• Cinematography

  Racking lense Fujinon TH16x5.5BRMU How To

  Posted by Omar Estrada on October 17, 2011 at 10:26 pm

  Hi All,

  I will be shooting a project in the rainforest in January where I will need racking the lense from the foreground to the background and viceverse for some scenes.

  I am preshooting some locations first in November with my JVC GY-HD100U, problem is that I don´t manage to get a good racking effect with this lens (th16x5.5brmu).

  I have set the back focus as the manufactures suggest in the manual, but the effect seems to be that everything is always on focus.

  I get this has to do with the difference between shallow/deep focus, but I don´t manage to get it right.

  I am more a visual artist than a DP so I have not really extended experience on shooting film; although I get it right most of the time 🙂 and yes, I am committed to learn and get it as perfect as possible all the time.

  I would appreciate some guidance on this. Is there anybody with some experience in racking this lense?

  Thanks a lot

  Omar Estrada replied 13 years, 10 months ago 2 Members · 3 Replies
• 3 Replies

• 

  Angelo Lorenzo

  October 18, 2011 at 2:48 am

  The issue moreso is with the size of the sensor in the camera.

  There are a few things in play but I’ll try to explain them in a clear manner. These are subject distance (closer = more blur), lens focal length (longer = more blur), aperture(more open = more blur), and circle of confusion size (larger = more blur).

  Let’s compare a 35mm still camera with your camcorder with it’s 1/3″ sensor.

  Subject distance needs no explanation. If the subject is very close to the camera, the throw in focus will seem greater than if the subject and background are both focused near infinity on your lens.

  If you use a standard 50mm lens on your still camera, it gives you a field of view (horizontal) of 39.6 degrees. If you want the same angle of view, your 1/3″ sensor camera would use a 4.7mm lens. This is an inherent disadvantage because the lens is designed for the smaller sensor size.

  A circle of confusion (CoC) is the largest size of an image area that is acceptably sharp or appears as a point when the lens is focused, it’s the diagonal size of your sensor in mm / 1730. A 35mm camera has a circle of confusion size of about 0.019mm, while your camera has a circle of confusion of about 0.006mm. In practical terms the smaller the sensor or film, the deeper and less cinematic the depth of field is because the CoC stays pretty small, even when out of focus.

  Your aperture is the ratio of your focal length to your lens iris. f/2.8 is inherently much smaller on a 4.7mm lens than a 50mm lens. A larger aperture increases the CoC size as things go more out of focus.

  https://www.dbp-consulting.com/Photography/CircleOfConfusion.html is a nice demo of CoC and aperture interaction

  —

  Our own Todd Terry wrote an article about DOF/Lens converters https://magazine.creativecow.net/article/focus-on-controlling-depth-of-field-with-depth-of-field-converters

  If you don’t go that route, try to keep your subject close to the camera and use a longer (more zoomed in) lens. You’ll have to compose a little tight, but it’s working with what you got. You can also have some extra ND filters handy to work at f/2.8 or f/4 when you’re outdoors.

  – Angelo Lorenzo
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• 

  Omar Estrada

  October 18, 2011 at 10:24 pm

  Thanks a lot Angelo,

  Obviously I have to get hands on duty and doing some tests with both lenses, the one I will be using in the pre shooting and the final to be used in the actual shooting.

  I appreciate a lot your explanation that now I will re read again and again until I fully understand it 🙂

  I love the technical part of filmming but I have to admit that my photography most of the times depend on my visual intuition more than in the necessary experience. I´m a visual artist by education (painting) and a self-taught filmmaker. So, time to study!

  Thanks again.
• 

  Omar Estrada

  September 9, 2012 at 7:58 pm

  Thanks a lot, Angelo!

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