Focus shifting (landscape)

blackstar

Senior Member
Determining the number of shots when doing focus shift in landscape photography is unnecessary as the camera stops when you reach infinity. Just set the number to 100 or 200 or a value that far exceeds what is needed. If you reach infinity after 12 shots, the camera stops.
Should you not reach infinity, when the camera stops, just continue with one more shooting, the lens will continue from the last focus distance.
The number of steps is the number of shots if you set the step to 1. In my experiment I have set the focus step to 2. Sometimes (before I became aware of the differences between the lenses) I have used 5 steps, resulting in blurry areas when I finally stacked the pictures.
The problem is that you don't know how big a focus step is for a certain lens. You want it to be 4/10 of DOF and that's a good assumption, but different lenses can give anything between 2/10 and 8/10 of DOF (or more).
Since information about this cannot be obtained from calculators based on the camera, you have to test what number of focus step you shall enter in the camera's focus shift menu, for each lens.
In my case I now know that for my Z 24-200 I should always use 1, but for my Z 70-200 (and Z 105) I can happily use 5.
The special thing about my project is the main subject in the landscape scene is very very far (miles) away and some other object (e.g., clouds) is even beyond it. I need a 600mm lens to catch the scene. This is very different from Macro/close-up, even normal landscape scenes (DoF is not that long).

Where do you set focus step? Are you talking about the second setting: "Focus step width"? If so, it is not the "focus step" you thought, but the number camera takes to calculate the "step width"... Actually, it determines the "overlap area of focus" between the succeeding two shots: smaller number (smaller step) = bigger overlap (more shots required); larger number (bigger step) = smaller overlap (fewer shots required). (this is my theory, maybe wrong)
 

Paliswe

Senior Member
Hi, just to be sure that I use the correct words, I looked it up in the English Z6 reference manual. In the menu, under Photo shooting Menu ("camera"), there is Focus Shift shooting and in the submenu you have "No. of shots" selectable between 1 and 300, then you have "Focus step width" selectable between 1 and 10.
Just for clarity I will call the focus distance between two shots for - focus distance (!). I may have been unclear on that. Sorry about that.
I don't think that the camera makes any calculations. It just performs the settings done in the menu. Take one shot - shift focus distance two steps (or whatever between 1 and 10) - take next shot and so on until all shots has been taken or infinity is reached.
What I wanted to say in my post #18 is that the focus distance vary depending not only what "Focus step width" you choose, but also what lens you are using. In the two pictures I have enclosed, my focal length is 200mm, picture taken from 4.15 m distance to "zero cube". While one of my lenses (70-200) shifts focus distance about 20-30 cm at 4.15 m, when the focus step motor makes 20 steps (10 frames x 2 step width), the other (24-200) under the exact same conditions shifts focus distance about 80 cm.
So to find out what "Focus step width" you shall use, to be sure to be within 4/10 of DOF, is just a matter of trial and error. All parameterns are known, except for how big a focus distance is for just your lens.
 

blackstar

Senior Member
...
What I wanted to say in my post #18 is that the focus distance vary depending not only what "Focus step width" you choose, but also what lens you are using. In the two pictures I have enclosed, my focal length is 200mm, picture taken from 4.15 m distance to "zero cube". While one of my lenses (70-200) shifts focus distance about 20-30 cm at 4.15 m, when the focus step motor makes 20 steps (10 frames x 2 step width), the other (24-200) under the exact same conditions shifts focus distance about 80 cm.
...
When you use 24-200mm and 70-200mm with FL=200mm, it is NOT under the exact same conditions: you have to use a ZTF adaptor for 24-200mm and it could make a bigger DoF. Or you could set a different aperture that also affects DoF (f4-6.3 for 24-200mm; f2.8 for 70-200mm). Remember large aperture makes a small DoF.
 

Paliswe

Senior Member
The 24-200 mm is a Z-lens. (Nikkor Z 24-200/4-6.3)
The results from my test with the rubber cubes has nothing to do with DOF. I just try to pinpoint how many cubes down the line that the lenses are moving the focus point by taking 10 pictures with 2 steps for each picture and I do no stacking on these pictures. It's just the last photo in a serie of 10 photos I have a look at.
If you however do a stacking (using Zerene Stacker or similar software) then the DOF would have impact on the stacked photo and the aperture will have affect.
But I suddenly realize that I have made one mistake; the number of focus steps in a series is 18, not 20. But never the less, the result is the same, different lenses moves the focus point different lengths for the same amount of focus steps. It is therefore necessary to check out each and every lens if you want to have control of the focus shift shooting.
In the attached figure I have tried to illustrate that DOF doesn't matter, it's only the distance between the vertical dashed lines that matters in my test.
 

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  • Focus shift.jpg
    Focus shift.jpg
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blackstar

Senior Member
Hi Paliswe, Evidently, according to the Exif, your experiments with 70-200mm and 24-200mm were taken under quite different conditions: different shutter speeds, different ISO, different shooting angles, and most importantly, different f/xx. Since you set f/2.8 for 70-200mm, you got very shallow DoF and thus reach not very far. The f/6.3 you set for 24-200mm makes it reach the far end with a larger DoF. I believe my theory stands on this case. (BTW, the vertical dashed lines you mentioned are just the last focal planes of the two lenses.)
 

blackstar

Senior Member
Did another try: # shots=100, FSW=6, Interval=0. Actual shots=56 (FL=600mm, iso=640, f/9.5, speed=1/125")
After stacking, realized have made a mistake: focusing the first spot on the bottom of the chimney! (thinking the closest point) From the images below, there are big power post and tree branches in the very close left-side foreground out of focus. Wonder if placing the focus point at the bottom (or just any spot) of the power post, will the center part of the images be affected (focusing) by this practice? (i.e., by saving side foreground to lose center and other areas)

1st shot image:
KFW_4087s.JPG

stacked image:
2023-04-15-07.58.43 ZS retoucheds.jpg
 
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