Lens: Nikon PlanApo 4x/0.20 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: $400-$900 in good used condition. Prices vary a lot online, shop around.
Controls: None.
Aperture: The aperture is fixed at a numerical aperture of 0.20 - corresponds to about f/2.
Basic Function: Requires a bellows to set focus and magnification
Extension | Magnification | Working Distance |
5 cm | 2.84 | 16 mm |
9.3 cm | 4.00 | 14 mm |
13 cm | 4.94 | 12 mm |
19 cm | 6.48 | 10.5 mm |
Est. Focal Length: 38.4 mm |
Appearance:


Corner Sharpness vs. Magnification:
The fuzziness on the periphery of the image is moderate for this microscope objective, but within the range of normal. Microscope objectives tend to concentrate on sharpness and resolution in the center of the field.
Testing done on a Nikon D200, a DX format digital camera (APS-C). On a full-frame camera the performance would be significantly worse. 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.
Sharpness and Resolution vs. Magnification:
This lens shows the highest sharpness and resolution in the center of the field that I have tested in this magnification range. Much higher than any other lens that I have yet tested. The performance is optimized for 4:1 magnification and falls off on either side.
Performance: 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 4x plan APO is in the outstanding category for all except the highest magnification for sharpness.
Performance: 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 4x plan APO is in the outstanding category for all magnifications for resolution.
Resolving 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.
Outstanding resolution, no problems.
Chromatic Aberration:
This lens shows fairly severe color fringing on the periphery, worst at lower magnifications. It varies from 0.044% at the highest magnification (minimal) to 0.48% at the lowest magnification (quite strongly visible in the right conditions). Just because a lens is apochromatic doesn't mean that there are no color fringes. Microscope objectives are made to work best in the center of the frame and are not made to cover a large detector.
This lens show very little axial CA (see image below). This is where apochromatic correction shows its stuff.
Longitudinal CA:

Image Contrast: Image contrast is extremely high 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 71 images, resized:

Pixel level crop from the image above:
This is as good as you are going to see at 4:1. You can see a little of the soft corners on the above image, not bad though. The strong measured CA in the corners is not particularly visible in real world images.
About 6.5:1 magnification, stack of 45 images, resized:

Pixel level crop from the image above:
Again, as good as you will see at this magnification.
Conclusion:
This is an objective that works very well as a bellows lens. The center field sharpness and resolution is higher than any other lens that I have tested from about 3:1 to 6:1. This lens is the standard by which all are compared in this magnification range (hyperbole, but true). This lens has fairly severe color fringes on the periphery, but not particularly noticeable in real world images. Due to the apochromatic correction, there is almost no axial CA present. This lens produces extremely high contrast images and has no visible flare.
This lens has a very large aperture for the magnification (working f-number of f/2.5 at m=4, equivalent to a f/2 lens since most lenses don't list a working f-number/NA). That means very little DOF in your images. Image stacking is important and it will take more images for your stack because of the large aperture.
The corner sharpness is OK but not as good as most bellows lenses. This lens was made to produce high resolution in the center and is not made to cover a large detector. It works well on a DX D200, but will have a harder time working well on a full frame detector (like a D700). It should work really well on the small detector interchangeable lens cameras such as micro 4/3 and Nikon 1 system. Working distance is adequate. These are hard to find on eBay and tend to be expensive.