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11-24-2010, 07:35 PM - 1 Like   #1
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Got my new K5 tonight and guess what...

My Tamron 17-50 2.8 is front focusing like crazy... It looks perfectly focused in the view finder, but shots are front focused. It needs -10 adjustment to be usable when wide open (-11 would probably be perfect if it were available).

BUT!

In live view, it focuses perfectly.

I'll be conducting more tests tomorrow in natural light (I tested it under cool CFL bulbs and fluorescent tubes).


Fortunately there is a bright side!

My M50 f1.7 focuses perfectly (both "by eye" and with trap focus) (it required -9 adjust on my K20d)

My Sigma 600mm mirror lens also focuses perfectly! (-10 on my K20d)

My DA55-300 also focuses perfectly (both in live view and thru viewfinder) (it required -8 adjust on my K20d)

I lent my DA18-55 and DA50-200 to my sister so I can't test them right now.

The funny thing is that ALL my lenses need minus adjustment on my K20d, but only my Tammy needs adjustment on the K5.

Looks like I might have to send it in to Tamron service...


Non lens related...

I have to admit the different button placement makes this camera a little odd to use, but I'll get used to it! The smaller form factor is actually quite pleasant. I love my K20d, but only when playing with the K5 (and grip) do I realize how bulky the 20 +grip really is!

I LOVE that it exposes perfectly with the green button when I am using manual lenses! My K20d consistantly over-exposed with manual lenses.

iso 1600 test shots BLEW ME AWAY! wow... I can't wait to start playing with higher iso's! This camera is going to be something else when taking pics at fire scenes at night.

And of course now I might just have to get myself a nice DA* 16-50 2.8... the weather seals alone make it worth it.

Pat

11-24-2010, 07:49 PM   #2
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Contests :-) I love mine and need to check lenses but so far only a few shots here and there.
11-25-2010, 07:02 AM   #3
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Welcome to the club!

Seems a little odd that your tamron is correct in live view but while perfectly focused in the viewfinder, is off by so much (assuming we're talking about AF here).

11-25-2010, 07:07 AM   #4
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QuoteOriginally posted by ve2vfd Quote
My M50 f1.7 focuses perfectly (both "by eye" and with trap focus) (it required -9 adjust on my K20d)
You applied AF adjust to a MF lens? I didn't even know that was possible.

11-25-2010, 07:42 AM   #5
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QuoteOriginally posted by audiobomber Quote
You applied AF adjust to a MF lens? I didn't even know that was possible.
The bigger question is how does the camera recognize K and M lenses to apply the settings if these aren't chipped?


I guess that AF correction with a wobbly sensor assembly is just another reality to live with... just like dust....
11-25-2010, 11:29 AM - 1 Like   #6
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QuoteOriginally posted by JeffJS Quote
Seems a little odd that your tamron is correct in live view but while perfectly focused in the viewfinder, is off by so much (assuming we're talking about AF here).
Makes sense to me. The phase AF takes place on a different sensor, which isn't on the CMOS sensor. So unless that sensor was perfectly calibrated to the sensor plane distance, any defect on that lens could cause FF/BF on phase AF. Since Live View AF (except phase-detect) uses the actual CMOS sensor for focusing, it's going to be sharp since focusing is done at the plane where the image will be captured; focus issues on the lens will be corrected at the sensor.

My First DA* 16-50 front-focused beyond what my K-7 could correct. But it worked great in LiveView.

- Jason
11-25-2010, 11:52 AM   #7
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QuoteOriginally posted by audiobomber Quote
You applied AF adjust to a MF lens? I didn't even know that was possible.
I have to go into lens correction and change the value every time I put on the M50 on my old K20d.

As inferno10 said, remember that the focus assist and viewfinder being in focus doesn't mean that the actual image sensor is in focus. On my old K20d all my lenses front focus between -5 and -10.

But I'm just glad my K5 focuses perfectly with all but my Tammy lens. Been playing with it all morning at work in natural light and I confirmed the findings of my original post.
11-25-2010, 12:19 PM   #8
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QuoteOriginally posted by inferno10 Quote
Makes sense to me. The phase AF takes place on a different sensor, which isn't on the CMOS sensor. So unless that sensor was perfectly calibrated to the sensor plane distance, any defect on that lens could cause FF/BF on phase AF. Since Live View AF (except phase-detect) uses the actual CMOS sensor for focusing, it's going to be sharp since focusing is done at the plane where the image will be captured; focus issues on the lens will be corrected at the sensor.

