K7 AF Myth

Maybe so, the OP suggests that the 30D is superior to the K7. All I am suggesting is that the 40D, with the same lens, is equal to the K7. I'm not sure comparing the 7D to the K7 is reasonable, the 50D perhaps...

ASA_5 said:

flash1100 said:

! Perhaps the Canon may be faster but the K7 is not far behind. I have used a 40D > with a Sigma 70-200/2.8 HSM and the K7 with the same lens and couldn't tell any > difference.

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You are comparing a two generation-old Canon released in 2007, to the K-7, and you make the point that the Canon is faster. That about sums it up doesn't it? Pentax's flagship DSLR is not even comparable to the present competition. Not even in the same league as the 7D which is considerably faster in every way than the 40d.

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Cheers

Gordon
Perth, Western Australia
K-7
http://www.flashpixx.net
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http://www.pentaxphotogallery.com/home#section=ARTIST&subSection=123519&subSubSection=0&language=EN

There used to be a technical paper on Canon's website, explaining their AF strategy, and the upshot was that Canon's AF system did not attempt to get a perfect focus lock at all, it only calculates the movement necessary to achieve a good A4 print quality and goes direct to that position. Mind you this was a few years ago but does explain the resulting quickness and inaccuracy in these days of 100% pixel viewing.

Brad99 said:

There used to be a technical paper on Canon's website, explaining their AF strategy, and the upshot was that Canon's AF system did not attempt to get a perfect focus lock at all, it only calculates the movement necessary to achieve a good A4 print quality and goes direct to that position. Mind you this was a few years ago but does explain the resulting quickness and inaccuracy in these days of 100% pixel viewing.

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I'm calling BS on this. You'll have to show us that Canon actually wrote that their AF strategy is to sacrifice accuracy for speed. I have only ever heard of this from Pentax users hoping to justify the slow AF of Pentax DSLR's.

flash1100 said:

Maybe so, the OP suggests that the 30D is superior to the K7. All I am suggesting is that the 40D, with the same lens, is equal to the K7. I'm not sure comparing the 7D to the K7 is reasonable, the 50D perhaps...

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Gordon,

Here are the test results of the 40d. Compare with the K-7 link before, and you will see that the k-7 is only competitive in bright light.

http://www.popphoto.com/Reviews/Cameras/Camera-Test-Canon-EOS-40D/Specifications-Certified-Test-Results

After EV6 the 40d blows the k-7 away.

Been a Pentax user for 2 decades, and the best Pentax AF body I have used was the Z-1p (never had the chance of using the MZ-S). Though it had primitive AF sensor, its speed, torque and tracking were the best I have experience from Pentax. All Pentax DSLRs are horrible in comparsion. The repeated "truth" in the Pentax circle that Canon sacrified accuracy for speed was total BS. I have experienced it myself. When I first shot 40D with ring USM lenses, the OOF rate dropped dramatically, and that included static subjects. Tracking moving targets at close distance were mission impossible with Pentax. Another problem with all Pentax DSLRs is that they have wide area AF sensors. This seems like a fine choice for the general audience, but as soon as you try to pin point focus, or the target was not very large, or you are using wide angles, the AF would be attracted to the background. Not theory, not from white paper, but repeated experience, something I never experienced with the Z-1p. But consider how Pentax is so hooked up to their 11 point sensor being used on most models, I don't see change any time soon. On paper, most Pentax DSLRs are almost perfect, but the practical performance can be very different. Pentax should address their AF shortcoming 2 decades ago, but it seems getting worse, instead of better.
--
Alan Chan
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No you are wrong here. The reason for the DA Star having slow focus is because that lens has a long focus throw. It has nothing to do with SDM.

The DA 17-70 SDM is one of the fastest focusing Pentax lenses ever made. How come? Because it has SDM? No, but because it has short focus throw.
The focus throw determines the speed of the AF.
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R
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Then in your sense all AF tests are of limited value.

You can't measure AF without the lens, AF is always dependant on the lens in use. What FOTO does is that they compare similar setups, but of course they don't test with exactly the se lens on all cameras. The cameras do have different lens mounts.
AF speed is not only about tracking or continous shooting.

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ASA_5 said:

I agree with the OP. AF is Pentax's greatest weakness. We keep fooling ourselves by comparing the k10d, k20d, k-7 to each other. The fact is they are all WAY behind the competition. Here is the proof:
http://www.youtube.com/user/55bduke

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A few things wrong with that test.

