Red Moon

March 20, 2014  •  Leave a Comment



We do not need to wait for a lunar eclipse to shoot at a Red Moon!



With the words Red Moon we usually refers to a very particular event: The Lunar Eclipse.

During this phenomena, the Moon does not disappear but it is enlighten by the solar rays that pass through the earth’s atmosphere east and west during the sunset and the sunrise.

The same phenomena of light scattering that make us sense the orange hues of twilight and dawn, casts the moon with the same colors.

Unfortunately the lunar eclipse is an event that cannot be observed on daily bases but, at every lunar dawn, the Moon passes through lower atmospheric layers and colors itself with the same reddish shades of the sunset.


Shooting conditions

That is the light I tried to catch using samyang 500 mm f6.3 lens mounted on my canon 7d.

Even if the shot seems that can be easily handled, it cannot for different reasons:


Finding the maximum exposure time: with a 500 mm lens it is important to consider carefully the maximum exposure time such as to avoid a blurred image due to the earth rotation that can be easily seen at this focal length.

Fortunately we can use a well know formula to calculate this time:

tmax = 550/(F*c*cos(d)) with:

tmax = maximum exposure time (sec);

F = focal length in mm;

c = constant (1 per Full Frame - 1,5 per APS);

d = declination of the sky portion we are shooting at;

In my case d = -5°, F = 500 mm, c = 1.5 and tmax = 0.74 sec. I decided to use 0.5 sec.


Finding the Moon position: even finding the right spot where the Moon will rise is very difficult due to the high magnification of the lens. Furthermore the haze on the horizon does not allow to easily catch the glare coming from the Moon before it rises (normally even 5 min. before). In this case the best thing to do is to use a smartphone app called Sun Surveyor that point out the spot by means of augmented reality.

Focus: to have the right focus I picked a star and manually adjusted the gear using live view and high magnification.

Iso management: This is the only variable that can be manipulated. I supposed to use iso 400 but after the first shot I quickly changed it up to 800.

Double exposure: I had to shoot also for 30 sec to catch the light reflection adjusting the scene until the Moon was not framed any more (more or less 1 min after; @ 500 mm the moon’s movement is very quick).

In the end, the shooting condition are:

Canon 7d, 500mm, f6.3, 0.5 sec for the Moon - iso 800, 30 sec for the sea - iso 400.

In camera raw every parameters @ 0; white balance equal for the two shots (same as the Moon shot): T = 5250 °C e Hue +8.


Luminosity and Contrast

The shot that will be used as background (fig.1) has got the following problems:

Presence of noise, high luminosity compared with the Moon, a lighter halo in the upper part (right hand side) and, above all, a dark round halo in the center (due to the secondary mirror of the lens).


Red Moon backgroundRed Moon backgroundRed Moon background fig.1



To start addressing these issues is it necessary to have a look at the three channels in RGB hoping to find one that can be used to reduce these defects; let’s see:

The red channel is too light, has got noise and the central halo is clearly visible (fig.2).

Red Moon background RRed Moon background RRed Moon background R fig.2



The green channel is slightly darker, has less noise (as can be normally expected from this channel) and the central halo is almost invisible (fig.3).


Red Moon background GRed Moon background GRed Moon background G fig.3



The Blue channel is too dark; For this reason I decide to :


  1. Duplicate the layer background;
  2. Apply the green channel on it;
  3. Change the blend option choosing “luminosity".


With these few steps I have: reduced the luminosity, the noise and the halo (fig.4).


Red Moon background luminosityRed Moon background luminosityRed Moon background luminosity



To further reduce the luminosity and increase saturation we can apply an adjustment layer curve with the following steps:

  1. Merge down the layers;
  2. Duplicate the layer background;
  3. Apply a layer curve with blending option set to multiply;
  4. Apply to the white mask the inverted RGB from the background;
  5. Apply a curve to the mask until the lights are completely open;
  6. Eventually we can use even the brush to finish off the work;
  7. Apply a gaussian blur amount 20 pixels (fig.5).


Red Moon background Mask1Red Moon background Mask1Red Moon background Mask1 fig.5



Now the sky and the sea are darker. Even the Moon reflection is darker but not as much as the rest of the shot thanks to the mask. We can fine tune the luminosity changing the opacity of the layer curve until we can distinguish a difference between the sea and the sky. We can also fine tune the reflection luminosity adjusting the mask opacity (fig.6).


Red Moon background MultiplyRed Moon background MultiplyRed Moon background Multiply fig.6


Next step is to reduce the halo in the photo’s upper part:

  1. Apply a layer curve in luminosity blending mode;
  2. Apply the RGB to the mask;
  3. Apply a curve to the mask until the shot gets dark and remains only the halo;
  4. Apply a gaussian blur amount 30 pixels (fig.7).
  5. Reduce the luminosity by means of the layer curve (fig.8).


Red Moon background Mask 2Red Moon background Mask 2Red Moon background Mask 2 fig.7

Red Moon background Top HaloRed Moon background Top HaloRed Moon background Top Halo fig.8



Merging the shots

To achieve the final result it is necessary to overlay the two exposures applying the Moon shot in lighten mode (fig.9).


Red Moon finalRed Moon finalRed Moon final fig.9



Fine tuning needs to be applied changing the layer multiply opacity  @ 80% and the mask1 density @ 90% such as to balance the Moon’s and background’s luminosity especially the light reflection.


We do not need to apply an Unsharpening mask (USM) for the following reasons:

  • The Moon's details have been twisted by the atmospheric haze that created also a mirage on the bottom part of the Moon;
  • The light reflection upon the sea is the result of a long exposition that created a kind of “silk” effect with few details to put in evidence;
  • In this case I preferred to avoid USM to preserve the image from an increase in the noise level.


In the end We can state that shooting at the Moon when it rises from the sea colored of red shades is difficult but not impossible especially if we first plan the shot at home. From the "post production" point of view, we can say that we do not need to apply any techniques that increase saturation and colors variation (CB e MMM): this kind of shot is a duo-tone image! We do not even need the USM since the original details are not noticeable.

It is important instead to spend time for a better luminosity allocation. Here is the image Before - After (fig.10).


Red Moon Before - AfterRed Moon Before - AfterRed Moon Before - After fig.10



Do not forget that even the best shot you can do will not compete with the nature show itself!!


If you think that this Tutorial could be useful to other astronomy and astrophotography amateurs, please feel free to share it!!

Paint the Sky, Share your Knowledge!!





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