DIY adapter with focus trap for industrial Nikkor

brightcolours wrote:

Not sure why you posted this. It looks like you want to explain something to me? I showed you what I made, and you go and tell me what I have done? Strange.

I was explaining how this can work on a wide range of cameras...  and BTW there is no such thing as the lens not "smoothly communicating" -- what you observe is the normal focus priority behavior with a lens that says it is trying to AF, but actually isn't.  It's cool that you hacked a chip out of an old lens for this, but the same can be done with many of the 3rd-party chips or chipped adapters and not just on Canons. I've hacked trap focus in similar ways on several cameras, mostly Sonys.

I'm very happy to see more folks doing this sort of thing. In fact, I explained this at DPReview several times before (here, for example) and even ran a challenge on using the hacked technique: Trap Focus

And you are wrong on that DSLRS fire when they sense focus. With AF lenses they do not, they sense where focus should be, tell the lens to go there and fire (for speed purposes). With badly calibrated lenses this results in back or front focus.

There are many different focus control algorithms in use on different cameras, and most individual cameras actually implement several. It varies, but in many "continuous" or "tracking" focus modes, cameras do in fact just try to focus the lens by returning to the position where they last sensed/estimate from PDAF that it will be in focus, and that obviously will not work for trap focus and is generally very prone to focus error in cameras where it is done open loop (in other words, those modes often put the camera into shutter priority, not waiting for final focus confirm). However, most normal single-shot AF mode implementations really do operate in focus priority: focus is acquired after the shutter button is (half) pressed and if you have quickly pressed the shutter button all the way, firing is delayed until focus is confirmed (closed loop).

By the way, one doesn't need to have PDAF for trap focus to work; the camera just needs to be able to sense when focus has been achieved. Normally, CDAF doesn't know that without going past focus and returning (because it doesn't know how high contrast can get otherwise), but there are some CDAF control algorithms that trigger when they hit a contrast threshold, and thus they can implement trap focus.  Some micro4/3 cameras actually do AF based on PSF detection rather than CDAF or PDAF, and that also can implement trap focus (and is actually superior to CD and PD).

Anyway, greetings from The Netherlands.

To you as well. I was just trying to explain the general applicability of the kind of hack you did here, I had no intention of criticizing your work -- it's a nice hack.