Depth of Field on Different Lenses

[tokenfemme]

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I have learned a ton reading this forum--thanks!! Maybe someone can answer this question for me: I read somewhere that either,

 

a) the depth of field is different from lens to lens at the same fstop.

 

or

 

the depth of field, let's say at f2, is different on the 28mm summicron on the M8 vs. the 35mm summicron on a film camera.

 

If ( is true, is it because each lens has different depth of field characteristics? Is it because the 28mm is effectively 37mm on the M8? Or is (a) true?

 

Shantel

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[Vivek Iyer]

In general (exceptions are the reality though), DoF is supposed to be dependent only on the magnification and the f-stop and is independent of the focal length of a lens.

 

However, you may find that does not always hold good because of the varying corrections of a particular lens characteristics (field flatness, other aberrations, etc).

 

DoF is derived from a calculated figure called the CoC (circle of confusion), so it isn't an objective figure as it is supposed to be.

[earleygallery]

edited - better explained above!

[johnjs]

I have learned a ton reading this forum--thanks!! Maybe someone can answer this question for me: I read somewhere that either,

 

a) the depth of field is different from lens to lens at the same fstop.

 

or

 

the depth of field, let's say at f2, is different on the 28mm summicron on the M8 vs. the 35mm summicron on a film camera.

 

If ( is true, is it because each lens has different depth of field characteristics? Is it because the 28mm is effectively 37mm on the M8? Or is (a) true?

 

Shantel

 

From Sean McHugh's excellent Cambridge in Colour site:

Understanding Depth of Field in Photography

[asfeir]

DoF is computed based on the circle of confusion, and some assumption concedrning the print size and viewing distance of the print. The site indicated above is a very good place to start... and to finish.

 

Practically speaking lenses have DoF indications engraved for every f stop. However, these will not hold for the M8 since it has a smaler CCD. A print from an M8 has to be enlarged 1.3 time larger than a full-frame 35 mm negative, and hence, DoF will be smaller. In practice if you are shooting at some f stop, you must use the DoF of the next larger diaphragm (smaller number) f stop. DoF on an M8 at f 16 is that indicated on the lens at f 11.

[tokenfemme]

Thanks johnjs—have just glanced at the website so far; it looks like everything I need and more—and everyone, thanks for your replies!

 

Shantel

[tom0511]

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DoF is computed based on the circle of confusion, and some assumption concedrning the print size and viewing distance of the print. The site indicated above is a very good place to start... and to finish.

 

Practically speaking lenses have DoF indications engraved for every f stop. However, these will not hold for the M8 since it has a smaler CCD. A print from an M8 has to be enlarged 1.3 time larger than a full-frame 35 mm negative, and hence, DoF will be smaller. In practice if you are shooting at some f stop, you must use the DoF of the next larger diaphragm (smaller number) f stop. DoF on an M8 at f 16 is that indicated on the lens at f 11.

 

ne thing to keep in mind is FOV. If you want to get the same FOV with M8 as 35mm on 35mm-film than you would use a wider lens (28mm) on the M8.

yes, you will magnify with the cropped sensor later but you also have the wider lens.

In the end this leads to the fact that you get more DOF when you shoot the same FOV at the same distance with a smaller sensor.

[andybarton]

FOV = "Field of View", BTW

[tokenfemme]

I've now read the Cambridge in Colour tutorial (great, very clear, good illustrations and fun calculator) and the Luminous Landscape article on this subject as well...looking forward to exploring this issue (when I get the camera).

Thanks again

Shantel