Minimum focus possible

[rui_alves_da_silva]

Hello,

I'm trying to focus my large format camera as minimum as possible. As

exempale jus want to focus one tree in a rank of multiple trees. What are the

movement I need to do. I tilt back and front to get minimum depth of field.

Now I have a line of focus.

Regards,

Rui

[leonard_evens]

If the tree is in one vertical plane, tilting won't do any good. Depending on the arrangement of the trees, you might be able to do it with a swing. For example, if the trees more or less lay in a single vertical plane which was at an angle to the back of the camera, you could minimize the extent to which anything but the one tree was in focus by setting the exact plane of focus at right angles to the plane of the trees and passing through the desired tree.

 

Otherwise, your only option would be to use as wide an aperture as possible on as long a lens as possible, perhaps combines with a swing. However, if you keep the magnfication of the image constant, the focal length of the lens might not make any difference. It could depend on how far you were from the tree at the desired magnification.

 

Generally limiting depth of field by aperture may be difficult in typical large format photography applications. For example, my f/5.6 150 mm lens has a hyperfocal distance of a little over 4 meters. Focusing on anything at that distance or more will have infinite back DOF. You could do what you want if the focusing distance were more like 3 meters. To see if you can do what you want with your setup, use one of the DOF calculators available on the web which allows you to set the format and plug in various apertures, focal lengths and focusing distances to see the range in focus. (Alternately, you could just use the standard DOF formulas. See below.)

 

Another alternative, if you scan, is to put the remaining trees out of focus digitally by applying a gaussian blur.

 

Formulas:

 

near dof = d^2/(h + d),

 

far dof = d^2/(h- d) provided d < h, otherwise infinite

 

where d is the distance at which you focus and h is the hyperfocal distance. The latter is give by

 

h = f^2/(Nc)

 

where f is the focal length, N is the f-number, and c is the diameter of the maximal acceptable circle of confusion. c = 0.1 mm is a reasonable choice for 4.5, but some people perfer a smaller value. Needless to say, all distances should be in the same units, e.g., mm.

[eric_boutilier_brown1]

Depth of field is largely controlled by your focal length, and your aperture, with movements being used to adjust where the depth of field falls within the three dimensional space of your image. The idea situation would be to start with a long lens with a larger aperture (so on a 4x5, perhaps a 300mm lens, with an f/5.6 lens). Then, if you had a row of trees from left to right, and wanted one in focus, you'd work at f/5.6 or f/8, and use a lens swing to issoloate one tree in focus. The area in focus will move across the foreground infront of the tree though...

[spodzone]

It depends on the scene you're shooting and the focal length of the lens.

 

With general flat landscape, you can apply tilts front and back to "reduce" depth of field (eg if normally you tilt front forwards for "more" DoF, do it backwards; at the same time, if you would tilt the rear backwards, do it forwards). On a 210mm lens, even stopped-down a bit (say f/11 or so), this gives a noticeable difference even over huge distances, so I hate to think what it would do closeup. Of course, swings are just tilts 90deg around, but bear in mind that the wedge-shape will be more obvious if you have them intersecting horizontal ground.

 

Go have a play - get yourself a loupe and use that to check focus all across the ground-glass before committing to film. After all, the whole point is that you can see what's going to come out, no DoF-preview required.<div></div>

[rui_alves_da_silva]

Thanks Leonard, Eric, and Tim.

 

Tim as you can see you have multiple areas os focus.

 

When I swing my camera (horseman LX) the horizontal line of focus move to a diogonal. I've tried a lot of combination movements, and never got want I want. Now I have a new idea, I'm gonna try it, and let you know what I got.

Regards,

Rui

[leonard_evens]

You would expect a swing to move a horizontal trace of focus on the gg to a diagnonal line as seen on the gg. The object would be to move this line so it crosses the base of the tree at right angles (in the subject, not on the gg) to the line of the trees. If you also want to move out of focus on that perpendicular line, there is literally no way to do that with view camera movements. The easiest way to do that is to scan and manipulate the image digitally. You could also do it with an enlarger by tilting the easel appropriately, but it would be harder to control everything else you might want in the image.

[steven_kefford2]

According to my calculations, a 150mm lens @f5.6 for 5x4 film has a hyperfocal distance of ~40m, not 4m.

 

Steve