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Stardust December 2015
by Alister Ling
Fakery, truth, art. Reality and experience. Human vision and perception are wondrous. Over the centuries, observant artists and scientists have illuminated a multitude of in-line and post-processing tricks the brain accomplishes before delivering the "final image" to our conscious mind. As amateur and professional astronomers, we are quite familiar with the "Full Moon Illusion": Luna can appear huge when near the horizon but considerably smaller when high in the sky. Despite the scientific accuracy of a properly-sized Moon in my pictures, feeling smug about it, and deriding those who violate it, I also recognize in myself a lingering dissatisfaction that some of them are not representative of the event.
Recall the recent total lunar eclipse of September 27?
It might be the truth, but it's not how I remember the experience! In my mind's eye, it was closer to:
So how can our memory be so different than reality? Part of the answer is that wide angle photography doesn't work in the same way as the eye. Consider a classic panorama, in this case the view looking east from Riverside Drive in Edmonton by Luca Vanzella (with permission):
The eye/brain system is incredibly sneaky: It functions at very low resolution except for the very small central portion, and through rapid sweeping picks up all the detail and stores it in memory, leaving you with the impression that you see everything at high resolution. For better proof, look at a classic calendar from 2m (6 feet) away. The month and days and the picture are all easy to see. But wait, look intently at the upper middle of the image, and without moving your eyes, you will be unable to read any of the dates, let alone what month it is! Or stare at a date on the first line, and you can't actually read the number two weeks below.
Panoramas only begin to seem realistic when they are some 30,000 pixels wide, when you are slowly scrolling across them. If you aren't careful with your terminology, you might say that you have the ability to "zoom in", but you're confounding magnification and ability to resolve detail, related properties to be sure, but not the same.
I figure that for me to get the right "feel", the image needs to closely match what I can see with my eyes, that is, I can just make out the various maria on the Moon but not in detail.
The following image, with focal length 120mm (on a smaller sensor) has too much detail for me, I don't see the Moon this well:
Whereas this one, at 80mm, seems about right:
Interestingly, 80mm on a smaller sensor is equivalent to 128mm on a full frame. Ha! Little wonder that so many photographers like the classic 135mm lens: it jives with their memory of the scene. Now, as I always like to say, an image or a time-lapse is a very poor substitute for actually being there in person. Go outside an look at the sky!
Because your eyesight is different from mine, your personal "focal length equivalent" or "memory magnification" will not be the same. When Alan Dyer and I were chatting about some of the worst composited images on the internet, I mentioned this memory-size phenomenon to which he replied for planetarium shows, they typically project the Moon at twice its real size - any bigger or smaller and it would jar people and ruin the experience. I just measured the Moon on my fake eclipse shot and it is 2.6x normal size - fairly similar. So it turns out I'm only 100 years behind Zeiss!
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