Bolex Kern Yvar 75mm f2.8 Lens Repair

ic-racer · May 4, 2024

I wanted a long lens for my Non-Rex Bolex H8 for the last Eclipse. I did not find on in time, finding a 150mm Yvar for my H8-REX camera.

Finally a 75mm Yvar that I liked did show up. This one is in mint condition with a frozen focus and appropriately low price tag.

It came with the original lens hood and front & rear caps.

This is a C mount lens, but I'll be using it on my H8 Non-Rex Bolex with a "C to D" adapter.

The optics are in great shape and the lens has no signs of tamper. I'll just be fixing the frozen focus.

ic-racer · May 4, 2024

Three screws around the perimeter of the focus ring allow the lens to be disassembled. Make sure to mark the two rotating pieces, otherwise the infinity setting will need to be re-done. This lens, as it is, focuses perfectly at in finity with the "C to D" adapter I got (2.2mm offset).

ic-racer · May 4, 2024

With the focus helicoid removed from the rest of the lens, my example came apart with exactly two turns so I did not need to make a second set of marks.

ic-racer · May 4, 2024

The old grease had turned into something resembling wax.

The multiple grooves are to enable roation of the lens so the marks are where you want them. Some cameras work best with the marks visible from the top, right or left side. In my case, the camera works best if the marks are visible on the left side of the camera.

ic-racer · May 4, 2024

The focus threads were cleaned with alcohol. This looks like simple threads as there is only a single start position.

ic-racer · May 4, 2024

Actually those threads were not frozen. The part that was frozen was the focus ring itself.

To get the focus ring off, the focus stop screw is first removed.

ic-racer · May 4, 2024

Under this caked-on grease there is a screw that needs to be reomved so the serrated piece can un-screw to free the focus collar.

ic-racer · May 4, 2024

After cleaning the old grease, the screw is visible and can be removed. The screw is on the end of the magnetized screwdriver in this picture.

ic-racer · May 4, 2024

The rear serrated piece can now unscrew. The focus ring came off. No mechanical problem here, just hardened grease.

ic-racer · May 4, 2024

Old grease removed and new grease applied.

ic-racer · May 4, 2024

For re-assembly, I want the marks on the lens to face the left side of the camera. That is where the marks on all the other lenses on this turred face.

You can also see the 2.2mm "C to D" adapter between the focus mount and the turret.

ic-racer · May 4, 2024

The focus ring is re-installed, with its focus-stop screw. The serrated tube is screwed back in place and locked with the little index screw.

The focus mount is slid back on the lens, catching the appropriate groove so the numbers align where I wanted them. All the while making sure these two marks stay aligned with each other.

To hold it all together, the three screws around the perimeter of the focus ring are replaced.

ic-racer · May 4, 2024

All finished, ready for use!

dxqcanada · May 4, 2024

Ah, no crusty green-brown hardened grease ... good job, especially as you actually draw your own notes.

Bill Burk · May 4, 2024

Last time I examined a Yvar I thought it had been intentionally locked in place. Was the grease that thick for you? That it wouldn’t budge at all.

ic-racer · May 4, 2024

Bill Burk said:
Last time I examined a Yvar I thought it had been intentionally locked in place. Was the grease that thick for you? That it wouldn’t budge at all.

Yes, very thick. But soluble in denatured alcohol.

Nitroplait · Jan 23, 2025

Thanks for the write up.

I used a similar approach for a frozen 36mm Yvar in D-mount.
I think it is fairly safe because you can separate the optical unit from the focusing helicoid and soak some parts if required to loosen them.

I have a frozen Yvar 13mm with the Visiofocus complication where also the aperture is very stiff. Everything is so tiny, and seemingly require much deeper disassembly. I wouldn’t know here to begin.

Bolex Kern Yvar 75mm f2.8 Lens Repair

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