Back focus vs front focus, is there a better terminology?

[Julian Vrieslander]

I am not not sure that "back focus" and "front focus" are universally understood terms. "Front" and "back" could be interpreted as relative to the direction that the photographer is facing, or relative to the position of the focus target. I think I have seen postings in this forum that use both interpretations.

My understanding is that backfocusing occurs when the camera is focusing at a distance from the camera that is further away than the intended target. This is the case when a Nikon DSLR's AF Fine Tune needs to be set at positive values. Am I right or wrong?

I think that a better (less ambiguous) choice of terms would be "near focusing" and "far focusing".

 

[steras]

Julian Vrieslander wrote:

I am not not sure that "back focus" and "front focus" are universally understood terms. "Front" and "back" could be interpreted as relative to the direction that the photographer is facing, or relative to the position of the focus target. I think I have seen postings in this forum that use both interpretations.

My understanding is that backfocusing occurs when the camera is focusing at a distance from the camera that is further away than the intended target. This is the case when a Nikon DSLR's AF Fine Tune needs to be set at positive values. Am I right or wrong?

I think that a better (less ambiguous) choice of terms would be "near focusing" and "far focusing".

I agree it can be confusing. I like the terms nearer- and farther focus.

As for Nikon's AF fine tuning: minus is pulling the focus nearer and plus pushing it farther away.

 

[Cenk]

Julian Vrieslander wrote:

I am not not sure that "back focus" and "front focus" are universally understood terms. "Front" and "back" could be interpreted as relative to the direction that the photographer is facing, or relative to the position of the focus target. I think I have seen postings in this forum that use both interpretations.

My understanding is that backfocusing occurs when the camera is focusing at a distance from the camera that is further away than the intended target. This is the case when a Nikon DSLR's AF Fine Tune needs to be set at positive values. Am I right or wrong?

I think that a better (less ambiguous) choice of terms would be "near focusing" and "far focusing".

I agree...

 

[Bob from Plymouth]

Don't know if this helps but I think back to my days with TV cameras and zoom lenses. Back focus was changing the distance between the tube or ccd sensor and the rear of lens, the focal plane position. Front focus was adjusting the lens itself.

The trick was to zoom right out and adjust the back focus, then zoom in and adjust the lens focus. As long as the camera to subject distance stayed the same you could then zoom in and out without the need to readjust focus. If the camera to subject distance changed it was the front focus which was adjusted.

The terminology has been hijacked to mean more or less Front Focus and this is causing confusion.

 

[michaeladawson]

Julian Vrieslander wrote:

I am not not sure that "back focus" and "front focus" are universally understood terms. "Front" and "back" could be interpreted as relative to the direction that the photographer is facing, or relative to the position of the focus target. I think I have seen postings in this forum that use both interpretations.

My understanding is that backfocusing occurs when the camera is focusing at a distance from the camera that is further away than the intended target. This is the case when a Nikon DSLR's AF Fine Tune needs to be set at positive values. Am I right or wrong?

The first part you have right. If the camera is auto focusing on a point in space that is behind your intended target then your camera is back focusing.

The second part is wrong. If your camera is back focusing then you need to enter negative fine tune values.

I think that a better (less ambiguous) choice of terms would be "near focusing" and "far focusing".

 

[Kaj E]

Julian Vrieslander wrote:

I am not not sure that "back focus" and "front focus" are universally understood terms. "Front" and "back" could be interpreted as relative to the direction that the photographer is facing, or relative to the position of the focus target. I think I have seen postings in this forum that use both interpretations.

My understanding is that backfocusing occurs when the camera is focusing at a distance from the camera that is further away than the intended target. This is the case when a Nikon DSLR's AF Fine Tune needs to be set at positive values. Am I right or wrong?

I think that a better (less ambiguous) choice of terms would be "near focusing" and "far focusing".

Front focus and back focus are well established terms (even Nikon uses them at their service centers).

Near focus means how well the lens focuses at close subject, far or distant focusing means how well the lens focuses at far or distant subjects.

 

[Julian Vrieslander]

michaeladawson wrote:

The first part you have right. If the camera is auto focusing on a point in space that is behind your intended target then your camera is back focusing.

The second part is wrong. If your camera is back focusing then you need to enter negative fine tune values.

OK, thanks for the correction. I just looked at some of my test shots to check this out. Indeed, when my D800E is choosing a focus distance farther from the camera than the intended target ("back focusing"), I needed to use negative AF Fine Tune values to correct it. My memory was wrong.

But I still think that "far focusing" and "near focusing" would be less ambiguous terms than "back focusing" and "front focusing".

 

[Robin Casady]

Kaj E wrote:

Front focus and back focus are well established terms (even Nikon uses them at their service centers).

