(STILL UPDATING) Nikon D600 and lens infinity focus test

I plan to take star photography and I may have to manually focus on the star since the camera with given lenses may not be able to auto focus on the stars because of the low light situation. My first thinking was to rotate the focus ring all the way toward infinity mark. Actually when I did that focus ring rotated passed the infinity mark and stopped at the left side of infinity mark. I took a picture at this setting and the resulting image was very blurred image. So obviously this method did not work.

Some websites recommended that to focus star manually move the focus ring all the way toward infinity mark then rotate back a bit. In my opinion, it's vague method and I wanted to know the exact focus location. There was one way to do it. Test it myself. I used four lenses (see the list below) on Nikon D600. I put camera on the tripod at the edge of backyard garden.

Camera: Nikon D600 DLSR
Lens:
1) AF-S NIKKOR 24-70mm f/2.8G ED
2) AF-S NIKKOR 16-35mm f/4G ED VR
3) PC-E NIKKOR 24mm f/3.5D ED
4) AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED

To see the difference in focus near infinity mark on the lens, I picked 4 targets - cloud in the sky, tree in far, tree near, edge of the house (most near). I put the camera on tripod and auto focused on the target. Then I looked at the focus ring on the lens and wrote down the location of the focus on note pad. Moved on to next target and repeated the process.

Four target location for the focus test

- T1) Cloud in the sky (overcast day with cloud of faint color difference. AF had some hard time focusing. When sun was behind, it was auto focused quick).
- T2) Top of tree in far (across the street) - 81m (270ft)
- T3) Top of tree in front yard - 27m (90 ft)
- T4) Edge of house - 4.8m (16 ft)

Since the cloud was the farthest distance from the camera in these targets I expected to see the location of focus ring to be relative to the target distance.

I also downloaded images EXIF data using Exiftool to acquire Focus Position and Focus Distance. I wanted to see if these values reflected the focus location on the lens. I was aware that the DSLR was no laser range finder and Focus Position and Focus Distance would not be accurate. But I was hoping the value would reflect the location of focus ring so that I could use these value to aid my findings.

In addition when I photographed target 2 (tree in far distance), I took three images:
1) Auto focused on the tree
2) Manually moved the focus ring all the way passed infinity mark
3) Manually moved the focus ring at the center of the infinity mark

I wanted to see how these image looked like in terms of blurriness. The result was quite shocking.

Summary:

For given zoom setting on the lens, tree in far gave most far for focus location on the lens. Tree near and cloud were about same location and nearer than that of far tree. It was puzzling to me. Order of focus location from farthest to nearest should be cloud, tree far and tree near. But it was not the case.

The day I tested was overcasted and contrast in the cloud was low. Sometimes autofocus struggled to find focus. Probably the low contrast cloud was not good target. I should try to test with higher contrast subject such as brightly lit moon or white cloud on blue sky. I plan to do so.

When I compared images taken from AF and two manually selected focus location for tree in far, the difference in sharpness was very different. Manually focused to the far limit produced very blurred image that is not usable at all. Manually focused at the center of infinity mark also produced blurred image. Auto focused image that was not at center of infinity mark was in focus and images shown below was increased to 100%.

I found that EXIF's Focus Position and Focus Distance values was not helpful for this test. The level of granularity is not small enough to distinguish among detail focus location. For example, it reported same value for focus ring moved all the way and focus ring at the center of infinity mark.

Test Images:

Followings are each test images that is blown up to 100% to show the sharpness.

Naming convention for each test image
1-4.24mm.T1-T4.AF/MF)lens number; focal length used (I tried both shortest and longest focal length); Target number (target 1 - cloud in the sky), Auto Focus (AF) or MF (manual focus)

Location of focus on focus ring relative to infinity mark:
I had difficulty describing the location in word. So far this is what I came up with.
center: cross section of infinity letter
edge: left or edge of infinity letter where letter end
fat loop: fattest part of round part of infinity letter

@24mm AF-S NIKKOR 24-70mm f/2.8G ED

1.24mm.T1.AF

Focus point on lens: Right edge of infinity
note: focus point is same as near tree but apparently closer than far tree. Cloud is farther than far tree. Why the focus point is not farther away from far tree target?

Focus Position: 0x71
Focus Distance: 2.51 m

1.24mm.T2.AF

Focus point on lens: Right fattest part of infinity

Focus Position: 0x91
Focus Distance: 3.35 m

1.24mm.T2.MF.1

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x01
Focus Distance: 6.68 m

1.24mm.T2.MF.2

Focus point on lens: Manually move the focus to the center of infinity

Focus Position: 0x01
Focus Distance: 6.68 m

1.24mm.T3.AF

Focus point on lens: Right edge of infinity

Focus Position: 0x71
Focus Distance: 2.51 m

I did not take photo of T4 with 24mm setting. I started doing it later.

