Lucky Image Processing

Introduction

Lunar, Planetary and Solar imaging share may common aspects when it comes to capturing the best images for these objects.  Lucky Image Processing is the method of capturing video or many successive images (hundreds or thousands) of the same object in a short period of time and then processing these images to obtain a final image better than any of the individual images originally captured.

Software

Imaging times

Reference: Guide to Planetary Imaging: Planetary Rotation and Detail Smearing

When using lucky Imaging, time is limited due to the fact the object may be rotating.  Here is a summary of rule-of-thumb imaging time limits for video capture assuming 0.5 arcseconds of detail smearing allowance:

Barlow Lens

Reference: Guide to Planetary Imaging: Sampling

First we need to determine the Optimal Magnification for our hardware.  We want to get the most detail possible given the seeing conditions, scope and camera capabilities  This is determined by the following variables:

• Imaging Scope Focal Ratio (Sfr)

• Imaging System Focal Ratio (Ifr)

• Camera pixel Size (Cps)

• Camera Sensor Dimensions

• Seeing Conditions - Scaled here as 5-7, where 5 is normal, 7 is exceptional

We start with the assumption that the Optimal Focal Ratio (Ofr) of the imaging system should be 5-7 times the camera pixel size based on seeing conditions (5 for average, 7 for exceptional), so we will go with 6 time the pixel size in these calculations.

Ofr = 6Cps

Assuming our camera and our scope are not easily changed, we can't change those variables, what we can do is change the Imaging System Focal Ratio by adding a Barlow lens if necessary to try to get to the Optimal Focal Ratio (Ofr), or use Eyepiece Projection.  Here we determine the appropriate Barlow Lens Magnification (Bx)

Bx = (5-7)Cps/Sfr

Here is what I have calculated for some hardware, where Barlow Magnification magnification is from good to excellent conditions (5-7):

Will it Fit?

References

• Guide to Planetary Imaging: Planetary Rotation and Detail Smearing

• Astronomy Tools: Field of View Calculator

Now that we know the Optimal Magnification and have determined what Barlow lens we need, we need to determine if the image will fit on our sensor, and what wiggle room we have, because as we are capturing the image, things tend to drift.  First consideration is the size of the object you are imaging.  While the sun and moon stay the same size throughout the year, the planets vary based on how close they are to the earth.

Apparent Size of common objects in the solar system

Field of View Calculations

* F Ratio of 20 is ideal for typical conditions

Planning and Preparations

References, Resources and Tutorials

Process Flow Diagram

Provided below is a basic process flow diagram outlining the general steps taken in processing images with lucking imaging.

Following the process diagram below is a more general review for each step

1. AutoStakkert – Using this application we test retention of 50%, 25%, 12% and 6% of frames from the captured view.  We determine the best looking image generated from these settings and will use this percent in the PIPP program.

2. PIPP – Taking the videos captured including Darks, Flats and Target Image we will generate a final AVI file with the determined percentage of frames to retain from the first step.  This AVI file will be used by one of the three imaging software applications to generate the single planet image.

3. AutoStakkert/AviStack/RegiStax 6 – Using one of these three imaging application we will generate a final image (TIFF).  All three imaging applications were created for Lucky Imaging processing and have their pros/cons.  Only on program is required to generate a final image.  Use your preference.   My current preference is:

4. Moon – AviStack

5. Planets – AutoStakkert, RegiStax 6

6. RegiStax 6 – Image Sharpening.  While both AviStack and AutoStakkert offer sharpening, RegiStax 6 is the best tool for sharpening images.  Import the image and perform sharpening on it in this application.

7. Microsoft Photos – Use this program for cropping and basic lighting adjustments. (TIFF)

8. GIMP – Used to add text and imaging setup information on the picture (TIFF).

9. IrfanView – Resize the image, Convert TIFF to JPG for general distribution, and create thumbnails from image.

Working Example

Setup: Primary Photography with Celestron C-11 HD | TeleVue Powermate 2x Barlow | ZWO ASI120MC-S camera |