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Forum: Pentax DSLR Discussion 04-07-2017, 01:56 AM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
They are not testing AF speeds, what they are testing is how long it takes for a camera to take a photo when the camera was already pre focused on the target. I would not interpret this as a AF speed test.

All of the differences that we might be seeing is that different cameras have different latency to trigger the camera to focus and make adjustments. With the K5-K3II when shot in AF-C have a latency that is around twice as much as the same camera shot in AF-S, this means that it takes a significant amount of movement or miss focus before the body decides to adjust AF.

I know with other camera bands that latency can be smaller meaning the camera is making more frequent AF changes, even when on a tripod you will see these camera continuously adjusting AF even when the target is static. This could slow down the speed simply by the software of the camera needing to confirming target has not moved with a higher degree of certainty.
Forum: Pentax DSLR Discussion 04-02-2017, 01:51 PM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
Let me correct your statement above "My AF works just great for my expectations with inexpensive lenses."

People have very different expectations with there equipment

If you are happy with this then that's okay

I would at least expect to have the focus plane near the front of the target



Especially given that you had the time to pre focus the camera prior to capturing the image

---------- Post added 04-02-2017 at 02:06 PM ----------



And people that don't look for better than average photographs are always quick to display




I for one an always looking for ways to take better photography









I am not in the least interested in taking images like yours ;)

Birds In Flight are not that difficult for a cameras AF unless they are erratic like swallows most birds fly at very consistent speeds



---------- Post added 04-02-2017 at 02:13 PM ----------



Here is my post Please point to the area where I said anything about AF speed



Better AF was the sum of my post and you interject AF speed into that, so maybe your not at 97% as you think ;) seeing as how you derived AF speed from 5 lines that refer to better AF with no mention of AF speed
Forum: Pentax DSLR Discussion 04-02-2017, 01:23 PM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
Show me where I have pulled a slight of hand by associating faster AF with more accurate?. If you had taken the time to read my post is was discussing better AF and with that I imply both speed and accuracy, with better accuracy comes less of the need to use more DOF ( the need to hide AF errors in that DOF) when the focus plane is better placed on the subject target less DOF is need to give the appearance of more of the subject is in focus.

As for slower AF is more accurate you can be no further than the truth, If we take a look at how and what people are shooting with for action photography and the shallow DOF they are using it would become very quickly evident when shooting the lenses that the correlation with speed and accuracy is not there.


This is where the cameras AF point was


and here is how much it missed by

This shot was taken of a target that is traveling at 30 meters per sec and the camera was ably to place the focus plane within 0.1 meters of the targeted area of the AF points. To give you an idea of the complexities of the calculations and accuracy needed to do this you have to look no further than how long it took that target to travel that 0.10 meters (30.5MPS / 0.1m= 0.003secs) Accurate and fast AF.

Here is another test that I have done that would argue against the speed and accuracy

For the 70-200 F4 it takes about 0.3sec to take this test and remember that the D800 can only take image every 0.25sec so during the test you really see no difference in the frame rate. I then take note to the accuracy.




In the same light the 70-200 F4 along with the 1.4 III can do it in0.3-0.4 sec with very little problems AF accuracy




as you can see that the tc has very little influence on AF in this light level, In this light level it would be about the limit that I would use 7-200 F4 with the TC anyhow.

The sigma 150-600 sport is a little slower at 0.4 sec but it’s a lot harder for a 400-600mm F6.3 lens to do the same thing in overcast light.



---------- Post added 04-02-2017 at 01:41 PM ----------



Its called prediction, Man can throw a ball and predict where the person running will be when the ball makes it to the player, no reflexes need for that.

If I rely on FPS to capture a car moving at 50 km per hour with a camera doing 7 FPS then the cars moves at around 2 m per frame is a very sure way of falling to capture that car in front of a banner or corporate logo,

Even with paintball and action you have to rely on timing to place the a player at key points in the field FPS seldom give you the key times in that actions. A person can travel 0.5 meters to 0.8 meters with a camera that can do 7-9 frames per sec.
Forum: Pentax DSLR Discussion 03-31-2017, 09:26 PM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
You can not have one without the other in action photography
Forum: Pentax DSLR Discussion 03-31-2017, 09:13 PM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
One of the problems is that it not hard to take photographs like the above, if the photos are not cropped any then they look to be taken at about 50-70 feet away, just because the photos are taken at F4 does not mean that the photo are taken with shallow DOF. Just by guessing and the settings in camera data and the display size you more than likely had 10-14 feet of DOF or twice as much DOF as the subject is tall. Now how have is this on a AF system ?
I can show a great deal of photo taken with the DS thru to the K3II that are great actions shots, but here’s the problem great AF was not responsible for taking the photographs. The AF deficiencies are hidden by DOF, pre focusing and spray and pray to take the photographs.

People that want better AF for actions work want so they can help their photography on many fronts

With better AF you need less spray and pray to capture that action shot.

You can use shallower DOF because of more accurate AF, this in turn allows photos to be taken with less noise.

With better AF you can rely on that AF so you can time the photo for peak moments in the action.

With better AF you can rely on the camera to track the action allowing you to focus more with the composition and placement of key targets in the frame.

With better AF you are not stuck into buying the most expensive lenses to see an improvement in how well the AF tracks in X,Y and Z movement.

With better AF you are open to other uses with the images that you have taken
Forum: Pentax DSLR Discussion 03-18-2017, 12:43 AM  
Pentax, autofocus and the future
Posted By Ian Stuart Forsyth
Replies: 287
Views: 30,338
Large R&D

A large professional user base that supplies feedback to R&D and a R&D that listens to that feedback and then improves on it.

They made huge AF improvements years ago that now can trickle down to the less expressive models .

They have the hardware and software that can recognise the target, track that target based on size and color thru the AF array.
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