@70mm AF-S NIKKOR 24-70mm f/2.8G ED

1.70mm.T1.AF

Focus point on lens: hair left from center of infinity.
Note: why the focus location of cloud is closer than that of far tree?

Focus Position: 0x04
Focus Distance: 6.68 m

1.70mm.T2.AF

Focus point on lens: left of the center of infinity.

Focus Position: 0x04
Focus Distance: 6.68 m

1.70mm.T3.AF

Focus point on lens: center or hair left of infinity.

Focus Position: 0x04
Focus Distance: 6.68 m

1.70mm.T4.AF

Focus point on lens: A bit left of right fattest loop of infinity.

Focus Position: 0x54
Focus Distance: 5.01 m

2. @16mm AF-S NIKKOR 16-35mm f/4G ED VR

2.16mm.T1.AF

Focus point on lens: A bit right of right fattest loop of infinity.

Focus Position: 0x73
Focus Distance: 2.00 m

2.16mm.T2.AF

Focus point on lens: Apex of right fattest loop of infinity.

Focus Position: 0x73
Focus Distance: 2.00 m

2.16mm.T2.MF.1

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x03
Focus Distance: 2.66 m

2.16mm.T2.MF.2

Focus point on lens: Manually move the focus to center of the infinity

Focus Position: 0x03
Focus Distance: 2.66 m

2.16mm.T3.AF

Focus point on lens: Same as 1.16mm.T2.AF (far tree)

Focus Position: 0x73
Focus Distance: 2.00 m

2.16mm.T4.AF

Focus point on lens: Very similar to 1.16mm.T1.AF (focus on cloud) or bit right than that.

Focus Position: 0x73
Focus Distance: 2.00 m

2. @35mm AF-S NIKKOR 16-35mm f/4G ED VR

2.35mm.T1.AF

Focus point on lens: Bit right of center of infinity

Focus Position: 0x04
Focus Distance: 2.66 m

2.35mm.T2.AF

Focus point on lens: Bit right of center of infinity

Focus Position: 0x04
Focus Distance: 2.66 m

2.35mm.T2.MF.1

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x04
Focus Distance: 2.66 m

2.35mm.T2.MF.2

Focus point on lens: Manually move the focus to center of the infinity

Focus Position: 0x04
Focus Distance: 2.66 m

2.35mm.T3.AF

Focus point on lens: Very similar to 1.35mm.T1.AF (far tree AF) but maybe bit right than that.

Focus Position: 0x04
Focus Distance: 2.66 m

2.35mm.T4.AF

Focus point on lens: Between center and the apex of right fattest loop of infinity

Focus Position: 0x04
Focus Distance: 2.66 m

3. PC-E NIKKOR 24mm f/3.5D ED

3.24mm.T2.MF.1

Focus point on lens: Bit left of letter 10. Bit right of center of infinity.
Note: Since it's MF only, I used live view's most magnification to focus.

Focus Position: 0x11
Focus Distance: 0.30 m

3.24mm.T2.MF.2

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x11
Focus Distance: 0.30 m

3.24mm.T2.MF.3

Focus point on lens: Manually move the focus to center of the infinity

Focus Position: 0x11
Focus Distance: 0.30 m

4. @70mm AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED

4.70mm.T1.AF

Focus point on lens: Bit right of center of infinity

Focus Position: 0x04
Focus Distance: 21.13 m

4.70mm.T2.AF

Focus point on lens: Apex of right fattest loop of infinity

Focus Position: 0x04
Focus Distance: 21.13 m

4.70mm.T2.MF.1

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x04
Focus Distance: 21.13 m

4.70mm.T2.MF.2

Focus point on lens: Manually move the focus to center of the infinity

Focus Position: 0x04
Focus Distance: 21.13 m

4.70mm.T3.AF

Focus point on lens: right edge of infinity

Focus Position: 0x44
Focus Distance: 17.78 m

4.70mm.T4.AF

Focus point on lens: At 20ft mark.

Focus Position: 0x22
Focus Distance: 6.31 m

4. @300mm AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED

4.300mm.T1.AF

Focus point on lens: Between center and the apex of right fattest loop of infinity

Focus Position: 0x03
Focus Distance: 21.13 m

4.300mm.T2.AF

Focus point on lens: Between center and the apex of right fattest loop of infinity. Same as cloud.

Focus Position: 0x03
Focus Distance: 21.13 m

4.300mm.T2.MF.1

Focus point on lens: Manually move the focus to most left of the infinity

Focus Position: 0x03
Focus Distance: 21.13 m

4.300mm.T2.MF.2

Focus point on lens: Manually move the focus to center of the infinity

Focus Position: 0x03
Focus Distance: 21.13 m

4.300mm.T3.AF

Focus point on lens: Right of between right edge and center

Focus Position: 0x03
Focus Distance: 21.13 m

4.300mm.T4.AF

Focus point on lens: Letter 2 of mark 20 ft.

Focus Position: 0x11
Focus Distance: 6.31 m

Last updated on 2013-05-09