[BruceBanner]

I'm no stranger to using Fine Adjustments, however normally they are performed with fast primes. This allows a more obvious front or back focusing issue.

I just tested my newish 55-300 PLM on both my K-1 and KP, and tbh, even when zoomed in, and selecting the extremes -10 and +10... the results didn't look that different from either, I wasn't seeing a significant difference between either of the extremes. I tested this also with just putting a bottle on the wall as well as focus sheets. Focus was fine at all focal lengths and attempts.

It could be I am less sensitive to front and back focusing issues with slower glass, but even when zoomed in I was expecting the subject to being quite a bit softer at either end of the FA spectrum. I'm now wondering if PLM is somehow a different thing altogether (as it does feel very accurate in the field) and thus the FA is something relevant to other focus driving systems only (Screw Drive/SDM etc)?

TIA

BB

[tduell]

I be surprised if the focus drive method has any effect on front/back focussing.
I'd also be surprised if you didn't see the effect of shots at -10 to +10 when shooting at the typical sloping scale and target, using wide open aperture, and using tri-pod, mirror up, and all the usual vibration reducing techniques...and checking the variation over a number of shots.
I'd like to be surprised, looking forward to the results of exhaustive controlled tests

Cheers,
Terry

[UncleVanya]

The fine adjust works on manual focus as well as all autofocus lenses when you use pdaf optical focus. It has zero effect on live view. I mention this just in case. Assuming pdaf and wide open what was the distance to the subject?

[BruceBanner]

I be surprised if the focus drive method has any effect on front/back focussing.
I'd also be surprised if you didn't see the effect of shots at -10 to +10 when shooting at the typical sloping scale and target, using wide open aperture, and using tri-pod, mirror up, and all the usual vibration reducing techniques...and checking the variation over a number of shots.
I'd like to be surprised, looking forward to the results of exhaustive controlled tests

Cheers,
Terry

I was surprised myself Terry.

Like I say, FA77 +8, FA43 +3, etc etc. I do do these tests enough to determine if a lenses sharpness can be improved in the field. It's a great feature to have.

I know FA's do not apply to any Live View focusing (CDAF), and thus I was expecting it to be like any lens and FA's to take affect for any OVF work (PDAF). I don't normally use f4.5-6.3 glass, and this maybe I am not seeing where the front or back focusing is really happening. It could be that the focus is 'good enough' at the centre of the chart and thus I am not paying attention properly to further away places, it was just a quick 10mins play around. But it did have me stumped at how little the extremes were doing to my shots. I tried more 'in the field' scenarios, bottle on the wall, a 0 shot, -10, +10, hardly any difference on any of them, which is what prompted this thread O.o

More testing clearly needed, I just wanted to ask because this is the ONLY PLM lens on the market for Pentax, and was wondering if somehow that unique focusing drive mode was somehow immune to FA's, and you just have to 'live with what you get'?

[tduell]

The focus fine adjustment values, as I understand it, tell the lens to move +/- a poofteenth more/less than the PDAF figured was necessary for correct focus, so if the lens is giving essentially the same result regardless of how the AF fine adjust was set, it suggests that the lens is unable to focus well enough for these differences to be seen, which surely would have cropped up in earlier user reports about this lens.
If I recall correctly, you have posted a few shots of felines using this lens that appear to be pretty sharp, but hard to be certain given the posting image size constraints. If your original full size feline images look consistently sharp, then the results from the AF fine adjust tests are probably suspect.

Cheers,
Terry

[swanlefitte]

I wonder if a fast prime would be the same at f4- f5.6? Might compare the limited and plm at 77 +-10.
Yet i suspect not because my 18-50 needed adjustment and it clearly helped.

[BruceBanner]

The focus fine adjustment values, as I understand it, tell the lens to move +/- a poofteenth more/less than the PDAF figured was necessary for correct focus, so if the lens is giving essentially the same result regardless of how the AF fine adjust was set, it suggests that the lens is unable to focus well enough for these differences to be seen, which surely would have cropped up in earlier user reports about this lens.
If I recall correctly, you have posted a few shots of felines using this lens that appear to be pretty sharp, but hard to be certain given the posting image size constraints. If your original full size feline images look consistently sharp, then the results from the AF fine adjust tests are probably suspect.

Cheers,
Terry

I wonder if a fast prime would be the same at f4- f5.6? Might compare the limited and plm at 77 +-10.
Yet i suspect not because my 18-50 needed adjustment and it clearly helped.

Ok, I just popped out to do 3 quick shots, 55-300 @ 300mm, f6.3, ISO 1600 on the K-1.

0


+10


-10


Maybe from these three shots you can see why I was a little stumped.

I am however seeing some differences, it's unknown if the differences are simply me pushing the shutter button or actual Fine Adjustment differences (as I wasn't using a remote to fire the shutter but just doing it as gently as I could on the tripod). I think it is working and it's just me showing my inexperience with stopped down glass in this type of scenario.

It's the sort of differences that chimping is not showing much, when on a computer you can see differences better.

Normally with wide open fast glass, its quite apparent on the back of the camera screen where the focus needs adjusted.

