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For Nikon DSLR: AI conversion for non-AI lenses ?
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PostPosted: Sun Apr 26, 2009 1:19 am    Post subject: For Nikon DSLR: AI conversion for non-AI lenses ? Reply with quote
to my understanding a full AI conversion will require to change the metal lens mount and the aperture ring (AI with plastic tap).

But ... for use on Nikon DSLR, is it necessary to have this AI aperture ring, or is only changing the mount sufficient?

How many different lens mounts are there (for instance are the screw position always on the same position)?

Depending on the above ... i may develop some metal AI lens mounts, such that non-AI lenses can be mounted on Nikon DSLR ... Wink

So ... Nikon users ... please help!


PostPosted: Sun Apr 26, 2009 3:36 am    Post subject: Re: For Nikon DSLR: AI conversion for non-AI lenses ? Reply with quote
hk300 wrote:
to my understanding a full AI conversion will require to change the metal lens mount and the aperture ring (AI with plastic tap).


No. The mount is the same F-mount from 1959, still used today.

What changes is the aperture ring, specifically the way that its position is conveyed to the camera. And those rings are specific to each model of lens.

hk300 wrote:
But ... for use on Nikon DSLR, is it necessary to have this AI aperture ring, or is only changing the mount sufficient?


Its the other way round. Changing the aperture ring to one with aperture indexing (AI) requires removing the mount, yes - to be able to remove and replace the aperture ring - but the same mount is then put back on when the new ring is in place.

hk300 wrote:
How many different lens mounts are there (for instance are the screw position always on the same position)?


One Smile well ok there are several mounts with five, three, etc screw holes but the point is that its not the mount which is changed.

hk300 wrote:
Depending on the above ... i may develop some metal AI lens mounts, such that non-AI lenses can be mounted on Nikon DSLR ... Wink

So ... Nikon users ... please help!


In summary, what would need to be developed is replacement aperture rings. Which are different for each lens, so I suspect would be uneconomic. But, perhaps you could search ebay completed listings on AI conversion kits to find out the most popular ones, and replicate those. Or, perhaps there are popular non-AI lenses for which Nikon never made a conversion kit, so making one would prove popular.

Hope this helps, happy to explain more if needed.


PostPosted: Sun Apr 26, 2009 5:06 pm    Post subject: Reply with quote
thanks Chris ... but i am still confused.

http://www.leitax.com/leica-lens-for-nikon-cameras.html

Leitax is making an adapter for Leica lenses to fit nikon cameras, but it this case no aperture control rings are supplied.

Please correct me if i am wrong ...
... Leitax says ... professional Nikon cameras can use AV mode, basic Nikon DSLR need to work in M mode. Is this because the basic Nikon DSLR needs the AI tab to work?

What does this mean? And does Leitax convert the lenses to AI or non-AI mounts?


PostPosted: Sun Apr 26, 2009 7:25 pm    Post subject: Reply with quote
hk300 wrote:
thanks Chris ... but i am still confused.

http://www.leitax.com/leica-lens-for-nikon-cameras.html

Leitax is making an adapter for Leica lenses to fit nikon cameras, but it this case no aperture control rings are supplied.


Correct. So the mount is now Nikon F, and the camera has no idea what aperture is selected. The photographer has to use stop-down metering (the iris is closed to the desired aperture and the metering is done stopped down). In low light, the metering will tend to be inaccurate because the available light is not all being used. Metering wide open (auto aperture) is more accurate.

This also means that to compose and focus, the aperture ring has to be moved to wide open to avoid a dark viewfinder. So when using a leitax lens, the photographer is moving the aperture ring twice per shot.

hk300 wrote:
Please correct me if i am wrong ...
... Leitax says ... professional Nikon cameras can use AV mode, basic Nikon DSLR need to work in M mode.

Also correct. For D200 and up, the camera will meter. But if, for example, you are shooting at f/8, the camera behaves as if you have an f/8 lens stuck at wide open, not, say, an f/2.8 lens stopped to f/8. I don't know what if anything gets written to the exif, but its unlikely to be correct.

hk300 wrote:
Is this because the basic Nikon DSLR needs the AI tab to work?

No. Its because the basic Nikon DSLR needs an electrical (CPU) connection to be able to meter at all. If you put a non-CPU lens like an AI or AIS lens on a D40, in any mode other then M, it will give you an error and say there is no lens.

hk300 wrote:
What does this mean? And does Leitax convert the lenses to AI or non-AI mounts?