My First DA* 16-50 front-focused beyond what my K-7 could correct. But it worked great in LiveView.

- Jason
Thanks, Jason.. Learn something new every day..



11-25-2010, 12:42 PM   #9
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QuoteOriginally posted by inferno10 Quote
Makes sense to me. The phase AF takes place on a different sensor, which isn't on the CMOS sensor. So unless that sensor was perfectly calibrated to the sensor plane distance, any defect on that lens could cause FF/BF on phase AF. Since Live View AF (except phase-detect) uses the actual CMOS sensor for focusing, it's going to be sharp since focusing is done at the plane where the image will be captured; focus issues on the lens will be corrected at the sensor.
- Jason
If you make an adjustment in the menu for front/backfocus like -10 do you only correct the AF-module and it does nothing with the contrast-AF that works with the sensor?
11-25-2010, 01:05 PM   #10
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QuoteOriginally posted by ve2vfd Quote
iso 1600 test shots BLEW ME AWAY! wow... I can't wait to start playing with higher iso's! This camera is going to be something else when taking pics at fire scenes at night.
Congrats on your new acquisition Pat. You'll see it's not just the high ISO it's all these details in the shadows, a side effect of the huge DR. I don't fear leaving the camera at -1 EV to protect the highlights. The K-5 is certainly the best Pentax DSLR to date, and a huge step up from the K20D.
11-25-2010, 02:11 PM   #11
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QuoteOriginally posted by RonHendriks1966 Quote
If you make an adjustment in the menu for front/backfocus like -10 do you only correct the AF-module and it does nothing with the contrast-AF that works with the sensor?
I believe that's correct. The AF correction corrects for this offset that phase AF sensor/lens combo has in relation to the actual CMOS sensor. With contrast-AF, there is no secondary sensor to have to correlate with; the CMOS sensor itself sees when the image is sharp.

- Jason
11-25-2010, 02:47 PM   #12
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that makes no sense. the phase detect system also knows when it's sharp or not. that's what it's designed to do. if the problem would be calibration between main sensor and af sensor, you would require one correction for all lenses on that body. this is not the way it works. most likely this correction has to do with play in the af mechanics of the lens (+those of the body+af sensor "calibration"), but i don't personally know, so i won't state it as fact. even using basic logic, it has to (somehow) have to do with the lens though, otherwise you wouldn't see variations between lenses, would you?

perhaps it's better to start by reading on how phase detect af works? just thinking out loud here..
11-25-2010, 02:48 PM   #13
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ve2vfd: have fun with your k5, good light
11-25-2010, 03:49 PM   #14
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The Tamron is known for FF/BF problems (also in other mounts)
11-25-2010, 07:54 PM   #15
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RE: OP

It sounds like your K20 was front-focussing all this time (rather than the lenses) and you didn't notice it!

QuoteOriginally posted by RonHendriks1966 Quote
If you make an adjustment in the menu for front/backfocus like -10 do you only correct the AF-module and it does nothing with the contrast-AF that works with the sensor?
Yes; the corrections are only for phase-detect AF, not the contrast detect of Live View.

QuoteOriginally posted by nanok Quote
that makes no sense. the phase detect system also knows when it's sharp or not. that's what it's designed to do. if the problem would be calibration between main sensor and af sensor, you would require one correction for all lenses on that body. this is not the way it works. most likely this correction has to do with play in the af mechanics of the lens (+those of the body+af sensor "calibration"), but i don't personally know, so i won't state it as fact. even using basic logic, it has to (somehow) have to do with the lens though, otherwise you wouldn't see variations between lenses, would you?
I believe the K-5 has two AF adjustments: One "universal" adjustment - which would adjust the calibration of the phase detector. The other is the lens adjustments. So yes, there must be something about the lenses which needs compensating for as well.

This doesn't affect contrast AF of Live view though, as contrast AF uses the "end product" image, coming directly from the sensor through the lens, to correct the AF. It is "blind" to all the irregularities and mis-calibrations of the lenses, it just knows that to get correct focus it needs to adjust the lens focus. So it adjusts it, and if it's still not right, it will adjust it again until it gets it right. It doesn't care whether the lens is calibrated correctly or not.
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