just a thought, Pentax made in the past a system that would make any lens an autofocus one by moving film plane, dunno why nobody is thinking of such an alternative, although obviously such an approach has its own drawbaks I expect mostly for tele lenses since the distance on which we can move the sensor is limited
That approach is limited to cameras implementing it. I find the Techart approach way more interesting: turn a manual lens (in their case any M mount lens) into an AF lens (on Sony E) by moving the whole lens.
Never tried it myself, but heard from others that it actually works quite well.
Out of curiosity, by how much does the lens need to be moved?
In other words, what is the maximum distance a lens would need to be moved (for most lenses, say from wide angle like 18mm to medium tele like 200mm)?
02-21-2020, 09:56 AM
(This post was last modified: 02-21-2020, 11:13 AM by MatjazO.)
I do not have a recollection of Pentax attempt. Moving film plane camera was made by Contax with AX model. It died soon as it was complex, costly and slow to focus. It also resulted in a very big camera for the time as it required complicated mechanical assembly. Lens AF technology itself proved to be way superiorin in every way.
Today, even less likely but for a kickstarter campaign. ;-)
3 lenses I have with me which are pre-floating element, so easy to measure (not thaaat accurate with tape measure):
135mm lens. infinity to 150cm: 15mm
55mm lens: infinity to 150cm: 2mm
20mm lens: infinity to 150cm: 0.4mm
You can extrapolate from those.
Why to 150mm? That is the MFD of this 135mm lens.
55mm lens: infinity to 24.1mm (1:2): 28mm
20mm lens: infinity to 20cm: 3.5mm
I just had a look at ebay - the Contax AX (with backplate AF) sells for quite an amazing amount of money. Collector's surcharge maybe.
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