Jeff
That is coming along now - you are getting the faint detail. APP has some pre-set filters for the Digital Development Process (DPP). See first image, in the red box. These pre-sets will apply black point and stretch (among other things). This is a case of where less is more. To process your data, I used all default settings in APP - no fancy processing.
Looking at the L frame histogram in FITS Liberator - black = 0 and white = 65535. Once the exposure hits 65535 (the histogram hits the right hand side, that is basically white and the data can never be recovered by software). If the histogram hits the left hand side, data is black and that means faint data is lost and can never by recovered by software. The ideal exposure will avoid the histogram hitting the left or right hand sides. With the 300s L frame there is a gap at the left - meaning we have all the faint data but the histogram hits the right hand side hard at 65535 - white and the detail is gone. The fix is less exposure.
Basically the 300s exposure blew out the bright core. The Holy Grail of M42 imaging is to retain the Trapezium (4 stars at the core) and capture the faint nebulosity. Images that achieve this will invariable be produced by combining frames with varied exposures even down to 4s. For my M42 on Astrobin, it took over 2 years of trial, error and study to achieve that.
The M42 60s histogram (3rd image) has maximum value which is less than 65535. This avoids the burn out (just).
I have an order in for some 60s and 20s frames on Pier 6. I will post the results once I have the data.
This APP
tutorial will give you a good idea of how the software is used. The data can be downloaded and the software can be evaluated for 30 days FOC.
Dave