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10-15-2015, 03:13 PM   #1
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Focus question

I have a K50 and wanted to know what would be the best focus setting for action type photos? I have been using single point for most things, but thought there may be an advantage to going with a different setting

10-15-2015, 05:06 PM   #2
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With single point focus, you might get slowed down if your subject leaves the center of the frame, since the camera would immediately try to focus on something else. 5-point or 11-point mode would be better if that's the case.

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10-15-2015, 05:21 PM   #3
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Stupor question:
How does it know what your subject is?
10-15-2015, 06:07 PM   #4
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It doesn't . That is why it would try to focus on something else. If the subject moved off the focus point.

10-16-2015, 04:35 AM   #5
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I read at some forum, for the same kind of question, that multi-point focus is slower because there are more points to calculate, and also that the middle focus points are more sensitive. Don't know if the first is true.
There is also the (very real) problem of the camera focusing on the wrong subject with multi-point (it seems to prefer clouds and trees to airplanes).
No arguing about the running out of focus, though.


Not sure if the new focusing methods on K-5 II/K-3 prevent that from happening.
Initial focus (button press) on middle-point with follow-up (when subject moves from middle) on the outer ones could be helpful for avoiding those problems.


I go for middle-point because then the camera will try (keyword) to focus on what I want. If the subject gets away, that's my fault.
10-16-2015, 03:23 PM   #6
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When I put a 2.8 lens on my K50, am I confusing it? I read that the K50 cannot handle any lens brighter than f3.5? I am trying to understand why I cannot get reliable focus on my K50. I have a 18-138 and a Sigma 50-150 2.8. I am getting so incredibly frustrated looking at great pictures ..... except for the fact that the subject i out of focus. We do a lot of photos of our dogs and moving objects, but even the stills have way more misses than I deem acceptable.

I am going to check the calibration now that I got my camera back from service and see if I have a FF / BF issue going on.

Any help would be great.
10-17-2015, 04:31 PM   #7
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I know of no reason fast glass won't work on the K50. I have the K30 and only a couple of my lenses are slower than 2.8. I prefer center point focus with back button focus. when I shoot moving subject I just hold the focus button down and keep the red confirmation on the subject. while tracking. then click when I see the shot I want.
You might also try catch in focus
10-17-2015, 09:17 PM   #8
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QuoteOriginally posted by nonstopnick Quote
Stupor question:
How does it know what your subject is?
QuoteOriginally posted by patrick9 Quote
It doesn't . That is why it would try to focus on something else. If the subject moved off the focus point.
Good question and good answer. The camera NEVER knows your intent. It is your job to give it hints*. Lacking a hint, it will attempt to focus on the easiest region available within its settings.


Steve

* Hints include limiting the active focus area and/or manually choosing the AF point. On cameras such as the K-3, the system's ability to track a moving subject may also be tuned.


Last edited by stevebrot; 10-17-2015 at 10:19 PM.
10-17-2015, 10:09 PM - 1 Like   #9
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QuoteOriginally posted by nonstopnick Quote
When I put a 2.8 lens on my K50, am I confusing it? I read that the K50 cannot handle any lens brighter than f3.5?
What is there to confuse? Seriously...I know that sounds flippant, but the camera AF system is more straightforward and stubborn than easily confused. It does what it does.

