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03-24-2017, 03:50 AM   #1
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Why is there no Nikon-F to K adapter without corrective glass?

Correct me if I'm wrong but doesn't the Nikon have a longer flange distance? Wouldn't an adapter that adds a couple millimeters work?

03-24-2017, 04:04 AM   #2
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BUT: There is a minimum adapter thickness needed to fit the bayonet mount and spring latching mechanism for the lens. I have a no-glass Nikon-lens-to-Pentax-body adapter. It's about 10mm thick (I'd have to check the exact size, but it's akin the shortest extension tube in a set of three). I use it to mount an old 600mm f5.6 EDIF Nikon. It eliminates infinity focus, but slightly improves close focus distance. The primary purpose of such a tele is wildlife photography, especially small birds, so the slight improvement in close-focus is helpful, and at the maximum distance the FOV could easily encompass two or three elephants. Set the diaphragm at f8 and use the lens as if it were a fixed-aperture mirror, but without doughnut highlights.

Just did a little checking. Pentax K flange (registration) distance is 45.46mm, Nikon F is 46.5mm, so you have only 1.4mm to fit a Nikon bayonet with its spring latch if you want to retain infinity focus, and that's not possible. And BTW: part of the reason the 600 Nikon works pretty well is that it focuses slightly past infinity, as is common for MF long telephotos (allows for some change of lens length because of temperature, which can be significant in a long lens).

Last edited by WPRESTO; 03-24-2017 at 04:17 AM.
03-24-2017, 04:10 AM   #3
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IIRC the bayonet mounts are close but not quite the same. Some claim to have forced the fit by inverting the Nikkor (so the f-stops are facing down instead of up as is usual), but it then does not lock in place and is a stop-down prospect only. From what I gather, the thickness of adapter required to clear the Nikkor bayonet away from the Pentax mount and interpose a locking Pentax bayonet is also sufficient to mess up the registry distance and require optical correction.

The blessing of the Sony mirrorless cameras is that their registry distance is so incredibly short that any adapter for any DSLR lens system needs extra physical dead space rather than optics. If Pentax ever went mirrorless in a big way, a simple AF/data pass-through collar that shipped with the camera would suffice to make all K-mount lenses compatible (and the argument would then rage over whether one could be built with a powered mechanical contrivance that could stop down Takumar lenses and allow green-button metering with them. This would open the way to a true Spotmatic D, but that's for another discussion).

---------- Post added 24-03-17 at 08:42 ----------

QuoteOriginally posted by WPRESTO Quote
BUT: There is a minimum adapter thickness needed to fit the bayonet mount and spring latching mechanism for the lens.
You got in while I was typing, LOL!
03-24-2017, 04:17 AM   #4
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QuoteOriginally posted by pathdoc Quote
IIRC the bayonet mounts are close but not quite the same. Some claim to have forced the fit by inverting the Nikkor (so the f-stops are facing down instead of up as is usual), but it then does not lock in place and is a stop-down prospect only. From what I gather, the thickness of adapter required to clear the Nikkor bayonet away from the Pentax mount and interpose a locking Pentax bayonet is also sufficient to mess up the registry distance and require optical correction.

The blessing of the Sony mirrorless cameras is that their registry distance is so incredibly short that any adapter for any DSLR lens system needs extra physical dead space rather than optics. If Pentax ever went mirrorless in a big way, a simple AF/data pass-through collar that shipped with the camera would suffice to make all K-mount lenses compatible (and the argument would then rage over whether one could be built with a powered mechanical contrivance that could stop down Takumar lenses and allow green-button metering with them. This would open the way to a true Spotmatic D, but that's for another discussion).

---------- Post added 24-03-17 at 08:42 ----------



You got in while I was typing, LOL!
What if the adapter were to just forgo the bayonet and have it be stop down only? Just make sure it can lock in properly, even if it is upside down.

03-24-2017, 04:30 AM   #5
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RE: You also have to consider the depth of the bayonet mount on the lens itself. If it is not sitting down into the opening on a Pentax, it is already farther forward than the Nikon registration distance. But to mount it, the adapter must have at least one metal plate in back of the lens bayonet which moves the lens outward a bit more. There is a company that makes a replacement bayonet plate that can be fitted to a Pentax DSLR body. It will allow both Pentax and Nikon lenses to be fitted directly on the Pentax, but no lens-latch, which means if you are careless, the lens may fall off while you're holding the camera, or the camera may drop off while you hold the lens. Bad news if you're out on a whale-watch or photographing NYC from atop the Empire State Building.

