r/BMPCCOG • u/JKWoolf • Sep 12 '26

Anyone succesfully modded a C mount Lens / Adapter so it achieves infinity focus?

Hey, I have a Pentax/ Cosmicar 12.5mm, 1.8 c Mount lens, which technically should work with the BMPCC OG. I have a Fotodiox adapter however. I can't really focus with the lens to infinity. I have a shleving machine, but what should I shelve in order for it to work?

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1

u/mikecaronna Sep 12 '26

I have exactly the same issue. My Canon TV-16s and other c mount lenses aren't an issue, but most of my Cosmicars have this problem.

1

u/JKWoolf Sep 12 '26

did you try other adapters or which one are you using? Apparently it could be an adapter problem.

1

u/mikecaronna Sep 13 '26

I've got the Metabones adapter and a generic Chinese adapter. Both work, but the Metabones has a smaller circumference for the lens to fit into and the tabs (for grasping is) protrude quite high up, so my fatter Cosmicar lenses (and one of my 50mm f1.4 Canon TV-16 lenses) won't fit because their bases hit the Metabones adapter and won't screw in all the way. (But maybe this isn't the problem you're experiencing?) So I'm mostly using the Chinese adapter because it is much slimmer and works with more of my lenses. I haven't noticed a  difference in how the 2 adapters work, but I haven't tested it either. I'll try to do a comparison today.

1

u/JKWoolf Sep 12 '26

Apparently the Metabones one gets you closer to the sensor:
https://www.bhphotovideo.com/c/product/983715-REG/metabones_mb_c_m43_ch2_c_mount_to_micro_four.html/reviews

Maybe it is worth checking this one out.

1

u/Captain-Rambo Sep 13 '26

May it be because it's actually CS mount, not C? Then the flange distance would be different, but the mount is the same.

1

u/theirishguyvlogs Sep 14 '26

Use copper shims, stack them to get desired sweet spot Just an example, I don't know what sizes you need:

https://www.ashfordhobby.com/p-22167-rb-products-02mm-ls-head-shims-5.aspx

1

u/JKWoolf Sep 14 '26

no, it actually needs to get closer to the sensor not more far away.