Trouble understanding the HDR or Stack process for multiple exposures of the solar eclipse

[Hindsight]

I have followed some non-eclipse tutorials for Affinity online but they don't seem to be working well for my use-case. 

I have bracketed exposures of the sun during the totality of the eclipse. The exposures range from 2 seconds up to 1/1600. I have followed the tutorials to merge them together in two different ways - one as a new HDR Merge, and one as a new Stack. For whatever reason, using the various adjustments shown in the HDR tutorials doesn't get me where I want to be - specifically the longer exposures just overpower the area around the moon and over-saturate the luminance. I can't pull those areas down. The opacity slider on the layers (not colors) area doesn't seem to work the way I would expect it to either - if I go to any single layer and change the opacity, the layer becomes invisible at any opacity value less than 100%, or fully visible at 100%. 

I have seen some folks post about eclipse processing in this forum but mostly it's people watching PS tutorials and trying to adapt it to Affinity, unsuccessfully, because they aren't the same program and work slightly differently. 

Any advice would be appreciated. 

[NotMyFault]

Welcome to the forum, @Hindsight.

The task you are facing is not easy to achieve, and you already hit several limitations of Affinity software which require workarounds.

15 hours ago, Hindsight said:

The opacity slider on the layers (not colors) area doesn't seem to work the way I would expect it to either - if I go to any single layer and change the opacity, the layer becomes invisible at any opacity value less than 100%, or fully visible at 100%. 

In case you have a live stack group, opacity / layer transparency does work differently, becoming binary on/off. 

So you need to remove all layers from the stack first if you want to work with layer transparency. This is an intended functionality (which i personally don‘t like).

15 hours ago, Hindsight said:

For whatever reason, using the various adjustments shown in the HDR tutorials doesn't get me where I want to be - specifically the longer exposures just overpower the area around the moon and over-saturate the luminance.

For such extreme variations of lightness the HDR persona comes to its limits. Remember that is primarily intended to reduce strong contrasts and map all color values into the SDR (standard dynamic range).

First you really work with source files of 16 or 32 bit color depth. Then stack the images and stay in RGB/32 color depth for all editing (except exporting, see below), and enable „ICC managed“ in 32-bit preview. It you’ll really help if you have a HDR capable GPU and display (supporting e.g. 1000nits max brightness and EDR/HDR with 32 bit input signals).

You might need to hand-select the best fitting source files (and exclude some who spoil the result). Sometimes you may get better result manually adjusting the brightness with help of curves, levels, or other adjustments.

If you want to finally export to jpeg (for social media), you then need a second HDR processing to reduce the dynamic range to 8 bit. There were some issues exporting directly from RGB/32 to RGB/8, so i prefer to save a copy of the file, do the final work ind tone map persona to reduce DR to SDR. Save again a copy, then open that file, convert dolor format to RGB/16 or RGB/8, and export the JPG (or JPGXL etc).

It takes a lot of practice and expermientation to achieve good results.  

[Hindsight]

Thank you very much for the reply NotMyFault. I will go through, step by step, the recommendations you provided and see what I can get. 

Thanks again!