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10-11-2019, 03:36 PM   #1
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Sensor shift AF

Autofocus could be improved with old screwdrive lenses with sensor shifting. By adding the 6th dimension to stabilization the small focus shifts could be done by sensor shifting. This could be faster and would be definitely more accurate. Plus could correct small AF errors with manual lenses.
Although it may make the camera bigger and heavier...

10-11-2019, 04:50 PM   #2
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QuoteOriginally posted by 08amczb Quote
Autofocus could be improved with old screwdrive lenses with sensor shifting. By adding the 6th dimension to stabilization the small focus shifts could be done by sensor shifting. This could be faster and would be definitely more accurate. Plus could correct small AF errors with manual lenses.
Although it may make the camera bigger and heavier...
Yes. I was thinking about the same these days.
Panasonic and Olympus have already focus stacking or bracketing.
10-12-2019, 05:00 AM   #3
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Focus stacking could be done with a regular AF lens too. The Nikon D850 does it for example without any sensor movement. Pentax AF isn't that bad with new lenses, but they should do something with the old screw drive system and manual lenses...
10-12-2019, 08:04 PM   #4
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Good idea for small changes to fine tune focus but not practical for actually "focusing" a lens since large shifts are typically needed for that. Focus would have to be done in live-view to gain that advantage since you're seeking to fine tune the actual image on the sensor, so an optical VF would be out for such an arrangement.

It would definitely would add complications to an already shift capable sensor such as the K-1 because the gimbals would have to be capable of moving the sensor in 3 dimensions instead of just 2. Also, not sure but some optical formulas may be designed for a specific focus distance behind the lens and changing that could have issues. But, a good concept for some cases.

10-17-2019, 07:18 PM   #5
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QuoteOriginally posted by Bob 256 Quote
Good idea for small changes to fine tune focus but not practical for actually "focusing" a lens since large shifts are typically needed for that. Focus would have to be done in live-view to gain that advantage since you're seeking to fine tune the actual image on the sensor, so an optical VF would be out for such an arrangement.



It would definitely would add complications to an already shift capable sensor such as the K-1 because the gimbals would have to be capable of moving the sensor in 3 dimensions instead of just 2. Also, not sure but some optical formulas may be designed for a specific focus distance behind the lens and changing that could have issues. But, a good concept for some cases.
Those shifts would depend on the focal length used. Manual ultra wide angle and macro lenses would certainly benefit from this in combination with an electronic viewfinder (in addition to the optical slr reflex finder like in the Fuji X100 series of compact, high end cameras).

10-18-2019, 12:20 AM   #6
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I think only the screwdrive lenses need some extra precision. In general they are fast enough, but not precise enough for tracking. I heard new lenses (DFA* 70-200, DFA* 50, DFA150-450,...) are much better then old FA lenses in focusing.
10-18-2019, 07:57 AM   #7
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QuoteOriginally posted by 08amczb Quote
I think only the screwdrive lenses need some extra precision. In general they are fast enough, but not precise enough for tracking. I heard new lenses (DFA* 70-200, DFA* 50, DFA150-450,...) are much better then old FA lenses in focusing.
The last part of the statement is true. There are also other lenses like the da 16-85 and 18-135 using dc rather than sdm that are quick.

But this first part about screw drive needing more precision? I regularly convert from sdm to screwdrive and I don't agree. The lenses focus just as well or better.

10-18-2019, 12:05 PM   #8
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Changing direction with screw drive for tracking has some trouble. The mechanics in its nature is a little wobbling. In single focus mode Pentax is good enough. I had issues with tracking. (The too big size of the focus points is my only problem with AF.S on pentax bodies.)
10-21-2019, 05:02 PM   #9
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FWIW, back-plane focusing is not a new concept. I actually own a camera that does so.



Despite having a bellows extension, my late 1950s vintage Mamiya-Six does not move the lens to focus. Instead, a thumb dial on the camera back moves the film pressure plate in concord with the coupled rangefinder to accomplish focus.


