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09-19-2015, 06:20 AM   #1
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Trouble Mounting an M42 lens via an M42-K Adapter onto K-mount Bodies

Hi.

I have a question for screwmount aficionados:

I have (carefully) tried mounting this lens, using a (genuine Pentax) M42-K adapter, to 3 different Pentax K-mount bodies (ME Super, K20D, K-3), and it seems to me that the lens cannot be mounted successfully.

[The M42-K adapter goes on and off the lens, and into and out of the body K-mount, both just fine.]

I have tried mounting the adapter to the body first, and I have tried mounting the adapter to the lens first, and, in each case, the chrome aperture tab (the one that protrudes slightly from the semicircular slot on the lens flange) bumps into all of the K-mount screws and electrical contacts, and, as the chrome tab starts contacting the K-mount flange surface, the aperture ring on the lens can no longer be moved (plus, the situation screams loudly "don't screw this lens in any more" and/or "don't screw this up any more").



I have not "forced the issue", since I don't want to damage either the lens or a camera, but it is clear that this lens does not want to be mounted on my K-mount bodies.

I have seen such a tab (often appearing longer) in pix of some screwmount lens bases before, so why is it ordinarily not a problem? Or...?

What do the "F/ST" markings on the lens mount mean? "For Screw Threads", or...?

What am I doing wrong?

Thanks for any help or enlightenment offered.


Last edited by fwcetus; 09-19-2015 at 06:48 AM.
09-19-2015, 06:54 AM   #2
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I think that this is for Fujica ST mount at least as I can remember...
also no infinity I think... Do not mount this lens as it is very difficult to get it off.
09-19-2015, 06:54 AM   #3
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F/ST = Fujica ST?

---------- Post added 09-19-15 at 06:55 AM ----------

(RAART was quicker than I)
09-19-2015, 06:59 AM   #4
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F/ST stans for Fujica ST...

As you have noticed it is not fully compatible with other M42 cameras...

09-19-2015, 07:09 AM   #5
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Thanks very much for the info, everyone.

Too bad -- it looks like an interesting lens to play with -- an RMC Tokina 35-105/3.5 Close Focusing Zoom -- (not that I was expecting it to replace my A 35-105/3.5).
09-19-2015, 07:14 AM   #6
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If you remove the locking pin and that pin/lever on the side (used for metering) than you will be able to use it...
09-19-2015, 07:29 AM   #7
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QuoteOriginally posted by fwcetus Quote
Thanks very much for the info, everyone.

Too bad -- it looks like an interesting lens to play with -- an RMC Tokina 35-105/3.5 Close Focusing Zoom -- (not that I was expecting it to replace my A 35-105/3.5).
If you just file off the protruding pin from the lens base, you should be able to mount it onto the m42 adaptor. I have one of the nice EBC Fuiji 70-150 f4.5 lens; the only thing I didn't like about it is that there is no A/M switch to stop down... so I can only use it wide-open.
09-19-2015, 01:33 PM   #8
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There are fixes for that, I believe. Someone who's done it should be able to advise you on how to stop the pin down to give you control back.

09-19-2015, 02:35 PM   #9
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I'm ~FAR~ from an expert here (since I didn't even know what "F/ST" stood for a few hours ago - LOL), but it does seem (to me) that the older Fujica F/ST lenses presented different problems (and involved different fixes for using) on Pentax gear, whether M42 or K-mount, than the later Fujica EBC lenses.

It seems as if the EBC lenses may sometimes get locked onto Pentax mounts due to an aperture locking pin (not unlike some of the Ricoh pins), while F/ST lenses (and, I would think, EBC lenses also) are problematic, due to that tab, for mounting for infinity focus (and, in my case, to prevent that tab from stopping the aperture ring from moving).

It would not seem be helpful in my case to file off that pin (which doesn't exist), but it might be helpful to file down that tab until it was flush with the mounting flange.

However, inasmuch as this was an eBay purchase, and I do believe that the seller just didn't know of this incompatibility, I will send it back before I experiment with it, I think.

Thanks again for everyone's help.

Last edited by fwcetus; 09-19-2015 at 02:43 PM.
09-19-2015, 02:51 PM   #10
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Here's a couple of sources that are (I think) talking about F/ST lenses:

Photographic equipment Folk Lore
"It is this lug (and the lack of it on non Fujinon lenses) that can cause compatibility problems between different manufactures' M42 systems. When auto Fujinon lenses are fitted to other camera bodies, the protruding lug can physically prevent the lens from being screwed fully home. The outcome of this will affect the extreme parameters of focus, but users will only notice the loss of infinity focus. There may also be some impairment of the aperture linkage, due to the gap created by the lug, resulting in failure to achieve full stop-down. Fujinon lenses can be adapted to work with non-Fujica bodies by filing-off the lug."

Fujinon M42 lenses - Rangefinderforum.com
"Something ye'll havetae bear in mind is that Fujinon lenses have a small lug on the lens body; Fujica cameras have a ring round the lens mount which rotates against a light spring pressure. This, coupled with a small stud on the camera body, locks at a precise distance and sets the maximum aperture of the lens being installed. Once the lens installs the metering knows the max aperture, which enables the full aperture framing and focusing. This small lug prevents Fujinon lenses fitting properly on SLRs/DSLRs as they do not fit flush thus preventing infinity focus - or worse. Ah've read that there are adapters available for digital but have been unsuccessful in finding them. The only alternative is tae butcher the lens by chopping off the lug. The lens will then work fully manually."

[I think the above sources are most relevant to my situation.]

And here's a couple of sources that are (I think) talking primarily (but not exclusively) about EBC lenses:

Fujica ST801 - Camerapedia
"The EBC lenses will not be able to mount completely on some other makes because of the open-aperture metering lug on the back of the aperture ring." [I think this would also apply to the older, non-EBC, S/ST lenses.]

Fujica ST801
"An open aperture feature makes the M42 mount non standard and when using a non Fuji lens you may cause difficulties to focus on infinity and what is worse the lens could stuck on the camera." [I am not sure if this is referring to the lug (or tab) or to the pin.]
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