Here are a set of bullet points regarding the PDAF system (used with the optical viewfinder) on your camera:
  • The camera cannot read your mind regarding the subject or what part of the subject is supposed to be in focus
  • If allowed to chose its own focus point, the system will choose the easiest element within the frame that matches the available focus area. For this reason, choosing the AF area manually is often preferable. Center point is a good option.
  • The AF point indicator in the viewfinder (red dot) is much smaller than the diameter of the actual area seen by the AF detector
  • The red dot being lit does not mean the camera has attained focus
  • Focus confirmation is indicated by the green hexagon at the bottom of viewfinder and by the audible beep
  • In AF-S mode the shutter will not release until focus is acquired
  • In AF-C mode the shutter will release even if focus has not been acquired
  • The ability of your K-50 to track a moving object is limited since the system on your K-50 is strictly reactive and not predictive. True predictive AF systems are relatively rare and limited to higher end cameras.
  • The ability of the system to acquire focus depends on adequate light and contrast. Much like your own eyes, the ability to function well is reduced in dim light or with some subjects.
  • If there is a curved surface or receding plane within the focus area, the system will focus on that part having the highest contrast. That may or may not match your intent.
  • The precision (ability to consistently attain the actual plane of focus) of the AF system on most SLR cameras is not as good most users would expect.
It is that last point that trips most of us up, particularly with lenses having fast maximum apertures. Conventional wisdom is that the AF system should work better since more light is available to the sensor. To a certain extent, that is true except that the ability of your K-50 to consistently attain accurate focus is the same with an f/1.4 lens mounted as with a slow f/5.6 lens (f/5.6 focus sensitivity). When the taking aperture is moderate, this is not a problem. Depth of field makes up for the lack of precision. At wider taking apertures the depth of field is often not adequate to cover for actual missed focus. On most moderately priced dSLRs, such as the K-50*, all of the focus points have f/5.6 focus sensitivity. More expensive cameras have one or more sensors (usually clustered around the center) with f/2.8 focus sensitivity. On the K-3 there are 5 such sensors in a vertical array at center.

In summary, a fast lens shot wide open using PDAF on your K-50 will result in a fair number of out of focus shots if focus is being critically evaluated. This is the case regardless of how well calibrated your camera is. The same may also be true with a K-3 or K-3II or Nikon D7100 or Canon 7D when shooting with a f/1.4 lens using the more sensitive center points.

So, now that is out there, what can we do? Here are the options when focus is critical:
  • Use the CDAF system available in live view. The CDAF system is slower, but has greater precision and accuracy than the PDAF system.
  • Use manual focus in magnified live view. This is best done on tripod , but is the gold standard.
  • Use manual focus in the optical viewfinder with an aftermarket focus screen having a split image focus aid.** The stock focus screen is somewhat better than the PDAF system, but has a focus sensitivity of only about f/4. Most split image focus aids have a focus sensitivity in excess of f/1.4.
When focus is not critical, you can:
  • Set the camera to use the fixed center AF point
  • Use AF-S or when using AF-C, take care to not make the exposure until the green hexagon is lit
  • Be aware of the AF system limits when shooting at fast apertures
  • Use depth of field to your advantage by shooting at moderate apertures


Steve

* I believe the list includes all but the flagship Pentax, all 4-digit Nikon models, and all Canon Rebel series.
** This the option I use, but requires some expertise to calibrate and also results in some loss of and/or modification in meter function.

Last edited by stevebrot; 10-17-2015 at 10:33 PM.
10-17-2015, 10:33 PM   #10
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QuoteOriginally posted by nonstopnick Quote
When I put a 2.8 lens on my K50, am I confusing it? I read that the K50 cannot handle any lens brighter than f3.5? I am trying to understand why I cannot get reliable focus on my K50.
I enjoy shooting action on a K-30, which is a brother to your K-50, using f2.8 lenses.

Can I suggest you set a single central focus point, AF-C mode?

This way you know that by keeping the subject in the middle of the frame, it's going to lock onto it and not a higher contrast object elsewhere, like a stick.

If you repeatedly have other objects crossing the line of fire of your shot while you track your subject, like other people, learn a technique called Back Button Focusing, which your K-50 supports.
10-18-2015, 07:59 PM   #11
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I also just ordered a Katzeye focusing screen for my K30 since I have ,and use several M lenses

---------- Post added 10-18-15 at 10:43 PM ----------

QuoteOriginally posted by stevebrot Quote
Use the CDAF system available in live view. The CDAF system is slower, but has greater precision and accuracy than the PDAF system. Use manual focus in magnified live view. This is best done on tripod , but is the gold standard. Use manual focus in the optical viewfinder with an aftermarket focus screen having a split image focus aid.** The stock focus screen is somewhat better than the PDAF system, but has a focus sensitivity of only about f/4. Most split image focus aids have a focus sensitivity in excess of f/1.4.
I have heard about CDAF and PDAF, but what are they. My live view focus is way off since it came back from warranty service. (unrelated issue) It is actually almost totally useless now,if I want focus. I am better of with the viewfinder and my eye. I have both afs and afc set to not release till focus is attained. My red square and my green confirmation dot light at the same time and go out at the same time as well.
10-18-2015, 09:07 PM   #12
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QuoteOriginally posted by patrick9 Quote
I have heard about CDAF and PDAF, but what are they.
PDAF = Phase Detect AF. This is the type of AF available when using the optical viewfinder. The title is not quite accurate since it is actually an optical rangefinder that works in a manner similar to the split image finder on may focus screens. There is a good description of the system at the Web page linked below:

