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04-25-2012, 12:24 PM - 1 Like   #1
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Focus Indicator Accuracy With Old Manual Lens

Gentlemen,
I noticed that AF assistant accuracy was way off when using old (K-, M-) lenses. I really mean it, it's way off. I tried AF adjustments on the legacy menu and then I moved to the service mode and found out, that I could either live with AF lenses or MF ones, but neither both:
- thru the service mode I can set AF adjustments that way (+150 um), that my 15Lim and Tokina's AF270 and ATX280PRO are within the range of legacy AF adjustments (e.g. 0 for the Lim and -3 for Tokinas). But old MF lenses (ancient M42 Industar 50/3.5 with no coatings at all, M42 Helios 44 multicoated, K-mount Helious 77) are too much off the focus when that focus indicator beeps on
- thru the service mode I can adjust AF to -120 so that all my MF are quite spot-on, but then even set to +10 on the legacy menu I can't get even close to any precise focus with AF lenses

Even if I try to put it into extremes and adjust AF thru the service mode so that some lens is having +10, and other -10 and 'all' -10 - it doesn't work, it's just out of the range available on the legacy AF menu and needed for all those lenses.

I gave a call to local Pentax service center and was told that it was the way it's supposed to be. AF system requires some data (oh... what?!) from a lens on order to work and since MF lenses do not provide that data, then AF is no way precise with them. AF assistant aka focus indicator will be way off with all those old lenses of K-, M- and even A- series. They could not answer on why pentax still offers M42-K adapter as well as adapters for 645 and 6x7 lenses and do not offer any split-screen focusing screens. LV focusing works well, but there're many scenarios when LV is useless (e.g. for action photography or in bright light).

Here in Mordor things are slightly different and reps are not quite client-focused. So I decided to doulbecheck it and contacted Pentax USA thru the live chat on their website. Paul started doing his best, but after he noticed my IP address he said I had to turn to Pentax of Mordor (which I had already done, see above) since it was my geographic location. And he refused to provide me with any email addresses for 2nd line technical support.

So I'm asking if anybody here could do me a favor and spend half an hour of his life on the live chat with Pentax USA on their website asking for details on the AF design and whether it is really not meant to work with M- and K- lenses missing those electronic chips.

TIA,
Zig


Last edited by Siegfried; 04-25-2012 at 12:28 PM. Reason: spelling, blind typing
04-25-2012, 01:00 PM   #2
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i am suprised that the focus indicator is that far off, so lets play 20 questions

- when focusing do you always start from either infinity or minimum focus,?
- do you stop the instant you get the red indication , or the green hexigon?
- do you move through the entire range where the green hexigon is lit and then back to the middle of that range, ?
- are youo a stable distance away, or are you moving the camera slightly towards the subject?
- is the subject a focus target?
- when you think the subject is in focus, based upon the focus indicator is it cleare in the view finder?
- did you adjust the view finder diopter?

and lastly can you post a few images?
04-25-2012, 01:39 PM   #3
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Lowell,
thanks for coming up. Although I wouldn't like this thread to turn this way (instead of getting in contact with different Pentax reps and confirming/busting that explanation I was given), here it goes:
1. when focusing I used to start from the previous focus position which can be at infinity or MFD or somewhere in-between; however, the picture is the same if I go from hard-stops from infinity or minimal focusing distance
2-3. I do understand that there's a certain focusing range within which PD AF assistant thinks we're in-focus. But it is way off focus whichever edge of that range is considered if withing factory AF settings (or settings optimized for AF lenses)
4. I'm stationary still when making a photograph, holding my breath and counting down
5. I don't enjoy making photographs of test targets or brick walls, but I do understand what are you talking about. My subjects have enough contrast and illumination (+see below)
6. There doesn't appear to be misadjustment in the mirror box or viewfinder assembly, WYSIWYG - if it is off-focus, it isn't clear in the viewfinder But APS-C viewfinders are small and it is very hard to achieve precise focusing w/o further assistance either from special focusing screens or some in-cam electronic gizmo
7. Yes, I have my viewfinder adjusted

I will get back with sample images of test targets as well as real-life subjects as soon as Pentaxforums stops stumbling. I have troubles posting that message as well as adding this one.

With all the respect to you and others who paid attention to that post, I'd like to move off the basics and quizing my shooting techniques and knowledge. Once again, the question is to contact other Pentax representatives in order to confirm or to disprove the response I received from Pentax Mordor which was that focus indicator in K-5 model isn't designed to be any way precise when working with M-, K- and A-series lenses.

Thanks,
Zig
04-25-2012, 02:41 PM   #4
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I'm not in the USA but just a data point: My focus indicator works passably well with M and A lenses. It's not good enough to use at very wide apertures but f2.8 and smaller is OK.

04-25-2012, 03:00 PM   #5
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Hi Zig, I find that interesting that you're finding the focus indicator that far off. I don't have any suggestions or solutions. I'm really new to my K5 with only a grand total of 140 images so far.

Almost half of them have been taken with either of my two most recent manual lenses, one an Adaptall II lens and the other with a fully manual Panagor 90mm macro. The focus indicator was turned to center spot. The subject in the image was centered, focus until the red indicator then I'd restructure the frame. Like I used to do with split image range finder focus aids. (gotta get that Nikon K screen cut down!)

