[BruceBanner]

So... I was doing some some focus chart testing today, calibrating and fine tuning some lenses, when I came across this review method which I think worked pretty well for the K-1 and KP. Now before you all jump on your keyboards and start screaming "Bruce!! Focus Peaking only works for Live View and Fine Adjustments are for PDAF (Eye Piece focusing only)!"... I know that. Here's what I did and I wondered if this was a bonafide recommendation for completing Fine Adjustments/Focus Chart work (or not);

1) Set everything up, camera, tripod, chart at 45 degree angle etc etc.
2) Use Live View and Manual Focus mode to get perfect focus on the centre of the Focus Chart. Turn on Focus Peaking (to help, but also just leave it on at this point).
3) Take a shot.
4) Review your shot, and if you're happy with what you see then toggle back to Live View with Focus Peaking enabled, zoom in a little on the chart and you should have the Focus Peaking highlight things perfectly symmetrical (the same amount of Focus Peaking Highlight information highlighted above and below the centre of the chart).
5) Now switch over to the PDAF (OVF/Eye Piece mode), take a shot like you normally would for a Focus Test Chart shot (Single AF Spot Point bla bla bla).
7) Ignore the Playback/Review.
7) Do not refocus
7a) Optional; if you can and feel comfortable, gently toggle the camera out of being in AF mode and place into MF mode
8) Hit the Live View Button which should also still have Focus Peaking on from last time.
9) Press the Ok Button to zoom in and check where the focus is, and essentially let Focus Peaking guide you as to how accurate the focus was from the shot before, how much front or back focus it has, does the focus peaking have more information ahead of the centre point or behind etc.
10) Make adjustments (if necessary) in Fine Adjustments, toggle back to PDAF/OVF, AF on and repeat.

Basically what I was finding is that once I took a shot through the OVF and get presented with a Playback screen, it's still hard to tell sometimes (lens dependent) where the focus shift is (if any). By ignoring the Playback screen entirely (turn it off in the menu if you like) and instead just toggle over to Live View with Focus Peaking enabled (after the PDAF shot), zooming in on Live Playback footage with Focus Peaking actually shows where the focus was when it was taken and thus provides better feedback to the user as to where the front and back focus issues may be.




Cheers,

BB

[tduell]

Hello Bruce,
There is another approach to this vexed subject, and it's called the 'dot tune' method, said to be 'simple'.
This link gives an explanation <https://www.fredmiranda.com/forum/topic/1187247/0>, and there are other sites which try to explain it as well.
I've been meaning to give it a try, but haven't got around to it yet.
Let's know how you get on if you give it a try.

Cheers,
Terry

[ramseybuckeye]

Sounds brilliant to me

[BruceBanner]

Hello Bruce,
There is another approach to this vexed subject, and it's called the 'dot tune' method, said to be 'simple'.
This link gives an explanation <https://www.fredmiranda.com/forum/topic/1187247/0>, and there are other sites which try to explain it as well.
I've been meaning to give it a try, but haven't got around to it yet.
Let's know how you get on if you give it a try.

Cheers,
Terry

Hi Terry, that sounds interesting, unfortunately I am not seeing the link to the video in the first post

[JohnX]

Youtu.be

Youtu.be

[rogerstg]

Focus Chart Review Hack

I've use a simplified method which is pretty much as you've outlined, except no photos are taken. I simply focus via OVF then switch to Live View. Focus peaking will show the range in focus, and obviously, the point of focus should be in the middle of that range. The focus peaked area is most apparent in the pattern areas of the testing chart. I've also used a window screen at ~ 30 degrees to confirm focus accuracy for a 500mm lens. I focused on a piece of black tape in the center of the screen, switched to Live View and noted that the tape was in the middle of the "peaked" area.

I've mostly used this to confirm adjustments made with the Dot Tune method of calibration.

[BruceBanner]

Hello Bruce,
There is another approach to this vexed subject, and it's called the 'dot tune' method, said to be 'simple'.
This link gives an explanation <https://www.fredmiranda.com/forum/topic/1187247/0>, and there are other sites which try to explain it as well.
I've been meaning to give it a try, but haven't got around to it yet.
Let's know how you get on if you give it a try.

