Ivanichek Petzvar 120mm to Bronica conversion

[shawn]

Working toward trying to convert the Ivanichek 120mm Petzvar from Pentacon 6 to early Bronica mount for the S2/EC series of cameras.

If you remove the trim ring/mount from the Petzvar the remaining portion of the lens has a diameter of 72mm. That will *just* fit inside of the Bronica without its helicoid in place. I have a large bayonet adapter design and printed that recesses the Petzvar a few additional MM into the camera. If I keep it flush with the surface it focuses to about 22 feet. With the recess (about 3mm) the furthest focus point is about 100' away.

The circles on the recess is the location of the 3 mounting screws on the Petzvar.

My current problem to work through is the location of those 3 mounting screws is not ideal as they cross partway into the throat of the adapter.

That might take out too much strength in the throat for this to work. I also might not have enough thickness in the adapter to recess the heads of the screws, I can gain more back by reducing the recess for the lens but then I loose some distance focusing.

The lens does have another section that I think I can remove (about 5mm thick) but it houses the keys for the helicoid so I'd need to see if I can transfer that to the adapter.

Even without the mounting screws this is such a close fit the lens mounts into the adapter and stays in place based on friction itself.

 

[shawn]

The big thing I don't know yet is if this is going to clear the mirror(s). The Bronica 100mm on the helicoid recesses about 25mm into the body. I need to measure the Petzvar better but I think it is less than that.

 

[Vince Lupo]

Pretty nice job - looking forward to seeing some photos from it.

 

[shawn]

I could almost shoot it as is but I want to get the lens better held in place so I don't have any issues.

This is just a quick shot of the focus screen to see what distance focus looks like, this is wide open so it is pretty close and it looks better on the screen compared to this snap.

The helicoid in the lens itself might have more movement too. There is a hard infinity stop, if that comes out the lens might screw in further which would help with my mounting. Externally, it looks like there is another 5mm or so before the aperture ring would have interference, don't know if the helicoid has that or not.

 

[shawn]

Removed the infinity stop but there no more movement in the helicoid. I was able to make the throat a bit thicker for more strength and also extended it into the body 10mm to cover the exposed helicoid on the lens. If all works I'll put a cap on it to cover everything but the optics.

Just starting the print, will see if it fits in about half an hour.

 

[shawn]

It does fit and the screws line up and mount fine. Had to switch to M2 x 4mm to attach the adapter.

and it does protrude less than the 100mm in the helicoid.

I'm making one last tweak and extending the exterior of the adapter to cover the gap at the top of the helicoid. The decorative ring originally covered this space

After that it will be ready to shoot, though the light is going away so it might be a little bit before I had pictures to show.

 

[shawn]

It works and no problems with mirror interference. I had to move the lens out slightly (1mm) to give the screw holes a little more strength.

Click the pic to see it in action.

IMG_5680

 

[Retro-Grouch]

You undertake some pretty amazing projects! And, even better, they work! 😀

 

[shawn]

Thanks, I was pretty psyched this one panned out. 3d modeling/printing is just so handy. It still blows my mind I can design a part while sitting on the couch, then hit few buttons (still on the couch) to fire up the printer, wait 30 minutes and go down to the basement to retrieve the physical object. Ended up with 14 prototypes on this project.

Next up is converting my Pentacon 6 mount Arsat 30mm fisheye to the Bronica.

 

[brianssparetime]

This is super cool.

I've been considering trying to do exactly this (as well as exploring other ways of finding a petzval-like lens for the Bronica). My thoughts were more along the lines of removing the focusing helicoid from the Ivanichek, and adapting the optical block to fit within the Bronica helicoid. Curious why you didn't take that approach....

Would you be willing to share your design? I'd love to do a similar mod.

I'm also very interested in the Arsat Fisheye. I've played with a Sankar .42x Fisheye attachment, which I found recommended on one of the old smonaghan pages. On the Nikkor 75mm lens, it vignettes heavily, and on the Zenzanon 100mm, it's a much more manageable fisheye. But it's far from sharp, and the CA is horrendous.

FWIW, my small contribution towards making the S2/EC platform the best in the world is making a CAD/guide for a laser cut plate that adapts a Kiev 88 metered prism to the S2, as a much brighter and better option than the native metered chimney or prisms.

 

[shawn]

Thanks, the STL is attached. This has 2mm of thickness for the screws to hold onto. That prevents focusing to infinity and really limits it to around portrait distance wide open. I originally had that at about 0.6mm but I was worried that wasn't enough strength to hold onto the lens.

I like your prism adapter. I have the S2 meter and it is a mess.

To add to the S2/EC I made a hood/filter holder for the 40mm. Haven't tried that fisheye adapter but have started using the Canon Wide Converter WD-H72 but not on the Bronica yet. It seems like it will cover the Pentax 6x7 45mm though.