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Lens: Nikon Plan 4x/0.13 phase microscope objective

Vintage: 1990's.

Lens Mount: RMS.

Needed Adapters: RMS mount adapters come in various forms. Some can be found to directly connect to a specific lens mount as this mount is also shared by many small bellows lenses. I use an RMS to T-mount adapter and then a T-mount to Nikon f-mount adapter. T-mount adapters are available for virtually all camera lens mounts.

Preferred Mounting: Normal, not reversed.

Filter Thread: None.

Street Price: $150-$250 in good used condition. Prices vary a lot online, shop around.

Controls: None.

Aperture: The aperture is fixed at a numerical aperture of 0.13 - corresponds to about f/3.1.

Basic Function: Requires a bellows to set focus and magnification.

Extension Magnification Working Distance
5 cm 3.12 16.5 mm
9 cm 4.13 15 mm
13 cm 5.15 13.5 mm
16 cm 5.93 12.5 mm
19 cm 6.70 11.5 mm
Est. Focal Length: 39.0 mm

Appearance:

nikon 4x phase top view nikon 4x phase side view

corner sharpness graphCorner Sharpness vs. Magnification:

The fuzziness on the periphery of the image is moderate for this microscope objective. They do improve to decent above a magnification of about 5:1. Despite the relatively high numbers, when imaging with appropriate sharpening, the corners are relatively sharp.

Compared to the previously reviewed Nikon MPlan 10x, it is considerably worse. This is not an objective that you will want if you desire extremely sharp corners.

Microscope objectives don't tend to produce a large image circle and don't tend to work all that well on full-frame digital cameras or at magnification levels considerably below their intended level. This objective shows mild vignetting (darkening of the corners) at the lowest magnification I tested (3.1:1). The vignetting resolves by the time you get to a magnification around 4:1.

resolution graphSharpness and Resolution vs. Magnification:

This lens shows very high resolution, but only good sharpness in the center of the field. I am not sure if the loss in sharpness is related to the fact that it is made for phase contrast microscopy and has a phase ring (etched ring on the glass as seen from the rear). I need to get a non-phase version of this objective to review. Despite the relatively low values for sharpness, the images it produces are very high quality.

The resolution is quite good though and the object can resolve details of about 1.5 um when used at the highest extension (19 cm). Very few lenses that are not microscope objectives can compete with this lens' resolution across its usable magnification range (4:1 to 7:1).

performance:sharpness graphPerformance: Sharpness vs. Magnification:

I have 4 lines that represent levels of performance from outstanding (top) to fair (bottom). This shows where this lens fits into the hierarchy that I have created.

The Nikon 4/0.13 Phase shows sharpness performance that is predominantly good across the magnification range of 3:1 to 6.7:1.

performance:resolution graphPerformance: Resolution vs. Magnification:

I have 4 lines that represent levels of performance from outstanding (top) to fair (bottom). This shows where this lens fits into the hierarchy that I have created.

The Nikon 4/0.13 Phase shows resolution performance that is very good to good across the magnification range of 3:1 to 6.7:1.

resolving power graphResolving Power vs. Magnification:

This graph represents the smallest details that are able to be resolved by this lens at various magnificaitons. If the number doesn't get smaller as the magnification rises, there is little benefit to going up in magnificaiton with this lens. This situation is also called empty magnification.

Good to very good resolution, no problems.

Chromatic Aberration:This lens show moderate color fringing in the center (about 0.50-2.0 pixels) and fairly severe on the periphery (0.7-5.4 pixels). Color fringes are another factor that microscope objectives tend to have depending upon the price of the objective. The most expensive, apochromatic objectives have the least, while the least expensive tend to have quite a lot. This objective falls in the middle of the spectrum.

Image Contrast: Image contrast is very good for this magnification range. This is another area that microscope objectives tend to excel.

Flare: This lens shows no significant flare during testing.

Distortion: This lens shows no significant distortion during testing.

Image Samples:

About 4:1 magnification, focus stack of 24 images, resized:

sample image

crop imagePixel level crop from the image above:

There is very good pixel level detail, no problems.

About 6:1 magnification, stack of 30 images, resized:

sample image

crop imagePixel level crop from the image above:

There is very good pixel level detail, no problems.

Conclusion:

This is an objective that works very well as a bellows lens. The center field sharpness is good but not great (doesn't seem to impact the image that much). The resolution is very high across the magnification range. The corner sharpness is not the highest, but adequate. The working distance is limited, but adequate. Limited working distance is the price you pay for high-resolution. These objectives are sometimes available on eBay and can be generally purchased for a reasonable price.

My guess is that the non-phase version will perform better than this objective. Another issue that may come up with a phase objective is that out-of-focus details will tend to show as a ring instead of a fuzzy circle. It will not affect details that are in focus.

Not all microscope objectives are suitable for this application. The Nikon CF finite tube length objectives are the best that I have come across (includes MPlan and CFN objectives). This objective is a CF finite tube length objective.