Lens: Minolta 12.5mm f/2 Rokkor-X bellows

Vintage: Uncertain.

Lens Mount: RMS

Needed Adapters: I use a RMS to t-mount adapter (from eBay) and a T-mount to Nikon adapter.

Preferred Mounting: Normal, not reversed

Filter Thread: None

Street Price: $250-$500 in good used condition. Prices vary a lot online, shop around.

Controls: Aperture setting

Aperture: 6 blades

Basic Function: Requires a bellows to set focus and magnification

Extension Magnification Working Distance
5 cm 9.1 7.5 mm
9 cm 12.2 7 mm
13 cm 15.4 7 mm
19 cm 20.2 6.5 mm
Est. Focal Length: 12.6 mm


minolta 12mm top view minolta 12mm side view

aperture graphResolution vs. Aperture:

The sharpest aperture is f/2.8 and the most resolving aperture is f/2. I prefer to use f/2.8 for most images because of the improved sharpness and only slightly less resolution. I wouldn't go any higher than f/2.8 because of the diffraction penalty. At 20:1 and an aperture of f/4 you will have an effective aperture of f/84 - not ideal. To get a reasonable picture, image stacking is necessary since the depth of field is razor thin.

corner sharpness graphCorner Sharpness vs. Aperture:

The corner performance of this lens is good to very good. Despite being at its worst at f/2.8, the slight decrease in corner performance is not particularly visible in images.

Testing done at 9:1 magnification. Numbers at each aperture setting will tend to improve as the magnification is increased and worsen as the magnification is decreased.

resolution graphSharpness and Resolution vs. Magnification:

This lens shows good sharpness and resolution across its usable magnification range of 9x - 20x. Compared to other lenses in its magnification range - other short focal length bellows lenses and microscope objectives - this lens does well against other bellows lenses but not as good as microscope objectives.

This lens has good corner performance - as good as or better than most lenses in this magnification range that I have tested.

At maximum magnification, this lens can resolve details down to about 1um, probably slightly better at f/2.

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 Minolta 12.5 score very good in sharpness across the board. The only lenses that will significantly beat this lens are microscope objectives.

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.

Minolta 12.5 show good resolution performance across the range. Again, microscope objectives are the only way to significantly improve on these ratings.

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 resolution, although losing some steam at the highest magnification. May be best to use f/2 at the highest magnification, will lose some sharpness, but should gain some resolution.

lateral CA graphChromatic Aberration:

This lens show minimal color fringing in the center and even better on the periphery (0.010 - 0.030%). Less than 0.04% is considered insignificant. This lens shows mild longitudinal CA on out of focus details and no significant long CA at the focus plane (see image below).

Longitudinal CA:

axial CA

Image Contrast: Image contrast is good across the magnification range. Not as good as a microscope objective, but good by any other standards.

Flare: This lens shows no significant flare during testing.

Distortion: This lens shows no significant distortion during testing.

Image Samples:

About 9:1 magnification, f/2.8, focus stack of 77 images, resized:

sample image

crop imagePixel level crop from the image above:

There is very good pixel level detail, no problems.

About 15:1 magnification, f/2.8, stack of 43 images, resized:

sample image

crop imagePixel level crop from the image above:

There is good pixel level detail, no problems.


This is a fairly hard to find lens that isn't too expensive. There really aren't that many choices in this magnification range - mainly Leica 12/2.4 and Zeiss Luminar 16 mm in the bellows lenses and 10x and 20x microscope objectives. Microscope objectives are the gold standard for resolution in the center of the field, but the bellows lenses tend to be more flexible and tend to have better performance in the corners.

This lens has good resolution and sharpness, but it does get slightly outperformed by microscope objectives owing to their larger apertures. It performs favorably compared to the Leica. I haven't tested a Luminar 16mm.

This lens has good to very good corner performance. There is very little loss in resolution or sharpness even in the extreme corners of the frame. This lens has extremely good CA performance in the corners. It does have a little longitudinal CA on out-of-focus details, but for me, at this magnification, I mostly want everything in focus anyway and use focus stacking to achieve that.

This lens has a magnification range of about 9:1 to 20:1 on a bellows. That means extremely narrow depth of field and typically focus stacking. Getting a good fine focus isn't always easy in this range. I prefer to use a micrometer stage to move the object I am imaging to get the focus (just like on a microscope). You can also use fine control of the extension to get the focus. Either way you will need a very stable setup to get the best out of this lens.