On the canon he is focusing from infinity to macro, and the pentax its the opposite way round.
Different lenses. (obviously)
And frankly there was almost no difference in the speed.
Were they ar full AF, or central point only???
do we know.
The Eos 700 has 1 AF point, and its not cross sensor.

The K-7 has 9 cross sensor and two other sensors. it has a light shift sensor to correct AF on the fly if there is interefetrence with AF. Thats a lot of processing needed compared to just one point.

ASA_5 said:

flash1100 said:

Maybe so, the OP suggests that the 30D is superior to the K7. All I am suggesting is that the 40D, with the same lens, is equal to the K7. I'm not sure comparing the 7D to the K7 is reasonable, the 50D perhaps...

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Gordon,

Here are the test results of the 40d. Compare with the K-7 link before, and you will see that the k-7 is only competitive in bright light.

http://www.popphoto.com/Reviews/Cameras/Camera-Test-Canon-EOS-40D/Specifications-Certified-Test-Results

After EV6 the 40d blows the k-7 away.

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Thanks for the link. I can only comment on my own real life in the field practical use tests.
--
Cheers

Gordon
Perth, Western Australia
K-7
http://www.flashpixx.net
http://www.pbase.com/gordonhaywood/

http://www.pentaxphotogallery.com/home#section=ARTIST&subSection=123519&subSubSection=0&language=EN

wlachan said:

Another problem with all Pentax DSLRs is that they have wide area AF sensors. This seems like a fine choice for the general audience, but as soon as you try to pin point focus, or the target was not very large, or you are using wide angles, the AF would be attracted to the background. Not theory, not from white paper, but repeated experience, something I never experienced with the Z-1p.

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This is to be expected IMO, purely due to the format, regardless of any other difference between brands. An AF system is limited by the need to achieve a physical accuracy baseline and also to fit into the region defined by a lens "virtual aperture" - so two things happen when you change format.

Firstly, each single AF sensor is a different size in relation to the overall field of view... the crop sensor includes less image overall, so each AF cross sensor will be effectively larger in proportion to this.

Secondly, the achievable spread or coverage where AF points can optically function will be a larger proportion of the cropped sensor than the uncropped sensor. IOW, on a smaller format the AF points can fall more toward the edges of the viewfinder and don't seem to cluster so tightly in the middle.

RP

ASA_5 said:

And that is with an f/1.4 lens!

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You do know that AF is built to a particular virtual aperture , and that this is often around f/4 or f/5.6? (MF using a textured viewfinder screen has the same limitation).

IOW, the general AF sensors do not use or benefit from any extra lens speed beyond this, but are built to the lowest common denominator... something guaranteed to be available most of the time whatever lens is fitted. This is AFAIK a design decision - if the AF system were built to work optimally with fast lenses, it would be rather less effective with consumer zooms than it is now.

Some (not all) cameras have one extra central AF cross sensor, which is optimised for a bigger virtual aperture of (say) f/2.8. This comes into play when a fast lens is fitted, assuming centre point AF is selected. But even this one will not benefit further if the lens is still faster than that; it "watches" only that predefined angle and ignores anything wider.

So in pure AF terms, it makes no difference whether the lens is f/2.8 or f/1.4 - and if the camera lacks this "fast lens" extra sensor, then it makes no difference in pure AF terms whether the lens is f/4 or f/2.8 or f/1.4.

Of course max aperture can be expected to make a direct difference in contrast detect (Live View) focusing; where the very fast lens may be at a dis -advantage in locking onto detail, due to lower contrast when wide open.

Either way, a fast lens is more demanding to focus to the required accuracy than a slower one.

RP

ASA_5 said:

pcarfan said:

...................but it is safe to say they are about the same focus speed at EV 4 or 5 and up. In low light it starts to get slower, but it takes much lower light than the K20d to start hunting.

ASA_5 said:

Eric
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be what it may - light, shade, and perspective will always make it
beautiful. - John Constable (quote)

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an exposure value chart is helpful for this. Ev4 woul require iso1600 at F/2.8 and a shutter speed of 1/30. Most home lighting is around ev4-ev5. SAFOX really starts to slow down after ev6.

ASA_5 said:

what is EV 4, how is EV quantified ?, how much light is that ?, what EV is light which gives a meter reading of iso1600, f2, 1/60th?

--

http://www.pentaxphotogallery.com/home#section=ARTIST&subSection=2323984&subSubSection=0&language=EN

K10D, K-7
Pentax Primes: DA21/3.2, FA*24/2, F28/2.8, FA35/2, FA43/1.9, FA77/1.8, F135/2.8
Sigma Zooms: Sigma 10-20, Sigma 100-300 F4

'Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... 'Wow! What a ride!'

