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F Ai to Z adapter
- Thread starter HeavyDuty
- Start date
michaeladawson
Veteran Member
I really would like that too. Seems a shame Nikon didn't do that with their own adapter. We'll have to wait and see what the specs are on the rumored MonsterAdapter F to Z. Maybe they'll surprise us. Although, if the photos on NikonRumors are real it won't.
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Mike Dawson
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monte12345
Veteran Member
The AI tabs on the cameras that provided that facility were all based on a Potentiometer (A Variable Resistor) to communicate with the camera body. The Z mount was not equipped with this provision and as a result does not feature the required circuitry.
michaeladawson
Veteran Member
The analog circuitry doesn't need to be in the camera body. It needs to be in the adapter. The adapter takes care of converting all the signals. If you can chip an AI lens and add electrical contacts you can certainly add an AI index tab and have the adapter read the aperture ring position.
The issue, if there is one, is what is then communicated to the camera body. The adapter doesn't know what the maximum aperture is of the attached lens so there probably needs to be some firmware support to match up against what is set in the Z setup menu for a manual lens.
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Mike Dawson
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monte12345
Veteran Member
I just mounted my 24mm f2.8 AF Nikkor to my ZF to see what the camera did for the aperture on that "chipped" lens. First it generated an error code if the aperture wasn't set to f22 on that lens. Second setting the aperture with the camera did function well. However, when you adjusted the aperture to any available aperture the lens stopped down to that value for both metering and focusing. Try manually focusing a 24mm lens at f22 and you will quickly see that does not work well. It's why way back in 1960 holding the aperture to wide open for focusing and metering became mandatory if you wanted to sell an SLR. BTW we can thank Asahi Pentax for that particular innovation.
BTW the current Z models hold the aperture to the camera setting if it's between wide open and f5.6. If the aperture setting is set to a smaller diameter than f5.6 it will hold the aperture at 5.6 for viewing and focusing and only close to the set aperture when the shutter is open. I suspect that in many cases of "missed focus" it's because the lens was set to a smaller aperture so the lens was NOT using the most discriminating aperture for focus and the misses were a secondary effect of focusing at f5.6. Frankly what Nikon is doing is DUMB. They should hold the aperture at wide open except for when the DOF Preview is pushed or the shutter is open.
Point is that the means for controlling the aperture of an AIS compliant lens does exist within the body of the the Z cameras. However there is NO means of any type to sense the position of the aperture ring with the exception of the minimum aperture switch within the AF Nikkor lenses. BTW that is a simple ON/OFF switch so it is a binary switch. I also suspect that switch is also used to enable the manual focusing aids available on the various Z camera models.
BTW the current Z models hold the aperture to the camera setting if it's between wide open and f5.6. If the aperture setting is set to a smaller diameter than f5.6 it will hold the aperture at 5.6 for viewing and focusing and only close to the set aperture when the shutter is open. I suspect that in many cases of "missed focus" it's because the lens was set to a smaller aperture so the lens was NOT using the most discriminating aperture for focus and the misses were a secondary effect of focusing at f5.6. Frankly what Nikon is doing is DUMB. They should hold the aperture at wide open except for when the DOF Preview is pushed or the shutter is open.
Point is that the means for controlling the aperture of an AIS compliant lens does exist within the body of the the Z cameras. However there is NO means of any type to sense the position of the aperture ring with the exception of the minimum aperture switch within the AF Nikkor lenses. BTW that is a simple ON/OFF switch so it is a binary switch. I also suspect that switch is also used to enable the manual focusing aids available on the various Z camera models.
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michaeladawson
Veteran Member
Yes, I know. That's the point of what I'm talking about. There is no AI index tab on a Z body. That is what you need. Along with firmware code that translates the position of the AI index tab into a f stop. An F to Z adapter can have that tab.
That tab will sense the position of the aperture ring. There is also a non-CPU lens section in the setup menu. This stores the maximum aperture of the lens that is attached to the camera. The camera firmware takes the relative aperture ring position and by knowing what the maximum lens aperture is the camera can calculate what the current lens aperture is.
I suspect that the missing piece for a Z camera is the firmware. So even if a 3rd party adapter had this index tab there is no function in the current Z firmware to accept the reading from the adapter and calculate an aperture. I don't suspect the firmware would ever be updated to do this unless Nikon were to make its own F to Z adapter with an index tab.
But it's all doable.
pluton
Veteran Member
My 1971 Pentax Spotmatic metered at shooting [set] aperture, not wide open. Focusing was, of course, at full aperture.
Joseph S Wisniewski
Veteran Member
If the NikonRumors pictures are real, it does not have the necessary feeler.
michaeladawson
Veteran Member
Joe, you're pretty educated on these matters. Am I correct in my assumption that even if an F to Z adapter with the necessary AI index tab was produced that it would need a firmware update on the camera to properly communicate the F-stop data? Or does the position/location of the feeler tab on the lens have the maximum F-stop already "built in"?
jiberlin
Veteran Member
... even if there is no chance.
