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03-12-2018, 01:10 PM - 2 Likes   #1
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In Body Focus range limiter

In the Exif Pentax strores a value called FocusRangeIndex having a value of 0-7. (very close to very distant)

Could this information be used for an in body focus range limiter to minimize AF operation time?

User defined values of say: Off, Macro (0-2), Close (3-6), Distant (7).

If the FocusRangeIndex value goes outside the selected range, the focus direction is reversed.

This function should also be able to be assigned to a customizable button and retained in User Modes.

03-12-2018, 03:47 PM   #2
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QuoteOriginally posted by alfa75ts Quote
In the Exif Pentax strores a value called FocusRangeIndex having a value of 0-7. (very close to very distant)
If, indeed, this is what that value represents, it may well be possible and might be something good. That being said, the labels attached by ExifTool* and other software to values in the MakerNote section in the EXIF are the developer's best guess as to function and interpretation. How accurate many of those assignments are and whether they are consistent is open to speculation.


Steve

* This is an ExifTool tag name, made up by the ExifTool team for values found at a specific location in the MakerNote section of the EXIF Filesystem. The string "FocusRangeIndex" is not found in the file.

Last edited by stevebrot; 03-12-2018 at 04:02 PM.
03-12-2018, 04:39 PM   #3
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Very true Steve, however I have checked many of my images and it does directly relate to the distance to the subject which is what we want.
03-13-2018, 05:40 PM   #4
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QuoteOriginally posted by angerdan Quote
With a firmware integrated and camera controlled focus limiter like the Olympus OM-D series cameras have, AF-speed of screwdrive lenses would increase.
All FA and later lenses do send the distance informations to the camera, so it would be possible to offer this feature.
Re: E-M1 MkII - "soft" focus limiter - not limited!: Micro Four Thirds Talk Forum: Digital Photography Review
High-speed Performance E-M1 Mark II | OM-D | Olympus
AF Limiter - focus range limiter [Gary Ayton's photography wiki]

03-13-2018, 07:41 PM   #5
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So Olympus have had it since 2016, I didn't know that.

At least it means somebody else thought it was a good idea.
05-20-2018, 12:15 PM   #6
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I wonder why Pentax didn't offer this yet. All the old scredrive and SDM tele lenses could be enhanced.



Only a few lenses do have integrated focus limiter.

Lenses for Pentax with focus limiter - PentaxForums.com
05-20-2018, 02:05 PM   #7
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QuoteOriginally posted by angerdan Quote
I wonder why Pentax didn't offer this yet. All the old scredrive and SDM tele lenses could be enhanced.



Only a few lenses do have integrated focus limiter.

Lenses for Pentax with focus limiter - PentaxForums.com
Probably because there are only eight zones and they are all relative.* The breakdown (from ExifTool) goes like this:

3.1 FocusRangeIndex int8u [Mask 0x07]
0x0 = 5
0x1 = 4
0x2 = 6 (far)
0x3 = 7 (very far)
0x4 = 2
0x5 = 3
0x6 = 1 (close)
0x7 = 0 (very close)
My understanding is that the value is returned by the lens and is an indication of focus ring position. I am not sure that all AF lenses return this information.


Steve

* It is not clear whether "0" means the same for a macro lens as it does for a 300mm telephoto.
05-20-2018, 02:58 PM - 2 Likes   #8
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QuoteOriginally posted by stevebrot Quote
* It is not clear whether "0" means the same for a macro lens as it does for a 300mm telephoto.
I did a quick look-see with my DA 50/1.8 vs. Sigma 50/2.8 EX DG Macro vs FA 77/1.8.

To test the extremes:
30 meters
DA 50/1.8: "7" (very far)
Sigma 50/2.8 Macro: "7" (very far)
FA 77/1.8: "7" (very far)
At 70cm (MFD for the FA 77/1.8)
DA 50/1.8: "0" (very close)
Sigma 50/2.8 Macro: "3"
FA 77/1.8: "0" (very close)
At 45cm (MFD for the DA 50/1.8)
DA 50: "0" (very close)
Sigma 50/2.8 Macro: "1" (close)
19cm (MFD for the Sigma)
Sigma 50/2.8 Macro: "0" (very close)

Steve

05-20-2018, 10:21 PM   #9
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QuoteOriginally posted by angerdan Quote
I wonder why Pentax didn't offer this yet.
Perhaps Olympus have a Patent. I don't know.

QuoteOriginally posted by stevebrot Quote
Probably because there are only eight zones
QuoteQuote:
I did a quick look-see
I don't think it really matters, it's not like most users will want to set it to a half metre range.

Heck, for myself, approximately 10 metres to infinity would make me happy. Just so long as it didn't always assume the target had suddenly moved to the far end of the focus range!

I still think off/close/medium/far would be very much welcomed by many users.

I'd almost be happy if they rewrote the software so that when focus is lost, it re-tries in the direction of the nearest end stop not the furthest as it seem to do.

Anyway, thanks for your efforts Steve.
05-20-2018, 10:48 PM   #10
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QuoteOriginally posted by alfa75ts Quote
I don't think it really matters, it's not like most users will want to set it to a half metre range.
Different for every lens. Looks like a slam dunk, eh?


Steve
05-20-2018, 11:03 PM   #11
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QuoteOriginally posted by stevebrot Quote
Different for every lens. Looks like a slam dunk, eh?
I don't think it matters, if 'close' is too close use 'medium' - if 'far' is too far use 'medium' - if 'medium' is too close use 'far etc. etc. If you're right on the border, that's a problem unless you have overlapping ranges.

The idea is to limit the focus range not define it.
05-21-2018, 01:08 AM   #12
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QuoteOriginally posted by stevebrot Quote
My understanding is that the value is returned by the lens and is an indication of focus ring position.
I am not sure that all AF lenses return this information.
Pentax was the first manufacturer which introduced focusing distance measurement for SLR cameras.
So i'd expect that the current lineup does transmit the exact distance to the camera.
AOHC - Asahi Optical Historical Club: Catalog

The data found in EXIF is a different topic.
05-21-2018, 07:33 AM   #13
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QuoteOriginally posted by angerdan Quote
So i'd expect that the current lineup does transmit the exact distance to the camera.
QuoteOriginally posted by angerdan Quote
The data found in EXIF is a different topic.
I will take your word for it. As for the utility of such, if actual distance (e.g. meters) were available, I can imagine huge usefulness for non-metered flash automation where duration might be adjusted based on distance and aperture rather than fiddling with a pre-flash.


Steve
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