Cheers,
Terry

YouTube

Ok, thanks for those links to the dot tune method, I have now had a chance to review this process for my K-1.

Here's my thoughts;

- I don't know if this test is that reliable for Pentax cameras as we have less feedback for our AF focus confirmation turning on. It's a green hex and it either is off or on, not flickering or any of that other stuff that might help more with other brands.

- Pentax has a smaller scale, -10 to +10 whereas at least in the video they get a full -20 to +20. At this point in time I am not sure they actually correspond to better fine tuning or actually a longer scale of which to make adjustments. This is quite interesting to me because my FA77 actually needs +8, and with the dottune scale it was not possible to find the other end of the spectrum..

I had already chosen some AF adjustments for certain lenses using my own LV Focus Peak assistance, I then sat about testing the lenses with the dottune method.

The FA43 on the K-1 I had given a +3 (before trying the dot tune), through my dottune testing i notted that the AF confirmation came on at -3 and +7 (-2 it was off and +8 it was off), using the dot tune calculator to find the midpoint it spat out +2 (close enough to my +3 I gave).

Where the test fell over was when doing the FA77 (which I have as a +8 before the test). The dottune gave me my first AF confirmation at +2 and it stayed on right through to +10 (and arguably would have stayed on past this point if we have more Fine Adjustments). If I used 2 and 10 I would be given +6 as a value however I feel +8 gives better accuracy (and focus peak confirms it).

What I like about the dottune test is not having to take images and thus spare the shutter count during a gazillion lenses to test, however on our Pentax platforms I am not sure we have a varied enough AF confirmation signals, we get either no AF confirmation or a permanently on AF confirmation, not a 5 sec always on marking point like the video illustrates. Nor do we have -20 to +20 as our scale.

So I would still use the Focus Peak as additonal assistance to help with the dottune test, what's nice is you can use them both to help fine tune.

[rogerstg]

Where the test fell over was when doing the FA77 (which I have as a +8 before the test). The dottune gave me my first AF confirmation at +2 and it stayed on right through to +10 (and arguably would have stayed on past this point if we have more Fine Adjustments). If I used 2 and 10 I would be given +6 as a value however I feel +8 gives better accuracy (and focus peak confirms it).

You just need a little ingenuity. When I fall off the range of the camera, I move the camera back or forth as needed until the first confirmation is at the other end of the range, then continue to find the opposite end. That gives me the range of acceptable focus from which I can find the center. In your example, I'd slide the camera until the first confirmation is at ~ -9. The other end of the range would probably be ~+3, giving a range of 12 increments. Half of that is 6 which added to the +2 originally found would yield a mid adjustment of +8.

I find that there is usually enough give in my acra mount to slide the camera front or back to quickly accomplish this.

[BruceBanner]

You just need a little ingenuity. When I fall off the range of the camera, I move the camera back or forth as needed until the first confirmation is at the other end of the range, then continue to find the opposite end. That gives me the range of acceptable focus from which I can find the center. In your example, I'd slide the camera until the first confirmation is at ~ -9. The other end of the range would probably be ~+3, giving a range of 12 increments. Half of that is 6 which added to the +2 originally found would yield a mid adjustment of +8.

I find that there is usually enough give in my acra mount to slide the camera front or back to quickly accomplish this.

Clever.

That raises the question, is the AF Confirmation range for Pentax always the same? Like do we ever need to find the other end of the spectrum or does one end suffice and adding (or taking away) x amounts always put us in the right place?

Example;

FA 43 for me is -3 and +7 for AF confirmation, giving +2 as being the middle point. That's a 10 point scale (-3 to +7) thus if you add or subtract 5 to the corresponding beginning of the spectrum you get your centre point.

In the case of my FA77 I only get +2 (and we cannot know what the drop off is as the scale stops at +10), but by adding 5 to +2 we get +7 (which is close to my +8 that I always gave it), thus perhaps that's all we need to do for all lenses (add or take away 5 depending on which end of the spectrum you use)? If the Pentax FA scale went to +20, my FA77 might be at +12 for the last AF confirmation point for my FA77 etc.

This of course falls over if the scale changes per lens, and sometimes the AF confirmation is only 6 increments rather than 10 like it seems to be giving me.