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Last edited by BruceBanner; 03-22-2020 at 02:10 AM.

[swanlefitte]

Very close. There is slight difference. Peeping on the stitch pattern on the f of focus the -10 is in front. 0 is the best. Probably different at 55mm anyway.

You are suppose to 25x mm away right? was this at 7.5 meters? Going from memory on this. Perhaps its the distance?

[WorksAsIntended]

Ok, I just popped out to do 3 quick shots, 55-300 @ 300mm, f6.3, ISO 1600 on the K-1.

0


+10


-10


Maybe from these three shots you can see why I was a little stumped.

I am however seeing some differences, it's unknown if the differences are simply me pushing the shutter button or actual Fine Adjustment differences (as I wasn't using a remote to fire the shutter but just doing it as gently as I could on the tripod). I think it is working and it's just me showing my inexperience with stopped down glass in this type of scenario.

It's the sort of differences that chimping is not showing much, when on a computer you can see differences better.

Normally with wide open fast glass, its quite apparent on the back of the screen where the focus needs adjusted.

Very baffling! Maybe try to clean the contacts, it may loose the lens id information and therefore not apply the differences?

[pschlute]

Are you doing the adjustment and saving using the Apply One setting ? In which case make sure the setting is still in APPLY ONE when you exit the menu ? *

if you turn the camera off or remount the lens, and go into the menu is the adjustment you made still recognised in the APPLY ONE menu ?

* If you exit the menu from the APPLY ALL setting, then that will be used instead (which may be zero)

[zapp]

What´s the Problem? Lens is in add adjustment. There is an effect between +/-10. Effect is small, but dof is large and also compensated for slight changes in af. Depending on lens, aperture, camera ... things can look quite different.

[BruceBanner]

Very close. There is slight difference. Peeping on the stitch pattern on the f of focus the -10 is in front. 0 is the best. Probably different at 55mm anyway.

You are suppose to 25x mm away right? was this at 7.5 meters? Going from memory on this. Perhaps its the distance?

There is a difference on all of them, I think its just very mild subtle, but the focus is shifting slightly in favour of the front and back focusing bias. It's just not dramatic like how a FA77 at f1.8 might highlight.

I've read focus charts are to be done with a distance that is close to minimum focus, but not quite. This gets you the closest to the chart to assess things best.

I hate and love focus charts, because on one hand they can be helpful, but... I don't often shoot an FA77 at something close to me at f1.8, so real life 'in the field' tests can also be useful, as long as u tripod or be quite consistent, hence bottle on the wall test shots too. In the past when I have done the bottle on the wall charts I can find them more useful for fine tuning a lens as they may correspond to a situation that is akin to real life. What I have also found is the results to being similar to focus charts, in that say using a FA77 @ 1.8 and having a bottle on the wall 6-7m away you can tell with the Fine Adjustments what is improving and what is worsening. Here, doing the same thing with the PLM (0, +10, -10) the results looked similar to the focus charts, each shot just had the bottle in perfectly fine focus with neither spectrum really differing that much to the other...

Very baffling! Maybe try to clean the contacts, it may loose the lens id information and therefore not apply the differences?

I can try that, but everything works as normal, I doubt its contacts.

Are you doing the adjustment and saving using the Apply One setting ? In which case make sure the setting is still in APPLY ONE when you exit the menu ? *

if you turn the camera off or remount the lens, and go into the menu is the adjustment you made still recognised in the APPLY ONE menu ?

* If you exit the menu from the APPLY ALL setting, then that will be used instead (which may be zero)

Yep, Apply One. Restarting camera and it will show the last used value (but during the test you can change the value and shoot, you do not need to power off and on for it to take hold).


Really I just wanted to know if any other PLM user found a similar experience, or whether this is just a telezoom thing with fairly stopped down aperture focus chart analyisis thing, and that things are actually normal here and to be expected?

[Rondec]

I would think the issue has to do with your depth of field at this distance and aperture. It isn't like an f1.4 or f2 lens where the differences will be dramatic.

[3by2]

There is a difference. The 0 looks sharpest at -10 but you've got more in focus behind it. I'd probably dial in -5 and do some real world testing, you're right though it isn't huge, I wonder if that's something to do with how zooms work/are made, so far I've only done primes.

[BigMackCam]

Depth of field due to the slow aperture is making this more difficult to see than with a faster lens.

It's easier to see the difference if you compare a limited area of the test shots side by side.

See below - on the left is a section of the +10 shot, and beside it on the right, the same section of the -10 chart. I've excessively sharpened the whole thing in GIMP which helps to exaggerate the in-focus areas. Rather than looking at the "0" mark, look at the "2" marks and the thin lines running through them, top and bottom, to see a more obvious difference. On the left hand image, the upper "2" is more blurred than on the right, while the lower left "2" is less blurred than the right. Look more closely, and I think you'll see the "0" on the left (the +10 image) is sharper.

Looking at this comparison (and assuming you're getting consistent results across multiple shots taken at each adjustment), I'd guess around a +6 or +7 adjustment should be optimal. It would certainly be very close to perfect - so close that there'd be no point trying to achieve any better.