The problem is that the Ai tab communicates the relative aperture, how much will the aperture close from wide open. To communicate the absolute aperture, the maximum aperture must be known, the adapter must have an option to set it.
My wich is a 'semi-dump' adapter, where the settings for the no-CPU lenses are programmed into the adapter, ideally multiple settings with a small switch to select the right, And of course this for a price much less then the FTZ.
The meter coupling ridge on the back of AI and AIS lenses signals (via the "feeler" on the camera) to the metering system both the the aperture setting and the maximum aperture of the lens. The position of the lug on that ridge defines the maximum aperture of that lens by providing a starting point for the travel of the "feeler".
The feeler in an adapter would be attached to a position encoder that provides the digital absolute aperture to the rest of the electronics.
The adapter would also need a sensor to determine if the lens has the AIS notch on its mount ring as processing is different for AI and AIS lenses.
Controlling the aperture via the camera is a different subject...
MJ_Photo38
Veteran Member
I can understand the "need" for it, but in my eyes, this is more a "nice to have" than anything else.
On F mount bodies, it was required otherwise the camera could not meter properly with a non-chipped lens, as the aperture was kept wide open at all times except when exposing.
On Z cameras using the FTZ, we have the ability to close those lenses down, and then it's only a matter of on-sensor metering. As long as I can set my adapted lens, I'm okay. I don't need the precise aperture information about my shots, unless I'm shooting a test chart, which is almost never.
A nice thing that Nikon could potentially include through firmware though, is the ability to set a maximum and minimum aperture : as AI lenses have the correct tab that will engage the little post (I forgot the name, if it has one) that says if the lens is fully closed or not. And through that, we would be able to control the aperture electronically like on G lenses (and AF(D) lenses too if I understand it correctly)
Don’t forget Nikon solved the maximum aperture detection issue years ago - IC lenses needed to be indexed on mounting. It’s so ingrained that I still do it, even with Ai and AiS cameras and lenses.
Theres no reason maximum aperture can’t be detected with a feeler just like in a Ai or AiS native camera body.
Theres no reason maximum aperture can’t be detected with a feeler just like in a Ai or AiS native camera body.
Joseph S Wisniewski
Veteran Member
The way I got around it was telling the camera the lens had the same min and max aperture, both whatever the current lens was set to. I'm sure Nikon has a more elegant way. I remember my old FA red the aperture, and then in S and P mode the camera would select apertures between wide open and wherever you set the ring. Set it at max and you get the full range, but take a 50mm f/1.4, set it at say f/8, and the camera would pick apertures from f/1.4 to f/8.
The maximum f-stop is read by a small feeler inside the mount at the bottom, unless the lens has a chip. Digital data always takes priority.
The setting of the aperture is read by the big feeler on the outside of the lens mount, at the right looking into the camera.
This is a thought, I had too. But it would only work correctly with AiS lenses. With AI and previous lenses, exposure will be off, when stopped down or your aperture set at the camera will be different to the aperture set by the camera at the lens. AiS, Series E and later lenses use a logarithmical aperture curve, while the older lenses use linear. With the aperture set at the lens, this doesn't matter.
Stavrosf
Leading Member
I also have the Neewer FE to Z adapter. This let you upload a txt file with the focal length, max and min aperture and allows trap focus as well.
TBH I do not really understand what will be the benefit of such adapter (I mean from the original post) other than Exif Info and to be able to see the aperture while you are shooting. Is there anytihing else that I haven't thought of?
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stavrosf
https://www.fourfourianakis.eu
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Joseph S Wisniewski
Veteran Member
The aperture coupler feeler (outside the lens mount, roughly at 3:00, looking into the camera) lets the camera know how many stops open the lens is from minimum aperture, but it doesn't provide any info on what the maximum aperture is. That's done by a second feeler inside the lens mount at 6:00, looking into the lens mount.
So the AI/AIS adapter needs two feelers, if you want hard apertures like f/8 for the display and for the EXIF. Otherwise you either have to set max aperture manually on the adapter with buttons or dial, or have the aperture and EXIF read "-2 stops" on an f/1.4 lens at f/2.8, instead of reading "f/2.8". I'm also not sure if the camera firmware even has provision to display and log relative apertures.
I'm pretty sure only four Nikon cameras ever had that feeler.
- The FA technocamera (yes, that really was Nikon's name for it) of course. That's where it was introduced.
- The F4 superbeast (no, Nikon never called it that. That's purely my name). F4 had a flip-down pre-AI lever, full AI and AIS capabilities including proper display like FA, and was the only AF Nikon that could focus both F3-AF internal-motor lenses and the newer AF/AF-D screwdriver lenses. Hence "superbeast".
- The F301/N2000 superchicken (well, if FA and F4 get nicknames, so should the rest. That's the best I could do on this short notice).
- The F501/N2020 supergecko (I'm really running out of nicknames), Nikon's first AF camera to use the new "screwdriver" lenses instead of F3-AF internal motors.