https://photographylife.com/how-phase-detection-autofocus-works

When you do AF fine adjust for a particular lens, you are applying a bias to the PDAF system. Accuracy of the PDAF system depends on appropriate calibration. Precision as well as ability to attain focus depend on the sensor design and available subject contrast. PDAF is can be very fast because both the degree of out-of-focus and the direction to correct available from the sensor.

CDAF = Contrast Detect AF This is the type of AF used in live view. The PDAF system is not available in live view because the mirror is up. True to the name, it works by focusing until the point of maximum contrast is detected. Since it reads directly from the sensor image at the focal plane its accuracy is much higher than the PDAF system. As with the PDAF system, precision and ability to attain focus depends on subject contrast. CDAF is fairly slow since the system must hunt for the point of highest contrast.

If your CDAF (live view) AF is "useless", you should talk to the shop. Of the two systems it should be the more dependable.


Steve
10-18-2015, 09:24 PM   #13
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QuoteOriginally posted by patrick9 Quote
I also just ordered a Katzeye focusing screen for my K30 since I have ,and use several M lenses

---------- Post added 10-18-15 at 10:43 PM ----------


I have heard about CDAF and PDAF, but what are they. My live view focus is way off since it came back from warranty service. (unrelated issue) It is actually almost totally useless now,if I want focus. I am better of with the viewfinder and my eye. I have both afs and afc set to not release till focus is attained. My red square and my green confirmation dot light at the same time and go out at the same time as well.
The Live View method (CDAF) is so accurate it's used to check for defects in the other system. You need to tell the warranty guys that's happening.
10-19-2015, 04:08 AM   #14
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QuoteOriginally posted by clackers Quote
The Live View method (CDAF) is so accurate it's used to check for defects in the other system. You need to tell the warranty guys that's happening.
Thanks. It has been almost a year now So I doubt it would matter. I have had the K30 for 3 years. I don't care much for Live view generally tho on occasion it WAS nice to have.
Maybe this is the excuse I need to get a k3.
10-19-2015, 06:54 PM   #15
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[quote=stevebrot;3405067]PDAF = Phase Detect AF. This is the type of AF available when using the optical viewfinder. The title is not quite accurate since it is actually an optical rangefinder that works in a manner similar to the split image finder on may focus screens. There is a good description of the system at the Web page linked below:

https://photographylife.com/how-phase-detection-autofocus-works

When you do AF fine adjust for a particular lens, you are applying a bias to the PDAF system. Accuracy of the PDAF system depends on appropriate calibration. Precision as well as ability to attain focus depend on the sensor design and available subject contrast. PDAF is can be very fast because both the degree of out-of-focus and the direction to correct available from the sensor.

CDAF = Contrast Detect AF This is the type of AF used in live view. The PDAF system is not available in live view because the mirror is up. True to the name, it works by focusing until the point of maximum contrast is detected. Since it reads directly from the sensor image at the focal plane its accuracy is much higher than the PDAF system. As with the PDAF system, precision and ability to attain focus depends on subject contrast. CDAF is fairly slow since the system must hunt for the point of highest contrast.

If your CDAF (live view) AF is "useless", you should talk to the shop. Of the two systems it should be the more dependable.



Thanks Steve.
Interesting article .
I generally don't miss focus with the viewfinder very often, even doing macro , but live view is almost never right since I got it back. I didn't notice for quite a while.Like about 3 or 4 months ago. It was repaired in Canada under warranty. ( Battery retaining lug broke). So I would bet getting it fixed would cost me now, and I don't use it often enough to spend the money to get it fixed .
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