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05-24-2019, 01:04 AM - 1 Like   #16
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I would like to further comment on the Pentax K-1 AF performance during tracking (in Af-C mode and the settings I mentioned above) and speak a bit about what I called the Pentax paradox What is weird is that although the AF-C tracking performance is said to be weak and laggs behind competition, I have found it to perform better in demanding conditions that require extremely fast tracking than in lower speed and less demanding ones! I can't fully explain my findings but they have been confirmed on quite too many occasions to be considered a coincidence! Although there are not a lot of opportunities to shoot airplanes head on during air shows as they turn away from the crowd as they approach for safety reasons, there are cases where the plane or planes may come towards you getting bigger and bigger in your viewfinder passing quite close to you with high speed, during the "dedication passes" for example. You may also find yourself in cases where the planes come head on and pass over your head on flat land or a canyon or even if you stand at the sides at the end of a runway as planes take off.

For better explaining my findings let’s take one of these scenarios an aircraft is flying low in a canyon coming towards you head on and finally passes almost over your head (like it happens at Rainbow Canyon, Axalp, Mach Loop etc). I have found that as you see the plane in along distance and focus on it to start tracking and take images with a mountain (terrain) in the background the camera quite often looses focus on the plane and focuses on the background especially in cases where there is not much separation between the plane (subject) and the background. During such bursts you can see some frames with nailed focus, some where the camera is not decisive (probably the focus is somewhere in between the subject and the background - and the shutter was released while AF was hunting) and some with focus on the background. Even if the plane comes straight towards you without directional changes or maneuvers the % of OOF images is quite high sometimes and for me this is quite strange, since there are not many changes happening in the viewfinder other than the plane getting slowly bigger and the whole scenery happens so close to infinity that I would expect the opposite, many keepers and less OOF frames. Five major factors affect the keepers’ rate in such cases, whether the first image has been in perfect focus, the available light, the contrast between the plane and the background, the contrast of the background itself and the distance of the background from the airplane.

My explanation for these misups is that the airplane might be too far away so very small in relation to the frame and the camera can’t put an AF point on it accurately and also the “Hold AF status off” that I use because I need it more often, here acts negatively and leads to the OOF shots even after the camera has found the plane and focused right on it. So during this relatively easy situation the AF is not decisive and hunts instead of focusing on a relatively steady target in the middle of the frame.
As I said if Pentax:
- Rectifies its AF-C tracking mode and not permit easy locking on infinity (AF-C and continuous shooting means tracking, so the camera should scan to find the subject).
- Enables the photographer to dial in an electronic “distance focus limiter”. Imagine the third wheel on the K-1 to be customizable and by turning it you could choose between distances that you have previously dial in and save e.g. from 10m to 100m / 100m – 1000m / 1000m – infinity how much helpful it would be forbirding, aviation shooting and other sport related AF-C tracking situations.
- Creates aspecial mode (like the TAv is unique to Pentax) where tracking is the highest priority, even if that mode could be offered with the fastest Pentax lenses in their focus limiter modes only.
It could take the AF-tracking performance to a next level, because it is proven that Pentax cameras can nail focus and acquire it quite fast (with the newest lenses).

Now the paradox is that as the plane comes closer still head on (the most difficult situation for precise AF tracking) and with its relevant speed to the photographer continuously rising which makes it harder to track the plane and have it entire in the viewfinder, the AF performance increases and you get more tack sharp images provided you have set the camera right! It seems that when the plane is very close and the details on it are clearly visible, the AF performs great and the only limitation is the photographer and whether he can follow the super fast action… When I first noticed that I said I was lucky as I thought that was way too fast to AF and shoot it, but the pictures turned out great! There are many ones that only parts of the airplane are in the picture but the AF-C tracking works great! And moreover it really tracks the plane without the need to refocus by releasing and pressing the shutter button continuously. It seems like the AF-C makes very fast readjustments in such cases which is impressive,as the distance between the photographer and the target changes fast and now as the plane comes closer the telelens DOF becomes narrower and misfocused images are easier to tell than when the plane and the background are close to infinity.

This behavior of the Pentax AF-C system is difficult for me to explain, but for some reason it works best under more demanding conditions, but conditions where there are data to fine adjust the focus (the subject fills the frame). It reminds me of the SR paradox where the SR works better in very low speed panning shots than in relatively easier faster panning shots – and I leave the mirror slap or shutter shock out of this equation. I mean in terms of how effective the SR is and the % of high quality images in a burst. Maybe Pentax engineers have optimized these systems for cases like those I describe, I would love to learn a few things from them written down in a white paper or even as a loose talk in the special web pages Pentax makes for the new releases (and are a joy to read).
If there are Pentaxians who have similar experiences or PF members that know more about how Pentax DSLRs function and think they have some explanations I would love to hear them. Maybe I can learn things that will help me further improve my techniques!

06-11-2019, 10:38 AM - 1 Like   #17
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I have some more findings concerning the Pentax AF and AF-C performance that we will discuss at some point later on, but I will also include some images as I told you and let them do the talk


Here is an example of a frame from a long continuous burst (16 frames). The F-18 is turning towards me on a very hazy day. The first 5 images (the aircraft is quite away) are not in perfect focus. From the 6th frame and on the aircraft is quite large in the viewfinder and all images are in focus, without any "tricks" with the shutter release button. As I told you the bigger the subject the better the results, despite the fact that the relevant speed keeps raising and it becomes difficult to follow the plane...


The 1st image is the whole frame SOOC without any PP (the Jpeg extracted from the RAW file in DCU-5) and the 2nd is a 100% crop of the unedited RAW file.
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06-20-2019, 02:06 AM - 2 Likes   #18
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Another photo of a F-18 (Spanish air force this time) from the same event, this time with some PP.
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