Focusing Problems Nikkor 105mm f/2.5 non-cpu lens

[Lonnie1212]

Hi Folks,

Last weekend I was using a Nikon D750 camera and a Nikkor 105 f/2.5 non-cpu lens. I consistently focused on the right eye of the young lady in the picture. The aperture is set at f/4. Her face is soft but the burlap on the back of the chair is in focus. What could cause this? It was happening all day with other models. But when I changed lenses everything seemed to work just fine. The non cpu lens data was set correctly in the shooting menu.

Thank you,

Lonnie

 

[ac12]

When you say changed lenses, was that to another manual focus lens, or to an autofocus lens?
The CPU in the lens or not should not have any effect on focus.

 

[Lonnie1212]

When you say changed lenses, was that to another manual focus lens, or to an autofocus lens?
The CPU in the lens or not should not have any effect on focus.

I changed to an 85mm 1.8 G, yes, autofocus

 

[RAZKY]

I changed to an 85mm 1.8 G, yes, autofocus

Hi Folks,

Last weekend I was using a Nikon D750 camera and a Nikkor 105 f/2.5 non-cpu lens. I consistently focused on the right eye of the young lady in the picture. The aperture is set at f/4. Her face is soft but the burlap on the back of the chair is in focus. What could cause this? It was happening all day with other models. But when I changed lenses everything seemed to work just fine. The non cpu lens data was set correctly in the shooting menu.

Thank you,

Lonnie

If her eye had been in sharp focus on the focusing screen when you released the shutter, it ought to have been in sharp focus on the sensor. How accurately have you adjusted your diopter? It doesn't sound like camera or lens error.

 

[smoke665]

Just a thought, but at the settings used, depending on the the distance your DOF would have been 4" or less. "but the burlap on the back of the chair is in focus" - if you look closely at the burlap you'll see there's only about a 4" section just under the front of the hair that's in sharp focus, coincidentally of the same plane as the hair in front of her face. If you look at the hair in front of the eye, it's also in sharp focus. I've had this problem before with auto focus locking on hair rather than the eye. When that happens I can sometimes use spot focus on an area free of hair and use my DOF to catch the eye, or switch to manual focus.

Another possibility, which AF mode were you Using? AF-C, AF-S, or AF-A?

There's always the possibility of a focus problem, I've only found that to be the case a couple times in my lifetime. If you have concerns here's the way to check it, there's a link in the article to download the focus chart. How to do a Camera Focus Test for Autofocus Issues

 

[ac12]

I changed to an 85mm 1.8 G, yes, autofocus

So the 85 is an AF lens, but is the 105 manual focus or autofocus?

 

[RAZKY]

The CPU in the lens or not should not have any effect on focus.

Nikon Non-CPU lenses are manual focus only.

 

[RAZKY]

Just a thought, but at the settings used, depending on the the distance your DOF would have been 4" or less. "but the burlap on the back of the chair is in focus" - if you look closely at the burlap you'll see there's only about a 4" section just under the front of the hair that's in sharp focus, coincidentally of the same plane as the hair in front of her face. If you look at the hair in front of the eye, it's also in sharp focus. I've had this problem before with auto focus locking on hair rather than the eye. When that happens I can sometimes use spot focus on an area free of hair and use my DOF to catch the eye, or switch to manual focus.

Another possibility, which AF mode were you Using? AF-C, AF-S, or AF-A?

There's always the possibility of a focus problem, I've only found that to be the case a couple times in my lifetime. If you have concerns here's the way to check it, there's a link in the article to download the focus chart. How to do a Camera Focus Test for Autofocus Issues

Nikon Non-CPU lenses are manual focus only.

 

[smoke665]

Nikon Non-CPU lenses are manual focus only.

I misread his post. Given the apparent focal plane from the hair in front of the eye to the section of burlap below, then as you said earlier, "It doesn't sound like camera or lens error".

 

[cgw]

Live View to the rescue?
What does the lens's DOF chart have to say?

 

[ac12]

Nikon Non-CPU lenses are manual focus only.

That is what I thought.

 

[wfooshee]

Is the 105 a new-to-you lens? It may just take some experimentation to find what aperture yields an approriate DOF. How shallow are you trying to make it? Did this come out shallower than you intended?

As to your original question, why is her eye not in focus when it was sharp in the viewfinder... unless you have a split-image rangefinder screen (and the D750 does not have interchangeable screens,) the ground glass simply isn't accurate for focusing. I'll use Live View for focusing a manual-focus lens, but of course I need the camera on a tripod; I can't freeze the camera in space after focusing if hand-holding!

 

[RAZKY]

Is the 105 a new-to-you lens? It may just take some experimentation to find what aperture yields an approriate DOF. How shallow are you trying to make it? Did this come out shallower than you intended?

As to your original question, why is her eye not in focus when it was sharp in the viewfinder... unless you have a split-image rangefinder screen (and the D750 does not have interchangeable screens,) the ground glass simply isn't accurate for focusing. I'll use Live View for focusing a manual-focus lens, but of course I need the camera on a tripod; I can't freeze the camera in space after focusing if hand-holding!

According to the original post, the issue has nothing whatever to do with depth of field.

 

[Lonnie1212]

When you say changed lenses, was that to another manual focus lens, or to an autofocus lens?
The CPU in the lens or not should not have any effect on focus.

I changed to am 85mm after lens-Nikon

 

[Lonnie1212]

I changed to am 85mm autofocus lens-Nikon