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05-29-2015, 11:47 AM - 2 Likes   #31
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QuoteOriginally posted by Mike.P Quote
Adam, can I ask what body you were testing it on?

I recently sold a bunch of photographic equipment and the money is either going on a K-3II/150-450mm or a 7DII/100-400mm MKII combo, to mainly be used at airshows and suchlike so AF speed is a must.
The K-3. If you're planning on shooting action I would honestly recommend the Canon, as much as I'd like to say that Pentax is more competitive with their latest offerings. I personally haven't used the 7D II yet, but I did shoot with the 7D + 70-200mm on several occasions and it worked exceptionally well for photographing RC airplanes.

With that said I have yet to test the 150-450mm with the K-3 II, but it's unlikely that things will change much if at all. I should have the K-3 II by the end of next week. The Pentax AF system needs an overhaul rather than minor tweaks to bring it to the level of the competition. It's certainly still usable, just slower in practice.


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06-02-2015, 03:02 AM - 1 Like   #32
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QuoteOriginally posted by MyTZuS Quote
Thanks everyone... didn't think of lenses since I'm using the new 55-300 HD DA ED WR exclusively for sports.

When I mean better, I mean faster.

Until I started shooting gymnastics I didn't really have an issue.

Two things specifically I noticed about gymnastics. One, I cannot shoot straight on, the lens cannot keep up with the subject running straight at me. Also, I got a lot of back focused area's from that type of shooting. Which actually made some of the shots more interesting due to what they captured in the background but frustrating since I'd like to have had SOME shots of the person running at me.

It is my hope that the FF will be more sports oriented since thats lacking in the Pentax line.

But until then I was hoping the K3 or II would fill the void but if not, meaning, its not much better at AF than my K5 IIs (and its not, because I've learned to compensate), then I'll stick with my camera and just buy another lens like the new 16-85 which might be better indoors.
55-300 = slow consumer lens not suitable for indoor sports as will approach ev levels that the AF stops functioning

It doesn't matter what body you put an f5.6+ lens on it will be hopeless under indoor lighting for sports.

Get a lens suitable for the task at hand then compare AF speed not before.

The 16-85 will not help you still a slow lens ..... the Sigma 70-200 f2.8, da*400 F4 , da* 50-135 f2.8 , da* 60-250 etc etc will
The new dfa* 70-200 shoudl be the fastest of the lot under indoor lighting

Remember the cameras EV rating fro AFis based on a 50 f1.4 lens (probably f2.8 due to AF mask) and each stop slower your lens is you lose about 2 EV sensitivity

i.e a f5.6 lens on a K3 will fail completely to focus somewhere around EV2

Last edited by awaldram; 06-02-2015 at 03:12 AM.
06-02-2015, 05:33 AM   #33
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QuoteOriginally posted by awaldram Quote
55-300 = slow consumer lens not suitable for indoor sports as will approach ev levels that the AF stops functioning

It doesn't matter what body you put an f5.6+ lens on it will be hopeless under indoor lighting for sports.

Get a lens suitable for the task at hand then compare AF speed not before.

The 16-85 will not help you still a slow lens ..... the Sigma 70-200 f2.8, da*400 F4 , da* 50-135 f2.8 , da* 60-250 etc etc will
The new dfa* 70-200 shoudl be the fastest of the lot under indoor lighting

Remember the cameras EV rating fro AFis based on a 50 f1.4 lens (probably f2.8 due to AF mask) and each stop slower your lens is you lose about 2 EV sensitivity

i.e a f5.6 lens on a K3 will fail completely to focus somewhere around EV2
Sorry, but the EV rating og the AF system is not dependent of the lens. The AF sensor is not capturing light from the whole area of the front element, but only from two small spots. These small spots are not dependent of the lens and a f/5.6 lens is just as capable to focus in dim light as a f/1.4 one. But there are of course mechanical differences on lenses which make AF more suitable on one lens compared to another one.
06-02-2015, 07:03 AM - 1 Like   #34
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QuoteOriginally posted by StigVidar Quote
Sorry, but the EV rating og the AF system is not dependent of the lens. The AF sensor is not capturing light from the whole area of the front element, but only from two small spots. These small spots are not dependent of the lens and a f/5.6 lens is just as capable to focus in dim light as a f/1.4 one. But there are of course mechanical differences on lenses which make AF more suitable on one lens compared to another one.
Sorry thats just wrong Pentax state the spec on their web site and include the conditions required to achieve it.

"Sensitivity range: EV -3 to 20 (ISO 100, 50mm F1.4)"

Af phase detect uses a baseline twin sensors to detect phase variance these are traditional spaced such that F5.6 works.

Unfortunately this means they can only detect DoF Phase changes of F5.6 so use logic to improve accuracy ... i.e swing left till phase varies not position swing right til phase varies note position move lens to center of readings , they use these both because of cost and so any cheap consumer lens can Auto Focus

More upmarket cameras have 'special' f2.8 baseline sensors 1 in the k5ii and 3 in the k3 these allow ev=-3 as per spec and over double the accuracy of f5.6 sensors .... BUT to utilize these sensor you must use f2.8 or better lens.

It makes no difference what portion your using for AF reading as the whole image dims as you close the aperture.

My statements are easy to prove ... Put an f2.8 lens on your camera reduce light until the AF struggles .... Put an f5.6 lens on the camera and it will no longer focus.

This is old news and was known as blackout in MF focus days with split prism panels and the reason it happen in AF is the same as MF.

