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Re: In need of a SharpCap tutor

Posted: Sat Jan 12, 2019 6:30 pm
by psy1280
Just wanted to touch base with everyone. My Evolution / StarSense scope refuses to align. I consistently get "Alignment Pointing Error too large, and then invariably, the SkySafari app freezes (this has happened consistently the last three disastrous attempts to observe). So, I just wanted you to know I haven't lost interest in pursuing SharpCap, I'm just trying not to throw my scope off the deck and find a new hobby!!! I'm waiting for a call from Celestron, not hopeful at this point since this has been going on and multiple calls haven't helped. Wish me luck.


Re: In need of a SharpCap tutor

Posted: Tue Feb 26, 2019 6:13 pm
by clangorous
I'm in same boat. The manual is good at explaining what each option does, but that is not the same thing as explaining how to use the software. There really needs to be tutorials for the major actions like Live Stack, and using the virtual camera to stack previously taken images. Can't really do much with the free version so I subscribed for a year in order to have the features available to learn, which is fine. But it's going to be a long tedious frustrating process to solve for what isn't explained.

Re: In need of a SharpCap tutor

Posted: Tue Feb 26, 2019 6:32 pm
by admin

Just to reiterate that there are SharpCap courses available from Gary Palmer for UK-based imagers. See Gary's website at

There may be similar courses available in other countries, but I'm afraid I don't have any information to share on them.

Cheers, Robin

Re: In need of a SharpCap tutor

Posted: Tue Feb 26, 2019 7:14 pm
by psy1280
Unfortunately, I'm in the United States, perhaps someone can ask whether these lectures/workshops can be made available online. I'd be glad to pay for them. More than glad!

Re: In need of a SharpCap tutor

Posted: Tue Feb 26, 2019 11:25 pm
by oopfan

Have you looked into joining a local Astronomy club?

Here is one that is a 20 minute drive away from you:

Here is a list of clubs in New York and New Jersey: ... p?State=NY ... p?State=NJ


Re: In need of a SharpCap tutor

Posted: Wed Feb 27, 2019 1:49 pm
by psy1280

Can't thank you enough! I see there are online courses available, I'll check it out.


Re: In need of a SharpCap tutor

Posted: Fri Mar 08, 2019 12:03 am
by poolemarkw
Dave (Turfpit),

I REALLY appreciate your explanations and the time you give to help those of us still learning!

1) Can you please explain exactly what you're looking for after taking a single exposure and opening the associated FITS file?
2) Can you please explain exactly how you are generating flats and using them within SharpCap?



Re: In need of a SharpCap tutor

Posted: Fri Mar 08, 2019 1:36 am
by turfpit

Thanks for the kind words - I am also learning. The description below was used for this The processes described below are how I go about capturing DSO data for later processing.

Single FITS capture
Having established the camera settings being used (gain, exposure, offset for CMOS or exposure for CCD), I take a test frame and inspect it in FITS Liberator. If certain criteria are met then I would proceed to capture a set of light frames. I am looking at the Min and Max values in the Image Statistics part of the display. I need to see Min > 0 (means I am not hitting the left hand side of the histogram and losing faint data) and Max < 65535 (not hitting the right hand side of the histogram to avoid over-exposing).

single-FITS-frame.JPG (75.33 KiB) Viewed 735 times

I then apply a stretch (usually arcsinh(x)) and hope to see the histogram pulled away from the left and the histogram 'fattening'. This indicates decent data has been captured. Compare the histogram from above with that below. The histogram shown is a classic shape for a DSO - rising steeply and then tailing off. I don't get too hung up if I have say up to 10 over-exposed pixels (see the pixel count in the SharpCap histogram) as we could be talking 10 out of 20 million.

stretch.JPG (24.88 KiB) Viewed 735 times
arcsinh-stretch.JPG (65.08 KiB) Viewed 735 times
A less than 5 minute check to ensure collection of good data I find to be time well spent.

Flat frame capture
To capture flat frames I use a home made flat generator. This consists of 2 pieces of plasticard, an electro-luminescent panel, battery and 2 plastic rods which allow the panel to be hung over the end of thes scope - all parts off eBay. The one below is for a 66mm refractor - cost ~£20. I have one for each telescope - 81mm refractor, Skywatcher 127 MAK and Celestron C8. The C8 frame cost £40 for a 250x250mm EL panel.

flat-panel1.JPG (75.87 KiB) Viewed 735 times
flat-panel2.JPG (78.82 KiB) Viewed 735 times
flat-panel3.JPG (80.61 KiB) Viewed 735 times

My thinking is that data capture and processing are 2 completely distinct processes, therefore I do no processing at the capture laptop. With a DSLR I would use Nebulosity and I also use Linux (Debian & Raspberry Pi). For this reason I work to 'lowest common denominator' i.e. I use a consistent process which can be applied across applications and operating systems. The means that the flats capture is in my hands rather than using the in-built facility in SharpCap. Why risk 'trashing' data at the point of capture is my view.

To capture flats, I hang the EL panel over the scope, switch on and capture frames. I leave the gain & offset as for the lights and reduce the exposure until the histogram is just left of centre - round about 40%. This usually means exposures in the range 50-150ms depending on optics, filters etc.

flat-capture.JPG (30.31 KiB) Viewed 735 times
To save the question being asked, this is my workflow for calibrating, registering and stacking the frames. I use SiriL, I follow this ... t_and_bias from the SiriL manual. I take lights, darks, bias and flat frames.

Capture steps are:
  • lights with defined gain, offset, exposure
  • darks with above settings, aim for temperature match to lights
  • bias, change exposure to minimum, other settings the same
  • flats, set exposure to obtain 40% histogram, other settings the same as for lights
Processing steps are:
  • stack bias frames, no normalisation
  • load flats and apply master bias to the flats
  • stack pre-processed flats, 'multiplicative' normalisation
  • stack darks, no normalisation
  • load lights
  • apply master dark and processed master flat to lights, debayering if applicable at this step
  • register
  • stack using 'additive with scaling' normalisation
  • background extraction
  • colour calibration if applicable
  • histogram transformation
  • export as 16-bit TIFF
  • final processing in GIMP
[Note: I select Winsorized Sigma Clipping for the rejection criteria when stacking].

Following the above has led to consistently satisfactory results for me over the last few months. The histogram is my friend.

As a working process, after a capture session, I backup all new data to a 4Tb drive on my network. I then copy the data from the 4Tb to an SSD in my workstation for subsequent processing. That is 3 copies of capture data before I go anywhere near the pixel mangling software ;)

Hope this helps.


Re: In need of a SharpCap tutor

Posted: Fri Mar 08, 2019 1:54 am
by poolemarkw
Thanks Dave! This is VERY helpful, thanks for taking the time to post a very detailed response.

Re: In need of a SharpCap tutor

Posted: Fri Mar 08, 2019 6:43 am
by turfpit
Cheers Mark. I suppose the real test of my post is the next time you have an imaging session. I would welcome any feedback once you have had time to use the info I posted. It did take quite some time and more than a few failures to piece all this together, see viewtopic.php?f=16&t=596.