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12-12-2015, 03:18 PM   #1
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Adapting Pentax 645 lenses

Hi,
I have been looking at Pentax lens adapters for the K mount and also the Fotodiox RhinoCam adapter.

These systems allow use of A and FA lenses to be mounted.

My main question is this: if I take a look at my 35A and 150FA, the have an aperture ring, but also an aperture lever on the rear of the lens. You can turn the ring, but the lens does not stop down until the lever is turned.

So...do the lens adapters for K mount and the RhinoCam adapters turn the lens aperture lever when you attach the lens to the mount? Is that how it works.

If somebody with experience with these sorts of adapters could comment it would be great.

Thanks

12-12-2015, 03:39 PM   #2
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QuoteOriginally posted by 2351HD Quote
Hi,
I have been looking at Pentax lens adapters for the K mount and also the Fotodiox RhinoCam adapter.

These systems allow use of A and FA lenses to be mounted.

My main question is this: if I take a look at my 35A and 150FA, the have an aperture ring, but also an aperture lever on the rear of the lens. You can turn the ring, but the lens does not stop down until the lever is turned.

So...do the lens adapters for K mount and the RhinoCam adapters turn the lens aperture lever when you attach the lens to the mount? Is that how it works.

If somebody with experience with these sorts of adapters could comment it would be great.

Thanks
The aperture function is essentially the same in all the lenses be it PK, 645 or 67. The lever is how the camera stops the lens down during exposure or DOF preview, while the ring is what determines its travel, e.g. which f-stop determined by which detent you set the ring at. You can see this off-camera like you were looking by selecting a wide open aperture on the ring, then moving the lever - the lens won't stop down because you're set to wide open. Now select a much higher f-stop then move the lever - the lens will stop to whichever setting you've selected.
All the adapters really do is provide a correct distance to the focal plane, a proper mounting lock for the lens mount type, and allow the "different" camera type to interact with that lever.

Short answer = "yes."
12-12-2015, 04:23 PM   #3
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Thanks
So there is a lever in the lens adapter that moves the lever on the lens.

This internal lever must be spring loaded or something since it needs to not only move the lens lever, but also move with the lens as its screwed onto the adapter. Is that correct?
12-12-2015, 05:06 PM   #4
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QuoteOriginally posted by 2351HD Quote
Thanks
So there is a lever in the lens adapter that moves the lever on the lens.

This internal lever must be spring loaded or something since it needs to not only move the lens lever, but also move with the lens as its screwed onto the adapter. Is that correct?
Not quite !! You cann read from the description on each adapter, like this:

" Although the lens will fit physically, automatic diaphragm, auto-focusing, or any other functions will not operate correctly while using this adapter. In this case "stop-down mode" will need to be used when metering since the lens does not have the ability to have its aperture controlled by the camera body. "

12-12-2015, 05:31 PM   #5
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QuoteOriginally posted by RuiC Quote
Not quite !! You cann read from the description on each adapter, like this:

" Although the lens will fit physically, automatic diaphragm, auto-focusing, or any other functions will not operate correctly while using this adapter. In this case "stop-down mode" will need to be used when metering since the lens does not have the ability to have its aperture controlled by the camera body. "
This is where it gets confusing for many... The camera DOES have the ability to stop the lens down, mechanically, which is engaging the lever, but it does NOT have the ability to "read" what the aperture actually is, this is why stop-down metering is necessary. In the case of most Pentax DSLRs the "Green button" achieves this: the camera engages the aperture which travels to the setting chosen on the ring, takes a meter reading, then returns it to wide-open for viewing once more.

QuoteOriginally posted by 2351HD Quote
Thanks
So there is a lever in the lens adapter that moves the lever on the lens.

This internal lever must be spring loaded or something since it needs to not only move the lens lever, but also move with the lens as its screwed onto the adapter. Is that correct?
So..... Essentially, yes. If you have an adapter it's easiest to see how it works with just the adapter mounted so you can watch. The lever sits in a recessed channel inside the mount, sticking out a bit, and makes contact with the body's arm mechanism.


Everything I described above pertains to the functionality of the 67-->645 adapter. Sorry for ADDING confusion. The PK adapters do not have a mechanism for stopping the lens down - it must be done manually, a meter reading taken, then manually returned to open for viewing/composing.

Last edited by chickentender; 12-12-2015 at 06:35 PM. Reason: i was dead wrong
12-12-2015, 05:50 PM   #6
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What is it that do you want to do, do you want to adapt the Pentax 645 lenses to your Pentax DSLR or contemplating a purchase of a RhinoCam adapter (unavailable in PK mount)? I can't help you if you want to buy a RhinoCam adapter, though it's an interesting idea - I've thought about doing something similar to utilize my 4x5 camera. If it's the former, I know for certain the genuine Pentax 645 to K adapter is able to adjust the aperture on the Pentax 645 lenses, there may be other 3rd party adapters capable of doing the same but none of the generic Chinese Pentax 645 to K adapter is capable of adjusting the aperture on the lens. Shooting mode is strictly in Av mode, just like an M42 lens.
12-12-2015, 06:09 PM   #7
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All true above.