Nikon F2 "blackout" with slower lenses [Archive] - Rangefinderforum.com

Modern dual baseline sensors is like having twin focus screens 1 allowing f2.8 to work OK and 1 allowing f5.6 to work OK but don't; fool yourself to get the advantages of EV-3 and high AF accuracy you must use fast lens which will activate the f2.8 sensors , Slower lens do not cover the f2.8 baseline and hence useless.

This isn't hard and fast as you can easily get a Pentax camera to focus with f11 max aperture but EV and performance drop accordingly ... There are many AF timing Vs EV available to Google just how slow AF becomes as you approach the Phase limits.

The big difference between Pentax and Canon implementation is Canon artificially kill AF if the sensor baseline is exceeded (hence why teleconverter stop working above f5.6)


Last edited by awaldram; 06-02-2015 at 07:11 AM.
06-02-2015, 08:14 AM   #35
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QuoteOriginally posted by awaldram Quote
Sorry thats just wrong Pentax state the spec on their web site and include the conditions required to achieve it.

"Sensitivity range: EV -3 to 20 (ISO 100, 50mm F1.4)"
That is the sensitivity range for the light meter and not the AF. The light meter is measuring the light on the matte screen and is receiving light from the whole area of the front lens. And therefore it is dependent of the aperture of the lens.

But not the AF.


Last edited by StigVidar; 06-02-2015 at 08:21 AM.
06-02-2015, 10:38 AM   #36
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QuoteOriginally posted by StigVidar Quote
That is the sensitivity range for the light meter and not the AF. The light meter is measuring the light on the matte screen and is receiving light from the whole area of the front lens. And therefore it is dependent of the aperture of the lens.

But not the AF.
Your right my mistake but still my main point is valid

This though Canon centric covers off why AF performance drops on slower (open aperture) lens
What apertures are required to enable autofocus, including cross-type or high-precision focusing, on Canon DSLR cameras? - Photography Stack Exchange

It's collated from the Canon manuals and basically says the same as I did above.
06-02-2015, 10:50 AM   #37
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QuoteOriginally posted by awaldram Quote
This is old news and was known as blackout in MF focus days with split prism panels and the reason it happen in AF is the same as MF.
It may not be clear, but "black out" with slower lenses and AF low light thresholds are two different things. Black-out happens even in bright light. The low light threshold while expressed as EV(100) is more of a puzzle. Pentax qualifies their specification on the Web site with the strange "ISO 100, 50/1.4 lens" statement*. Whether this means luminance equivalent to EV(100) -4 at the sensor or luminance equivalent to EV(100) -2 from the subject is not clear. Either way, the actual light to the sensor is attenuated a full 4 stops when shooting with at f/5.6 maximum aperture as opposed to f/1.4.


Steve

* Similar language is historically used for meter sensitivity specs in some Pentax user manuals going back several decades...go figure...

Last edited by stevebrot; 06-02-2015 at 11:07 AM.
06-02-2015, 11:31 AM   #38
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QuoteOriginally posted by stevebrot Quote
It may not be clear, but "black out" with slower lenses and AF low light thresholds are two different things. Black-out happens even in bright light. The low light threshold while expressed as EV(100) is more of a puzzle. Pentax qualifies their specification on the Web site with the strange "ISO 100, 50/1.4 lens" statement*. Whether this means luminance equivalent to EV(100) -4 at the sensor or luminance equivalent to EV(100) -2 from the subject is not clear. Either way, the actual light to the sensor is attenuated a full 4 stops when shooting with at f/5.6 maximum aperture as opposed to f/1.4.


Steve

* Similar language is historically used for meter sensitivity specs in some Pentax user manuals going back several decades...go figure...
Hi Steve,

My point on blackout was related to f5.6 and f2.6 baselines on PD sensors not directly low light AF capability.
I was trying to explain why an f5.6 lens cannot utilise f2.8 baseline sensors.

06-02-2015, 02:22 PM   #39
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QuoteOriginally posted by awaldram Quote
Hi Steve,

My point on blackout was related to f5.6 and f2.6 baselines on PD sensors not directly low light AF capability.
I was trying to explain why an f5.6 lens cannot utilise f2.8 baseline sensors.
I know. I just added my two bits in case anyone got confused. As you are aware, the matter of the f/2.8 sensors is a matter of recurring confusion on this site with many users thinking it has something to do with light intensity and the -3 EV lower limit for the system.


Steve
06-02-2015, 07:28 PM   #40
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Soooo..... I mentioned the new 16-85 since it has a faster AF motor. Just like the new 55-300. And I would guess the new 70-200 has the same motor.

Soooo.... still sticking with my K5 IIs but waiting to hear about AF in the K3 or K3 II. Thanks.
06-04-2015, 11:26 AM   #41
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QuoteOriginally posted by MyTZuS Quote
And I would guess the new 70-200 has the same motor.
Fairly sure that is not the case. The 70-200 and 150-450 have a new motor design. What exactly it is has been speculated on but I've not seen anything official yet explaining what it is. But I don't think it is the same as 18-135 and 16-85 DC motors.
QuoteOriginally posted by MyTZuS Quote
I mentioned the new 16-85 since it has a faster AF motor. Just like the new 55-300.
And no that is incorrect as well. The 55-300 uses the screwdrive system with the motor in the camera. The K-3 is supposed to have a more powerful (faster?) motor than the k-5 but I cannot say from personal experience. The 16-85 uses a DC in lens motor similar (or identical) to the one in the 18-135.
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