Distance scale on Nikon 18-70mm zoom lens

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Gary Jones" <nonesuch1960@hotmail.com> wrote in message
news:1f986b38.0501231210.2da3998e@posting.google.com...
>I don't know why I didn't notice this before but...
>
>
> It seems that the distance scale on the Nikkor DX 18-70mm lens (the
> lens that comes with the D70 as a kit) is set to be accurate only at
> maximum telephoto. When set to widest wide-angle, the distance scale
> is quite a way off. I did a test on maximum wide angle with a subject
> (practically) at infinity. The distance when autofocussed was
> (according to the scale) closer to the 2m mark than the infinity mark.
> (I know the scale isn't linear, but was still suprised where the
> autofocus seemed to end up.) The image came out fine. I also tried
> manual-focussing and set the focus by setting the distance scale to
> infinity. This second image was noticeably out of focus.
>
> I'd already noticed that if a subject is in focus at a particular
> focal length, changing the zoom doesn't move the focus ring and the
> image goes out of focus. I assumed this is standard behaviour; but it
> didn't occur to me until now that this implies that the distance scale
> only works at a particular focal length.
>
> Could someone set my mind at rest and confirm that the lens is
> behaving as expected? The last time I used an SLR, I had separate wide
> and telephoto lenses, and it's a bit embarrassing to confess to this
> level of ignorance regarding zoom lenses.
>
> Thanks.

Keep in mind that when set to wide angle you get a heck of a lot of depth of
field, so the focus can be way off but the image, and everything around it,
will still be in focus. I'm not sure how the camera decides to focus on
anything, but maybe it's trying to give you the max depth of field,
especially when using small apertures. This is just a hunch on my part,
BTW.

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Mon, 31 Jan 2005 21:21:53 -0700, in rec.photo.digital.slr-systems
"Sheldon" <sheldon@XXXXXXXXsopris.net> wrote:


>. I'm not sure how the camera decides to focus on
>anything,

It depends on the modes and Focus Area settings. In many scene modes
closest subject is chosen. To enable manual selection set Custom 3,
AF-area mode to single or dynamic. Read pp 64-69 of the manual.
----------
Ed Ruf Lifetime AMA# 344007 (Usenet@EdwardG.Ruf.com)
See images taken with my CP-990/5700 & D70 at
http://edwardgruf.com/Digital_Photography/General/index...

Archived from groups: rec.photo.digital.slr-systems (More info?)

Gary Jones wrote:
>Could someone set my mind at rest and confirm that the
>lens is behaving as expected? The last time I used an SLR,
>I had separate wide and telephoto lenses, and it's a bit
>embarrassing to confess to this level of ignorance regarding
>zoom lenses.


There could be a simple answer to this. Your "zoom" lens is in fact
"varifocal", meaning that the point of focus changes as you zoom.

I have one lens that does this - it is a Pentax 35-105mm "zoom". There
is a very big difference between the infinity focus position at 35mm
and at 105mm. The explanation is that this lens is a "varifocal"
design.

A true "zoom" lens does not do this. It keeps the point of focus the
same as you zoom. But it is probably cheaper to make "varifocal"
lenses ... and if you use autofocus, the change in focus point doesn't
bother you. Of course my Pentax lens is not autofocus ... I was very
worried when I first bought it. It was a second hand lens and I
thought it had maybe been dropped. But it is OK. I bought another
used one in almost new state and its focusing is exactly the same.

So do not worry. Just take some care when focusing manually and
looking at depth of field.

Archived from groups: rec.photo.digital.slr-systems (More info?)

