D850 focus shift question.

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arshuter

arshuter

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I tried my first attempt at focus shifting yesterday. I was at an overlook checkin out the fall foliage and remember the 850 had this feature. I never used it but watched a few you tube vids on it. The view was, guessing, close to a mile across the valley. My f stop setting was 5.6 on the first try, it only took 1 image. Readjusted to f/7.1 second attempt only took 1 image. In the menu I am set at 100 images, 0 delay, focus step with was 7 and then 4. I tried several times at each and other settings with the same results.
Later at a different set-up I tried a closer shot of a fern growing out of a tree and got 32 images. What am I doing wrong on the landscape shots? I would really like to figure this out as most of my photography is landscape and what I call intimate landscape. Thanks, Alan
 
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arshuter said:
What am I doing wrong on the landscape shots?
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Nothing, it's just that focus stacking using the D850's Focus Shift feature doesn't really apply in the distant trees scenario.

arshuter said:
The view was, guessing, close to a mile across the valley.
Click to expand...

If the Depth of Field (DoF) is sufficient then the image will be captured with sufficient sharpness in a single image. When you shoot a landscape from far away you can get more than enough DoF with a fairly wide aperture. It's when you start including foreground objects, especially very close foreground objects typically with a wide angle lens that you'll start to need more DoF than what you can get at a moderate aperture.

You didn't mention the focal length of the lens and DoF decreases with increasing focal length for the same aperture and subject distance but taking the example of a 200mm lens at f/5.6 with the lens focused to 5000' (nearly a mile) here's what you'd expect to see for DoF on a full frame sensor:
5000ft DoF.jpg
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Basically this says that when focused at 5000' with a 200mm lens at f/5.6, everything from 670 feet to infinity will be in acceptable focus in a single shot. The Focus Shift feature in your D850 understands this and only captures a single shot as it won't achieve sharper focus with multiple shots in that scenario.

If you play with any of the DoF calculators you'll see the need for focus stacking in landscape images really starts when you have very close (sometimes inches) and very far (sometimes many miles) objects in the same scene that you want to keep in focus and doesn't really apply to a scene that is all very far away.

The DoF calculator I referenced is located here: https://www.dofmaster.com/dofjs.html

[Edit] Perhaps a simpler way to think of this it that when using Nikon's Focus Shift feature you set the nearest focus distance and the camera calculates the best focusing distance for the next shot in the series. The camera is programmed with the same DoF mathematics used in those online calculators so it can determine how far to move the focusing for the appropriate amount of DoF overlap. When the camera is focused out near infinity already (trees nearly a mile away) and calculates a very wide DoF based on that distance, lens and aperture it determines that there is no need for a second shot and couldn't move the lens focus that far past infinity anyway so it doesn't capture any more images.
 
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