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09-10-2014, 05:41 AM   #1
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K5 lens calibration for Ronikon 85mm f1.4

Hi,

I just got Ronikon 85mm f1.4 for my Pentax K5. It is a manual lens. I found it extremely difficult to get focus right using viewfinder focus confirmation. Turns out it is not calibrated because no exception sharpness increases significantly if I ignore focus confirmation and focus slightly further. So I decided to use "AF Fine Adjustment" to compensate for this. For this particular lens I only have APPLY ALL on the "AF Fine Adjustment" menu and no matter what that value is (-10~+10) there is zero impact on focus confirmation. So I got surprised and tried the same thing on my SMC 50mm f1.8 lens both with APPLY ALL and APPLY ONE both -10/-10 to +10/10 expecting extreme focus difference but I hardly notice any difference even on f1.8.

I assume I am missing something obvious. Thoughts?

Cheers

09-10-2014, 05:51 AM   #2
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Unfortunately, with manual focus lenses, there is no per lens AF fine adjustment, you can only use the APPLY ALL +10 to -10 adjustment.
09-10-2014, 05:53 AM   #3
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QuoteOriginally posted by James78 Quote
Hi,

I just got Ronikon 85mm f1.4 for my Pentax K5. It is a manual lens. I found it extremely difficult to get focus right using viewfinder focus confirmation. Turns out it is not calibrated because no exception sharpness increases significantly if I ignore focus confirmation and focus slightly further. So I decided to use "AF Fine Adjustment" to compensate for this. For this particular lens I only have APPLY ALL on the "AF Fine Adjustment" menu and no matter what that value is (-10~+10) there is zero impact on focus confirmation. So I got surprised and tried the same thing on my SMC 50mm f1.8 lens both with APPLY ALL and APPLY ONE both -10/-10 to +10/10 expecting extreme focus difference but I hardly notice any difference even on f1.8.

I assume I am missing something obvious. Thoughts?

Cheers
Viewfinder AF confirmation is subject to a considerable amount of tolerance, so if you want to rely on it your best bet is to stop the lens down. If you want to make sure the focus is perfect, you can also use live view magnification.

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09-10-2014, 06:02 AM   #4
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QuoteOriginally posted by aleonx3 Quote
Unfortunately, with manual focus lenses, there is no per lens AF fine adjustment, you can only use the APPLY ALL +10 to -10 adjustment.
I am fine with this limitation cause currently my only MF lens is this Ronikon 85mm f1.4

---------- Post added 09-10-14 at 11:09 PM ----------

QuoteOriginally posted by Adam Quote
Viewfinder AF confirmation is subject to a considerable amount of tolerance, so if you want to rely on it your best bet is to stop the lens down. If you want to make sure the focus is perfect, you can also use live view magnification.
I an currently using live view to get away with it. However I found focus confirmation being reasonably accurate in my case just slightly (like 5%) closer than what it should really be. As I said I get consistently better result to manually focus further AFTER focus confirmation beeps. So I am pretty sure it's a calibration issue.

Any idea why my "AF Fine Adjustment" setting on APPLY ALL is not effective for my manual lens?

09-10-2014, 06:43 AM   #5
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Your best bet to focus a super fast lens is:
-focus screen like KatzEye or from Focus screens com or Jin Finance. Matte or split prism focusing screens can help with such focus a lot, but can affect spot metering and darken the viewfinder with slow lenses
-Live view + magnification. And focus peaking, if your camera has that (K-5 doesn't, I think)
-Catch in focus aka focus trapping. Lots of threads about this feature, and it can be pretty useful
-zone focusing, if your lens has calibrated distance scales

Finally, the focus confirm on the camera (the hexagon below the viewfinder, not the red square). With manual lenses, I think only the centre point is active. You can use global adjust or possibly debug mode and global adjust there. It should work, don't know why its not effective in your case. There are many threads about focus adjustment with focus charts you can find online, as well as other techniques

Edit: And btw, I think that Samyang/ Rokinon 85mm f1.4 is known for difficulties with focusing, especially due to miscalibrated distance scales and razor thin DoF.
09-10-2014, 06:44 AM   #6
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You can also try to set catch-in-focus to quickly validate the result; also depending on the DOF and how far you stop down, there could be a difference between focusing from "near-to-far" and "far-to-near".
09-10-2014, 08:05 AM   #7
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QuoteOriginally posted by James78 Quote
I am fine with this limitation cause currently my only MF lens is this Ronikon 85mm f1.4
Well, if you use APPLY ALL, my understanding is that the bias applies to ALL lenses using the AF system. That would include your AF lenses too.

