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Lloyd Godman
Film - Digital
What
is a bellows focusing unit lens?
Another
way to allow the lens to focus on a subject to a much
closer distance is to use a bellows unit. These are manufactured
to fit on 35mm and 120 cameras between the camera body
and the lens to extend the focus of the lens for doing
close up work. Because these units allow the focus point
to be precisely located within their range, - they can
be extended out to any length - they give much more flexibility
than a series of extension rings which have a set focus distance.
Because
the focus is often very critical, when using both an extent
ion ring and a bellows unit it can be difficult to locate
the subject in the viewfinder, a technique for overcoming
this is to move the camera closer and further away from
the subject until the objects appears in a recognizable
way in the viewfinder. From here you can use the normal
focus of the lens to complete the critical focus.
Move over
image to see roll over image
If
we use a standard lens on the camera ( say a 50mm on a
35mm DSLR) with extension tubes or a bellows unit we migh
find that the lens is phyically so close to the subject
it blocks out the light. By using a longer focal length
( a telephoto say 100mm lens we find to fill the subject
in the viewfinder the camera position is now moved back
consderably. This allows light to fall uninhibated on
the subject. We can also augmet this with a flash
light.
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Tillandsia plant taken with a standard 50mm lens on maximum focus |
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Taken with a 100mm lens on a bellows unit |
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With the bellows unit fully extended |
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Enlargement of a section of this image |
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