Since there are occasional questions about the steps for getting a moon exposure and the required post processing, here is a basic "How To".
Getting a Good Moon Exposure
There is no substitute for getting a good exposure, but, at the same time, there is no single “right” set of parameters to do it. In getting a good exposure, some camera setting work better than others and I have found the following work the best for my preferences when using the equipment that I have. Don’t even think about trying to get an automatic exposure – well, OK, you can think about it, but even with spot metering, you will still have to play around with exposure compensation. Set the camera to manual exposure, ISO to 100 (or lower if you have it), aperture to f/8 for most high quality long telephoto lenses, and shutter speed somewhere between 1/30 second and 1/500 second. When the moon is just a very thin crescent, an exposure time in the vicinity of 1/30 second might be appropriate and for a full moon, an exposure time of about 1/400 second might be appropriate. There is a great deal of variation in the necessary exposure because the elevation of the moon in the sky and atmospheric clarity affect the amount of light that we get from the moon. The exposure time of the moon in the example presented here is 1/160 second and it was made very close to the first quarter with the moon almost at the zenith. The aperture was f/8 and ISO was 100. The lens used was the Canon EF 400 mm f/5.6L USM on an XTi body.
Accurate focusing, on the other hand, is an absolute requirement. Nobody that I know of has ever complained that a Moon image was focused too precisely. No amount of sharpening can do anything to a soft fuzzy image other than make it ugly and fuzzy. In addition to focusing, eliminating shake and vibration are just as important in achieving a tack sharp image. A solid sturdy tripod is essential and I prefer a gimballed head that pivots about the center of mass of the camera/lens combination in order to minimize cantilevered loads, which can exacerbate low frequency structural vibrations in the mounting system. My tripod gimbal mount is a Wimberly Sidekick on a Manfrotto 486MGRC2 ball head. Next, a wired remote shutter cable is very desirable because it allows you to trip the shutter without touching the camera and it also allows you to get a very rapid sequence when you want to “stack” a number of images. Finally, when the mirror flips up, it produces some high frequency vibration in the camera that slightly blurs an image. By enabling the mirror lock-up feature, the sharpness of images are improved considerably.
Needless to say, shooting in RAW will allow you far greater latitude in post processing the image compared to processing a JPG image. I do all of my post processing in the Adobe CS3 Bridge / Camera Raw / Photoshop Extended suite.
Getting a RAW Deal
You’ve got your perfectly exposed and perfectly focused RAW image of the moon, so if you are wondering where to go from here, …… here’s where:
- From Bridge, select the image and open it up in ACR (or Lightroom, if that is what you use). I highly recommend always using ProPhotoRGB as the colorspace in Camera RAW and always working with 16 bit files. If you do not have ACR set up that way, you are discarding part of the captured RAW data right off the bat.
- When shooting, I generally use AWB and it seems to give good results for moon shots, so I rarely change the “As Shot” setting in the Basic tab. (NOTE: you can use any WB that you want as it makes no difference whatsoever to what is captured – the sensor sees what it sees – end of story. The only thing that does change is the metadata tag which is simply text data that lists camera settings.) Next I want to be able to see a histogram so I enlarge the moon image to 100% and then use the crop tool to draw a small box of roughly 100 X 100 pixels, but the size is not especially important. I move it around over the face of the moon to make a subjective evaluation about the exposure and then decided that I needed to add about 1/3 stop additional exposure (+.35) to more or less center the “hump” of the histogram as shown in Image 1 below.
Image 1 -- Tweaking the Exposure
- Next, I zoom in closer to 200% and look at details near the edge of the lunar disk to make the remainder of the tonal adjustments. No Recovery or Fill Light adjustments are needed, so they stay at zero. The setting for the Blacks slider depends on whether you plan to use the image alone or in a stack. I will be using this image alone, so here is the procedure – Hold down the Alt key (for Windows, or Cmd for Mac) while moving the Blacks slider. The goal is to be able to see details in the dark area along the terminator, but not allow quantization noise in the black sky to be visible. By holding down the modifier key while the slider is being adjusted, the black point becomes very evident. If I were going to use the image as part of a stack, then I would increase the value of the Blacks slider slightly to eliminate stray noise that can confuse the image alignment algorithm. The remainder of the tonal adjustments are intended to help emphasize details in the lightest areas of the image. The values that I used are fairly typical of what I always use: Brightness = 45, Contrast = 39, and Clarity = 35. Both Vibrance and Saturation can be left at zero for moon images. Image 2 below shows the results of these settings.