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Thanks...I was thinking exactly of home interiors. I would consider my living room as very brightly lit, and the scale mike gave gives it an EV of 6, and I usually get 1/60th shutter with my f2 lenses with an iso of 1600 and thus my question, and very astute of you to figure out the reasons.

But, at other homes I find myself needing to boost the iso to 3200 if I was to keep the shutter close to 1/60th.
--

http://www.pentaxphotogallery.com/home#section=ARTIST&subSection=2323984&subSubSection=0&language=EN

K10D, K-7
Pentax Primes: DA21/3.2, FA*24/2, F28/2.8, FA35/2, FA43/1.9, FA77/1.8, F135/2.8
Sigma Zooms: Sigma 10-20, Sigma 100-300 F4

'Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... 'Wow! What a ride!'

I upgraded from a K100D and I cannot be happier with the autofocus, especially on my Sigma 105 Macro. The focus on the K100D was 3-5 seconds to autofocus from a blurry screen to a sharp one, this is under 1 sec every time. And neither does it hunt in low light. from the 3 lenses that I have used, all different lenses in usage, manufacturer and focal length.
--
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Roland Mabo said:

Then in your sense all AF tests are of limited value.

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Basically, yes. There's one AF test I do care about, though: using the actual camera, in real life conditions. If you do that, you too will see that the K-7 and D300 are miles apart, when it comes to AF performance.

Roland Mabo said:

You can't measure AF without the lens, AF is always dependant on the lens in use. What FOTO does is that they compare similar setups, but of course they don't test with exactly the se lens on all cameras. The cameras do have different lens mounts.

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I understand that, but that is also why the results are so limited in value. Even the tiny part of the overall AF system performance measured in the FOTO tests, isn't directly comparable between the test subjects.

Roland Mabo said:

AF speed is not only about tracking or continous shooting.

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Speed without high tracking, lock-on, and continous AF performance is, at best, of limited value. No chain is stronger than it's weakest link.

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Take care,
Jorgen

Probere necesse est.....

ASA_5 said:

pcarfan said:

what is EV 4, how is EV quantified ?, how much light is that ?, what EV is light which gives a meter reading of iso1600, f2, 1/60th?

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an exposure value chart is helpful for this. Ev4 woul require iso1600 at F/2.8 and a shutter speed of 1/30. Most home lighting is around ev4-ev5. SAFOX really starts to slow down after ev6.

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Just to give som sort of reference to a market leading AF system:

I just tried to focus in a more or less dark room, with my Nikon D3 and a 50/1.4 lens. It focused well, if focusing at areas with reasonable contrast (e.g. books in a bookshelf). Only minor "hunting".

How dark was it then? Minus EV1, i.e. 4sec @ f1.4 @ 200ISO
(Room with no window, door to the next (semi-lit) room open 20-30cm)

The AF system in the D300 is basically the same, but slightly less able due to less computing power etc.

--
Take care,
Jorgen

Probere necesse est.....

canon af from 20d to 50d was very similar, so a very good af and still a very good one.
only with the canon 7d the af is totally new.
as far as the k7 vs k20d..for me things are two:

• user problem
• faulty k7

k7 vs k20d is day and night in af, especialy in low light.

i think af in pentax is more problematic in use compared to canon, for example auto mode is far more weak than comparable mode in canon and nikon.
with pentax the best settings is one focus point, sespecially the central.

Marques Lamont said:

I just got my hands on a K7. Here is a myth I found out about it:

Faster AF - MYTH

I found the AF to be the same "experience" as K20 and K10. Granted, it might be a split faster... but it has the same hunting experience more or less, which IS the real AF "speed" problem. No exagerration. I thought the AF would be overhauled, reading through the reviews and such, and to my surprise, it's more of the same. Where are people getting this "much faster" AF from?

My Canon 30D is still faster. The AF on the 30D is pretty satisfactory, being actually 4 years old now (yikes! ) and I thought Pentax would at least get it to that level with the K7. Almost, but not really. It's along the same lines as the K20 and K10 far as hunting goes. Different techically, because it may turn the barrel faster, but it's still on the same spectrum.

"Hunt, hunt, hunt... focus, beep."

