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10-02-2013, 10:09 AM   #1
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How reliable is focus confirmation with manual lenses...

How reliable is focus confirmation when using manual lenses on a K-x? I'm getting to know my new super tak 105mm, and I'm noticing that I am missing more shots than usual due to poor focus. My previous manual focus experience is mostly with a promaster 28mm. It seems that I have been able to catch more in focus shots with the promaster. With the promaster there is much less turn of the focus ring necessary when going from over focused to under focused. With the super tak I am allowed to turn the focus dial more before the in and out of focus becomes obvious to my eyes. When using the promaster, I didn't need to wait for the focus confirmation beep. I seemed to trust my eyes more with it than I do with the super tak. I have played around with my pentax 50mm DA by comparing my manual focus with the auto focus and there doesn't appear to be much of a difference. My eyes are perfect, but they aren't terrible either. I have not messed with the diopter settings (yet). I understand that missing some shots due to poor focus is part of the shooting manual game, but my batting average is suffering with the super tak...but when I do catch a shot in focus, this lens is awesome.

Unrelated question: What is the lowest shutter speed that most of ya'll are comfortable with while shooting hand held?

10-02-2013, 10:24 AM   #2
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I've found focus confirmation has too much tolerance, and focusing with a good aftermarket screen gives better results, once your eye is used to judging focus. The standard screens are not good for determining focus, as they are designed for bright view for composition, relying on auto focus. The 105 f2.8 has little DOF so needs better than focus confirmation can give, in my experience.
I put a S-type screen in my K-5 and can focus much better - but it doesn't affect the confirmation or autofocus, so you need a good eye. The screen is dimmer, but easier to judge focus.
10-02-2013, 10:38 AM   #3
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A couple considerations. Apparent depth of field is greater with the 28 than the 105, so focus errors are more obvious with the 105. I'd guess the 28 is a f3.5 or perhaps 2.8, what speed is the 105? I'd guess 2.8, which at that focal length gives very little depth of field. A good portrait length! For using the focus confirmation you need to consider where the camera is "looking" I'd suggest using only the central spot. Then of course the question is how big an area does that red square really cover? Maybe more than you think! You might draw a cross line down a sheet of newspaper and shoot focused on the line with the sheet of newspaper at an angle. Ideally only the center of the cross line would be in focus. For portraits the usual advice is focus on the eyelashes, YMMV. On my K10 I installed a KatzEye replacement screen which made manual focusing much easier, although it impaired spot metering. Off hand I can't remember whether you can change screens on the K X.

The difference in needed turns of the focus ring is standard for wide angle versus telephoto lenses. With the teles you need to be able to make small adjustments easily.

Lowest shutter speed? The old rule of thumb is/was 1/focal length, so at 55mm 1/60 sec. Using Shake Reduction, I seem to be able to get away with three stops, so using that focal length at1/8 sec looks fairly good. But, and this is an enormous but, for the best quality at almost any shutter speed, SR or not, use a tripod. My example would give a reasonable 5 x 7, but probably not a good 8 x 10. Again, YMMV.
10-02-2013, 11:52 AM   #4

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Knock, I've done a lot of manual focusing with the stock screen on the K-x,
including with f/1.4 lenses.

I'd recommend you to set up for the central focus point,
like @grhazelton said.

I have the beep turned off, it's just too annoying.
So I only work with the green hexagon.

The way to think of it,
the green hexagon can be lit up over a range of focus distances,
depending on the lens.
So try and find the boundaries each side,
then back off to the middle of that range.
That should improve your batting average.

With some fast lenses,
stopping down from fully open can shift the focus point.
(This is called "focus shift".)
So a lot of times, it may be worth making several shots,
all at slightly different distances from the subject,
and then choose the sharpest one --- "focus bracketing".

10-02-2013, 11:55 AM   #5

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QuoteOriginally posted by Knock Quote
What is the lowest shutter speed that most of ya'll are comfortable with while shooting hand held?
The old rule of thumb is one-over-the-focal-length,
so 1/50 sec for a 50mm, or 1/15 for a 15mm.

With Shake Reduction, you can usually double those times,
so 1/25 sec for the 50mm or 1/8 sec for the 15mm.
10-02-2013, 12:00 PM   #6
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The reliability of focus confirm is the same as the underlying AF system that drives it. As a result, you are dependent on what the camera sees as being in focus. My experience with the K10D is that focus confirmation is much less precise than the split-image on my aftermarket Katz Eye focus screen.

My personal experience with manual focus on my Pentax dSLR (K10D) can be summarized as:
  • The stock focus screen sucks (apparent DOF is too deep for critical focus with long/fast lenses)
  • Focus confirm is not adequate
  • An aftermarket screen with good matte field or focus aids is pretty much essential

10-02-2013, 12:11 PM   #7
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All good advice. I have a few manual lenses (including a 135 f3.5 and 200 f4) and I don't personally have a custom focus screen. I also have a K-x and a K-5. I have had pretty good results using the cameras focus indicator - as long as the focus is calibrated correctly. I spent some time with with focus charts and debug mode on the K-x and it made a difference for me. I like to see a solid focus indication (not flickering in / out) and then the focus is usually spot on - I just have to hold the camera still!