F-401/N4004, the first AF camera to drop the aperture coupler, didn't need it, of course.
F-601/N6006 and F-801/N8008 didn't have it either, although they had the UI for it.
Yes. The AIS notch signals that the lens has a calibrated aperture mechanism. (There's a second notch that signals the camera the lens is 135mm or longer that informs program mode to use a "sports" program). A given position of the aperture actuator (inside the mount at 9:00, looking into the camera) gives you a given number of stops down. Without that, you can always get wide open right, and always get fully-stopped-down right, but apertures in between can be off. My experience trying to control AI lenses is that the worst errors are around f/5.6.
This is not a problem in P or S modes, because the camera measures exposure, sets aperture, then measures exposure again and corrects the shutter. Even the original Nikon FA could do this. They called it "servo aperture".
But in M mode, you could be a stop off. Been there, done that.
It's actually the same subject.
In order to control aperture by camera (front command dial, P and S modes, etc) you need to know the lens's maximum (wide open) aperture, how many stops from minimum to maximum aperture (I think. It's possible Nikon assumes that's always seven: like my 50mm f/1.4 goes to f/16, while my 55mm f/2.8 goes to f/32) and if the lens is locked at minimum. The maximum aperture is determined by a feeler inside the lens mount at the bottom.
There's also the issue of the aperture being calibrated. The aperture actuator (inside the lens mount, left side looking into the camera) originally was just a "stop down" lever, back in the AI days. AI-S introduced the "calibrated" aperture so moving that lever to a certain position would open the lens up a certain number of stops. There's a signal notch outside the lens mount at 2:00 (looking at the camera) that says "hey, I'm an AIS lens with a calibrated aperture". There's a feeler inside the lens mount at 6:00 that says the max aperture.
So a proper AI/AI-S converter needs two feelers, and one or two notch reading pins.
(A chipped lens does all of this digitally, identifying: min aperture, max aperture, flagging the lens as AI or AIS, and focal length. You would still need one feeler for the aperture ring if you wanted to be able to adjust aperture from the ring instead of the front command dial or P and S modes.
The problem is that the popular "Dandelion" chip has a big error. It correctly fills in the focal length in the field the camera uses for EXIF, but not the field the camera uses for setting up vibration reduction or focal-length dependent programs). It always sets that one to 50mm, so you always get a short-focal-lenght program and you get decreased VR performance the farther the lens deviates from 50mm).
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Joseph S Wisniewski
Veteran Member
Or the adapter must have a feeler to read it. There's a tab on the lens at 6:00 that is read by a feeler inside the lens mount to determine max aperture.
I know FA had that feeler. I'm not sure which other cameras had it. My N8008, F100, D3, and D90 were in easy reach, so I checked them. None of them have it.
There would be a lot of switches. Min aperture, max aperture, and focal length.
You would still need an aperture motor, otherwise you'd have to meter and shoot stopped down, and you'd only have A and M modes, no P or S, no front dial aperture control, and the noise of viewing at very small apertures. (Normally Z cameras view and focus at apertures f/5.6 or wider. Set f/1.4 and your view and focus at f/1.4. Set f/16 and you view and focus at f/5.6, and the camera stops down to f/16 when shooting). So the adapter would be FTZ + one or two feelers + one plunger switch. It would cost more than FTZ.
Joseph S Wisniewski
Veteran Member
Only in the middle of the range. Wide open and fully closed are always right.
You are close.
AI-S, series E, AI-P, AF, and AF-S lenses use a log curve. It's generally referred to as a "calibrated curve".
AI and pre-AI lenses use... nothing. It's basically a random curve for each lens. Had it been linear, the AI-S detection tab would have been enough to switch in the proper compensation.
Which brings us to my stupid idea...
When you're using P, S, or A modes, the Z's perform old-fashioned "servo aperture" first introduced on the FA.
- They meter wide open (or at whatever you set between wide open and f/5.6 on the Z).
- Set the aperture.
- Meter again.
- Tweak the shutter speed to compensate for however much exposure just changed.
But a Z is a mobile computer: a pretty big one. So it would be no problem to use those mid-range corrections to build a linearizing curve. Store the compensation curve in with the manual lens selection data.
This could also be done with a camera remotely operated by a PC.
Now, if we assumed the error curve was always relatively smooth and just added one 2nd order correction point at mid range, we could store that in a chip like a Dandelion. That way, the community could share mid-range compensations and you'd know to set a 55mm f/3.5 up with max aperture f/3.5, min aperture f/32, focal length 55mm, and mid range compensation -1.5.
Until it does.
With the aperture set at the lens, you lose a lot of low-light capability. Nikon limits the aperture for viewing/focusing to the range of wide-open to f/5.6. You're fine outdoors (I use my Voigtlander 40mm f/1.2 outdoors frequently stopped down below f/5.6). But indoors? Stop down two more stops to f/16 and the viewfinder starts to get noisy and the update rate drops. f/32? Forget about it.
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