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04-19-2013, 03:00 PM   #1
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AF Limits - firmware update suggestion

Pentax medium to long glass is limited in its usefulness for sports photography, due to the inherent in-camera motor limitations; elsewhere in the forum it is recommended to drop the 50-135DA* for a Sigma if that's what you need to shoot. I have an idea that should be simple to implement, and would allow what Pentax provides to work well in fast-moving sports scenes, as long as you know the sport well and can anticipate where you'll need to shoot- roughly.
I would truly love it if they could set an option for the green button wherein you manually focus your lens to a near range (I shoot volleyball. Let's but this at 15 feet, or about 3 meters). Then a manual focus out to, say, 25 feet, 8.3 meters, and a second touch of the green button. Now, AF is restricted to the range from 15 to 25 feet, until the green button is touched a third time. The ability to define a working range, coupled with some knowledge of where the action is likely to be ahead of time, as well a quick program in, program out interface, would allow me to maximize the performance of the hardware in most situations, for a relatively minor investment in software code writing.
The only risk is if I have just described something knowledgeable Pentaxians already know how to do using some simple technique clearly spelled out in the manual I happened to totally miss.

Matt "D" Hat

04-19-2013, 03:33 PM   #2
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that sounds like a great idea, but don't think the lens actually tells the camera where its focused, it just says based on microcontrast (i think thats the term) a subject is in focus

lens based focus limiters are litteraly that, mechanical limitations placed on the focusing apparatus

i hope i'm wrong, cuz i think that might even be handy for BIF images in a lot of instances
04-19-2013, 03:48 PM   #3
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That's an interesting idea - could be helpful with sports like volleyball (as you say) and other situations.


I have a different problem. When I'm shooting runners, I know almost exactly where they're headed, but they're moving there at full speed (and usually straight toward me). Therefore I need fast AF-C speed using a fixed focus point, so I've gone to fast focusing screw-drive primes on a K-5 IIs (which works pretty well).

Volleyball has extremely fast motion, but at least it has a relatively small court and fairly limited movement of the players (compared to a field sport).
04-19-2013, 04:09 PM   #4
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Sony A99 works that way, but I think it needs special lenses for that too. I doubt that Pentax lenses sends accurate enough feedback to the camera fr that but I could be wrong.

04-19-2013, 05:40 PM   #5
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Catch-in-focus? Is that an option? Or some adaption of that.

Otherwise it sounds like the focus limiter option you get with macro lenses would be needed, but usually, as has been mentioned, that is a mechanical solution on the lens.
04-19-2013, 05:48 PM   #6
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QuoteOriginally posted by rawr Quote
Catch-in-focus? Is that an option? Or some adaption of that.

Otherwise it sounds like the focus limiter option you get with macro lenses would be needed, but usually, as has been mentioned, that is a mechanical solution on the lens.
Most other camera makers puts limiters on their better tele's too, but sadly Pentax forgets it. Sony A99 have limiters controllable from the camera body and Sigma will have customizable ones with their new sport lenses and the USB hub. There is actually no real reason to skip limiters at all.
04-20-2013, 02:13 AM   #7
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When I look into PhotoMe into exif information off a RAW image. There are 4 types of information about AF-distance:

- unknown
- macro
- nearby
- far away

(my translation, since I got Dutch).

So there is information transferred from the lens to the camera.
04-20-2013, 03:23 PM   #8
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Clarification/speculation

So, if we think the idea has merit, from a technical standpoint, I'm not sure you need Contrast/phase data, whatever, from the lens. You are using a specific lens in a specific setting. You set your near limit, and either manually or by AF focusing the camera elsewhere down range set the far limit, and use a "marker" press of the green button or the function button at each point. The camera only has to count the number of turns of the motor between each point, and limit AF to that range of turns, from beginning to end. THEN whichever AF system you've selected (although, honestly, I can't see Live View in a quick sports application like this) hunts for a focus point between the "turns points" you specified. I think that means less hunting, and quicker to in focus. Perhaps this can't be done through firmware alone- perhaps the hardware isn't sufficiently sophisticated. Perhaps they'd need to either put a turn count sensor on the motor (my choice, you only need to add it once), or in the lens (which might give the system some advantage because different lens require additional turns to cover their focus range. A means something for the next body, say that full frame- and B means it could be in new iterations of lens as they appear. To the Lords of The Forum I Pray- communicate with the Elder Gods of Pentax Land and suggest this idea. I won't even ask for the patent rights- promise!
Matt

04-20-2013, 03:48 PM   #9
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QuoteOriginally posted by nomadkng Quote
but don't think the lens actually tells the camera where its focused
I think you're right, the exact distance isn't transmitted. Technically all the camera needs is the ability to turn the AF ring in either direction

Adam
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