Mars at Opposition: Day 1

Goal: Capture Mars near the Oct. 13, 2020 date of closest approach (Opposition).

Reconfigured the Meade LX10 EMC SCT for planetary imaging.  Exchanged the 0.63 focal reducer for a 3x Celestron X-Cel LX Barlow.  The optical train was assembled (staring at the SCT threads) with the Celestron T-mount adapter connected to eyepiece projection cell (with Barlow lens inside sans its eyepiece holder) to the T-mount to the Zwo ASI120MC-S.  No filters.

In the late afternoon, started by setting up the Celestron CGEM DX with a rough north-oriented alignment, mounting the OTA (initially sans guider scope) and using ASI capture software on the cell phone, began working to focus the overall system with the Zwo ASI-120MC-S on distant trees.  

And the nextdoor streetlight --where the field of view barely contained the base of the bulb.

With evening  darkness, aligned the mount with the polar scope and worked to focus to a star.  No luck was found trying to use the ASI capture software on the cell phone to find a star & capture in order to focus to infinity (the trees and nearby street lamps were not close enough to infinity to work effectively).  

Swapped the Zwo ASI120MC-S for the Canon T3I...initially attempting to find a star & focus with the Barlow.  Gave up... removed the Barlow and found stars & was able to focus at prime focus.  With a bright star centered in the frame, inserted the Barlow into the optical train, found the star still in the frame and refocused.

Mounted the guide scope back onto the OTA after finding that plate solving from the Canon was just not working (timeouts).  Using the guide scope (with the ASI120MC-s), was able to quickly point to Mars and begin capturing video & still frames with the Canon T3I.  

Used PIPP in batch mode and Autostakkert to pre-process, crop, normalize, sort & stack the top 10%, 20%, 50% and 70% of the available frames.  Immediately noted a lack of any real detail from the SER files (as well as individual stills).

Analysis of the still frames indicates approximately 232 pixels spanning planet disk (measured using coordinates in rawtherapee).  Found the apparent size of Mars in the sky in arc seconds for 10/15/2020 as 22.25", providing 0.171 arcseconds per pixel with the Dawes limit for the 8" OTA being around 0.59" (in a perfect world).  This results in an effective focal length for this system as 5,173mm @ ~F25 using 206.2648 as the conversion factor.  

Initial result after using Autostakkert on the four SER files was disappointing with no features or contrast: 

Nice tutorial on computing effective focal length:  Planetary Imaging Tutorial

Lessons learned:  

1) Focus at prime first... then switch to a Barlow.

2) Guide scope is critical because plate solving with a camera at high magnification is futile when so few stars are visible (even at extended integration times). Plate solving using astrometry on Indi/Ekos with DSRL frame sizes is especially hopeless.

3) Over exposure in the video capture is bad.  Indi/Ekos lacks a histogram in the video capture window, making it challenging to see what the current levels (or even saturation) are for the pixels in the frame.

4) Over sampling makes focus & exposure harder.  The 2000mm SCT needs (at most) at 2X Barlow.  The 3X Barlow is well suited to the 1200mm CN-10 Newtonian, however.

5) Frame rates on the DSLR are not great (~7.8 frames / second).

6) Use PIPP in "join" mode, not "batch" mode so that multiple SER video files can all be processed into one result.  

7) Do not select "Equalize R, G and B Channels individually" in PIPP if usable color output is desired.