Just did some additional checking. The replacement bayonet for Pentax bodies is called the "PK + MM Multi Mount." Price: $98.
Features:
1) Nikon, Olympus and Contax-Yashica lenses can be mounted with infinity focus; Konica lenses can be mounted but will not focus to infinity; Pentax K lenses mounted as usual;
2) Some lenses must be modified, for example, the diaphragm actuating lever of C-Y lenses must be shortened or the mirror will strike it;
3) There is no lens-to-camera communication of any kind; no AF, strictly manual diaphragm operation, and no EXIF data (except PK lenses which function normally);
4) The fit is strictly friction, no latches, so a lens may twist and drop off unexpectedly (except for PK lenses);
5) The replacement flange can only be mounted on non-weather sealed Pentax bodies, so it can go on a K20 or K5*, but not on a K3 or K1.

*MAYBE The manufacturer/seller does not list these Pentax bodies as tested-to-be usable.

Last edited by WPRESTO; 03-24-2017 at 05:42 AM.
03-24-2017, 05:12 AM   #6
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QuoteOriginally posted by WPRESTO Quote
Pentax K flange (registration) distance is 45.46mm, Nikon F is 46.5mm, so you have only 1.4mm to fit a Nikon bayonet
My math OCD is acting up: 1.04mm. That's more of a shim plate than an adapter.

QuoteOriginally posted by ZombieArmy Quote
What if the adapter were to just forgo the bayonet and have it be stop down only? Just make sure it can lock in properly, even if it is upside down.
The problem is the bayonets are so similar. If you shim the lens outwards, the F-mount bayonet lugs can't lock into the K-mount bayonet socket, unless you also machine 1.04mm off the forward edge of the bayonet lugs on the lens itself, which may not be desirable or possible. To avoid this, the adapter has to provide a new bayonet socket, which has to be outside the K-mount.

Edit: maybe this will make it clear: take one of your K-mount lenses, insert it almost all the way into your camera (all but about 1mm), then try to turn it. It won't turn because the bayonet lugs are hitting the sides of the socket instead of sliding behind them.

Edit 2: IIRC, the MultiMount plate includes a shim for F-mount lenses.

Last edited by THoog; 03-24-2017 at 05:30 AM.
03-24-2017, 05:37 AM   #7
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QuoteOriginally posted by THoog Quote
My math OCD is acting up: 1.04mm. That's more of a shim plate than an adapter.
I think you slightly misinterpreted my point. It isn't possible to make an N to PK adapter that is only 1.4mm thick. You could not simply put a shim between the camera and the lens because then the lens could not be forced to grip on the Pentax body bayonet. Seems to me there are four choices for mounting a Nikon lens to a Pentax body:

1) Force the lens onto the PK body bayonet in which case if there is a hard stop for infinity on the Nikon lens (eg it is a near normal or WA lens), that infinity stop will be incorrect - you have to focus the lens slightly closer to get infinity.

2) Use a Nikon to Pentax adapter that has a lens in it = basically a simple 1.4X teleconverter. You have infinity focus, but you pretty much defeat the purpose of mounting normal or WA lenses, and IQ will probably suffer more than you'll be willing to accept;

3) Use a glassless Nikon to Pentax adapter, which loses infinity focus but retains the lens' IQ. With normal or WA lenses this would only be good for macro, but with longer telephoto lenses it is a viable method, the longer the lens the more satisfactory it will be.

4) Install a PK + MM multi mount, provided you have a Pentax body that will accept it and you are willing to deal with the various caveats. This method might be attractive if you have a second Pentax body that will accept the replacement flange.

Regardless of the method used, there will be no lens-camera communication, therefore: no AF, no EXIF, and manual diaphragm operation only.
03-24-2017, 05:48 AM   #8
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QuoteOriginally posted by WPRESTO Quote
4) Install a PK + MM multi mount, provided you have a Pentax body that will accept it and you are willing to deal with the various caveats. This method might be attractive if you have a second Pentax body that will accept the replacement flange.
this is the route I was thinking - pick up a second-hand body and swap the mount...

03-24-2017, 05:49 AM   #9
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QuoteOriginally posted by WPRESTO Quote
I think you slightly misinterpreted my point. It isn't possible to make an N to PK adapter that is only 1.4mm thick.
No, no, I understood you perfectly, and agree on all points - I was only correcting the math. (46.5-45.46 = 1.04)
03-24-2017, 06:12 AM   #10
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Remember there is an adapter mount installed on camera, allows for Nikon Konica Contax/yashica and maybe one more other type of lens to be mounted directly on the camera? It still supports Pentax lenses' AF and aperture. A guy in Singapore designed and one posted here. Not all Nikon lenses are supported though.
03-24-2017, 06:14 AM   #11
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QuoteOriginally posted by WPRESTO Quote
5) The replacement flange can only be mounted on non-weather sealed Pentax bodies, so it can go on a K20 or K5*, but not on a K3 or K1.

