Gear Talk > What the Nerds Do
alternative Ai conversion (aperture hook)
richardHaw:
Hey, guys!
really busy these days.
https://richardhaw.com/2016/10/09/mod-alternative-ai-conversion-method/
this is basically the same as what buddy shared, in fact his claw is taller at the end which is good for some lenses that have a REALLY thin aperture ring like the 2.8cm f/3.5 :o :o :o
I may mass produce these one of these days (complete with ears for DP-1) but the market is really small.
Matthew Currie:
There's a similar problem with some old Vivitar lenses. Here's the version I made for an old 20 mm. Vivitar, using copper. Because it's folded over, it need not be very stiff. In this case, as you see, there's only the one screw to hold it all, and at the time I did this the lens was being shared between an F and an F3, so the claw stayed on.
e.t.a. Since the AI tab is not at the same aperture on all lenses, I wonder if you could mass produce a tab with slotted screw holes, which one could then adjust to different lenses. I don't know whether it would be possible to make tight enough, but perhaps with the claw over the top it would, or perhaps once positioned right you could use a little dab of adhesive to keep it from shifting.
Roland Vink:
I should point out it is important to get the correct position of the hook. Even more so if you are milling the aperture ring!
On https://richardhaw.com/2016/10/09/mod-alternative-ai-conversion-method/ there is a picture showing the AI stop at f/8 for a 50/2 lens, this is not correct. The table at http://pindelski.org/Photography/2013/02/06/nikkor-ai-conversions-diy/ is not accurate either.
The basic rule is this:
* For any lens with max aperture f/2 or slower, the AI tab starts 4 2/3 stops down from the max aperture setting.
* For any lens f/1.8 or faster, the AI tab starts 5 stops down from the max aperture setting.
This means f/2 and f/1.8 lenses have the AI tab in the same location, even though there is a 1/3 stop difference between the two. Fast lenses are probably indexed a little differently due to the way they interact with the camera meter, so some compensation is required to provide consistent metering compared to slower lenses. Below is a table with the lens max aperture and the position of the AI tab:
4 2/3 STOPS DOWN
5.6 22 +2/3 stop
4.5 22
4.0 16 +2/3
3.5 16 +1/3
2.8 11 +2/3
2.5 11 +1/3
2.0 8 +2/3
5 STOPS DOWN
1.8 8 +2/3
1.4 8
1.2 5.6 +1/2
Richard, you may want to add this table to your AI conversion page, and remove the link to the inaccurate data :o :o 8)
richardHaw:
Hello, Roland.
Thanks for the info :o :o :o
I now check the position using existing Ai lenses ::)
I have updated the site. Thank you very much!
richardHaw:
--- Quote from: Matthew Currie on October 16, 2016, 16:32:38 ---There's a similar problem with some old Vivitar lenses. Here's the version I made for an old 20 mm. Vivitar, using copper. Because it's folded over, it need not be very stiff. In this case, as you see, there's only the one screw to hold it all, and at the time I did this the lens was being shared between an F and an F3, so the claw stayed on.
e.t.a. Since the AI tab is not at the same aperture on all lenses, I wonder if you could mass produce a tab with slotted screw holes, which one could then adjust to different lenses. I don't know whether it would be possible to make tight enough, but perhaps with the claw over the top it would, or perhaps once positioned right you could use a little dab of adhesive to keep it from shifting.
--- End quote ---
Hello, Matt!
I actually have a easier idea for that but I would need to file a patent :o :o :o
Sometimes, I am thinking if mas producing this is worthwhile since the market is so small and there is a big chance that the manufacturers in mainland china would just bootleg it resulting in me not meeting any ROI. it happened to somebody i know (flash modifier) who happens to be a schoolmate so it could happen to me,too.
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