A reasonably straightforward weekend trip along the north rim of Yosemite Valley (up Snow Creek, across to North Dome, down Yosemite Falls) turned in to a seriously long slog through knee to waist-deep snow above about 7200′. Oh, we brought too much food to fit in the three bear cans we had too. Another great Yosemite trip though, even with the minor (major?) setbacks. Looking forward to my week-long solo trip in July!

Recipe

Took a quick daytrip out to the Anza Borrego desert last Friday (2 April) to check out the desert wildflower bloom. The park’s website claimed that the bloom was still going strong (a 7/10 on their scale). That being said, I think the only way I’d go back is if it were a 9 or 10/10. Most of what we saw was typical San Diego desert – rocky and boring. The one exception was a couple of acres of wildflowers blooming on the north side of Henderson Canyon Rd. in Borrego Springs. Maybe I was expecting too much? In any event, we saw plenty of Desert Sunflowers, Sand Verbena, Dune and Brown-Eyed Primrose, Desert Pincushion and Desert Dandelion. There was also lots of Purple Lupine on the drive out.

More photos

Just playing around with my new 85mm f/1.8 lens. The depth of field wide open at the minimum focusing distance is RAZOR THIN! The curvature of the beer bottle was enough to pull either side of the label out of focus!!

Also tried out some new PS effects (bleach bypass and a kind of cross processing/split toning effect).

Horsetail Fall is a pathetically small (at least by Yosemite standards) seasonal waterfall that flows off the east side of El Capitan. Despite its size and fickle nature, this waterfall puts on one hell of a show. During the last few weeks of February, the setting sun’s rays strike El Cap at the correct angle to illuminate the falls and make it glow like flowing lava. In order for this “natural firefall” to occur two conditions must be met: there has to be sunlight hitting the falls and the weather has to be just right. If there’s one thing that I’ve learned about winter in the Sierras, it’s that it is far from consistent, making the observation (and photography) of this natural phenomenon even more elusive.

I happened to be in Yosemite at the right time last year and I tried to shoot the falls, but a few hours before sunset the skies were completely overcast. I didn’t even bother sticking around to see if things cleared up. I decided that I’d try again this year, but wanted to be more prepared than I was last time. I’ve compiled what I learned about how and why the firefall happens, and included some information on how I shot the falls below.

Sun

Warning: My analysis ended up getting a little technical. If you don’t care about the technical aspect of why this happens (geographically and astrologically), skip ahead to the Results section.

The falls are located at 37.7310, -119.6268 (37°43′53″N, 119°37′36″W in DMS) and start falling from about 6100′. There are only a few weeks during the year that the sun sets at the correct azimuth through the valley to illuminate the falls. In order to determine the minimum and maximum solar azimuth which will result in sunlight hitting the falls, it is necessary to view a topo map and find the smallest and largest angles (with respect to north) which allow for an unobstructed view of the falls at 6100′. The map below illustrates the minimum and maximum solar azimuth which results in any sunlight hitting the falls.

When the sun sets with an azimuth between 246° and 263°, sunlight will hit the falls. The optimum solar azimuth occurs when the sun sets through the lowest elevation unobstructed straight line to the falls through the valley. This occurs at an elevation of approximately 5120′ with a corresponding azimuth of 255.5°. Good conditions should exist for several degrees on either side of of the optimal azimuth. The optimal sunset azimuth has been overlaid on the maximum minimum and maximum azimuth map from above:

The azimuth of the sun at sunset with respect to north is given by:

where is the declination of the sun and is the local latitude. The declination of the sun is given by:

where is the number of days elapsed since 1 January. Plotting the sunset azimuth throughout the year, it is possible to find the days which will result in ideal viewing conditions.

It can be seen that there are two windows which exist where the sun will strike the falls at the correct azimuth during sunset – in late February and late October.

Results:
The first condition that must be met for the firefall to occur is for the sun to set with an azimuth between 246° and 263°, ideally between 252.5° and 258.5°, with the optimal sunset azimuth being 255.5°. This window occurs, on average, between 15 February and 28 February and peaks on 22 February. (It should be noted that this window fluctuates a little each year because of the leap year which occurs every 4 years. It should also be noted that the sun sets within the required azimuth range in late October as well, but the falls do not flow in October.) The above calculations (and resulting plot) were done assuming a solar elevation angle of 0° (i.e. when the sun is level with the local horizon). It turns out that a solar elevation of about 2° actually provides a better effect because more of the waterfall is illuminated by the sun’s rays. Taking this in to account, the optimal dates shift about 2 days forward, moving the best viewing window to between 17 February and 2 March (in non-leap years) and the peak viewing date to 24 February.