As to what you may be missing:
  • The AF system (that includes focus confirm and catch-in-focus) is not very precise, particularly with faster lenses.* I usually suggest that a user do a best of five attempts when evaluating AF calibration. I also usually suggest a high contrast flat target affixed to a wall with the camera on tripod about 10x to 15x the focal length, 2s shutter delay, and care taken to make sure the sensor is parallel to the target.
  • Conventional wisdom is that manual focus using the viewfinder and a high quality focus screen is superior (particularly with fast lenses) to focus confirm (see point above)
  • It may be that your Ronikon 85/1.4 is not very sharp even when in focus. As suggested above, evaluate your AF results against focus using magnified live view. The magnified live view focus results should act as your baseline for expectations.

Steve

* All but the center AF point of the K-5 II/IIs has a focus sensitivity tuned to f/5.6 with the center point being tuned to f/2.8 (on K-5, I believe that all are tuned to f/5.6). What that means is that your f/1.4 lens stopped down to f/2.8 (or f/5.6 depending on focus point) will focus with the same degree of precision as at f/1.4.
09-11-2014, 05:57 PM   #8
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QuoteOriginally posted by stevebrot Quote
Well, if you use APPLY ALL, my understanding is that the bias applies to ALL lenses using the AF system. That would include your AF lenses too.
Fair point. I ended up using APPLY ALL main for the sake of my Ronikon lens, then compensate for this by APPLY ONE on lens-by-lens basis. A bit painful but currently only option I could think of.

I spent more time on the calibration and concluded that viewfinder focus is not disappointingly inaccurate. In low-light, for 200cm subject distance, focus confirmation is on over a distance of roughly 7cm which is something that I could live with. Compared to Live View though I would definitely get better focus by Live View on 6x~8x zoom. So altogether I am happy with how accurate focus confirmation COULD be however I still struggle with the calibration issue. So I spent more time...

...turns out for 200cm distance focus point goes further by few centimeters from 0 to -10 and this is the max I could achieve. Seems like the lens is way off which seconds the opinion on Ronikon 85mm F1.4 focus calibration issues.

09-15-2014, 04:40 PM   #9
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QuoteOriginally posted by Na Horuk Quote
And btw, I think that Samyang/ Rokinon 85mm f1.4 is known for difficulties with focusing, especially due to miscalibrated distance scales and razor thin DoF.
I am coming to the conclusion that there are issues with the lens. With maximum calibration focusing improves but still consistently focuses ahead of subject. When you say these lenses are known for difficulties with focusing do you mean as in lens design issue? What I am experiencing right now makes it useless except for Live View. I can clearly sense that focus accuracy is reasonable only problem is that it ALWAYS focuses ahead of the actual subject even if I focus from further distance closer. %100 a calibration issue but K5's maximum APPLY ALL calibration is not enough. I can set it to -10 but seems like what I really need for this lens is something like -18. Thoughts? Right now I'm considering to return the lens. I wonder whether I'll have same focus calibration issues with Bower/Samyang.
09-16-2014, 11:16 AM   #10
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QuoteOriginally posted by James78 Quote
I wonder whether I'll have same focus calibration issues with Bower/Samyang.
I'm pretty sure Samyang makes all the lenses and they simply get rebadged as Rokinon, Bower, and many others.
The problems I heard are a stiff focusing ring and general QC (quality control is a problem for Samyang lenses, there is a reason why they are so cheap. Many of us had to exchange a Samyang lens because it did not perform as it should). And then there is the extremely shallow DoF, which makes focusing difficult because modern DSLRs are designed for AF - they have a small viewfinder and the focusing screen is not designed for such fast lenses. Try one of those DoF calculators online to see how shallow the DoF is.
09-18-2014, 03:18 AM   #11
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I just purchased an SMC Pentax-M 50mm F1.4. I have exact same focusing issue. So with default settings with focus confirmation peak focus is ahead of the subject. When I set AF Fine Adjudtment to max -10 it gets better but still slightly ahead of subject.

