A well exposed moon looks sort of like this. The moon is ok, the rest is underexposed.
well exposed moon, f5.6 1/50 second ISO100
Exposing for the rest of the landscape might look like this with a blown out moon and flare around the moon to a sizable extent.
exposed for foreground, 2 seconds, f5.6 ISO100
The big problem here is how to fix the sky flare in the target exposure image. Here is a step by step method. I will show crops of the problem area because it does not always look bad at reduced scale.
Crops of effected area.
crop to show flare and blown moon
Step 1, Isolate the sky: Starting with the bright exposure use your favorite selection process to place the sky on a separate layer. I leave the processing of the rest of the image to your taste. I like to get the foreground processed first ignoring the sky layer and then do the following steps to the sky layer when the rest is done.
Step 2. Remove the moon.
In photoshop CS6, the content aware method works very well. Draw a lasso around the area that contains flare, in this example it is probably 75% of the shown area and irregular in shape. Get all of it. Right click and select fill. Choose content aware, opacity 100%, mode normal.
Here is what it should look like.
Moon removed using content aware fill
Step 3. Fix the unevenness in texture and some blotchy illumination.
I start with a light NR step which could have been done earlier in the work flow. This step gets rid of normal camera noise, the rest of the noise work is to fix unevenness from the content aware step. I used Topaz denoise lightest but your own NR tool will work fine.
Add noise, under filter>add noise> amount 2.45, uniform.
It looks like this:
After light NR and uniform noise added
Then I run Topaz denoise strongest. It now looks like this:
Topaz heaviest NR
Step 3. Prepare the moon.
I use a medium NR to get rid of any visible noise.
Add some contrast I use a curve layer.
Sharpen to taste. My version looks like this.
Moon file, NR>curves>sharpened
Step 4. Insert the moon.
Select and copy the dark exposure moon image after it has been processed.
Paste the moon layer at the top of the light exposure image.
Set “lighter color”. The moon automatically appears in the light image like this.
Moon inserted into fixed sky image
Here is a final image.
final image
