What do Diopters do exactly?

[Scott Talbot]

Hi everyone,

I'm looking to use diopters on a set of Zeiss Standard Speeds on a project coming up. I've watched a couple videos that do a horrible job explaining diopters.

My question is, does it magnify or change the focal point? For instance if I have a 32mm with a close focus of 3" and I put a diopter on does it:

magnify or crop the image (making it a longer lens) and keep the 3" focus
-or-
keep the 32mm distortion and field of view and make the close focus even closer

?

Hopefully that makes sense and I'm not just over thinking it.

 

[D Fuller]

Hi everyone,

I'm looking to use diopters on a set of Zeiss Standard Speeds on a project coming up. I've watched a couple videos that do a horrible job explaining diopters.

My question is, does it magnify or change the focal point? For instance if I have a 32mm with a close focus of 3" and I put a diopter on does it:

A- magnify or crop the image (making it a longer lens) and keep the 3" focus
-or-
B- keep the 32mm distortion and field of view and make the close focus even closer

?

Hopefully that makes sense and I'm not just over thinking it.

The answer is B. a diopter makes the lens focus closer. With the caveat that there may be some breathing in the focus and that may change the field of view slightly -- as you'd expect with any lens that breathes, but not more than that.

 

[Ryan Patrick O'Hara]

You will also lose the ability to focus to further distances depending on strength used. So don't plan on focusing to 5" and then rack focusing to 30'.

 

[Anton Shavlik]

The rating of a diopter is the inverse of its maximum focus in meters. Any lens set to inifnity with a +1 diopter focuses to 1 meter. +2 to 1/2 meter. +.5 to 2 meters, etc. They also bring your close focus closer, but calculating that is a bit trickier and chromatic aberration will be worsened, so it's usually better to go to a higher power than focus closer with a lower power.

They are also great for use with anamorphics because you can keep the anamorphic set near infinity to avoid "mumps" type distortion as well as astigmatism.

There is some magnification involved, but I would say anything +2 and below won't be noticable. +4 will magnify noticeably, +10 will seem like a longer lens, albeit one with a maximum focus of 10cm.

Also, it does technically decrease your depth of field. On long lenses the effect is stronger. As I recall, the effect on a 35mm is like a 7% reduction in depth of field, where as a 100mm might be 20% with a +4 diopter.

edit: remembered the numbers wrong