Now I'm thinking whether my K5 has some focusing calibration issue. Thoughts?
09-18-2014, 03:46 AM   #12
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QuoteOriginally posted by James78 Quote
Hi,

I just got Ronikon 85mm f1.4 for my Pentax K5. It is a manual lens. I found it extremely difficult to get focus right using viewfinder focus confirmation. Turns out it is not calibrated because no exception sharpness increases significantly if I ignore focus confirmation and focus slightly further. So I decided to use "AF Fine Adjustment" to compensate for this. For this particular lens I only have APPLY ALL on the "AF Fine Adjustment" menu and no matter what that value is (-10~+10) there is zero impact on focus confirmation. So I got surprised and tried the same thing on my SMC 50mm f1.8 lens both with APPLY ALL and APPLY ONE both -10/-10 to +10/10 expecting extreme focus difference but I hardly notice any difference even on f1.8.

I assume I am missing something obvious. Thoughts?

Cheers
James, I have this lens too. You can't be blaming it for the AF system's mistakes! ☺

There's no margin for error at f1.4 - hard enough at 50mm, something again at 85mm. That's so fast even Live View can be hard to get right on my K-30 and NEX-7 - a speck of red here or there!

Instead, I have in the K-30 a Katzeye split prism focusing screen and that works well of course if there's an edge to use in the target area.

Last edited by clackers; 09-18-2014 at 03:51 AM.
09-18-2014, 04:18 AM   #13
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QuoteOriginally posted by clackers Quote
James, I have this lens too. You can't be blaming it for the AF system's mistakes! ☺

There's no margin for error at f1.4 - hard enough at 50mm, something again at 85mm. That's so fast even Live View can be hard to get right on my K-30 and NEX-7 - a speck of red here or there!

Instead, I have in the K-30 a Katzeye split prism focusing screen and that works well of course if there's an edge to use in the target area.
I would expect inconsistent results. However I consistently get focus ahead of subject. Focusing from near/far to subject cones to same point. I struggle to accept this is inaccuracy in focusing because with some practice whenever focus confirmation (hexagon light) is on if I blindly focus slightly further I get sharper results and this works consistently. So it cannot be random. I wish I could compare with another Pentax just to check if I have bigger calibration issues.

Last edited by James78; 09-18-2014 at 04:26 AM.
09-18-2014, 01:07 PM   #14
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QuoteOriginally posted by clackers Quote
James, I have this lens too. You can't be blaming it for the AF system's mistakes! ☺
Yes, absolutely. The lens just tells you that the focus confirm feature is not working well.

QuoteOriginally posted by James78 Quote
if I blindly focus slightly further I get sharper results and this works consistently
It was not clear from your description whether this is still the case when you are focusing both near-to-far and far-to-near? The reason I ask is that there is often a fairly large amount of focus ring travel (several degrees of arc) where the green hexagon is lit. What this means is that every thing looks great to the PDAF system when things are really not that good.

The reason for this is that with the exception of the center point, the PDAF sensors have the same focus sensitivity (ability to detect out-of-focus) at f/5.6 as at f/1.4. The center point has focus sensitivity equivalent to f/2.8. This is the design specification with no workaround. As a result, the precision of both the AF system and focus confirm sort of sucks when using truly fast glass.* Getting the same focus point twice is difficult. An assessment of focus accuracy should, as a result, require multiple attempts. I would suggest a minimum of best of five, making careful note of the focus ring position (arrow-shaped pieces of tape are helpful) for each attempt.

It may well be that your AF system is out of calibration, but I would consider that to be a different problem than your difficulties with manual focus on your K-5. To put it succinctly:
  • The PDAF system on your camera (and all other currently dSLRs regardless of brand) is not sufficiently sensitive for lenses faster than f/2.8. Translation? You will seldom get the same focus point twice. (Yes, I am repeating myself.)
  • Focus confirm (catch-in-focus included) is not a good option for fine focus due to the above point. Calibration will not improve your percentage of in-focus shots with fast lenses. I know. I have been there and tried that.
  • Your options include magnified live view and the optical viewfinder.
  • The stock focus screen offers focus sensitivity on the same order as the PDAF system. Based on user accounts on this site, this may be compensated for with a viewfinder magnifier.
  • An appropriate aftermarket focusing screen is capable of focus sensitivity adequate for your f/1.4 lenses.


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09-18-2014, 01:59 PM   #15
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QuoteOriginally posted by James78 Quote
. I wish I could compare with another Pentax just to check if I have bigger calibration issues.
Calibration? Again, that's of the camera's AF settings, not the lens. You say you get sharp images, but the green hexagon's coming on at the wrong time.

Manual focus is what you want for portraits at f1.4. Otherwise, the camera can go for the nose when you wanted the near eye. You'd do the same with macro photography, to get the stamens of a flower in focus rather than a closer leaf.
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