Monday, April 13, 2009

Fisheye Fun!

I love fisheye lenses! With a field of view (FOV) of 180 degrees, you can be assured you can get everything in the picture! Back in my Kitt Peak days, they had a 6mm fisheye that actually had a 220 degree FOV - it was difficult to keep your shoes out of the photo. Not that you would ever hand hold it at nearly 10 inches diameter and close to 15 pounds! I've got slides somewhere, but I've never seen one other than the one I used at the Observatory. Here is what it looked like with a standard film camera - remember what those were?

More modern fisheyes are much more manageable in size. The Tucson Amateur Astronomy Association (TAAA) has an 8mm Nikon on long term loan from Steward Observatory, and since I still work at Steward, I'm it's current keeper, so get to use it a lot. It is the size of a telephoto and weighs about 2.5 pounds, but is about 4 decades old, so optical and coating quality are a little suspect, especially when shooting stars - always a difficult task because of their infinitely small size.

Manufacturers are also currently making fisheyes - Sigma makes one pretty much indistinguishable from a normal lens. At F/4 it is a little slow for astronomy, but just the lat year they started making an F/3.5. Friend Tom Polakis has the F/4 that he has allowed me to borrow several times - and in fact, images have appeared here before. This one on the left appeared in November when Tom, Jenn and a friend stopped by the Mirror Lab for a tour. Set down on the ground at our feet looking straight up, it still caught all of us and is a pretty cool shot. The 8mm fisheye is designed to give a circular image covering horizon to horizon (if pointed straight up) if you used a full 35mm format. With the APS sized sensors I use, it gets the full FOV horizontally, but crops a little vertically. Still, the 8mm is a nice field if it is sharp enough for astronomy.

A couple weeks ago at the Messier Marathon, I knew Tom and Jenn would likely be there, so I again asked to use it under a dark sky. They were more than willing, so I was finally going to be able to use it in a direct comparison with the older Nikon 8mm fisheye. In the early evening, I was busy with the 14", capturing Comet Lulin in the western sky, so put off the fisheye tests, though I did take a self-portrait with the lens a couple feet behind me in the Messier Marathon post.

Finally, with that sequence done, I took a set of 4 frames of the setting Winter Milky Way, and of the gegenshein to the south. The brightest glows visible are of urban origins. In the first one to the left, the brilliant glow to the right is that of Phoenix and Casa Grande to the north. The more celestrial glow is of the Milky Way, and of course, nearly all the Winter constellations are visible in the west, the most obvious being Orion, trailing the Hyades and Pleiades star clusters. A fainter nearly vertical glow, brighter at the base, is the Zodiacal Light - the reflection of sunlight off dust particles in the ecliptic plane (where the planets and asteroids orbit). Total exposure is 15 minutes with the lens wide open at F/4.

This next shot is of the gegenshein. This is a very faint, diffuse glow, again, reflected sunlight from dust particles (in fact, the gegenshein is part of the Zodiacal Light), this time from enhanced reflection on the sky exactly opposite the sun. Difficult to see or image unless from a very dark site, a wide angle lens like the fisheye is just about perfect for capture. The urban glow is from Tucson to the southeast this time, and the layering effect of that edge is from the stacking of the 4 frames as the Earth rotated between frames. The constellations in this part of the sky are less spectacular than the bright winter ones, but Saturn is brightest to the upper right of the gegenshein, and Leo above Saturn. Sixteen minutes total exposure with the Canon XSi.

Unfortunately, the clouds over Tucson moved in, and I wasn't able to take photos for a direct comparison with the older Nikon fisheye, so it will have to wait for another time under a dark sky. But the fisheye view will always have a place in my photographic heart!

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