(edit - removed wrong information - I was confusing the 67-645 adapter with PK adapter)

It also matters whether or not this important to you. Stop-down metering still works - it's just more work. You can still take a photo.

So, as excanonfd asked.... What the heck do you want to do?

Last edited by chickentender; 12-12-2015 at 06:32 PM.
12-12-2015, 06:12 PM   #8
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QuoteOriginally posted by chickentender Quote
This is where it gets confusing for many... The camera DOES have the ability to stop the lens down, mechanically, which is engaging the lever, but it does NOT have the ability to "read" what the aperture actually is, this is why stop-down metering is necessary. In the case of most Pentax DSLRs the "Green button" achieves this: the camera engages the aperture which travels to the setting chosen on the ring, takes a meter reading, then returns it to wide-open for viewing once more.
What brand of P645 to K adapter do you have that gives you automation equivalent to an M lens mounted on your Pentax DSLR? It's been a long time since I'd looked for an adapter but not even my oem Pentax 645 to K adapter is capable of doing what you've described above.

12-12-2015, 06:28 PM   #9
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QuoteOriginally posted by excanonfd Quote
What brand of P645 to K adapter do you have that gives you automation equivalent to an M lens mounted on your Pentax DSLR? It's been a long time since I'd looked for an adapter but not even my oem Pentax 645 to K adapter is capable of doing what you've described above.
You're absolutely CORRECT. My huge apologies! It is only manual stop-down metering when going to PK mount. I'm so used to my 67-->645 adapter it erased that limitation from my brain. (I've not used the K adapter in forever)
12-12-2015, 06:43 PM   #10
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QuoteOriginally posted by chickentender Quote
You're absolutely CORRECT. My huge apologies! It is only manual stop-down metering when going to PK mount. I'm so used to my 67-->645 adapter it erased that limitation from my brain. (I've not used the K adapter in forever)
No worries, I was just hoping there was something out there that can do that.
12-12-2015, 06:52 PM   #11
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QuoteOriginally posted by excanonfd Quote
No worries, I was just hoping there was something out there that can do that.
Now I remember wishing it as well. Truth be told though, I so rarely pull out a larger lens for a K body that I don't particularly care. There are K lenses that do just as good a job if not better at 1/4 the size/weight.

As to the OP - here: https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/98683-...-aperture.html

These adapters lock the stopdown lever in place so that manual stopdown metering with the aperture ring is the only possibility.
(sorry I made it so long a road to such a simple answer) haha
12-13-2015, 12:22 AM   #12
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What am I wanting to do....

I would like to adapt my lenses to either the new FF, or a K3, plus I want to buy a RhinoCam to use with my Nex6.

I see from the Rhinocam photos that there is some sort of lever.

It appears nobody here has ever used an adapter for 645 to other mounts so it's all speculation.

Just looking at my A35, the stop down lever follows the aperture set lever that's linked to the aperture dial. So there must be 2 levers inside the adapter that are coupled, and they must move with the aperture set lever, and must be on some sort of spring loaded mechanism so that they follow the aperture set lever when the lens is attached to the mount.

Last edited by 2351HD; 12-13-2015 at 12:27 AM.
12-13-2015, 12:39 PM   #13
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QuoteOriginally posted by excanonfd Quote
What is it that do you want to do, do you want to adapt the Pentax 645 lenses to your Pentax DSLR or contemplating a purchase of a RhinoCam adapter (unavailable in PK mount)? I can't help you if you want to buy a RhinoCam adapter, though it's an interesting idea - I've thought about doing something similar to utilize my 4x5 camera. If it's the former, I know for certain the genuine Pentax 645 to K adapter is able to adjust the aperture on the Pentax 645 lenses, there may be other 3rd party adapters capable of doing the same but none of the generic Chinese Pentax 645 to K adapter is capable of adjusting the aperture on the lens. Shooting mode is strictly in Av mode, just like an M42 lens.
QuoteOriginally posted by 2351HD Quote
What am I wanting to do....

I would like to adapt my lenses to either the new FF, or a K3, plus I want to buy a RhinoCam to use with my Nex6.

I see from the Rhinocam photos that there is some sort of lever.

It appears nobody here has ever used an adapter for 645 to other mounts so it's all speculation.

Just looking at my A35, the stop down lever follows the aperture set lever that's linked to the aperture dial. So there must be 2 levers inside the adapter that are coupled, and they must move with the aperture set lever, and must be on some sort of spring loaded mechanism so that they follow the aperture set lever when the lens is attached to the mount.

Yes, Rhinocam has an adapter for Pentax 645 lenses but the NEX itself has no actuating lever of any kind!
12-15-2015, 02:10 PM   #14
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QuoteOriginally posted by RuiC Quote
Yes, Rhinocam has an adapter for Pentax 645 lenses but the NEX itself has no actuating lever of any kind!
Do you have a RhinoCam and the Pentax 645 adapter? If so, can you answer the Op's concern of being able to adjust the aperture on the Pentax 645 lens mounted on the RhinoCam? Because there are many more Pentax 645 to K adapters that only let you shoot wide open than adapters that can adjust the aperture (for sure, the oem 645 to K adapter).
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