I especially like using a loupe when I need one degree of tilt out of the detent on a camera without geared tilt. That's REALLY fun.
I especially like using a loupe when I need one degree of tilt out of the detent on a camera without geared tilt. That's REALLY fun.
A loupe is a reasonably sized pain in the butt. It is still neccessary to achieve reasonable focus. I hate it, but it is.
I perfectly understand the delicate point raised by Scott F., being myself short-sighted and affected by astigmatism to a point where it is out of question for me to to look through any optical instrument or focusing any GG image without my ophtalmic glasses on.
For looking through the eyepieces of a telescope or binoculars, I cannot use anything but modern high eyepoint eyepieces (or long eye relief ? not sure of the right English terminology), similar to B-type for binoculars.
As far as GG focusing is concerned. The main point is that you should use a loupe with a large exit lens element or a well-designed loupe with a long eye relief like B binoculars, or a pair of clip-on or additional binocular "loupes" as mentioned by Brian E..
I'm using a 6x9 camera so the GG surface it is actually too small to properly focus all the image including fine tuning of camera movements without a loupe or a viewfinder. This might be considered as a severe limitation of 6x9-only view cameras, and yes, a binocular viewer with reflex mirror and 2x loupes is superb (but bulky) ; this is another story ;-)
For a 8x10" camera on the other hand with a pair of reading glasses or clip-on watchmaker's binocular loupes you can easily switch from a global view (without loupes) to precise focusing (with a monocular or binocular loupe system).
In size, 4x5" apperers to be in between 6x9 (where a loupe is mandatory) and 8x10" where photographers gifted with an excellent vision and not affected by presbytia can even do the job without any loupe.
There is an interesting physiological point explained to me by Philippe Vogt (the boss of Arca Swiss, who is also a passionate photographer).
Philippe Vogt's point is that you should be able to focus as fast as possible and, if possible, avoid to rack the GG back and forth forever. Beyong a certain amount of time spent trying to find the best focus, your eyes get strained and things become worse.
I'm not sure that I fully get the point but my understanding is that you should be as comfortable as possible and you should try to avoid any strain as much as possible. The problem is that one might not be immediately aware of eye strain. This is a well-known problem for people looking at an aerial/virtual image through a pair of binoculars when the instrument totally offset w/respect to the best possible left+right focus setting ; in principe looking at a GG is less a problem since the eyes actually know where to focus, the image is real and "materialised" by the GG ; you can almost touch it with your hands ;-).
Another interesting point explained to me by Henri Gaud, a French professional LF photographer specialist of monastic architecture deals with proper focusing in low ligh levels.
When he has to focus a LF camera in very dim light, he does not try to find the best focus. On the contrary he tries to find as quickly as possible on both sides of the expected best focus two similar points where blur is roughly identical in the sense of : identically un-acceptable. Then he sets the best focusing point just in between.
This practical rule supported by years of professional practice is also perfectly supported by the simple model of what happens in a de-focused camera even when the back is tilted : the two limit planes of (un-)acceptable sharpness are parallel and placed at an equal distance on both sides with respect to the ideal best focus plane. So try and find those two equally unacceptable positions, and set the focus in the middle. Well this does not help one to precisely set the best tilt angle, but is saves a lot of eye strain finding the best position for the longitudinal focusing rack & pinion movement.
Emmanuel,
I may have misunderstood what you said. When you tilt, the two limit planes of acceptable sharpness are not parallel. They intersect in the hinge line which is (usually) vertically below the lens when the back is vertical. As the tilt decreases, the distance of the hinge line below the lens increases, approaching infinity as the tilt approaches zero. At that point, the lens plane is parallel to the back, and so are the limit planes and the best focus plane.
Also, the ideal focus plane splits the two limit planes in the following sense. Again, with the back vertical, if you draw any vertical plane parallel to the back, the section of that plane between the limit planes is bisected by the best focus plane.
Good post Emmanuel. Very interesting.
I believe it is correct that past a certain point ... focusing just gets more problematical. I had never been certain about it but HAVE noticed that racking back and forth while using a loup definitely loses 'certainty' so to speak, after a bit.
I may have misunderstood what you said
I was speaking of course about image space near the slanted 'focus' plane, not object space where slanted planes intersect at the pivot point.
Sorry for misunderstanding, I was speaking about parallel planes near the best possible position for film. Whether you move the front of the rear standard for focusing, this does not change the situation but it is simpler to imagine focusing by translation at rear.
For readers not familiar with Leonard's paper, the reference is here :
Leonard Evens, "Some Thoughts on View Camera Calculations",
www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf
5.2 Getting adequate depth of field when lens is tilted
The key figure is Figure 7: Depth of field wedge for tilted lens...
...shows the usual fan-shaped rays in the objet space and plane and parallel plane in the image space.
From this excellent source I realized some time ago that I was mistaken, so I have redrawn figs 6, 7, 8, 9 and 10 in an updated version of
www.galerie-photo.com/profondeur-de-champ-et-scheimpflug.html
and, shame on me ! I did not take time to upgrade the English version....
Now I know I have to do it quickly...
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