Other than that, the camera is stellar. The size is great and to my surprise, video is great, which I have absolutely no plans on seriously using. It was nice to fiddle around with it though and I could see how photogs can get caught up in it. I haven't gotten bit by the video bug yet but I can see him pretty clearly. He does have teeth and quite a bite.

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way beyond?= it doesnt seem to me.

pentax k7 is slightly slower due to double check to accurate focus. as said pentax is slower but far more accurate.

in this video the lens used from canon is faster. but the differnce doesn't seem to me so big.

ASA_5 said:

I agree with the OP. AF is Pentax's greatest weakness. We keep fooling ourselves by comparing the k10d, k20d, k-7 to each other. The fact is they are all WAY behind the competition. Here is the proof:
http://www.youtube.com/user/55bduke

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shooting a rally race.

in my position was completely dark.pouring rain.

i was 90 meter after a bend so car coming very fast at least 90 km oper hour. i had not a lot of space, i was on the side.

i used central point. focuson the camera shoot and little panning to follow the car. the flash was fundamental to light the car cause also at iso 1600 the car was completely dark.

this shot is from the camera. there is a lot fo noise cause i need to push a lot to have abright camera, but i havent applied any noise reduction. it's a a fast conversion to point that AF on k7 is very good and can cope also with difficult situation.

i use only DA* and thought they are not as fast as usm from 0 to infinity, they are accurate and very fast from point to point.



crop



the image is far from perfect but as u can see the focus is spot on.
behind me a guy with a nikon d200 told me: i go it's impossible to take a photo.

i never blame the camera but only myself. canikon are better, but k7 af is really a great improvement.

if i shoot sport or wildlife full time and specialize i will go d3 for sure, but i'm not a specialized photographer and i find the k7 a far robust offer than 7d, at least for my needs.

Marques Lamont said:

I just got my hands on a K7. Here is a myth I found out about it:

Faster AF - MYTH

I found the AF to be the same "experience" as K20 and K10. Granted, it might be a split faster... but it has the same hunting experience more or less, which IS the real AF "speed" problem. No exagerration. I thought the AF would be overhauled, reading through the reviews and such, and to my surprise, it's more of the same. Where are people getting this "much faster" AF from?

My Canon 30D is still faster. The AF on the 30D is pretty satisfactory, being actually 4 years old now (yikes! ) and I thought Pentax would at least get it to that level with the K7. Almost, but not really. It's along the same lines as the K20 and K10 far as hunting goes. Different techically, because it may turn the barrel faster, but it's still on the same spectrum.

"Hunt, hunt, hunt... focus, beep."

Other than that, the camera is stellar. The size is great and to my surprise, video is great, which I have absolutely no plans on seriously using. It was nice to fiddle around with it though and I could see how photogs can get caught up in it. I haven't gotten bit by the video bug yet but I can see him pretty clearly. He does have teeth and quite a bite.

Click to expand...

--
http://www.pbase.com/jon1976

the canon 40d as a super af , in fact many pro used canon 40 d also together 1 d series.

canon 7d has shown some problems with focus accuracy, u can go to canon forum and ask...there are a lot of people that needs to send back their camera.

ASA_5 said:

flash1100 said:

! Perhaps the Canon may be faster but the K7 is not far behind. I have used a 40D > with a Sigma 70-200/2.8 HSM and the K7 with the same lens and couldn't tell any > difference.

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You are comparing a two generation-old Canon released in 2007, to the K-7, and you make the point that the Canon is faster. That about sums it up doesn't it? Pentax's flagship DSLR is not even comparable to the present competition. Not even in the same league as the 7D which is considerably faster in every way than the 40d.

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i use DA* and screw drive.

as i said from 0 to infinity screw drive is faster, from point to point the sdm is faster. as far as accuracy there is no comparision. the % of missed shots is near the 2% with k7.
the slowness of k7 is due also to double check.

ASA_5 said:

Here is the AF test link for the k20d. Note that according to the Popular Photography test, the k20d is in fact FASTER than the k-7 at AF.

http://www.popphoto.com/Reviews/Cameras/Camera-Test-Pentax-K20D/Camera-Test-Pentax-K20D2

IMO the reason for this is that the k-7 test used a 55/1.4 lens which is SDM, and anyone who shoots Pentax knows that SDM is considerably slower than screw drive. Also notice as I mentioned before, as with the K-7, the k20d AF speed falls apart after EV6 in a nonlinear way. The competition does not do this. EV6 light is pretty bright, and as Jorgan mentioned, AF tests in bright light are next to worthless (unless all you do is shoot in the studio or on sunny days.)

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