Lens Compression - A Tale of Two Lenses

Lens Compression

Using Focal Lens to Control the Background

This weekend's assignment was to photograph 18 horse portraits for the C.O.P.S Mounted Patrol Unit. The challenge was to find a green background so this years images match last years photographs.

There wasn't a nice green background available, but there were some trees in the distance. So, the solution was to use a telephoto lens. It enlarged the background relative to the subject and the desired background was achieved.

The image on the left was shot with a 50mm lens. I got close in order to fill the frame, waited for the horse to pose, and then shot.

The image on the right was shot with a 70-200mm lens at about 120mm. I had to move back to fill the frame with the head and then zoom in. Zooming in made the background larger as well. So, both heads filled the frame about the same, but the zoom at 120mm effectively made the background about 2 1/2 larger than the first image. 

50mm f4, 1/750th @ ISO 100                          120mm f4, 1/750th @ISO 100

I could have gone to f2.8 for a creamier background, but I shot f4 to ensure the head was sharp from tip of ear to tip of nose.  

I could have gone to 200mm for an even creamier background, but that presented a problem. There's a white fence in the background. It's distant at 50mm and then it gets larger at 120mm. At 200mm it could have ruined the image, or create a ton of work to eliminate through cloning. 

There are four variables if you want a super creamy background:

1. The Aperture - The lower the aperture the blurrier the background.

2. The Focal length of the lens - The large the lens, the blurrier the background.

3. Photographer to Subject Distance - The closer to the subject, the blurrier the background.

4. Subject Distance to Background - The longer the distance, the blurrier the background.

So, f4 with a telephoto at 120mm, and being close to the horse while having a lot of distance from horse and background created a nice blur. 

There wasn't an obvious background around, but once I started thinking telephoto then two or three spots emerged.

Mike 

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