Help with Huge Dynamic Range Overlay

astrostu · Aug 28, 2007

I'm trying to process some of my eclipse images from last night. For the umbral eclipse, when half the moon was brightly lit and half was dark, I took exposures at 1/50-sec and 2.5-sec to properly expose each part. Now I'm trying to merge them.

Unsuccessfully.

An HDR does not seem to work for this, and the various blending modes don't, either. The problem is that for the 2.5-sec shots, the brightly lit part is completely saturated. I can't seem to figure out how to basically do an overlay of the 1/50-sec part on top of that such that it blends well.

Has anyone done this type of thing before or does anyone have ideas?

Garbz · Aug 28, 2007

Basically you'll have real problems here. HDR is great for pushing a few stops beyond the 5 that film has, but based on the shutter speeds I was using there was more than a 14 stop difference between the bight part and the dark part of the moon.

When you expose for the dark side, at least in my case, I ended up with such a huge blown out glow from the light side that I don't think HDRing will help even after bracketing 9 stops as the images simply aren't similar. That said I am by no means an HDR expert someone else may know a way.

astrostu · Aug 28, 2007

Yeah, hence why I'm looking for different blending mode options. I think that's a 19-ish stop difference (my 1/50 to 2.5-sec) for the same phase of the eclipse.

Any other ideas?

gizmo2071 · Aug 29, 2007

Isn't 1/50th ~ 2.5secs like only 7 stops difference?
If you post the images I could have a play and see whats possible with it.

astrostu · Aug 29, 2007

I figured out a way. I overlaid the image of the full moon without being eclipsed over the longer exposure. I set the opacity to around 50% and blend mode to Multiply. That did it. I'll be posting the montage within a few hours.

As for 7 vs. 19, I just forgot to divide by 3.