.5 pixels]
Parameter [Outside ROI Influence] set to [3 %]
--- Color
Very tricky to balance. Wipe didn't have much to go by and the stars are all colourless.
Assuming colors could be recovered, I used the "balancing by known features and processes" technique (see here).
Known features are purplish/blue outer rim, yellowish core for M81, while M82 has orange and red outflows.
Parameter [Cap Green] set to [To Yellow]
Parameter [Bias Slider Mode] set to [Sliders Reduce Color Bias]
Parameter [Style] set to [Scientific (Color Constancy)]
Parameter [LRGB Method Emulation] set to [Straight CIELab Luminance Retention]
Parameter [Dark Saturation] set to [2.30]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [190 %]
Parameter [Green Bias Reduce] set to [1.76]
Parameter [Red Bias Reduce] set to [2.52]
--- Life
Isolate preset to suppress noise.
--- Wavelet De-Noise
Switching Tracking off.
Parameter [Grain Size] set to [8.6 pixels]

Hope this helps.

Ivo - thank you so much! Re lack of calibration data: The exposures are short (30 sec subs) but I have retained bias files. The darks would add noise in such short exposures (Starlight Xpress recommend not using darks below ~ 60 sec or so to avoid adding noise. I do have darks though. I am using an f2 Celestron 11" Edge scope with wide f.o.v. I will now go through your procedure carefully. This is the best image that I have seen

Thank you!

Lawrence

Sorry - forgot to answer questions:

No filter used. Stacking choice DSS and Maxim DL v5.23. I usually use DSS for most calibrations (all settings as per ST). Earlier reference to manual implied better to use no filter.

Lawrence