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04-22-2011, 12:23 PM   #1
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b4 mount to k mount? video lens on SLR?

I am sure this is not possible but i have to ask.
Can you put a b4 mounted video lens on a k mount SLR. I have seen Cmount to Kmount adapters, I have seen b4 mount to C mount adapters. I predict that combination will not project the image on the sensor correctly, right? (how off in and what direction?)

I ask because the local university surplus has a different b4 lens on the sale rack every couple weeks or so. They normally sell for $10-30 after being listed as 50 for 3 months with no takers. A Canon PH15X7B (7-105mm) is there now, perfect shape, HUGE objective lens. like these (the servos are removable)


Hate to let these pass me by if there is any way to make them fit.
I have seen (online) people put B4s on canon eos slrs before (cant seem to find the link today).
Thanks

04-22-2011, 12:56 PM - 1 Like   #2
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PK-mount register (flange focal distance) is 45.46mm. C-mount register is 17.526mm. C-mount cine lenses won't work on Pentax, can just barely finessed to work on Sony NEX. But B4-mount register is 48mm, nicely beyond Pentax, so it CAN be aadpted with infinity focus -- in fact, there is almost 2.5mm margin.

I am not familiar with B4-C-mount adapters. But I *do* have a C-M42 adapter, a simple 25-42mm step ring (wide flat disc really). You should be able to use a chain like this:
B4 lens --> B4-C adapter --> C-M42 adapter --> M42-PK adapter --> Pentax camera
The M42-PK adapter should be a cheap safe flanged NIF (no infinity focus) type. Its flange reduces the register disparity to about 1.5mm. You can probably finesse that by just not screwing-down all the adapters tightly, maybe using white glue or gaffers tape to hold them in place.

Yes, the adaptation sounds quite do-able. Hay, if you see any extras selling for US$10, I'll take one! Or more! PM me, ok?
04-23-2011, 06:29 AM   #3
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Thanks for the insight RioRico. (Rio see PM) The mount distances will help me figure this out.
Unfortunately b4 mount to C, or B4 to most anything is pretty expensive, very expensive. like 4 or 3 figures.

I really wish I had a mill to make mount adapters.

Last edited by cadmus; 04-23-2011 at 03:03 PM.
04-23-2011, 02:22 PM   #4
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QuoteOriginally posted by cadmus Quote
I have seen (online) people put B4s on canon eos slrs before (cant seem to find the link today).
I was mistaken. It was PL mount that the canon 7D slrs can be modified to take. As shown here:
Chrosziel DSLR accessories and carbon design - editorial-content | TVBEurope Magazine Online & In Print
PL to Canon EF Mount Film and Digital Times: News
Original link is gone.


QuoteOriginally posted by RioRico Quote
The M42-PK adapter should be a cheap safe flanged NIF (no infinity focus) type. Its flange reduces the register disparity to about 1.5mm.
Ohhhh I think that answers an other issue i had. So your saying a M42 on one of these is able to focus to infinity if using a proper m42 lens but these can not because the flange because the sensor is then the width of that flange too far away.


QuoteOriginally posted by RioRico Quote
PK-mount register (flange focal distance) is 45.46mm. C-mount register is 17.526mm. C-mount cine lenses won't work on Pentax, can just barely finessed to work on Sony NEX. But B4-mount register is 48mm, nicely beyond Pentax, so it CAN be aadpted with infinity focus -- in fact, there is almost 2.5mm margin.
Where are you finding stuff like this? Is this listed somewhere? You and several other shoot these specs out so quick? So that i save some of your time in years to come how do i calculate or look it up?



It seems complicated to have so many adapters, and expensive.
Since i don't need it to be a B4 I wonder if i can unscrew the b4, attach a threaded 42mm tube to the end to a flanged m42 to K adapter? Those are cheap. Better would be 2 m42 tubes one with reverse thread and a female threaded collar to fine adjust the length.

I got lots of similar projects rattling around in the vacuum I call my head. Like this one. And this one. I wonder if having some aluminum tube with the same tread and diameter as an m42 would be a good platform for all of them. Where would one buy that?
Man, I need a metal shop.

So the sensor on a b4 mounted video camera is likely not the same as my k200d. How will that alter the image?


Last edited by cadmus; 04-23-2011 at 03:19 PM.
04-23-2011, 03:24 PM   #5
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QuoteOriginally posted by cadmus Quote
Where are you finding stuff like this? Is this listed somewhere? You and several other shoot these specs out so quick? So that i save some of your time in years to come how do i calculate or look it up?
Wikipedia has a nice list of all the flange distances. After that it's just memorization.

Lens mount - Wikipedia, the free encyclopedia
04-23-2011, 06:06 PM   #6
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QuoteOriginally posted by cadmus Quote
Ohhhh I think that answers an other issue i had. So your saying a M42 on one of these is able to focus to infinity if using a proper m42 lens but these can not because the flange because the sensor is then the width of that flange too far away.
Exactly right. The wide-flange NIF (no infinity focus) adapter is 1mm thicker than the thin-flange adapter, and so is fine for applications where infinity is irrelevant, or for modding other-mount lenses.

QuoteQuote:
Where are you finding stuff like this?
I copy the Wikipedia data that boriscleto mentioned into my own database, juice it up a little, and don't bother memorizing it. Except 45.46mm -- that's burnt into my cerebellum somewhere. Hmmm, I should update that Wikipedia page someday soon.

QuoteQuote:
It seems complicated to have so many adapters, and expensive.
Welcome to GearLand. The admission charge is infinite.

QuoteQuote:
Since i don't need it to be a B4 I wonder if i can unscrew the b4, attach a threaded 42mm tube to the end to a flanged m42 to K adapter? Those are cheap. Better would be 2 m42 tubes one with reverse thread and a female threaded collar to fine adjust the length.
That sounds like a plan. As I said, I am totally unfamiliar with the B4 mount, so I don't know how it's attached or anything. But my friends in mount-modding are 1) cheap M42 & PK macro tubes, 2) cheaper M42 & PK body caps, 3) really cheap PVC pipes, 4) contact cement, and 5) many M42, PK, T2, and other adapters and step rings.

QuoteQuote:
So the sensor on a b4 mounted video camera is likely not the same as my k200d. How will that alter the image?
From my paltry research, it seems B4 cams use "2/3 inch" sensors, 6.6x8.8mm with an 11mm diagonal. That's in the neighborhood of 16mm cine. Compare to our APS-C sensors, around 16x24mm with ~28mm diagonal. That B4 lens likely projects an image circle less than 16mm in diameter. So you'll probably get a nice circle centered in your camera frame. It's probably the same effect as putting a 49-20mm step-down ring onto a Takumar, eh?
04-23-2011, 06:21 PM   #7
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QuoteOriginally posted by RioRico Quote
I copy the Wikipedia data that boriscleto mentioned into my own database, juice it up a little, and don't bother memorizing it. Except 45.46mm -- that's burnt into my cerebellum somewhere. Hmmm, I should update that Wikipedia page someday soon.
Too late.
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