Tuesday, August 30, 2016

High altitude flight over New York with the Leica SL

The altitude limit for typical helicopter traffic over the city is 2000'. Above that and you enter into the jurisdiction of the local airport traffic control requiring permissions to move about. I did a recent blog post featuring sub-2000' aerials over New York. This time my flight took me up to 7500' over the city where I could shoot straight down and include the entire island of Manhattan in one photo. The idea of a high altitude flight like this is to capture the shape of the city defined by its lights.

My main camera for this flight was the Leica SL with a 24-90mm Leitz Vario-Elmarit f/2.8-4 ASPH lens.  I find little reason to use a long zoom at high altitude, since the whole purpose is to include as much area as possible. The SK is a full-frame camera built on a very sturdy platform with a menu system that is extremely easy to navigate, a very helpful feature when flying at night in high winds and no doors. It also has a large accessible knob on top for changing the over-under exposure. This enabled me to set the camera in auto-aperture mode and simply adapt the exposure by turning just one knob.

When photographing night time aerials of a city there are three main considerations: The first is noise caused by using a high ISO.  The second is motion blur exacerbated by the moving helicopter coupled with gusting winds from the open doors, and movement from hand-holding the camera at low shutter speeds. Third is achieving a correct exposure that doesn't lose detail in the highlights when the camera tries to expose for the overall, dark scene.

I prefer not to go over 3200 ISO to keep the noise under control, and even like to drop that one or two stops by using a fast aperture lens. In this case I had a variable aperture f/2.8-4 zoom. An aperture of f/4 is more than I normally like, but I knew from experience that I would be using the lens mostly at the shorter 24mm focal length where it works at f/2.8. I often pack a second camera with an f/1.4 prime 24mm. This allows me to drop the ISO one to two stops or increase the shutter speed by the same amount. 

Our helicopter flight began over Governor's Island where we cork-screwed up to our cruising altitude of 7500' picking up different perspectives of the city as we went up.  This is a 24mm view from about a mile high. 
Using shorter focal length lenses also allows for shower shutter speeds to stop action. At 24mm I find that a minimum of 1/90th of a second is about as low as I can comfortably go before I begin picking up considerable blur. With the extreme motion caused by the moving helicopter and high winds, even 1/250 second can be a problem. The best way to protect against motion blur is to put your finger on the shutter release and hold it there to capture as many exposures as possible. I call this "bracketing the shutter". It is not uncommon to end up with only one in ten images acceptably sharp. 

Being able to compose and focus easily on the rear screen is a major plus for using a mirrorless camera, like the Leica SL
The Leica SL is a mirrorless camera, which is easier to use for night photography than a DSLR because you can compose and focus on the rear LCD. The winds were so strong that I found myself lifting the camera over my head and composing with the rear screen in an effort to keep it closer to the ceiling of the helicopter where the winds were calmer. 

In a tight shot like this of  brightly lit Broadway I under exposed by -2 to -2 1/2 stops to maintain detail in the extremely bright highlights. No need to worry about the shadow noise in a scene like this because the shadows are not important to the scene.
Achieving a correct exposure that holds highlight detail is a matter of under exposing the image from the meter reading. I find myself work at -1 to -2 stops under exposed depending upon the importance of the lit areas. When shooting in tight on something as brightly lit as Times Square at -2 stops was mandatory. When I pulled back to capture the entire city I set the camera to under-expose by only 1-1 1/2 stops. 

There is another technique I use, and that is to set the camera to auto-bracket by taking three shots. I combine this with a 1-stop underexposure setting to arrive at a final bracket of three images, one exposed for the meter plus a -1 and -2. 

This is what the city looks like facing south from over Central Park at our maximum 7500' altitude and a 24mm focal length.

The large knob on top of the camera made it extremely convenient to bracket my exposures with a simple twist. 
The Leica SL coupled with exceptional Leica optics delivered sharp results with no coma or blurring along the edges of the frame. The noise level, even at 3200, was very controllable in later post-processing, and the color rendition was spot on. 

The unique helicopter flight was supplied by FlyNYON, which specializes in offering photographers daily, open-door flights over the city -- definitely one of the most exhilarating ways of seeing New York.

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