Many modern lenses have ‘floating elements’ in them that change position within the lens to help achieve focus on a close subject. Using an extension tube can sometimes cause image quality issues when a lens is used fully extended at its minimum focusing distance. We can see a clear example of this extension tube issue with the photograph above that was captured with an M.Zuiko PRO 12-100 f/4 IS zoom when it was fully extended at its minimum focusing distance.

Depth of field microscopeformula

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Unless we understand how our lenses perform in terms of their minimum focusing distance, we can inadvertently move in too close to our subject and miss our shot.

Compare the distance to subject measurements between each of the lenses, and the size of the subject in each photograph. It is easy to see why understanding the minimum focusing distance of a lens can be an important issue.

When this lens is used with a 16 mm extension tube it focuses so closely on a subject that the lens can block light from reaching the subject or cast a shadow on it. As a result I don’t use this lens with extension tubes.

Excellent article – so many AF lenses nowadays are very disappointing in this respect, though old lenses on FILM cameras are much worse! Naturally I would not just use AF for close up work, but the limitations apply in manual mode too, and at least for insects the opportunity to move to get focus is all too often not available (they fly away).

Field ofviewmicroscopedefinition

Microscope mirrors are occasionally knocked out of alignment at some stage during viewing, with the result that the subject is lit with an off-axis light source ...

Resolutionmicroscope

Minimum focusing distance can be a significant issue when using long telephoto lenses. It is common for the minimum focusing distance of a 150-600 mm or a 200-600 mm full frame zoom lens to be in the 2.2 to 2.8 metre (~7.2 to 9.2 feet) range. Prime full frame long telephoto lenses can have even longer minimum focusing distances.

One of the many things that I enjoy about interacting with readers is learning about how they use their equipment. I had to smile when you mentioned your use of manual focus for close up work. While I have used manual focus on occasion to acquire approximate focus on a subject, I always switch to auto-focus to nail it down just before capturing my image. This is so easily done with the focus clutch on M.Zuiko PRO lenses. In all of the time that I’ve been using interchangeable lens digital cameras, I don’t recall ever creating a handheld image only using manual focus. It’s interesting how different we can be as photographers as each of us ply our craft.

It can also be an important factor when using long telephoto lenses for nature and bird photography. Often subjects may be positioned inside the minimum focusing distance of the telephoto lens being used. In many cases the photographer would then have to back away from the subject, or simply miss their shot.

when it comes to doing close-up or macro photography I have three options that I use depending on which camera format I choose. The Nikon 1 system does not have a dedicated macro lens so I always use extension tubes with this gear. My Olympus TG-5 has a microscopic setting which works well in situations where I can get the camera basically right on top of a subject (i.e. within a couple of centimetres). I have the M.Zuiko 60 mm f/2.8 macro which is what I always use for macro photography with M4/3. I use my M4/3 extension tubes with my M.Zuiko PRO 40-150 f/2.8 on occasion. This is typically when I want to shorten the minimum focusing distance when photographing flowers.

In situations where we are using a long telephoto zoom lens we still may be able to capture our image. To do this we may have to zoom to a wider angle focal length and settle for a photograph where the subject is much smaller in the frame than we would have liked.

All of the photographs in this article were shot handheld (my preferred shooting style) to help determine how each lens could be used when fully extended with close-up subjects. With each photograph I moved in as close as possible with my lens fully extended until it would not auto-focus. Then I slowly moved back a tiny bit until it would auto-focus and I could capture my image.

Table 1 shows some example calculations of DOF with green light and air. I usually chose a smaller step size than the calculated DOF for green light. Below is an example of two butterfly wing scales that are upside down. This is a focus stack with 255 photos, 0,00055 mm step size, Nikon BD plan apo 40x NA 0.80 microscope objective, Canon 6D camera, stacked in Zerene Stacker.

Depth of field microscopedefinition quizlet

Numerical aperture (NA) can be used to calculate the Depth of Field (DOF). Calculating DOF is useful for deciding the (largest) step size for focus stacking.

Depth of field

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From time to time I still do that today when using my Nikon 1 or Olympus kit. It’s like having a bit of insurance in your camera bag. The image above is an example of using an extension tube to change the minimum focusing distance of a lens.

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Photographs were captured hand-held using camera gear as noted in the EXIF data. Images were produced from RAW files using my standard process. All photographs are displayed as 100% captures without any cropping.

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Example calculations of Depth of Field (DOF) using a simplified formula for DOF and using the wavelength (λ) for green light 0.550µm. Case #1: NA=0.14 for example Mitutoyo M plan 5xDOF = 0.550µm / 0,14^2 ≈ 28µm or 0.028mm

We recently added three M.Zuiko lenses to our Olympus kit. Whenever I buy a new lens I always take some time to do some hands on tests pertaining to minimum focusing distance. This article shares some quick test images that I did with each lens fully extended.