What you get is non AI.

However, I suspect that you are mixing up two things here about pre-AI lenses. One is their functionality (how they communicate the aperture to the camera) and one is the physical mounting compatibility.

Firstly, functionality.

On a pre-AI lens, the position of the aperture ring is communicated by the "rabbit ears" on the aperture ring, and a small lever on the camera, which fits between the ears.

On an AI or AIS lens, the position of the aperture ring is communicated by the AI ridge on the back of the aperture ring, and a corresponding sliding lever on the camera.

On an AIP, AF, AF-D or AF-S lens (all CPU lenses) the aperture is communicated by a series of electrical contacts . Indeed some of those lenses don't have an aperture ring at all; the aperture is set on the body.

OK so that is three different methods from different historical dates to communicate aperture position - rabbit ears, AI ridge, CPU contacts.

The leitax-converted lenses have *none* of those three methods. The camera has no idea what aperture is selected.

Secondly, mount compatibility.

An SLR with a CPU enabled lens typically allows the aperture to be set by the camera (in modes S and P; optionally in mode M also). Thus, the aperture ring (if the lens has one) needs to be set to its minimum (smallest) aperture, e.g. f/22. To indicate this, a CPU lens and also an AIS lens has a small protrusion on the aperture ring, which is read by some sort of switch on the camera body. Its a straight on-off, is the lens at minimum aperture or isnt it, arrangement.

On Nikon D40, D40x and D60, this switch works by being pushed in (towards the back of the camera). On D70, D80, D90, D200 and up this switch moves round the lens mount.

Nikon pre-AI lenses have an aperture ring which protrudes past the lens mount, all the way around. I'm not sure why; perhaps it helped to keep dirt out of the join between camera and lens.

This is fortunate though because to convert a pre-AI lens to AI, instead of having to make an AI ridge and a min-aperture protrusion by adding metal, it can be made by machining away the excess to leave just the parts that are needed.

However, it does mean that on cameras which have a min-aperture sensing switch which moves around, mounting a pre-AI lens will press on that switch as the lens is mounted, possibly even breaking the switch off. This is the safety and physical compatibility aspect.

(On D40/D40x/D60, the pre-AI lens harmlessly presses the switch in towards the body, so nothing breaks).

The aperture ring on the leitax converted lenses does not overhang the mount like a Nikon pre-AI lens. So it can be safely mounted on all Nikon DSLR.

Is that clearer?

I know, pictures would be better. This was complicated to write; if you were here with me in the room I could show you some lenses, point to what I mean, and it would be simple and easy.


PostPosted: Mon Apr 27, 2009 6:30 pm    Post subject: Re: For Nikon DSLR: AI conversion for non-AI lenses ? Reply with quote
hk300 wrote:
to my understanding a full AI conversion will require to change the metal lens mount and the aperture ring (AI with plastic tap).

But ... for use on Nikon DSLR, is it necessary to have this AI aperture ring, or is only changing the mount sufficient?

How many different lens mounts are there (for instance are the screw position always on the same position)?

Depending on the above ... i may develop some metal AI lens mounts, such that non-AI lenses can be mounted on Nikon DSLR ... Wink

So ... Nikon users ... please help!


Hi,
How about a nice Fujinon adaptor? It would be nice to use the X-mount lenses on Pentax or Nikon cameras. No one offers anything like this in the world!


PostPosted: Fri May 01, 2009 8:00 am    Post subject: Reply with quote
Here is an article to modify yourself!

http://www.zi.ku.dk/personal/lhhansen/photo/repair/aimod/aimod.htm


PostPosted: Fri May 01, 2009 7:07 pm    Post subject: Reply with quote
Chris

Very concise and accurate description


patrickh


PostPosted: Sat May 02, 2009 6:30 am    Post subject: Reply with quote
The process seems easy and at one level is. The biggest problem you will have is disassembling the lens - some are more tricky. And then reassembling. Almost invariably the arm which changes the aperture (i.e. that connects the aperture ring to the metal iris/aperture assembly) will move and then be out of alignmment when you come to reassemble it. This happens even if you are cautious enough not to move the actual aperture ring itself. This creates some headaches till you work out how to get it realigned - usually by trial and error


PostPosted: Wed May 13, 2009 7:52 am    Post subject: Reply with quote
Very good topic, I'm looking at a possible DIY modification as I can't find the required kit anywhere (#44 for Nikkor-Q 135/2.8 ).

Thank you for the valuable information!
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