Some Googling reveals that "back focus" has a traditional meaning that is different from what we have been using in AF discussions.

The traditional meaning refers to the distance from the back surface of the lens to the film plane when the lens is focused at infinity.

However, "back focus" seems to be heavily used to refer to for AF focusing further away than the desired focus point. It would take a major campaign to change that use.

Nikon seems to be using the traditional meaning for "back focus" on their web pages. I could not find any instance of their using it to refer to focus errors. Even Nikon Europe's AF Fine-tune instructions don't use it.

Nikon Imaging
Back focus
Back focal distance, meaning the distance (length) from the tip of the lens's furthest rear surface to the film surface where the image is focused.

Dictionary.com
back focus the distance between the back surface of a lens and the focal plane when the lens is focused at infinity. Photography noun 1895–1900 Origin:

Mirriam-Webster
Definition of BACK FOCUS: the distance from the rear glass surface of a photographic lens to the focal plane when the lens is focused on a very distant object.

--
Robin Casady
http://www.robincasady.com/Photo/index.html
"The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts."
— Bertrand Russell

 

[Kaj E]

In my dealings, both spoken and written, with Nikon Melville and another local Nikon authorized service center they have used back and front focusing as used n this forum.

Should have said in my first post that this is for the verbs or adjectives for the terms.

--
Kind regards
Kaj
http://www.pbase.com/kaj_e
WSSA member #13
It's about time we started to take photography seriously and treat it as a hobby.- Elliott Erwitt

 

[Robin Casady]

Julian Vrieslander wrote:

But I still think that "far focusing" and "near focusing" would be less ambiguous terms than "back focusing" and "front focusing".

"Far focus" is used to mean when a lens is focused on a distant object, and "near focus" is used to mean the lens is focused on a nearby object.

For example, "The AF-S 70-200mm f/2.8 VRII is very sharp at near focus, but not so great at far focus."

How about "focus behind" and "focus in front"?

 

[Julian Vrieslander]

Robin Casady wrote:

Julian Vrieslander wrote:

But I still think that "far focusing" and "near focusing" would be less ambiguous terms than "back focusing" and "front focusing".

"Far focus" is used to mean when a lens is focused on a distant object, and "near focus" is used to mean the lens is focused on a nearby object.

For example, "The AF-S 70-200mm f/2.8 VRII is very sharp at near focus, but not so great at far focus."

For those cases, I usually say "close focus" and "infinity focus" (or "distant focus").

How about "focus behind" and "focus in front"?

There is still an ambiguity in those terms. Suppose we are looking at a badly focused photo of a person (or persons) that are facing away from the camera. If we say that it is "focused behind" or "back focused" are we using the frame of reference of the subject or of the photographer?

This may seem like nitpicking, but I have read comments from people who are using "back focus" and "front focus" in the opposite sense of the majority's convention, and I suspect that the ambiguity about frame of reference is the reason. I think that "near focus" and "far focus" are less ambiguous in this context, although (as you say) they have another usage.

 

[Bob from Plymouth]

Robin Casady wrote:

Kaj E wrote:

Front focus and back focus are well established terms (even Nikon uses them at their service centers).

Some Googling reveals that "back focus" has a traditional meaning that is different from what we have been using in AF discussions.

The traditional meaning refers to the distance from the back surface of the lens to the film plane when the lens is focused at infinity.

However, "back focus" seems to be heavily used to refer to for AF focusing further away than the desired focus point. It would take a major campaign to change that use.

Nikon seems to be using the traditional meaning for "back focus" on their web pages. I could not find any instance of their using it to refer to focus errors. Even Nikon Europe's AF Fine-tune instructions don't use it.

Nikon Imaging
Back focus
Back focal distance, meaning the distance (length) from the tip of the lens's furthest rear surface to the film surface where the image is focused.

Dictionary.com
back focus the distance between the back surface of a lens and the focal plane when the lens is focused at infinity. Photography noun 1895–1900 Origin:

Mirriam-Webster
Definition of BACK FOCUS: the distance from the rear glass surface of a photographic lens to the focal plane when the lens is focused on a very distant object.

--
Robin Casady
http://www.robincasady.com/Photo/index.html
"The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts."
— Bertrand Russell

I believe that's what I said earlier in this post. "Back focus was changing the distance between the tube or ccd sensor and the rear of lens, the focal plane position. " to quote myself.

The term has been adopted along with front focus to describe whether autofocus is accurate or not and whether a positive or negative offset is required.

 

[eNo]

I like to think of it as plus or minus AF offset, plus if the focus point goes beyond my subject, and minus if it falls short (is in front of) my subject. If my AF has a plus/positive offset, I need to apply minus AF fine-tuning to compensate, and if it has minus/negative offset, I need to apply plus AF fine-tuning to compensate.