That said I find the k-5 easier than the K-x to use manual lenses with due to:
1. Bigger brighter viewfinder - I can actually tell when things are hopelessly out of focus and quickly get to the correct focus area
2. Slightly more responsive focus confirmation
3. Viewfinder focus points - while these are generally useless (IMO) they can be handy with manual focus because they come on earlier than the hexagon when you are close to be in focus.
10-02-2013, 01:07 PM   #8
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I appreciate all of the advice folks! As usual, the help from this forum does not disappoint. It looks like a new focus screen will be the easiest solution (I'll try to avoid the cheap replacements...either Katz eye or FocusingScreen look like the best to choose from). I'll save myself lots of frustration if I can find something that comes close to producing a focused image like my old spotmatic--there isn't so much guess when I'm shooting with it!

10-02-2013, 08:53 PM   #9
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If I'm using a stock screen, I don't pay a lot of attention to the focus indicator. I'm looking for where the front and back edges of the focus are, then estimating the point in the middle of that range. That's the point of focus. It takes practice but it does work. Changing to a different screen makes focus much easier, once the screen is properly shimmed.

If you can stick to sharp lenses with very good contrast, those features make seeing the details in the viewfinder much easier. I have done some comparison testing of say six or eight 28mm lenses, and can just about put them in sharpness order only by focusing them. The ones that seem to pop right into focus are going to be the sharpest. If I can't really decide if the test area is in focus yet, that lens will rank low on sharpness.

I have looked at EXIF data for my shots and I do fine at about two stops slower than the old rule of 1/focal length. So at 120mm, I can shoot at 1/30 reliably. I will try to shoot at three stops slower and it sometimes works, but I take more shots to be sure of getting one good one. Subject motion becomes a big factor too.
10-02-2013, 11:36 PM   #10
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I have a K-x. I find that if I come up from the short focus distance side towards what I am focussing on, then when the focus confirm first comes on, I am pretty well on the mark (maybe continue focussing towrds infinity for a fraction more for some lenses). If I come down from infinity focus until I get focus confirm, I am a little off. Works reliably for the 3000 or so manual focus photos I have taken on the K-x using my M series glass. One caveat - this is with global focus adjustment set via the debug menu at +50um which is the correct calibration for myTamron 17-50 zoom. I might have a different result if the focus adjustment was set somewhere else. The message is that if you can work out initially what technique works for your K-x, you should be able to rely on that approach.
10-03-2013, 10:12 AM   #11
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I used a K-x for around 3 years I think, stock focusing screen, and mostly manual lenses. I used the same technique as southlander, start closein and focus outwards until the focus confirmation gave me a beep, and it worked fairly well, even after my viewfinder was scratched up so bad I could barely see, focus confirmation helped me get a lot of good shots.

When I had time to look things over good, like tiny flower macro shots, it did exceptionally well, with moving subjects like birds in flight it was iffy, but the same was true for film bodies with no electronics...My K-x did a pretty good job, I had no complaints. The K30 I'm shooting now doe seven better. I've always kept both set on center spot, both for metering and focus.
10-03-2013, 07:06 PM   #12
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I put mine on burst mode and take 5 or 6 shots moving slowly through focus. One is usually the right one.
10-04-2013, 07:42 AM   #13
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i find, as others have mentioned that a split image focusing screen is very good for hitting focus but can still get errors, especially at longer focusing distances, i.e. near infinity.

the focus indication can be effectively used by finding the limits of the focus confirmation and then moving to the middle point.

as for hand held shutter speed, that is too variable on its own these days.

the rule of thumb was 1/focal length, but that, like depth of field was based upon acceptable focus / sharpness of a point when blown up to 8x10 inch on a full frame being 1/100 of an inch in diameter.

cropped sensors, and cropping in on a subject, or enlarging past 8 x 10 inch all change this golden rule, so there is no longer a good definition of acceptably sharp when people zoom into the pixel level.

BUT, having said all that, i will point you to an image, shot at 1/40 with a 510mm lens. it is possible to go well beyond the 1/(FL x 1.5) golden rule as applied to APS-C sensors. it is called technique, and not every one can do this, and even i cannot do it every time,

Last edited by Lowell Goudge; 10-04-2013 at 07:48 AM.
10-04-2013, 12:25 PM   #14
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1/<focal length> is still a good rule of thumb. Combined with shake reduction, it can cover minor sins in camera handling technique. I aim for 1/<focal length X 150%> to offset the APS-C crop factor - - - if I can get away with it without adversely affecting my image with reduced DOF or noise from a higher ISO. Just remember that this IS an approximation, not an absolute.

I'll sometimes even take this a step further.... if you plan to crop the final image, increase shutter speed according to the level of crop. If you only use half the image, double the shutter speed.
07-20-2014, 06:30 PM   #15
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I've had the same problem! This thread has helped, thank you all!

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