M42-Nikon Adapter Ring with Glass. Quality Test
In the market, you can find an M42-Nikon adapter with compensating lens. With this adapter, you can mount M42 lenses on a Nikon camera with infinity focusing.
The lens is likely to have multi-coating as molds green tint. This makes me happy.
A bit of theory, or what the adapter has a lens
Compensate lenses there are set to compensate flange focal distance. Flange distance M42 system - 45.5 mm, and the system Nikon F - 46,5 mm. If you mount the M42 system lens on the Nikon camera without this adapter, it will not focus on infinity. Therefore, the glass compensates for the 1 mm flange distance difference.
Helios 44-2 2/58 and the adapter
But it did not happen just like that. Going this way, we lose picture quality because of adding glass to the optical design of the lens and even the backside. I doubt that Chinese manufacturers make these lenses with high-quality glass. So, the first question arises when using this adapter: "And as far as it degrades the quality of the photos?". We carry out a small test.
Quality of M42-Nikon Adapter with Corrective Lens
For the experiment, I mount the Helios 44-2 2/58 on Nikon D3100 and made test shots at aperture f/ 2 and f / 5.6 without an adapter and with an adapter. Here are shots and crop 100% size of these images.
Crop 100% size of the previous image
f/ 5.6 Crop 100% size
As you can see, the sharpness deteriorated, but not so much. In addition to the focal length of the field changed and collapsed on the floor around half aperture stop. On the picture at aperture 5.6, sharpness dropped insignificantly. However, the wider the aperture is open, the more you can see the difference in picture quality. In a heavily veiled diaphragm, quality deteriorates not so much because the diaphragm works for the entire optical system, and resorption of aberration contributes to imaging adapter lens.
Examples are taken with the adapter M42-Nikon with corrective lens
Shootings took with the lens Helios-44-2 2/58 and Camera Nikon D3100. Export expansion from RAW without any post-processing.
M42-Nikon adapter with glass can be easily installed M42 lenses on Nikon camera with infinity safe. But the price for easy mounting it's deteriorating image quality, especially sharpness. So if you want to use the M42 lens on a Nikon camera seriously, better adapt it without a corrective adapter lens.