6 replies to this topic

[Johnb]

If I am using a lens with a fixed aperture, how do I deal with the depth of field issue. Are there tricks using ISO settings. 

[Ron]

Depth of field is totally dependent on lens focal length, aperture and focus distance.... with circle of confusion thrown in for good measure. ISO has no direct bearing on depth of field unless changing ISO somehow also changes one of the other lens factors as well.

 

--Ron

[TBonz]

When you say a fixed aperture, do you mean that there is only one aperture setting that can't be adjusted?  When I read your post, I was thinking of a "constant" aperture such as an f2.8 vs a variable aperture like the kit lenses have - f5.6-f6.3 as an example...

[Johnb]

OK so what your saying is that you cant really explain how to control it, it just comes with experience and maybe some trial and error. 

 

Thanks Ron

[Merco_61]

As you gain experience, a DOF calculator becomes less important. 
 

 

Here is a good one to play with as you learn.

[Jerry_]

There are number of articles on internet that explain the DoF and it could be helpful to read some (search Google f.i. for «photo depth of field »)

What is troubling in your question is the mention of a lens with a fixed aperture.

Looking at the gear you list your 35/1.8 lens has a fixed focal length of 35 and a MAX Aperture of 1.8. Your 200-500/5.6 has a variable focal length, but for any chosen focal length offers a MAX aperture of 5.6
However for both lenses, the indication is about a max (but not a unique/single possible aperture). Knowing that a camera focuses at the widest open, the smaller the number (which is a fraction) the more light it can get for focussing and thereby focus faster.
On the other hand, f.i. Your 10-20/4.5-5.6 has a MAX aperture of 4.5 at a focal length of 10, while having a MAX aperture of 5.6 at 20.
All this is therefore a physical characteristic of the lens.

What would be good to know is whether you are looking for a shallow DoF (with nice Bokeh) (best achieved with lenses that can wide open the aperture) or a maximum DoF (large number for the aperture, for it to be small).

Indeed testing with your lenses will allow you to get experience. But it has concrete physics behind.

[Ron]

OK so what your saying is that you cant really explain how to control it, it just comes with experience and maybe some trial and error. 

 

Thanks Ron

What I said was that there is no way to control depth of field through ISO. If you change the point at which your lens focuses, then you're also changing depth of field. The same is true when you open up or close down the aperture of your lens. And, if you change lenses from one focal length to another, you're also going to change depth of field.

 

As Jerry said, there are many articles on the web that go into great detail about this subject and perusing some of those should be a part of any photographer's education.

 

A depth of field calculator can come in handy too.

 

--Ron