[rogerstg]

That raises the question, is the AF Confirmation range for Pentax always the same?

How could it be? Depth of field changes with focal length, aperture and distance. That's why you sometimes need to move closer when doing calibration, so that the depth of field is smaller, making it measurable/observable.

Also, one should keep in mind that camera brands with twice as many adjustment points don't necessarily have twice the range of adjustment. They only have twice as many increments.

[JensE]

Here's what I did and I wondered if this was a bonafide recommendation for completing Fine Adjustments/Focus Chart work (or not);

I'm using a similar procedure for most of my zoom lenses - tedious to get through several focal lengths otherwise. Or maybe I just have too many (lenses x cameras) ...
As Roger pointed out, you don't need to even take a picture. I take some around the final values however, for an even closer inspection on a nice large monitor :-)

Hints/Remarks:

1. On #1 "chart at 45degrees" - my setup is focus chart parallel and evaluation chart, safely outside the AF-area, angled.
   Focusing on a slanted chart may lead to an unexpected distance for PD-AF.
2. For lenses which exhibit focus shift on closing down the aperture (e.g. FA50/1.4), I evaluate the live view at target aperture, for which I want to calibrate.
   For the FA50/1.4, my target was f/2.0, so I close down the aperture using the ring around the trigger (or aperture ring) during LV. When I use it at f/1.4, I tend to focus-bracket anyway, because it's not very consistent - see the 2nd method for details.
3. Have not tried it, but I need to test connecting an external big monitor via HDMI for easier evaluation.
4. An observation: For many lenses which exhibit chromatic aberations (green/purple), the color-neutral point is different from the point of best sharpness, i.e. highest resolved detail.

An alternate, even easier to evaluate and quick method for lenses with useful distance scales (in my case LTDs, F/FA primes, two Sigma zooms):

1. Use focus chart parallel to the camera. I have one on a door, and the floor has a perpendicular line to the door, which I align the camera position with. Horizontally, I use the digital level.
2. Set up the camera at a target distance, which approximately focuses in a way that some distance marks are aligned with the center, or actually any other line (e.g. a DoF mark). All you need is repeatability.
3. Move the focus in MF so that the chosen lines line up perfectly.
4. Move the camera back/forth to fine-tune sharpness in magnified life view. I use a long Arca-style base plate or, when I feel fancy, my macro stacking rail.
   Alternatively to 3./4., you can use CD autofocus in life view to make sure it ends up at the aligned distance marks from both sides, i.e. from short and long distances (on average). Again, do this at the target aperture!
5. Switch to PD-AF, focus from both sides and adjust until the average stopping point is the focus distance mark alignment. Do several runs, you get a good feeling for focus consistency this way.

To make the lens focus from short/large distances, just put your hand in front of the lens shorter than minimum distance and half-press the shutter. Doing it twice usually goes to the opposite end of the focus range. To rule out parallax errors, you can place some kind of guide above the camera, or make sure that e.g. a tripod leg aligns with the viewfinder while judging the focus scale. Afterwards, I usually do one round of confirmation shots on a parallel+slanted target like described above. A nice thing with this 2nd method is that you can use a large focus target and this way get a feel for field curvature.

Exiftool can btw. read the correction value for a particular shot. I use it to rename test pictures automatically for 'classic' evaluation methods.

[BruceBanner]

How could it be? Depth of field changes with focal length, aperture and distance. That's why you sometimes need to move closer when doing calibration, so that the depth of field is smaller, making it measurable/observable.

Also, one should keep in mind that camera brands with twice as many adjustment points don't necessarily have twice the range of adjustment. They only have twice as many increments.

Yeah, after posting this I realised the error of my thinking, however it also made me realise that perhaps aiming for a Fine Adjustment where '+/- 5' from either spectrum (10 in total, 5 being midway) would give the best accuracy, and if you were only getting a margin of 6 in total (3 being midway) then this was too small a scale to use, move in closer etc. Because the rule of 50x focal length I think doesn't always work well for some lenses.

And also, do we know however that the -20 to +20 is the same scale as ours just with higher accuracy/increments, or is it just more scope for adjusting? We don't really know do we? (that was my point).