Imagine yourself on a park bench and having a rare butterfly land next to you about 475 mm (~18.7 inches) away. Assuming that you have no room to move away from the butterfly, and you have to photograph it immediately, only two of the five lenses noted in this article would be able to acquire focus on it when fully extended.

The photograph above was taken with the M.Zuiko 75-300 mm f/4.8-6.7 II. You’ll note that I had to use an aperture of f/6.7 when this lens is fully extended. The distance to subject of 1.4 metres (~4.6 feet) was almost three times further than was the case with the M.Zuiko 14-150 mm f/4-5.6 II.

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What isthe focal distanceofamicroscope

The exact dimension of a 35mm sensor measures 36×24mm, which doesn't seem to have any logical relation. That's because the name is in reference to 35mm film.

Skipping one of the 0.00055mm steps that I used means that the step size is approximately 0.0011mm. In the video below you can see that this is (barely) visible. The video shows two alternating stacks. In one of them one single photo is deleted. At this enlargement the area used from one photo is just a thin band of sharp pixels. The difference with and without one photo is a small flickering band of sharp/unsharp.

In practice the step size in focus stacking is usually a bit smaller than the calculated DOF. The reason for this is to have some overlap between the in-focus areas.

The M.Zuiko 14-150 mm f/4-5.6 II was used to capture the sample image above. You can see that the distance to subject was 500 mm (~19.7 inches). This allows a photographer to achieve a reasonable degree of subject magnification without being too distant from it.

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It is important to do some testing with your lenses before using extension tubes with them when they are fully extended and shot at their minimum focusing distance. Don’t assume that a lens that performs well when fully extended at its minimum focusing distance will also perform this way when an extension tube is used.

Depth of fieldvsdepth offocusmicroscope

When I used to shoot with full frame camera equipment and a 150-600 mm zoom lens, I started carrying extension tubes with me just in case I needed to shorten the minimum focusing distance of my lens.

If a photographer does a lot of close up work, or intends to use extension tubes with specific lenses, considering the minimum focusing distance is important.

Our first sample image was captured using the M.Zuiko PRO 12-40 mm f/2.8 zoom. As you see, I was able to get in quite close to the subject. The 200 mm (~7.9 inches) distance to subject is suitable for flowers and still life subjects. When photographing insects or animals that my sting or bite, this distance is often not very practical.

Whathappens to thedepth of fieldas total magnification decreases

DOF = Depth of Field in mm λ = Wavelength of the light used in mm. n = Index of refraction NA = Numerical aperture of the objective used

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When increasing the resolution from 2µm to 1µm the largest step size decreases from 0.028mm to 0.006mm. For an object that is 1mm from top to bottom the NA 0.15 objective needs at least 36 steps/pictures (1/0.028) and the NA 0.30 needs at least 167 (1/0.006) steps/pictures. Using a smaller step size to have some overlap increases the necessary steps/photos even more.

Our sample image above was captured with the M.Zuiko PRO 12-100 f/4 IS with a distance to subject of 450 mm (~17.7 inches). You’ll notice that there isn’t very much difference in subject size in this image to the one captured with the M.Zuiko 14-150 mm f/4-5.6 II.

Vissible light goes from violet approximately 0.380-0.450µm to red approximately 0.625-0.740µm. Green ligth is approximatlelight 0.500-0.565µm. Green light or 0.550µm (0.000550 mm) is a good starting point for the calculations.

The sample image above was taken with an M.Zuiko PRO 40-150 mm f/2.8 with a distance to subject of about 700 mm. Even though this lens has a longer focal length than the M.Zuiko PRO 12-100 f/4 IS, the subject is close to the same size in the frame. That’s because the distance to subject measurements are quite different,  i.e. 700 mm vs 450 mm (~27.6 vs 17.7 inches).

Focal length = the distance from the subject to the lens + the distance from the lens to the camera sensor. You also need to understand if your lens is concave ...

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For higher NA and or for other media than air I recommend the formula from the article “Depth-of-Focus in Microscopy” written by I.T. Young, R. Zagers, L.J. van Vliet, J. Mullikin, F. Boddeke, H. Netten. To get the “normal” 2-sided DOF I have multiplied their formula with a factor 2.

One of the attributes of a lens that is sometimes overlooked is its minimum focusing distance. There are many important factors to consider when investing in a new lens such as focal length, aperture, lens construction/weatherproofing, sharpness and colour rendition. So, it is not surprising that minimum focusing distance is sometimes not given much consideration.

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