Green Flash at Sunset in Sardinia
GREEN FLASH seen near Portoscuso in south western Sardinia. As the top of the sun passes below a clear horizon, its light is bent so much that its colour occasionally changes to green for a few seconds . Long thought to be an illusion, myth, or hoax, the proliferation of modern optics and digital cameras means that the green flash phenomenon is now well documented, especially by astronomer Andrew T. Young , who has commented "This is a mock-mirage flash, which is not surprising, as these seem to be common in a Mediterranean climate". He also has lots of advice on how to observe a green flash and KEEPING YOUR EYES SAFE (his Rule No. 3). In the right conditions, it is apparently not that difficult to see it to some extent. However, watch out for artifacts also.
I have been aware of the green flash phenomenon for some years and I have often watched out for it on clear evenings when I have had a clear horizon - usually not in Dublin! I had checked for it during on our ferry crossing from Corsica the previous evening – unfortunately a band of cloud obscured the sun as it approached the horizon – oh well . . . someday.
The following evening, as I was birding on a hillside overlooking the sea, I noticed the sun was split by the horizon and I realized the conditions were promising but I hadn’t much time to prepare – once the sun hits the horizon, it’s surprising how quickly it sets. Fortunately, I had my 100-400mm birding lens on the camera and I switched to my emergency birding setting (C1 – aperture priority f5.6, ISO 1600 (for when an American passerine pops up in a wet, windy and gloomy garden in the southwest!) AI focus, high speed shooting, auto white balance, spot metering, RAW, image stabilization on, focus limiter 6.5m), braced myself on the roof of the car, and – just in case – started shooting as the top of the sun moved towards the horizon . . . and then a BRIGHT GREEN FLASH flared in my viewfinder!! Unfortunately, I think the flare peaked in between the shutter openings but I am still delighted to have captured it at all. I also called out to the birders I was with but the flash was gone before they could get on to it.
On the next opportunity – I will check before the sun gets to horizon, let any people I am with know in advance, and tweak the settings as follows: use a tripod; a slow exposure of perhaps 1/30th so that the shutter is open more of the time to try to catch the flare at its maximum - subject to checking if this keeps the sun’s rim sharp; ISO 400 or lower if possible to reduce noise level, and JPG to allow a longer shooting sequence – the 40D can shoot bursts of up to 75 JPGs at 6.5 frames per second but only about 6 RAWs before slowing severely.