Lens: Rodenstock APO-Rodagon 75mm f/4 Fixed Aperture
Vintage: Current, but not sure for this particular lens
Lens Mount: M39
Needed Adapters: M39 to camera-specific mount, easily available on eBay
Preferred Mounting: Normal, not reversed
Filter Thread: 40.5 mm
Street Price: $150-$300 in good used condition. Prices vary a lot online, shop around.
Controls: None
Aperture: The aperture is fixed at f/4
Basic Function: Requires a bellows to set focus and magnification
| Extension | Magnification | Working Distance |
| 5 cm | 0.39 | 230 mm |
| 9.5 cm | 1.00 | 120 mm |
| 13 cm | 1.48 | 91 mm |
| 19 cm | 2.29 | 72 mm |
| Est. Focal Length: 73.8 mm | ||
Appearance:
Corner Sharpness vs. Magnification:
The corner sharpness of this lens shows its tuning for 1:1 magnification where the corner sharpness is virtually the same as the center sharpness. The corner sharpness fades significantly on either side of 1:1 magnification.
Testing done on a Nikon D200, a DX format digital camera (APS-C). On a full-frame camera the performance would be significantly worse.
Sharpness and Resolution vs. Magnification:
This lens shows very good center field sharpness and resolution at lower magnifications, outperforming the detector below 1:1.
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 Rodenstock 75/4 is very good to outstanding at 1:1 and below and good below this for sharpness.
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 Rodenstock 75/4 is outstanding below 1:1 and very good above 1:1 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.
No problems here, compatible with its resolution performance.
Chromatic Aberration:
This lens shows minimal color fringing on the periphery at 1:1, and mild to moderate color fringing at magnifications above and below 1:1. It varies 0.004% at 1:1 magnification (minimal) to 0.08 - 0.09% at 0.40:1 and 2.3:1 (moderately visible in the right conditions). This lens is clearly optimized for 1:1.
This lens show mild axial CA (see image below), moreso than I would like with and apochromatic lens.
Longitudinal CA:
Image Contrast: Image contrast is very good although not as high as a modern macro lens.
Flare: This lens shows no significant flare during testing.
Distortion: This lens shows no significant distortion during testing.
Image Samples:
About 1:1 magnification, f/4, resized:
Pixel level crop from the image above:
This lens shows very good fine detail at 1:1, the magnification where it is made to work.
About 2.3:1 magnification, f/4, stack of 8 images, resized:
Pixel level crop from the image above:
Again, no real problems, although you can see a little axial CA in the upper left of the image. This is not a big problem since this is not the magnification this lens is made to run at.
Conclusion:
This is an objective that works very well as a bellows lens as long as you plan on shooting images at 1:1. Once you stray form this magnification, the performance suffers (but not too much). The center field sharpness and resolution is very good. This lens shows minimal lateral CA at 1:1 and moderate above and below this magnification. This fringes are not particularly visible in real world images. There is mild axial CA present, more than is typically seen with an apochromatic lens. I have read in an optical design reference book that there are very few truly apochromatic lenses out there, and most that are labelled APO are really semi-apochromatic.
This lens produces high contrast images and has no visible flare. The corner sharpness is outstanding at 1:1 and deteriorates on either side of this magnification. Working distance is good, but the somewhat short focal length does limit this lens a little for coin imaging below 1:1. I generally prefer lenses 100mm and above.
This lens was made to produce high quality images at 1:1 and it does. The performance slides on either side of 1:1. This tuning for a specific magnification somewhat limits its usefulness in general macro imaging. These lenses are not too hard to find used on eBay and about the price of a typical bellows lens.