Lens: Minolta 12.5mm f/2 Rokkor-X bellows
Vintage: uncertain
Lens Mount: RMS mount
Needed Adapters: This lens is easy to adapt to most cameras. I use a RMS to t-mount adapter
(from eBay) and a T-mount to camera-specific adapter to get it onto my bellows..
(from eBay) and a T-mount to camera-specific adapter to get it onto my bellows..
Preferred Mounting: Normal.
Filter Thread: None.
Controls: This lens only has an aperture control.
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Resolution 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.
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 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.)
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.)
Sharpness 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.
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.
Street Price: ~$250 - $500 in good used condition, hard to find.
Chromatic 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).
(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).
Image Contrast: Image contrast is good across the magnification range. Not as good as a microscope
objective, but good by any other standards
objective, but good by any other standards
Flare: No significant flare is evident during lens testing
Conclusion:
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.
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.
Basic Function: Requires extension tubes or bellows to focus.
Appearance:
Aperture: 6 blades.
Image Samples:
About 9:1 magnification, f/2.8, focus stack of 77 images, resized:
About 9:1 magnification, f/2.8, 1 to 1 crop of a
single source image from above:
Good pixel level detail for the magnification.
single source image from above:
Good pixel level detail for the magnification.
About 15:1, f/2.8, focus stack of 43 images, resized:
About 5:1 magnification, f/2.8, 1 to 1 crop of a
single source image from above:
Again, good detail for the magnification, although you
can see how diffraction is starting to erase detail
compared to what you would see at lower
magnification.
single source image from above:
Again, good detail for the magnification, although you
can see how diffraction is starting to erase detail
compared to what you would see at lower
magnification.
Distortion: There is no visible distortion with this lens.
Performance: Sharpness vs Magnification:
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit 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.
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit 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 vs Magnification:
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Minolta 12.5 show good resolution
performance across the range. Again,
microscope objectives are the only way to
significantly improve on these ratings.
This is a new graph that I recently constructed. I
have 4 lines that represent levels of performance
from outstanding (top) to fair (bottom). This
shows where this lens fit into the hierarchy that I
have created.
The Minolta 12.5 show good resolution
performance across the range. Again,
microscope objectives are the only way to
significantly improve on these ratings.