Creating Flats with Solar Images

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sandconp
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Creating Flats with Solar Images

#1

Post by sandconp »

I am trying to create and apply flats to my solar image. When I create the flats, there is an option which is automatically checked to apply the new flat to my image.

I am attaching a snapshot of what I am getting when I apply the flat.

What I am doing wrong?

Is there a procedure documented somewhere when applying flats to a solar image?
flats.docx
(324.86 KiB) Downloaded 83 times
flat2.docx
(206.53 KiB) Downloaded 57 times
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turfpit
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Re: Creating Flats with Solar Images

#2

Post by turfpit »

sandcomp

My flat frames for a mono camera look something like this with the histogram somewhere around 50%.

mono-flat.JPG
mono-flat.JPG (58.79 KiB) Viewed 1572 times


The usual way to acquire a solar image is to capture a video in SER format (using the fastest fps possible to beat atmospheric conditions) and then stack with a program such as Autostakkert. A master flat can be created in Autostakkert (from a set of captured flats) and applied to frames during the stacking process.

Dave
sandconp
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Re: Creating Flats with Solar Images

#3

Post by sandconp »

Maybe I have the exposure set too high for that flat which will be different from the exposure of the Sun? Should I still use the Flats tool in Sharpcap but tell it not to apply it after creating it?

I am assuming the flats will be a FITS file that I would apply in AS!2?
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turfpit
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Re: Creating Flats with Solar Images

#4

Post by turfpit »

Sandcomp
Maybe I have the exposure set too high for that flat which will be different from the exposure of the Sun
Use the gain & exposure camera controls to set the the histogram something like the image I have posted. Expect the image capture exposure and flat frame capture exposure to be different.
Should I still use the Flats tool in SharpCap but tell it not to apply it after creating it?
Creating a master flat using one application then applying using another application usually ends badly (same with master darks).
I am assuming the flats will be a FITS file that I would apply in AS!2?
Yes, the master flat would be a FITS file if the individual flat frames were captured as FITS.

This is what I would do for solar imaging:
  • Capture a SER file, 1000+ frames.
  • Capture some flat frames as FITS.
  • Use Autostakkert to create a master flat under 'Image Calibration'.
  • Load the Master Flat under 'Image Calibration'.
  • Analyse and Stack the SER file. The master flat will automatically be applied to the individual SER frames during the processing.
  • Sharpen the final stack using Registax.
  • Final processing in GIMP or Postscript to apply colour, contrast etc.
Depending on the solar filter you are using, the final image may be white. False colour can be applied - see https://www.thelondonastronomer.com/it- ... et-science under the section CREATING FALSE COLOUR IMAGES OF SOLAR PROMINENCES. Some solar images https://www.thelondonastronomer.com/#/sun/.

Don't expect instant success with this, there is a lot to assimilate. Even a step such as focusing can take a lot of practise to achieve good results.

Always take sensible precautions and use undamaged solar filters - the sun is dangerous, treat it with respect.

Dave
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admin
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Re: Creating Flats with Solar Images

#5

Post by admin »

Hi,

difficult to be sure from your screenshots, but it looks awfully like you have an image of the sun visible on the camera when taking the 'flat' - that is incorrect. A flat frame should be pretty much uniform grey except for possibly dark splodges from dust on the sensor or darker corners due to vignetting.

The usual approach to taking a flat is to either cover the end of the telescope completely with something translucent and white (a single sheet of white paper for instance) or to use some sort of even illumination (electroluminescent panel, etc) applied directly to the aperture of the telescope.

Apologies if this *is* what you are already doing and I've misinterpreted your screenshots.

Robin
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turfpit
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Re: Creating Flats with Solar Images

#6

Post by turfpit »

Sandcomp

viewtopic.php?f=23&t=1376. Some ideas for generating flat frames - using a cheap tracing panel or home made with an EL panel (off eBay).

You could try without flat frames as a starter.

Dave
sandconp
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Re: Creating Flats with Solar Images

#7

Post by sandconp »

admin wrote: Wed Jun 16, 2021 7:53 pm Hi,

difficult to be sure from your screenshots, but it looks awfully like you have an image of the sun visible on the camera when taking the 'flat' - that is incorrect. A flat frame should be pretty much uniform grey except for possibly dark splodges from dust on the sensor or darker corners due to vignetting.

The usual approach to taking a flat is to either cover the end of the telescope completely with something translucent and white (a single sheet of white paper for instance) or to use some sort of even illumination (electroluminescent panel, etc) applied directly to the aperture of the telescope.

Apologies if this *is* what you are already doing and I've misinterpreted your screenshots.

Robin
Hi Robin,

So since I am running Sharpcap Pro, I should be able to eliminate the step that Turfpit (Dave) mentions above about having to use Autostackkert and Image Calibration with a master flat correct?

So I should be able to use Sharpcap Pro, Capture Flat and apply it real time as I am imaging the sun correct?

Conrad
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Re: Creating Flats with Solar Images

#8

Post by admin »

Hi Conrad,

yes, that's possible for you with SharpCap Pro - as you say, just capture a flat and then let SharpCap apply that flat to every frame in real time, so that the saved SER file will contain already-corrected frames.

A good way to check you have good flat correction is as follows...

Once you have created and applied your flat in SharpCap, leave the flat frame illumination in place. At this point you should see a very uniform image, since the flat correction should be cancelling out any dust shadows or vignetting. Next, halve the exposure of the camera to reduce the brightness of the image on screen - you should still see a basically uniformly bright image (you may see a small hint of any dust/vignetting). If, in either of those checks, you see a problem with the image (bad dust shadows or inverted areas where the dust shadows are brighter), try taking the flat again or adjusting flat settings.

cheers,

Robin
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