Image 2 -- Tone Adjustments
- Next, I go to the Curves tab and select the Point curve option. The built-in Medium Contrast curve works quite well, but I have created a Moon curve that gives a bit more contrast in the mid tones – contrast in any given region is determined by the steepness of the curve through that region. The Moon curve is an XMP file that is available for download by clicking on the following link: . Image 3 below shows the point curve.
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Image 3 -- Curves Adjustments
- The next step is capture sharpening. Capture sharpening is simply sharpening that is done to counteract the slight loss of sharpness that is the natural result of the RAW file demosiacing process and, because of this, should not be thought of as the sum total of all sharpening needed during image processing. Here is the procedure for capture sharpening:
- First of all, zoom the image scale to 100% (or even 200%). In order to see the result of what you are doing, you will need to hold down the Alt key (for Windows, or Cmd for Mac) while adjusting the sliders in the following steps.
- While holding down the modifier key, adjust the Amount slider for maximum image sharpness. You will notice that when you are doing this, the image will change from color to B/W in order to best see the luminance detail. For RAW files from my camera, the best sharpness amount is almost always in the range of 40 to 50. I selected 48 for the Amount. Resist the urge to go much further in Amount because very fine details begin to disappear at the expense of sharp edges for larger details.
- Set the Radius to 0.7. You can try different values, but for my camera, this value is almost a universal constant. The larger the Radius value, the more “blocky” the image becomes.
- The Detail slider determines how much of the sharpening should be revealed. The further that the value is increased, the “crunchier” the image becomes. I generally stick with a value between 15 and 45, and most of the time, the value is around 30. In this case, I used a value of 20.
- The Masking slider is used to create a mask to hide areas with less contrast from sharpening done by the Detail slider. This is where use of the modifier key is critical to see what is going on as the slider is being moved because the amount of masking is very dependent upon the image. In this instance, a value of 45 seemed to be about right. Do not use excessive masking or it will hide too much of the sharpening. In this instance, I used a value of 45. Image 4 below shows what the image looks like when this adjustment is being made while holding down the modifier key.
- For Noise Reduction adjustments, you do not hold down the modifier key. I almost always leave the Luminance slider at zero because it tends to slightly soften fine details in an image. If I need to do any luminance smoothing, I wait until the image is in Photoshop and then I will use the NeatImage plug-in. In order to properly use the Color noise reduction slider, zoom the size to 100% or greater (I often use 400%) and then find an area that is fairly neutral in color and about mid luminosity or maybe slightly less. You will probably see faintly colored splotches. Slowly increase the slider value until the color splotches disappear. At ISO 100 on my camera, this usually is in the neighborhood of 15 and that I what I used. Do not apply any more color noise reduction than necessary.
- First of all, zoom the image scale to 100% (or even 200%). In order to see the result of what you are doing, you will need to hold down the Alt key (for Windows, or Cmd for Mac) while adjusting the sliders in the following steps.
Image 4 -- Sharpness Adjustments
- Minimizing chromatic aberration always helps to improve the sharpness of an image. Mathematically, chromatic aberration can be resolved into two vector components: axial and radial. In very basic terms, the speed that light transmits through glass is dependent upon the wavelength of the light and is the reason that white light through a prism spreads out (known as dispersion) to produce a spectrum of its constituent colors. The axial component of chromatic aberration (also known as longitudinal chromatic aberration) results in a difference in focal lengths for light at the blue and red ends of the visible spectrum and the result is a “circle of confusion” that limits how sharply a lens can focus. This problem can only be addressed in lens design using different types of glass with the goal of having all visible colors focusing at the same point. The other vector component – “radial” chromatic aberration (also known as lateral or transverse chromatic aberration) is the result of off-centerline axis light that produces a “size effect” – meaning that light at the two ends of the visible spectrum are not magnified precisely the same amount. The typical result of this component of chromatic aberration is a red or blue fringe along high contrast edges, which is most pronounced at the outer edges of an image and is more prominent in super telephoto lenses than in wide-angle lenses. A really useful thing about digital imaging is that image-processing algorithms can be used to effectively minimize this component of chromatic aberration. Here is how to use the Chromatic Aberration Tool in Adobe Camera RAW:
- First of all, this works best if you can find a high contrast edge near the edge of the image. If your moon is very small and near the dead center of the image then you will not be able to use the tool very effectively, but the good news is that you may not need to use it in that case. Zoom to 400% view and go to a high contrast edge that is as close to the edge of the frame s you can find.
