Pete Askew
Admin
David responded to someone saying that a technical camera looks complicated (http://www.realphotographersforum.c...ment/9261-large-format-macro-photography.html) by saying that aren't and pointing out that it was just a lens connected to a back by a bendy tube. True, but why is it bendy and what use are all those knobs etc? Well, here is an illustration about one of the reasons that they are bendy in the middle. As you know, you can increase the depth of focus of an image by reducing the aperture that you shoot at. However, the closer you get to a subject the harder that becomes and eventually you run out of acceptable aperture (and light). Another way to get all of what you want in focus (and only what you want) is to manipulate the relationship between the planes of the subject, the lens and the film / sensor. And what better way to illustrate than using a plane: a Junkers JU-52!
Here is a shot of a model plane taken in a convention manner at f1:16 with a 120mm lens.
Note that even at f1:16 the tailplane is not quite in focus whereas the cockpit etc is. The next shot was taken using some swing on the front standard (illustrated further down) to change the relationship between the subject and image planes.
Note that the tailplane and the cockpit are now in focus; the aperture is still f1:16. The next shot shows the setup used.
And in the following two shots you can see that the front of the camera has been swung such that the left side of the lens-board is nearer to the subject than the right (you need then to re-compose and adjust focus).
The mathematical and technical basis of this effect (which can be done with the vertical tilt as well - and indeed both at the same time) is described in the Scheimpflug principle (see Scheimpflug principle - Wikipedia, the free encyclopedia) and a simple way to visualise it (think about the rotation of the lens panel) is the diagram on this Wikipedia page.
You can also swing / tilt the lens the other way thus reducing the amount of the subject plane that is focus on the image plane and that is how people achieve either very selective focus or the toy-town look that is in fashion at the moment.
I hope this makes sense.
Here is a shot of a model plane taken in a convention manner at f1:16 with a 120mm lens.
Note that even at f1:16 the tailplane is not quite in focus whereas the cockpit etc is. The next shot was taken using some swing on the front standard (illustrated further down) to change the relationship between the subject and image planes.
Note that the tailplane and the cockpit are now in focus; the aperture is still f1:16. The next shot shows the setup used.
And in the following two shots you can see that the front of the camera has been swung such that the left side of the lens-board is nearer to the subject than the right (you need then to re-compose and adjust focus).
The mathematical and technical basis of this effect (which can be done with the vertical tilt as well - and indeed both at the same time) is described in the Scheimpflug principle (see Scheimpflug principle - Wikipedia, the free encyclopedia) and a simple way to visualise it (think about the rotation of the lens panel) is the diagram on this Wikipedia page.
You can also swing / tilt the lens the other way thus reducing the amount of the subject plane that is focus on the image plane and that is how people achieve either very selective focus or the toy-town look that is in fashion at the moment.
I hope this makes sense.
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only joking pal lol
