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12-21-2017, 06:36 AM   #1
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Focus indicator not accurate with manual lenses

I've been practicing with some manual lenses on my K5IIs and I
noticed that when I use the focus indicator, the photos are not as
sharp as when I ignore it and focus strictly by eye. When I use
autofocus lenses, however, it seems to be fine. I was just wondering
why the camera is acting like that and if there is anything I can do
about it.

12-21-2017, 06:47 AM - 3 Likes   #2
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Hi! There are many possible reasons
a) Lens needs focus adjustment. The global focus adjustment goes for manual lenses as well. Many lenses might require some focus adjustment, that is why most modern DSLRs have that function. There are threads about this, though I would not change the focus adjustment just for manual lenses, because it the global adjustment will affect the adjustment of your other lenses as well (and they seem to be fine without adjustment)
b) You are looking at the AF overlay (red square in viewfinder) instead of the Hexagon beneath the viewfinder. The AF overlay indicates which AF points have been locking focus, but the bottom hexagon is the actual AF lock confirm
c) Manual lenses only work with central AF point, not others
d) Sometimes AF locks correctly, but the DoF is so shallow that it locked into a different, more contrasty part than user expected. AF is optimized for lenses that are f2.8 and slower, so if you use an f1.4 lens, AF might not be "accurate" enough. Many people buy viewfinder loupe and focusing screen for fast aperture lenses

Anyway, if going by eye works better for you, then just go by eye. That's the way it should be done. You don't need some machine's approval
12-21-2017, 07:26 AM   #3
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I find the same thing in my K-5 II. When shooting with my 400/5.6, I have to focus a bit further beyond what the indicator, uh, indicates. When I use my 200-500/5.6, I have to focus ever so slightly before - when the indicator first starts to flicker. With my 300/2.8, it's spot-on. Go figure.

Once you know how the equipment behaves and have a few hundred reps, the necessary adjustments are almost second nature.
12-21-2017, 07:41 AM   #4
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I would concur with luftluss. Familiarity and practice with particular lenses is part of getting best focus results. I am using a 1.36x ovf magnifier (lives on my K5) but I haven't changed the VF screen. I did go with a split and microprism screen cannibilised from a derelict ME super on my k-r for a good while but ended up unconvinced of it's utility with the relatively slow telephoto lenses I use a lot. Jumping to/from live view to corroborate focus is an important back up. I was just taking a few test pics with a new lens - a sigma 400mm - of the neigbours chimney, with this lens visual focus and lv focus coincided exactly.


Last edited by marcusBMG; 12-21-2017 at 07:49 AM.
12-21-2017, 09:30 AM   #5
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I found manual focus tricky with my old K10D and got a split prism focussing screen for it so it reminded me of my old MX. Now i have the K1 I find manual focus much easier, perhaps the brighter bigger viewfinder helps. If need be I can also use LV to focus manually zoomed in.

The green hexagon is not accurate enough in my opinion for manual focus

Last edited by pschlute; 12-21-2017 at 09:36 AM.
12-21-2017, 09:52 AM   #6
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When you adjust the focus for a newer lens, the camera remembers the setting every time you put
that lens back on the camera. But on an old manual lens, I dont think there is any type of communication,
so wouldnt I need to make the adjustmants every time I put the lens on the camera?
12-21-2017, 10:48 AM   #7
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QuoteOriginally posted by Na Horuk Quote
Anyway, if going by eye works better for you, then just go by eye. That's the way it should be done. You don't need some machine's approval
What they said ^ ^ ^

I read an article yesterday (should have kept the reference) about AF strategies and limitations. The last sentence was sweet. To paraphrase, it said something to the affect that "The real truth is that PDAF (by nature and physics) truly sucks for critical work, but since it is fast and adequate most of the time we put up with its failings."