Because my calculations do not take in to account leap years, the actual dates move slightly, but the angles are correct. Any time the solar azimuth is between 252.5° and 258.5° at a solar elevation angle of 2°, the solar conditions will be right to produce the firefall. Exact dates that this happens every year can be obtained from the Navy’s Sun or Moon Altitude/Azimuth Table.

Weather

Having the sun in the correct location is only part of the equation. The weather is even more important – both on the day you hope to catch the firefall and on the days leading up to it. Most importantly, there has to be water in the falls. The falls are fed by snowmelt from the top of El Cap; ideal weather conditions being a decent snowfall followed by a few warmer days to melt the recently fallen snow. If the falls looks like they aren’t flowing, don’t be discouraged – they will often times only start flowing after the afternoon sun has had a chance to warm everything up a bit.

The other (more variable) weather condition that must be met is (relatively) clear skies on the viewing day. Conditions change by the minute, and several people I talked to mentioned overcast skies clearing just minutes before sunset. Others mentioned rogue clouds obscuring a completely clear sky and ruining the entire show. Getting good sunset sky/cloud conditions is purely luck.

Viewing Locations

There are two popular viewing locations, both giving a slightly different view of the falls. The first is from the El Capitan Picnic Area off of Northside Drive and the second is on Southside Drive east of the Cathedral Beach Picnic Area. I’m sure there are plenty of other locations in the valley to view the falls from. The most important thing here is to be east of the falls as the sun sets to the west. After scouting both locations, I decided that I liked the view from Southside Drive better. It is also worth mentioning that you should probably consider showing up several hours early to guarantee you get a good spot. I parked and headed down towards the river about 3 hours before sunset, and there were already 3 other photographers set up. An hour before sunset, there were more than 30 tripods and several hundred thousand dollars worth of photo gear onsite. The map below shows the two popular viewing locations, along with the approximate location of the falls.

View Horsetail Falls in a larger map

Since I’m always trying to push my own limits with my photography (I love shooting things from angles or locations that very few, if any people have shot from), I’m curious if the falls could be shot from Sentinel Dome. You can pretty much draw a straight line between the falls, the El Capitain Picnic Area, and the summit of Sentinel Dome, so the angle is definitely right. Logistically, shooting from here would be a nightmare, but I’m definitely considering it. First, I’d have to snowshoe to Sentinel Dome from Badger Pass (I’ve made the 21-mile round trip hike from Badger Pass to Glacier Point twice, but it’s not exactly what I’d call an “easy” hike – especially with gear). Next, I’d have to have a SERIOUSLY long lens. I’m talking somewhere in the range of 500-600mm. Those are big, heavy lenses. Obviously, the weather is a huge variable here too, but I’m thinking about at least scouting the location this summer.

Gear

I shot the falls with the following kit:

• Canon 5D + grip
• Canon 70-200 f/4L IS + 1.4x extender (rented from BorrowLenses for the week)
• CPL filter
• Feisol CT-3401 tripod with Markins Q3 ballhead
• Canon TC-80N3 Remote

Important gear considerations: I took about 150 shots in 30 minutes, so make sure you’ve got the battery power and memory card capacity for that. Most of my shots were in the 185mm range (on a full frame sensor) but I do have a couple of shots from >200mm. That being said, I would call the 1.4x extender completely optional – especially on a crop sensor. If I could do it again, I’d probably skip the extender. A tripod is absolutely necessary. Don’t even bother trying without one. I also consider a remote shutter to be necessary, but I saw plenty of people out there shooting without one. That’s more of a personal preference I guess.

I wasn’t sure about the CPL so I shot for 15 minutes without it and 15 minutes with it. I liked the shots with the filter better, but it’s tough to say whether the CPL made the difference or if the sun was just in a better position during those 15 minutes. It definitely didn’t hurt anything, so I’d use it again.

In terms of camera settings, I set my camera to aperture priority mode and shot at f/11. My ISO was set to 400, and I shot bracketed exposures at +/- 2EV. Everything was captured in RAW.

End Result

3 exposures blended in Photomatix, levels and curves adjusted in Photoshop:

Blogging: Never before have so many people with so little to say said so much to so few.