Shorter dof

[christian_r]

Hi

How do I get shorter DOF on my CWD?

Is there rings or extensions to get?

If so, what´s the alternative?

 

[michaelhcothran]

Christian,
Your inquiry is unclear (at least to me). Do you mean being able to focus closer than the lens is capable of, or decreasing the amount of area in the image that is in focus?

If you're asking about shortening the focusing distance, there are ways of "shortening" the minimum focus for each lens: For rear mounting on your lens, Hasselblad has made several lengths of extension tubes over the years. In addition, there are many fine quality 2-element, multi-coated close-up diopters available for front mounting. Each has its advantages and disadvantages.

If you are trying to actually shorten the depth of perceived focus area, ie, making less of the image in focus, and more of it out of focus, then your only means is to shoot wide open. The closer you focus will also can increase the amount of out of focus area.

If none of this is what you're asking, then please ignore my confusion and posting.

Michael H. Cothran

 

[polypal]

Less DOF

DOF is determined by the aperture used and the focal length of the lens.
Large apertures and longer lenses will give less DOF.

DOF goes down dramatically with the use of extensions.
An 80 mm lens with 80 mm extension gives 2,6 mm DOF at F11.
Of course the object distance and size of the object recorded are also greatly reduced.
In this case, 80 mm lens with 80 mm extension, the max object size is 56 mm. Object distance is 104 mm.

 

[christian_r]

Sorry if I was a bit unclear.

I want to make more of the image out of focus, even when shooting at max aperture. As if I had a much bigger aperture, like 1.8 or bigger.

Will a extension tube do the job? Shorten the DOF? Which sizes are available, and what is the downside with them?

 

[polypal]

Extension rings

Rings start at 8 mm.
That one could be a good start for you to try and see whether it gives what you are looking for.

Keep in mind the objectdistance will be reduced as is the maximium size of the object.
You will loose focusing at greater distancen no infinity.

Rings can be found for 50-100 euro.

Sizes are 10/21/55 for the first series and 8/16/32/56 for the second model.

 

[CarstenW]

IIRC, depth of field is a function of only focal length, aperture and subject distance, given a fixed viewing distance and circle of confusion. This means that no amount of rings would change the DoF. You need a new lens, unless you can frame tighter and move closer.

 

[polypal]

Hi Carsten,

Technically ou are absolutely right.
It all depends on the manification factor.
Still the use of a small ring may give some more possibilities to get closer and isolate the subject from the background.

Paul