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10-22-2019, 03:18 AM   #10
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Contax AX did autofocus with moving the film, it's not new:
An early swansong? Reviewing the CONTAX AX: autofocusing manual lenses | EMULSIVE

However no one used it in a digital camera even as a focus helper. (As I know...)
10-22-2019, 09:56 AM   #11
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Pentax is in need of some sort of innovation in the AF department, so this would be a pretty good idea and yet another use for the SR mechanism.
10-22-2019, 10:22 AM   #12
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Pentax also needs a new AF sensor. (According to the pics of the K-new it comes!)
-The focus points are too big!
-The coverage is too small. (For example in the Nikon D500 the focus points spreads across the whole frame horizontally)
-The density is too small, for reliable tracking with more coverage Pentax needs many more focus points.
-All focus points should focus down to -3EV and could be F2.8 accurate.
-More modes would be welcomed: with my Nikon there are the range modes where in the range the camera selects the focus point, the group mode where in the group the nearest point get tracked and the 3D tracking which is what Pentax has in SEL1 mode, but much more reliable. It tracks that exact point across the range. Eye tracking would be welcomed also.
10-22-2019, 10:33 AM   #13
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QuoteOriginally posted by 08amczb Quote
Pentax also needs a new AF sensor. (According to the pics of the K-new it comes!)
-The focus points are too big!
-The coverage is too small. (For example in the Nikon D500 the focus points spreads across the whole frame horizontally)
-The density is too small, for reliable tracking with more coverage Pentax needs many more focus points.
-All focus points should focus down to -3EV and could be F2.8 accurate.
-More modes would be welcomed: with my Nikon there are the range modes where in the range the camera selects the focus point, the group mode where in the group the nearest point get tracked and the 3D tracking which is what Pentax has in SEL1 mode, but much more reliable. It tracks that exact point across the range. Eye tracking would be welcomed also.
I certainly hope the new AF sensor rumor is true because as good as the K-3/K-3 II's AF is, it's way behind the competition. 27 AF points just isn't enough.
10-25-2019, 06:02 AM   #14
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QuoteOriginally posted by 08amczb Quote
Pentax also needs a new AF sensor. (According to the pics of the K-new it comes!)
-The focus points are too big!
-The coverage is too small. (For example in the Nikon D500 the focus points spreads across the whole frame horizontally)
-The density is too small, for reliable tracking with more coverage Pentax needs many more focus points.
-All focus points should focus down to -3EV and could be F2.8 accurate.
-More modes would be welcomed: with my Nikon there are the range modes where in the range the camera selects the focus point, the group mode where in the group the nearest point get tracked and the 3D tracking which is what Pentax has in SEL1 mode, but much more reliable. It tracks that exact point across the range. Eye tracking would be welcomed also.
I agree that the focus area on single point is far too big. It makes the result unpredictable . You never know what bar in a fence that is used, silhouette portraits are impossible if you want the edge of the nose sharp, the environments of the nose are disturbing. I always use single point af, more focus points means more disturbance. I have no experience with tracking. The last month I have places my KP on the shelf because I am tired of bad autofocusing. If the photos with analogue slr are out of focus I am to blame, not the camera . I am close to drop the dslrs
10-25-2019, 06:38 AM   #15
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QuoteOriginally posted by niels hansen Quote
I agree that the focus area on single point is far too big. It makes the result unpredictable . You never know what bar in a fence that is used, silhouette portraits are impossible if you want the edge of the nose sharp, the environments of the nose are disturbing. I always use single point af, more focus points means more disturbance. I have no experience with tracking. The last month I have places my KP on the shelf because I am tired of bad autofocusing. If the photos with analogue slr are out of focus I am to blame, not the camera . I am close to drop the dslrs
I had the same problems and its definitly easier with my Nikon D750, but I have to blame myself for the out of focus images. I knew my KP and I knew when to double check the focus. I never ruined an event or portrait session because the AF. Although I wouldn't switch back from Nikon to any current Pentax with it's AF system.
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