Filtering by Category: Photography

Focusing

Added on by Bill.

I compare two approaches:

  1. Traditional focusing where the film and lens plane are parallel leveraging the depth of field proportional to aperture so that the near and far subjects are in focus.
  2. Tilt to focus on the plane of sharp focus which passes through the near and far subjects.  

The diagrams below demonstrate each technique:

Traditional focusing techniques may be simpler; they certainly are more familiar.  However, not every lens can stop down enough to get both near and far in focus.  For my 150mm I needed to set the aperture to f/64 and a correspondingly long exposure.  As one will notice, on this mildly breezy day motion blur can be seen in the leaves of the trees.  

Tilt focusing introduces some complications; or at least until the technique becomes familiar. Like traditional focusing techniques the depth of field lies on either side of the plane of sharp focus.  However, when the lens is tilted so is the plane of sharp focus.  Thus the depth of field projects along the plane and perpendicular to it.  The second diagram shows this by highlighting the areas in focus.  

Lower Don

Added on by Bill.

Last weekend we biked along the Don River.  For me it was another chance to explore focusing with a tilted lens.  

Tachihara, Nikkor-W 150mm 1:5.6, ISO 100, f/32, 1/15s, tilt 11.3 degrees, D76 1:1

The Scheimpflug Line

Added on by Bill.

Looking inside a view camera can be quite startling.    

There is nothing there.  

This is in stark contrast to the innards of modern cameras which are packed with various technologies used in the production of an image or are related to that process.  

This emptiness quite clearly exposes how simple it can be: A lens; a gap; a piece of film.  

It's easy to be mislead by the wood and brass construction that there is no technology at all.  But there is; the various knobs, levers and slides provide capabilities not available on most cameras: swing, tilt and shift.  

In the normal camera the film plane, lens plane and focus plane are all parallel.   

Swing and tilt (of the lens) change the relationship among these planes.  Tilting the lens forward, for example, tilts the plane of focus proportionately such that it slides under the camera and projects off into infinity.  

As I explored the subject of tilt I came across Scheimpflug.  Captain Theodor Scheimpflug was an Austrian Army and Naval officer, born in October 7, 1865 and died in August 22, 1911. In the early 1900's he used cameras suspended from balloons for aerial photography for the purpose of creating accurate maps.  To resolve the various distortions that result from imperfect alignment he developed a number of principles, one of which bears his name.


In order for a view camera image to be sharp, the rules of optics state that the film plane, the lens plane and the plane of sharp focus must intersect along a common line in space. That line is the Scheimpflug line. [Merklinger, Focusing the View Camera].


The objective of my first experiment was to get a sense of how it works--the set up and the execution--by walking through the steps. The first step is to establish the things to be in focus. Or more precisely, what is the plane of focus?  Standing in a field (picture below) I picked the distant trees and a spot just under the camera.   With the plane picked I determined how far below my camera the plane passed (J).  With J, I could then calculated the necessary tilt of the lens [a = arcsin (f/J), where f = the focal length of the lens in meters]. I estimated the plane ran 1 meter below the plane of the lens, which was just about ground level. The result was a tilt angle of 8.62 degrees.  [Note: implicit in the equation above is some a relationship between the tilt angle and the angle of the plane of sharp focus which I do not yet understand.]

I levelled the camera and then tilted the lens the prescribed amount. Rather than calculate the depth of field I set the aperture to f/22 and the speed accordingly.  

Inspection of the shot confirmed the angled plane of focus was present.  Point #3 corresponded to my estimation of the far point of the plane and point #2 the near point.  Both have focus.  In contrast is point #1 (which is on the approximately the same vertical plane as point #2) that is completely out of focus.  

I have more work to do to fully understand the maths, but given the results are there to be had, I'm encouraged to explore further along this path.   

Darkroom

Added on by Bill.

For the last month I've been working on my darkroom.  It has been a long process, but a satisfying one.  This phase of the project was to build a sink for the wet area.

As noted in my previous post, phase one of the project completed the dry area which hosts my PC, scanner, printer and a work area for framing prints.  Phase three, and it is hoped to be the last phase, will connect the sink to the plumbing.

The sink, located on the left, is 2 feet deep by 4 feet wide. The bowl of the sink is 6 inches deep.  It is made of PVC on a wood frame. The PVC sheets (three 2'x4') were purchased on eBay from a store in Missouri as I was unable to find any locally.   The wood was sourced from my reserves (that is, I had a lot of extra wood that I wanted to get rid of).  I only had to buy one 2'x4' sheet of plywood for the sink base.

The original idea for building the sink was described in an article, How to make a custom darkroom sink out of PVC.  It provided the basic instructions and importantly they key parts.  With that information, and the inventory of wood I had available, I created my own plan (pdf). 

 

Hydrangea

Added on by Bill.

The hydrangea are in bloom.  

Tachihara Field Camera 4x5, Nikkor-W 150mm 1:5.6, Kodak TMAX, f/64, 5 sec, ISO 100, D76

Hydrangea are an interesting subject; globes of small-petalled flowers on a background of large-leafed stems.   Compositionally this offers a natural contrast.  However, now my attention is directed towards the Zone System to ensure proper capture and development.

In the digital world results are immediate and each shot can be used to iteratively hone in on the right exposure and composition. There is really no cost to taking another shot.  In the film world results come only later after development and processing and each shot costs about $2.00.  It takes me between 5 and 10 minutes to set up and complete a shot. Mistakes are costly in terms of time and money. Attention to detail and a consistent process is important.  Therefore, planning the shot and ensuring proper exposure are important. As I get better at this, I expect this to increase; and then may be at some point it will decrease.  

My attention right now is on getting the tones right and understanding what constitutes right.