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View Poll Results: Do you want to be able to use trap-AF with all lenses?
Yes 4488.00%
No 612.00%
Voters: 50. You may not vote on this poll

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10-27-2009, 06:45 PM   #1
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Trap AF focus

How many of you wish you could use trap-AF with all lenses? This includes both newer lenses without an AF/MF switch and older lenses like M42 with a genuine adapter.

If you vote no, please explain why you wouldn't want this option available. Keep in mind this is a pretty trivial firmware fix.


Last edited by Eruditass; 10-28-2009 at 09:11 PM.
10-28-2009, 07:08 AM   #2
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As for implementing it, what do you guys suggest? These are for lenses without an AF/MF switch on the lens, of course.

One option is to change the AF button to have another option, where if you hold it down, it is in trap-AF mode.
10-28-2009, 08:46 AM   #3
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Also, my main beef is that when using the genuine M42 adapter, you don't get trap-AF focus without shorting some pins. This has to be fixed! Flanged 3rd party adapters currently have the advantage there.
10-28-2009, 08:47 AM   #4
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sorry, what's trap-AF?

10-28-2009, 09:13 AM   #5
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Also known as catch-in-focus, when you hold the shutter down, it will trip the shutter once something is in focus. Helpful if you pre-focus with sports or animals, or if you are using a manual focus lens you can slowly rotate the focus ring and it wil snap several pictures as the object becomes in focus.

Focus Trap or Catch In Focus |Photography Rulez
10-28-2009, 09:56 AM   #6
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If you vote no, explain yourself!
10-28-2009, 12:19 PM   #7
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I fail to see why you want to use trap focus on an AF lens. It's using the same system and the results should be the same. I know some AF lenses have the switch but it seems they have stopped making lenses with that option. I voted yes as the tin foil trick on M42 lenses is a pain but I'm not sure if it's possible. Flanged adapters cause you to lose infinity focus so that isn't a solution. I can't see Pentax going out of their way to make using old glass more convienent. They stopped making M42 Taks in the mid 70's. To be honest, I'm surprised they are still making the adapters. (but grateful)
10-28-2009, 12:25 PM   #8
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QuoteOriginally posted by reeftool Quote
I fail to see why you want to use trap focus on an AF lens. It's using the same system and the results should be the same. I know some AF lenses have the switch but it seems they have stopped making lenses with that option. I voted yes as the tin foil trick on M42 lenses is a pain but I'm not sure if it's possible. Flanged adapters cause you to lose infinity focus so that isn't a solution. I can't see Pentax going out of their way to make using old glass more convienent. They stopped making M42 Taks in the mid 70's. To be honest, I'm surprised they are still making the adapters. (but grateful)
If I'm doing sports with a slow auto-focusing lens, waiting for the action to become in focus results in significantly better photographs. Also, I can leave my camera focusing on a bird feeder and it will take shots of birds when they land. If I'm in macro mode with an AF lens, I can use the closest focusing length a lot easier. If my lens is having trouble in normal use with AF, I can do a focus bracket and twist the ring myself so it only takes pictures in focus, like with MF lenses. Also, if I want to be quieter.

On M42, yes its possible. The firmware tells the chip to only activate the function when two of the inputs are equal (shorted together). This check could easily be disabled. I don't see where this could cause a problem. Flanged adapters cause you to lose infinite focus, yes, so there is definitely a trade-off, but you gain hassle-less trap-AF. And its harder to get off. But it sucks that a 3rd party crappy adapter has a feature that the genuine one does not.

10-28-2009, 12:59 PM   #9
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I've never felt wanting this feature on an AF lens. If the scene is bright enough for the camera to register a subject in focus, then may as well use AF. For fast action the technique is important to using AF effectively, and you can help a 'slow' AF lens out by prefocusing around infinity, then following the subject meticulously with the AF point to avoid the camera having to hunt back and forth.
10-28-2009, 08:24 PM   #10
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QuoteOriginally posted by Ash Quote
I've never felt wanting this feature on an AF lens. If the scene is bright enough for the camera to register a subject in focus, then may as well use AF. For fast action the technique is important to using AF effectively, and you can help a 'slow' AF lens out by prefocusing around infinity, then following the subject meticulously with the AF point to avoid the camera having to hunt back and forth.
Of course technique is the most important, but more tools always helps. What about indoor sports with bad lighting?
10-28-2009, 09:02 PM   #11
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In that situation I would think subjects are moving too fast to trap focus all that effectively - may as well just focus manually the whole time if AF simply won't work...
10-28-2009, 09:08 PM   #12
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I disagree, I've found I can trap-AF just fine in low light, as I would be panning keeping them in the frame as they run across me. Instead of AF just going back and forth and keep being a bit too slow, it can just wait for them to pop in focus and snap it. Also, if they are stationary like returning a ball or shooting, I find the K10D I used would hunt as opposed to me just moving the AF ring slowly and do some focus bracketing.

And of course, do you use any M42 lenses? Would you like hassle-free trap-AF?
10-29-2009, 07:11 AM   #13
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I shoot a lot of sports although mostly outside in daylight so I'm not trying to follow ith action in bad light but that must be difficult in more ways than just focusing because if the light is poor enough to make the AF to hunt then you may not be using a fast enough shutter speed to stop action and you may be seeing motion blur and not lens blur. However, if trap focusing is working better for you by all means use what works. I recently used a 500 mm T mount mirror lens to shoot an inter squad rowing scrimmage that my daughters crew team did on her colleges parents weekend and used trap focus. The results between the 500 and the cropped shots done with an AF Sigma 70-300 are about the same as far as getting the focus. There are other issues with mirror lenses that can cause IQ problems but I can notice no real difference in focusing accuracy between AF and trap focus. Those shots are on my picasa page at Picasa Web Albums - Richard - SLU Parents W...
Another thing to consider is using the quick shift feature on lenses that allow it.
10-29-2009, 07:17 AM   #14
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Whenever I shoot sports, indoor or out, I always try to freeze the action. Indoor I go as low as 1/500 when they are moving and if I can keep the noise low, I go up to 1/1000 sometimes. So I don't think it's shutter speed.

AF does work better for me in good light, but indoor with my slow Tamron 70-300mm, hunting is a real pain, even just listening for it. I get better results with a 135/2.8 and trap-AF but some sports I need more reach or a variable focal length.
10-29-2009, 09:01 AM   #15
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Trap focus has it's good points. It comes real handy when you want to get a picture of the finish line. You set the camera on a tripod, prefocus, and use a cable release with a lock to have a picture of the winner without having to actually hold the camera. That way, I can use a second camera with a long lens to get facial expressions of the runners.
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