SMC wrote:
> Gary Jones wrote:
>> Could someone set my mind at rest and confirm that the
>> lens is behaving as expected? The last time I used an SLR,
>> I had separate wide and telephoto lenses, and it's a bit
>> embarrassing to confess to this level of ignorance regarding
>> zoom lenses.
>
>
> There could be a simple answer to this. Your "zoom" lens is in fact
> "varifocal", meaning that the point of focus changes as you zoom.
>
> I have one lens that does this - it is a Pentax 35-105mm "zoom".
> There is a very big difference between the infinity focus position at
> 35mm and at 105mm. The explanation is that this lens is a "varifocal"
> design.
>
> A true "zoom" lens does not do this. It keeps the point of focus the
> same as you zoom. But it is probably cheaper to make "varifocal"
> lenses ... and if you use autofocus, the change in focus point doesn't
> bother you. Of course my Pentax lens is not autofocus ... I was very
> worried when I first bought it. It was a second hand lens and I
> thought it had maybe been dropped. But it is OK. I bought another
> used one in almost new state and its focusing is exactly the same.
>
> So do not worry. Just take some care when focusing manually and
> looking at depth of field.

From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
cheap):
"(!) · Be sure to finish zooming before focusing. Changing the zoom ring
after focusing can affect the focus."

Which lenses do _not_ show this effect?


--
Frank ess

"Because of the Swiss Cheese nature of everyone's life experience and
education, the Whoosh Bird can drop a load on anyone's head, without
warning." -Albrecht Einstein

Archived from groups: rec.photo.digital.slr-systems (More info?)

Frank ess wrote:

> From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not cheap):
> "(!) · Be sure to finish zooming before focusing. Changing the zoom ring
> after focusing can affect the focus."
>
> Which lenses do _not_ show this effect?

Two would be the Maxxum 28-70 and 80-200 f/2.8's 'hold' their focus during zoom.
However, if you focus at the wide end and then zoom in, the error from the
wide end focus appears and a slight tune is needed to get it perfect. Going the
other way (narrow to wide) there is no discernible error, of course.

By error I mean the error of the eye or the AF. What is not perceptible as a
focus error wide shows up when you zoom in more detail.

I suspect the same meaning applies to what you quoted above.

Cheers,
Alan



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Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ieCdnX7NAe8rYJ3fRVn-gA@giganews.com>,
Frank ess <frank@fshe2fs.com> wrote:
>SMC wrote:
>> Gary Jones wrote:
>>> Could someone set my mind at rest and confirm that the
>>> lens is behaving as expected? The last time I used an SLR,
>>> I had separate wide and telephoto lenses, and it's a bit
>>> embarrassing to confess to this level of ignorance regarding
>>> zoom lenses.
>>
>>
>> There could be a simple answer to this. Your "zoom" lens is in fact
>> "varifocal", meaning that the point of focus changes as you zoom.
>>
>> I have one lens that does this - it is a Pentax 35-105mm "zoom".
>> There is a very big difference between the infinity focus position at
>> 35mm and at 105mm. The explanation is that this lens is a "varifocal"
>> design.
>>
>> A true "zoom" lens does not do this. It keeps the point of focus the
>> same as you zoom. But it is probably cheaper to make "varifocal"
>> lenses ... and if you use autofocus, the change in focus point doesn't
>> bother you.

[ ... ]

>From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
>cheap):
>"(!) · Be sure to finish zooming before focusing. Changing the zoom ring
>after focusing can affect the focus."
>
>Which lenses do _not_ show this effect?

Are you asking about the Cannon in particular? The "Subject: "
header refers to the Nikon lens which comes with the D70 kit. I have
the D70, but with a:

28-104mm AF Nikkor 1:3.2-54. D

and this does not show this behavior.

Neither does the 70-205 mm Nikor which I seldom use with this
camera, simply because it does not have the CPU, so I am back to a
handheld meter with it*. And the fellow who does the CPU conversions
does not want to handle converting this lens (I guess bad experience
with another), so I guess that I am stuck here. (Unless Nikon will
convert them?)

*) A handheld meter is not a real problem (other than convenience)
with shorter lenses, but this puts me a bit too far out to be
convenient. Especially since I am likely to be shooting
subjects which would be spooked if I walked up to meter them
properly with a handheld.

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Archived from groups: rec.photo.digital.slr-systems (More info?)

