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Chipped adapters: importance of direction
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PostPosted: Sat Oct 13, 2007 9:49 pm    Post subject: Chipped adapters: importance of direction Reply with quote
I read somewhere that in order to make the most out of chipped adapters, it is important to understand from which direction the focusing works better, for each lens-adaptor couple.

What it means is that chipped adaptors would have one preferred direction, some would focus more accurately when focusing from infinite towards near, others would do better when operated from nearest towards infinite.

This behaviour would vary not only from one chipped adapter to another, but also from the associations with different lenses.

I have not made any tests yet, but I am curious about it, and will probably do.
Have you ever noticed discrepancies of this kind in your chipped adapters? Is someone else willing to also make tests and compare?


PostPosted: Sat Oct 13, 2007 9:57 pm    Post subject: Reply with quote
This sounds interesting. I have not experienced that, but I have never really tested it, since I was not aware of this possible aspect.

I have encountered three different problems with chipped adapters, though:
ERR99, ERR01 and a high pitched sound (like a tiny whistle) when mounting the adapter.
The ERR01 or the sound can be removed by demounting and remounting the lens. The ERR99 I mostly can remove by cleaning the contacts with a small pencil rubber.


PostPosted: Sat Oct 13, 2007 10:06 pm    Post subject: Reply with quote
I can't remember where I read this, but I remember that the author made as suggestion to write upon each lens' cap the best focusing direction, as a memento.


PostPosted: Sun Oct 14, 2007 5:41 am    Post subject: Reply with quote
Mmmm... this make sense to my experience. With shorter lenses, focusing turns to be quite difficult and there is some "hysteresis" when focusing: I use to go twice left-rto-right and righ-to-left, and usually there is a small range in the middle (the camera beeps in different places when coming from one side or the other). So finally I never know wich is the right point. And I end closing the aperture as much as I can keeping a reasonable shutter speed, just to get enough DOF to compensate the deviation.

Best regards,
Jes.


PostPosted: Sun Oct 14, 2007 7:50 am    Post subject: Reply with quote
Jesito wrote:
...the camera beeps in different places ...


Yes, I confirm that. I guess this is also caused by the focus tolerance of the cam.


PostPosted: Sun Oct 14, 2007 2:44 pm    Post subject: Reply with quote
Jesito wrote:
the camera beeps in different places when coming from one side or the other.


I know absolutely nothing about how auto-focussing works, but common sense suggests the software algorithm looks for the point where a particular point or area of light or colour is covered by the minimum number of pixels. So when focussing manually, as the focus becomes sharper and the number of pixels is reducing, the algorithm is watching and waiting for the point where the pixels start increasing again before beeping, therefore slightly past the optimum point. Then when you turn the focus ring the other way, the process is reversed. The optimum point has to be midway between the two beep points. Or is this idea too simple? Smile


PostPosted: Sun Oct 14, 2007 4:43 pm    Post subject: Reply with quote
AF uses contrast measurements to focus.


PostPosted: Sun Oct 14, 2007 7:55 pm    Post subject: Reply with quote
LucisPictor wrote:
AF uses contrast measurements to focus.


As far as I know the AF of DSLR mostly uses phase detection instead of contrast measurement. This is the reason for the difficulties of the manufacturers with live view. They have to integrate a second AF system with contrast measurement - and this should not be remarkable inferior to the normal AF of the camera.

Michael
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