Lens: APO El-Nikkor 105 mm f/5.6 enlarging lens
Vintage: 1960's?
Lens Mount: M39.
Needed Adapters: An M39 to Nikon adapter will suffice for mounting this lens in normal or reversed configuration.
Preferred Mounting: Normal, for below 1:1. Reversed for above 1:1.
Filter Thread: 40.5 mm.
Street Price: Typically upwards of $2000 in good used condition.
Controls: Aperture setting.
Aperture: 8 blades.
Basic Function: Requires a bellows to set focus and magnification.
Extension | Magnification | Working Distance |
7.5 cm | 0.28 | 444 mm |
10 cm | 0.52 | 271 mm |
13 cm | 0.81 | 200 mm |
16 cm (rev) | 1.18 | 187 mm |
19 cm (rev) | 1.47 | 147 mm |
Est. Focal Length: 104.3 mm |
Appearance:


Resolution vs. Aperture:
This lens is at its sharpest and most resolving at f/5.6, although f/6.3 and f/7.1 are very nearly as good.
Corner Fuzziness vs. Aperture:
There is visible corner fuzziness at the sharpest aperture of f/5.6. Corner fuzziness improves rapidly and by f/8 is very good and above. If you want sharper corners, you can certainly feel good shooting images at f/7.1 or f/8 as there is very little loss in sharpness or resolution.
Lateral CA vs. Aperture:
There is consistent minimal/mild lateral CA at all apertures. No problems here.
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.
Sharpness varies from outstanding at lower magnifications to good at higher magnifications.
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.
Resolution is predominantly very good with a small amount of outstanding at the lowest magnifications.
Corner Fuzziness vs. Magnification:
Corner fuzziness at f/5.6 gets worse as the magnification rises toward 1:1. Above 1:1, with the lens reversed, the corner fuzziness starts to improve as one would expect in this situation. This behavior suggests that this lens is optimized for some magnification below 1:1 when mounted normally.
Resolving Power vs. Magnification:
This graph represents the smallest details that are able to be resolved by this lens at various magnifications. If the number doesn't get smaller as the magnification rises, there is little benefit to going up in magnification with this lens. This situation is also called empty magnification.
Resolving power at f/5.6 improves throughout the magnification range, no problems.
Chromatic Aberration:
This lens show minimal color fringing in the center (about 0.06 - 0.26 pixel) and minimal/mild on the periphery (0.023 - 0.052%). There is a peak around 1:1 compatible to the corner fuzziness.
There is the slightest amount of axial CA on out-of focus details (see image below) compatible with apochromatic correction.
Longitudinal CA:

Image Contrast: Image contrast is very good, similar to high-quality macro lenses.
Flare: This lens shows no significant flare during testing.
Distortion: This lens shows no significant distortion during testing.
Image Samples:
About 0.6:1 magnification, f/5.6, resized:

Pixel level crop from the image above:
There is very good pixel level detail, no problems.
Pixel level crop from the corner:
There is slight fuzziness in the corners, not bad.
About 1.2:1 magnification, f/5.6, stack of 12 images, resized:

Pixel level crop from the image above:
There is good pixel level detail, no problems.
Pixel level crop from the corner:
There is slightly worse corner fuzziness at this magnification.
Conclusion:
The APO EL-Nikkor 105 mm f/5.6 enlarging lens is a very good although very expensive lens. It has central sharpness and resolution compatible with high quality macro lenses, high contrast, very little CA. It's main limitation is in its corner sharpness. This limitation is likely related to the lens being optimized for a magnification somewhere below 1:1, compatible with its being an enlarging lens. This means that its performance when mounted normally worsens as the magnification rises toward 1:1. To combat this decrease in performance, the lens should be reversed above 1:1. With the lens reversed, the performance will improve again as the magnification rises beyond 1:1. Reversing this lens is easy in that it has a built-in M39 thread on the front of the lens (covered by a black ring during normal usage). Increasing the aperture to f/7.1 or f/8 will also improve the corner performance at all magnifications with very little loss in sharpness or resolution.
All-in-all this is a very good lens for macro work although the price and rarity of this lens is what would scare me off.