DoN. Nichols wrote:
> In article <ieCdnX7NAe8rYJ3fRVn-gA@giganews.com>,
> Frank ess <frank@fshe2fs.com> wrote:
>> SMC wrote:
>>> Gary Jones wrote:
>>>> Could someone set my mind at rest and confirm that the
>>>> lens is behaving as expected? The last time I used an SLR,
>>>> I had separate wide and telephoto lenses, and it's a bit
>>>> embarrassing to confess to this level of ignorance regarding
>>>> zoom lenses.
>>>
>>>
>>> There could be a simple answer to this. Your "zoom" lens is in fact
>>> "varifocal", meaning that the point of focus changes as you zoom.
>>>
>>> I have one lens that does this - it is a Pentax 35-105mm "zoom".
>>> There is a very big difference between the infinity focus position
>>> at 35mm and at 105mm. The explanation is that this lens is a
>>> "varifocal" design.
>>>
>>> A true "zoom" lens does not do this. It keeps the point of focus
>>> the same as you zoom. But it is probably cheaper to make
>>> "varifocal" lenses ... and if you use autofocus, the change in
>>> focus point doesn't bother you.
>
> [ ... ]
>
>> From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
>> cheap):
>> "(!) · Be sure to finish zooming before focusing. Changing the zoom
>> ring after focusing can affect the focus."
>>
>> Which lenses do _not_ show this effect?
>
> Are you asking about the Cannon in particular? The "Subject: "
> header refers to the Nikon lens which comes with the D70 kit. I have
> the D70, but with a:
>

Just curious about how important such a consideration is to lens
sellers. I'm certain designers know its value.

I remember learning early in my pre-digital life to focus at long zoom
and go wider from there. Were old-time film zooms less subject to the
drift?

Come to think of it, I _would_ like to know about current Canon lenses'
tendencies. Maybe I'll start a thread ...

Meantime, thank you for the information.

<snip information>


--
Frank ess

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ctr9mc$obi$1@fuego.d-and-d.com>,
DoN. Nichols <dnichols@d-and-d.com> wrote:
>In article <ieCdnX7NAe8rYJ3fRVn-gA@giganews.com>,
>Frank ess <frank@fshe2fs.com> wrote:

[ ... ]

>>From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
>>cheap):
>>"(!) · Be sure to finish zooming before focusing. Changing the zoom ring
>>after focusing can affect the focus."
>>
>>Which lenses do _not_ show this effect?

[ ... ]

> Neither does the 70-205 mm Nikor

Oops! I meant 80-200mm Nikor (after checking it).

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <xKqdnYEpveZr35zfRVn-3Q@giganews.com>,
Frank ess <frank@fshe2fs.com> wrote:
>DoN. Nichols wrote:
>> In article <ieCdnX7NAe8rYJ3fRVn-gA@giganews.com>,
>> Frank ess <frank@fshe2fs.com> wrote:

[ ... ]

>>> From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
>>> cheap):
>>> "(!) · Be sure to finish zooming before focusing. Changing the zoom
>>> ring after focusing can affect the focus."
>>>
>>> Which lenses do _not_ show this effect?
>>
>> Are you asking about the Cannon in particular? The "Subject: "
>> header refers to the Nikon lens which comes with the D70 kit. I have
>> the D70, but with a:
>>
>
>Just curious about how important such a consideration is to lens
>sellers. I'm certain designers know its value.
>
>I remember learning early in my pre-digital life to focus at long zoom
>and go wider from there. Were old-time film zooms less subject to the
>drift?

This is more than just drift, I think. *Good* old time lenses
were carefully crafted to maintain focus from maximum effective focal
length to minimum. Obviously, going the other way, you have a bit of a
handicap, as it is difficult to focus as well at minimum effective focal
length.

These days, with good autofocus available, the camera
manufacturers can simplify the design of the lens a bit, knowing that
the camera will touch up the focus when you reach your desired focal
length and start to take the shot.

>Come to think of it, I _would_ like to know about current Canon lenses'
>tendencies. Maybe I'll start a thread ...

It will be interesting to see what you get, there.

>Meantime, thank you for the information.

You're welcome.

Enjoy,
DoN.

--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---