Zenit Helios & Jupiter M42 Mounts to Nikon Conversions:

Warning - Error Code on FX Nikon Bodies 

This article covers all M42 lens conversions including:
- Zenit Helios 58mm f 2 - Model 44 , 44M2 through 44M8

                                             (44, 44-2, 44-3, 44-4, 44-5, 44-6, 44-7, 44-8)

- Zenit Helios 50mm f1.8 Model 77 - all variants  

- Select Zenit Helios 50mm f2 - Model 81 variants with generic M42 conversion                                                          mounts without automatic aperture

- Zenit Zenitar M 50mm f1.9

- Russian Arsat 50mm f1.4

- Russian KMZ Jupiter 9 85mm f2

- Russian KMZ Jupiter 11 and 37: 135mm - all variants

- Russian KMZ Jupiter 21 200mm f4

- All other lenses with M42 mounts that were converted to Nikon F

(It is important to note that this excludes the Zenit / Zenitar Helios 40M1 and 40M2 (40-1, 40-2) 85mm f1.4 and f1.5, as these lenses were manufactured with Nikon mounts and are not conversions!)

 

Old lenses have become popular in recent years due to their special optical qualities and flaws that can generate great artistic effects.  Many of these lenses are former Soviet-era lenses with M42 screw mount originally made for Praktica and Zenit cameras as well as for the export market (Pentax bodies).  The proliferation of M42 / Nikon F conversion mounts has made it easy for an entire cottage industry of conversions to flood the internet market.

 
The addition of a Nikon F mount converter does cause problems, the distance of the lens to the focal plane changes and causes the lens not to reach infinity.  Many technicians take different steps to resolve this problem which is not the subject of this article. 


There are two additional problems that are of great concern.  Some conversions place the rear element (or the rear element housing) too far into the mirror box, which causes the mirror to hit or scrape the lens. It is critical to verify clearance or measure the projection into the mirror box in order to avoid potential mirror damage. 

Many photographers hear or feel a distinct “thump” sound when pressing the shutter release. Most assume that it is the mirror hitting the lens, and after checking for clearance, they assume that it is the normal sound of a clunky old lens.

 
What is actually happening is that the body aperture lever (which normally closes the lens aperture on an AI lens) is hitting or scraping the lens mount.  This will damage the operation of the camera and some bodies (D800 / D810 / D850) will display an error message after each exposure.  These bodies are equipped with a safety system alerting the photographer of a problem. Clearing the error message is done by switching the camera on and off. 

More concerning are those models that do not display an error message and are used inconspicuously, leading to camera damage.

 

The image below shows the scraping done by the camera lever hitting the conversion mount. Note that it is on the opposite of the lens mount lock.

 
It is recommended that the lens / mount is inspected in order to determine that there is enough clearance for the camera lever to travel properly.  A scratch or wear mark on the paint or anodizing is a certain indicator of a problem.  An easy way to confirm clearance is to apply an even amount of marker with a white grease pencil over that area.  A scrape or contact area will immediately be noticeable. 


If the camera lever hits the mount, a crescent or half moon shaped clearance cut should be made into the mount with a Dremel type rotary tool.  Before attempting this, it is important to seal off all optics as metal shavings/dust will contaminate the lens optics and mechanism.  It is important to cut away enough metal from both sides of the contact area, as the lever needs to travel further and unobstructed from the contact marking that revealed the problem.

 
Below you will see a crude cut done with a Ryobi rotary tool.  The photo was taken before any final polishing was done.  The lens was tested several times during the cutting process in order to guarantee that the new clearance was deep and wide enough.


Once the cut was completed, the lens and camera performed flawlessly and the alarming “thump” sound disappeared immediately.   
 

 

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