*MAYBE The manufacturer/seller does not list these Pentax bodies as tested-to-be usable.
That information is for the old version that isn't sold anymore...the new version is for WR cameras and costs S$117 (US$83).

Pentax K+ Multi Mount (WR version) - Adaptist

It should be noted that installing it requires removing the mount seal, so the camera is less than WR after it is installed.

Leitax makes a replacement mount for Nikon and Zeiss ZF lenses...(Manual Nikkor lenses only, no CPU contact,) There are two types of Nikkor mount, and only one of them can be converted. You can't tell which unless you open the lens. All Zeiss ZF lenses can be converted, but some need special screws.

Leitax Nikon to Pentax-K mount

Nikon and Zeiss ZF lenses for Pentax cameras

Conversion service is available for an extra 75 Euros plus shipping...

Last edited by boriscleto; 03-24-2017 at 06:27 AM.
03-24-2017, 06:15 AM   #12
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You can replace the mount on the camera with

http://adaptist.weebly.com/pentax-k-multi-mount-wr-version.htm

You need a small gasket using Nikon lenses as the flange distance is a millimeter longer (46.5 mm vs 45.46mm).

Bah! boris was a few seconds faster than me because I looked up the flange distances

Last edited by Not a Number; 03-24-2017 at 06:28 AM.
03-24-2017, 06:20 AM   #13
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QuoteOriginally posted by WPRESTO Quote
RE: You also have to consider the depth of the bayonet mount on the lens itself. If it is not sitting down into the opening on a Pentax, it is already farther forward than the Nikon registration distance. But to mount it, the adapter must have at least one metal plate in back of the lens bayonet which moves the lens outward a bit more. There is a company that makes a replacement bayonet plate that can be fitted to a Pentax DSLR body. It will allow both Pentax and Nikon lenses to be fitted directly on the Pentax, but no lens-latch, which means if you are careless, the lens may fall off while you're holding the camera, or the camera may drop off while you hold the lens. Bad news if you're out on a whale-watch or photographing NYC from atop the Empire State Building.

Just did some additional checking. The replacement bayonet for Pentax bodies is called the "PK + MM Multi Mount." Price: $98.

5) The replacement flange can only be mounted on non-weather sealed Pentax bodies, so it can go on a K20 or K5*, but not on a K3 or K1.

*MAYBE The manufacturer/seller does not list these Pentax bodies as tested-to-be usable.
The Adaptist mount is no longer available for non-weather sealed bodies. They now only sell the version made for weather sealed bodies. The k5 and k20 are weather sealed as far as I know as is the k3.
Adding the adaptist mount reduces weather sealing due to the specifics of the mount fitting and the use of this mount with other lenses.

As for "force fitting" Nikon on Pentax I have done it. It works reasonable well. I have also seen another forum member who did this and marked where his lenses turned and then carefully drilled a small recess into the mount where it lined up with the Pentax lens release/lock pin. This makes the fit more secure.

Remember that this only works with non-AI lenses unless the plan is to remove the AI tab.

---------- Post added 03-24-17 at 09:22 AM ----------

Oh and if you want the lens scale to be accurate you can add a shim. This is more complicated if you drilled a recess for the lock pin since the shim would need to have a hole and be lined up with this.

---------- Post added 03-24-17 at 09:25 AM ----------

Pentax K+ Multi Mount (WR version) - Adaptist
03-24-2017, 08:04 AM - 1 Like   #14
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If one must, the Leitax solution is probably the most transparent and usable option. Even then, I would only consider this solution for a Nikkor that is unique or classic to the brand or a third-party lens that is difficult or impossible to source in Pentax-K mount. When all is said and done, it may be cheaper and easier to buy a mid-tier Nikon or Sony body used.


Steve
03-24-2017, 08:13 AM   #15
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QuoteOriginally posted by stevebrot Quote
When all is said and done, it may be cheaper and easier to buy a mid-tier Nikon or Sony body used.
True, but it may be viable for the person who desperately wants to shoot Nikkor against Asahi glass on a DSLR (e.g. with a split focusing screen fitted) and needs everything else (sensor, processor, etc) to be held constant.
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