WAITING FOR THE SHADOW

Astronomical Observing and Photography - Joseph Cali

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Total Lunar Eclipse -  November 8th 2022  - Event Information

Lunar Eclipse Photography
How big will the Moon be in the frame with my lens?
The  exact size of the lunar disc on your sensor  is easily calculated. It is the focal length ÷ 114.  So a 200mm lens will produce a 1.8mm lunar disc on the sensor but what will that look like. It is often easier to see the size of the lunar image reprsented relative to the camera frame.  This illustration shows the size of the lunar image diameter at different focal lengths relative to a full frame sensor(outer box) and APSc sensor(inner box).






Eclipse Exposure Guidance
The difficulty photographing total lunar eclipses is that they vary in brightness.  As mentioned above, light absortion by the Earth's atmosphere is one reason for this, the other factor is umbral depth, in other words, how deep inside the Earth's shadow cone does the Moon travel?

If this eclipse, turns out to be a dark eclipse like the 1993 event, then it will be very difficult to record. The exposure recommendations below are for a more typical bright coppery red eclipse. However if mid-eclipse is very dark, don't despair because totality will be brighter just after the beginning of totality (21:17) and just before end of totality 22:42.

There is no single "correct" exposure for lunar eclipses because
Use the recommendations below as a starting point, check your images as you go and shift exposures as necessary.



Moon at first contact
ISO 400  f5.6 1/250s




Moon: Half immersed, exposed for sunlit side
ISO 400  f5.6 1/250s

Moon: Half immersed, exposed for umbral shadow
ISO 400 f5.6 1/15s




Moon 3/4 immersed, exposed for  sunlit side,
processed for umbral shadow
ISO 400 1200mm f5.6 1/30s 
Raw processed with shadow boost
and highlight suppression


Moon 3/4 immersed, exposed for umbral shadow
ISO 400 1200mm f5.6 1/6s 
Raw processed with shadow boost
and highlight suppression for sunlit part

Moon 9/10 immersed, exposed for sunlit crescent
ISO 400  f5.6 1/20 s



Moon 9/10 immersed, exposed for  umbral shadow
ISO 400  f5.6  2s 
Equivalent to ISO 1600 1200mm f5.6 1/2s 
Raw processed with shadow boost
and highlight suppression





Moon at totality
ISO 1600  f5.6  4s
Equivalent to ISO 6400 f5.6 1s
Raw processed with shadow boost
and highlight suppression




How Long Can You Expose without movement?
Some of the exposures shown above are up  to 4s long.  I used an 8 inch telescope mounted on a high precision tracking mounting to take these images. As the Moon gets deeper and deeper into the shadow,  the required exposures get longer and longer. If the eclipse is very dark, much longer exposures may be required.  If you use a telephoto lens on a fixed tripod, the Moon's image will eventually begin to move during the longer exposures and show blur.

Using the "Cali's Stationary Stars" formula, you can find the longest recommended exposures you should use for a given focal length to avoid image blur.

The  table below is based on the Cali Stationary stars formula, a formula I derived in 2012.


Focal Length mm
Max Exposure(s)
No pixel blur
Max exposure(s)
3 pixel blur
Suitable for full screen laptop view
12
 5s
 14s
14
 4s
 12s
16
 3s
 10s
24
 2.5s
 7s
28
 2s
 6s
35
 1.5s
 5s
50
 1s
 3s
70
 0.7s
 2s
105
 1/2s
 1.5s
135
 1/3s
 1s
200
 1/4s
 0.7s
300
 1/6s
 1/2s
400
 1/10s
 1/3s
500
 1/10s 1/3s
600
 1/10s 1/3s
800
 1/15s
 1/4s
1000
 1/25s
 1/8s
1200
 1/30s
 1/10s
  
The formula is a very accurate way of determining longest exposures taking pixel size and output size into account compared to crude and inaccurate methods like the "600 rule."

MAXIMUM EXPOSURE(s) = 14 x P x N ÷ F
P -  Pixel size (in microns)
N - Number of pixels of blur*
F - Focal length of lens (mm)

The quantity N, number of pixels blur relates to the final display size. If you want to view the image at 100%, N=1.
Let's say that you have a 24MPx Sensor 6000 pixels wide, and want to view on a full laptop screen 2000 pixels wide.
N=6000÷2000=3 pixel allowable blur (right hand column)

The smaller the display size, the bigger N can be, the longer you can expose.
In the above table, I used a pixel size of 4 microns, a decent average value for many cameras. If your camera is very different to this, use the formula to calculate your own table or a value for your lens focal length.

Read more about this method:  https://joe-cali.com/astronomy/articles/tripod_astrophotography_using_DSLR.html

Wide-Angle Photography
If you don't have a tracker, all is not lost. A fast telephoto lens and keeping exposures below the stationary star shutter speed with work just fine. Lot's of good possibilities exist to capture nightscape style photographs without tracking using standard and wide angle lenses.The early part of this eclipse occurs near the horizon and is ideally positioned for this type of imaging.

Here are a couple of examples from eclipses in  I've observed in the past.

      



Photo Credit:   Capture Felicity Latchford     Processing:  Joe Cali                  .





Good luck!

Joe