- In order to see the result of what you are doing, you will need to hold down the Alt key (for Windows, or Cmd for Mac) while adjusting the sliders. First, while holding down the modifier key, adjust the Red/Cyan slider until the red and cyan images coincide.
- Next, do the same thing with the Blue/Yellow slider. In this case, the change will not be as distinct, but try to discern when the edge color transitions from blue or yellow to neutral.
- Finally, set the Defringe drop down menu selection to All Edges. I have tried Highlight Edges and it does not seem to be nearly as effective.
- Image 5 below shows the result of chromatic aberration corrections and, in this particular case, not much correction was necessary. If you have a teleconverter installed on your lens, you may find it necessary to add a lot of correction to eliminate the color fringing. One thing that you will notice it that it is not possible to completely eliminate chromatic aberration so your goal needs to be to find a satisfactory minimum.
- First of all, this works best if you can find a high contrast edge near the edge of the image. If your moon is very small and near the dead center of the image then you will not be able to use the tool very effectively, but the good news is that you may not need to use it in that case. Zoom to 400% view and go to a high contrast edge that is as close to the edge of the frame s you can find.
Image 5 -- Chromatic Aberration Correction
- On the Camera Calibration tab, select one of the predefined calibration profiles such as Adobe Standard Beta 2 or if you have calibrated your camera, select the appropriate profile. In my case, I have calibrated my camera so I used my camera’s “Canon EOS Rebel XTi ISO 100” custom calibration profile. I have found that the Adobe Standard Beta 2 profile is quite close to my camera’s calibrated profile. I prefer it to the Canon camera styles which I perceive as being overly exaggerated. Image 6 below shows the final Camera RAW result after all of the above adjustments have been made.
Image 6 -- Camera Calibration / Style
- Now that the RAW image post processing is finished, it is time to go to the conversion to a standard image file format. Click on Open Image to open the image in Photoshop.
In Photoshop, the first thing that I did was to crop the image to get rid of all of the useless black space that is just taking up … uh … space (in every sense of the word). Now I had a workable image that was mostly moon surrounded by a minimum of emptiness. I examined the image and it still looked a bit drab to me. Sometimes, I use the Shadows/Highlights panel to improve contrast, but it did not give me the results that I wanted in this case, so I decided to use Image > Adjustments > Curves. It takes a very fine touch to use curves without producing really gaudy looking images. The learning “curve” (please excuse the bad pun) is steep until you get an intuitive feel for what is going on. A good place to start is to select one of the predefined curves and then slightly modify it – for moon images, the linear contrast curve is a good starting point. An important thing to understand about curve adjustments is that contrast is a function of the steepness of the curve because what you are attempting to accomplish is to map the input data over a greater output range (the ordinate or vertical axis of the graph is the output and the abscissa or horizontal axis is the input). I wanted to primarily expand the range of the midtone values and the very gentle “S” curve gave me the results that I was seeking. Image 7 below shows the result of the curves adjustment.
Image 7 -- Curves Adjustments
The coup de grâce for a nice moon image is to add a bit of unsharp mask sharpening to the image so that it looks crisp, but still looks like it was not sharpened. I previously used channels sharpening for moon shots, but I really liked the USM sharpening that POTN forum member Bernoulli uses for his moon images – so, that is what I did: Amount = 150, Radius = 1.0, and Threshold = 0. (I still use channels sharpening fir bird photography where very subtle results are desired). I generally do late binding for web images, so now is the time to click on Edit > Convert to Profile and select sRGB as the output color profile since the image destination is the web. Next, select Image > Mode > 8 Bits/Channel and then save the image by selecting Save As and typing a file name and choosing JPG as the file type in the save menu. Image 8 below shows the final result of editing the moon image.
I have found that with this lens and these processing step that I can enlarge the final image to 2X size before saving and still get a sharp image.
Image 8 -- Final Moon Image
..... and, that's all that there is to it.