Here are a few bullet points:
  • Focus confirmation performance uses the PDAF (auto-focus) sensor and provides the same performance (accuracy and precision) as autofocus with the same lens
  • A manual focus lens may exhibit front/back focus with the PDAF sensor the same as an auto-focus lens
  • Except for a few newer lenses (e.g. Irix), per-lens PDAF fine tuning is limited to auto-focus lenses. That is because most manual focus lenses lack the "data" contact on the mount that supplies the camera with a lens id code.
  • Even with the f/2.8-sensitive center AF point on the K-5II, precision lags for lenses faster than f/2.8 when compared to magnified live view or a well-calibrated split-image finder and will be no better than an f/2.8 lens
  • Note the word precision in the point above. Precision is the ability of the system to assign the same point of focus consistently. The system may be well-calibrated for accuracy, but if precision is poor, missed focus will be more common. This will be more obvious when shooting at wider apertures. At narrower taking apertures, DOF will often cover the deficiency unless one is pixel peeping.
  • The stock focus screen has its own precision issues, but discussing it fully here would be a deep hole
  • Magnification for manual focus with the stock screen has proven valuable for many users
  • Replacing the stock screen with one having focus aides (e.g. split-image) or an enhanced matte surface (e.g. Canon S-type) has potential to work very well, but often requires calibration using shims
  • Focus using magnification in live view (with or without focus peaking) is the Gold Standard for both accuracy and precision for manual focus with a given lens
  • No amount of focus technique will make a soft lens sharp
  • Most fast primes (f/2.0 and wider) are fairly soft wide open
  • A soft lens is harder for both you and the AF system to bring to acceptable focus
Emphasis should be placed on the point above regarding magnified live view. When fine focus is essential, one can do no better than live view with magnification. The sad part is that using the feature without a tripod is a waste of effort.

As noted in comments above, practice helps with manual focus as does learning what to expect from a particular lens. In the dim past (before pixel peeping), photographers using hand-held 35mm cameras photographers were a bit less picky simply because few took the time to examine their negatives under magnification. Ignorance was bliss and we were generally quite blissful.


Steve
12-21-2017, 11:04 AM   #8
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I was hoping to be able to use the indicator for "catch in focus", but I guess
that wont be possible if it is inaccurate.

12-21-2017, 11:18 AM   #9
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When using the AF system with manual lenses, there is some tolerance on both sides of the correct focus point. As others have said, getting accustomed to each lens is key. Stopping down may help improve your CIF results.

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12-21-2017, 11:23 AM   #10
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QuoteOriginally posted by jeryst Quote
wouldnt I need to make the adjustmants every time I put the lens on the camera?
Yes, though one might question whether it is worth the effort. A simple test* might help demonstrate:
  • Use a flat, high contrast target in good light. Newsprint or a lens test target both work well. We want to make this easy for the system.
  • Manual focus prime (50mm to 150mm focal length) with aperture wide open*
  • Camera on tripod
  • Target at 20x-30x the focal length distance
Starting at minimum focus distance, slowly move the focus ring until the green hexagon lights. Continue rotating the ring until the hexagon goes out. That extra rotation gives an indication of the focus precision you can expect from focus confirmation with that lens mounted. The true point of focus lies somewhere within that range. Do the test from infinity focusing down just for completeness.


Steve

* This range is an effort to make sure there is reasonable focus throw and working distance.
12-21-2017, 11:34 AM   #11
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QuoteOriginally posted by jeryst Quote
I was hoping to be able to use the indicator for "catch in focus", but I guess
that wont be possible if it is inaccurate.
There is no harm in giving it a try. Many users on this site are very happy with the technique, though it works best with K-mount lenses where focus may be done wide open with the lens automatically stopping down to a narrower aperture for exposure. Additional points to consider are the subject moving past the plane of focus (when trapping action) and/or the plane of focus moving past the subject (when racking focus to catch) before the shutter trips.


Steve
12-24-2017, 08:52 AM   #12
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Play around with the white balance settings..The K5iis tend to slightly misfocus based on the hexagon with wild light colors..I know this experience with all my manual focus lenses.
I wont discuss this beyond what I said, but there is a good reading about this at the DP Pentax forum.
12-25-2017, 02:48 PM   #13
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I just can't manually focus my K5, period, even after hundreds of attempts, except with live view. I have only one MF lens and need to dispose of it. I didn't have much trouble with MF on my Spotmatic or Canon A-1.
12-25-2017, 03:09 PM   #14
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How does Colour affect Autofocus? | Reikan FoCal Blog Automatic Lens Calibration Software

Here is a good read about the issue. Although it discusses around autofocus, it could apply to manual focusing, the hexagon indicator works with the same system
12-25-2017, 04:43 PM   #15
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If you get the same effect with any lens (try manually focusing AF lens) then it is either the camera flange setting (AF fine global) or if with AF lenses PDAF works fine but the viewfinder focus point is out (with any lens), then it is the focus screen shim that is wrong. I would try carefully dropping down both the focus screen and the shim holder frame clips and reseating these.

Does the best PDAF focus correspond to that of expanded live view ?
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