Regarding hardware & AF, what the rep in Mordor was indicating doesn't ring true to me. I think the focus indicator and the algorithms that drive it are all contained in the image processing engine. I am pretty sure that the Pentax DSLRs, K5 included, use a contrast detection method. The highest level of contrast on adjacent pizels on the sensor is achieved when in focus. This is also why my K100 has more trouble focusing in dim light than the newer cameras with higher sensitivity sensors. It is also why focus helper lights are there. With that said, a faster lens will likely perform better in dim light situations, with regard to in focus indication and autofocus - but that is, I think, the full extent of the lens's part of it.

The calculation of in focus or not is done entirely in the image processing engine of the camera which in turn triggers the indicator(s) in the view finder.

I could be wrong on the contrast detection methodology, but even if it is a phase detection method - it is still calculated in the image processing engine of the camera and not in or with the lens.

PT
04-25-2012, 05:57 PM   #6
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Although it is awkward, live view provides very precise focusing if you use the magnified settings (8-10x). It beats the focus indicator on my K-X every time.
04-25-2012, 06:48 PM   #7
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@ Siegfried... I think their story about manual-focus lenses is bunk. I have not spoken with Pentax, but the mere presence of the catch-in-focus feature should indicate that they can play nicely. Front/back focusing issues could, of course, still apply to the focus indicator, and the "play" (looseness) of the focusing zone could also cause inaccuracies. But there should be no reason that they are not compatible. I think you got a dud rep at the service center.
04-25-2012, 07:31 PM   #8
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QuoteOriginally posted by Siegfried Quote
So I'm asking if anybody here could do me a favor and spend half an hour of his life on the live chat with Pentax USA
There are ways of making your ip address appear to be in the US, Proxy server and VPN are two methods that come to mind.

04-25-2012, 08:43 PM   #9
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QuoteOriginally posted by Siegfried Quote

I gave a call to local Pentax service center and was told that it was the way it's supposed to be. AF system requires some data (oh... what?!) from a lens on order to work and since MF lenses do not provide that data, then AF is no way precise with them.

You were told a load of bunk.
04-25-2012, 08:48 PM   #10
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QuoteOriginally posted by Popeye.Tom Quote
Hi Zig, I find that interesting that you're finding the focus indicator that far off. I don't have any suggestions or solutions. I'm really new to my K5 with only a grand total of 140 images so far.

Almost half of them have been taken with either of my two most recent manual lenses, one an Adaptall II lens and the other with a fully manual Panagor 90mm macro. The focus indicator was turned to center spot. The subject in the image was centered, focus until the red indicator then I'd restructure the frame. Like I used to do with split image range finder focus aids. (gotta get that Nikon K screen cut down!)

Regarding hardware & AF, what the rep in Mordor was indicating doesn't ring true to me. I think the focus indicator and the algorithms that drive it are all contained in the image processing engine. I am pretty sure that the Pentax DSLRs, K5 included, use a contrast detection method. The highest level of contrast on adjacent pizels on the sensor is achieved when in focus. This is also why my K100 has more trouble focusing in dim light than the newer cameras with higher sensitivity sensors. It is also why focus helper lights are there. With that said, a faster lens will likely perform better in dim light situations, with regard to in focus indication and autofocus - but that is, I think, the full extent of the lens's part of it.

The calculation of in focus or not is done entirely in the image processing engine of the camera which in turn triggers the indicator(s) in the view finder.

I could be wrong on the contrast detection methodology, but even if it is a phase detection method - it is still calculated in the image processing engine of the camera and not in or with the lens.

PT

The K-5's reguilar AF system is phase method using a half mirror and AFsensor in the bottom of the camera. The K5 alos has a Live view AF method using the main sensor which is contrast method, but it's a lot slower.'


Two methods explained

Autofocus: phase detection

Autofocus: contrast detection
04-25-2012, 08:55 PM   #11
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If you have fast lenses then the Canon ee-s screen cut for the K-5 by focusingscreen.com is a great alternative.
04-25-2012, 11:27 PM   #12
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Fellas,
I appear to be misunderstood. Thanks a bunch, but I'm not looking for an advice on any workaround like LV focus or 3rd-party focusing screen. I only asked to contact other Pentax reps regarding that answer I was given and which I can hardly buy. Yes, I can come up from some NYC or Big Shoulders IP (I'm an IT geek working for an elfish company), but after I have already talked to Pentax USA they would be surprised to get about the same questions in the same writing (we all have unique writing... though... i can go this way... like i'm high... or smth... really... i know what time it is... Peace, bro!)

Nevertheless, for those of you who do not have this issue or who doubt on whether it's real or who are just curious and eager to see the samples, here are the images requested. Since I'm running out of space here on PF, they're hosted on my personal server (which is scheduled to go offline for most of May, sorry). Subject-to-sensor distance was about 2.2 meters (in order to be of x40-x50 of lens focal length), lens used was Helious MC 77K at f=1/1.8 (I usually do not go this wide, preferring smth around 2.8-5.6, but I'd like to put it into extremes to be more illustrative). K-5 files were dark-roomed thru DxO optics and ist DS files went thru Lightroom.

Focus indicator goes on from this focus ring position

to this position

The result:

It is way off focus, obviously.

Ok, let's twist things a little:


It's much better, isn't it? (hint: it's a rhetorical question, a figure of speech)

It was Saab logo in the center of the page (having enough contrast and provided with enough illumination) which I used to focus on.

K-5 AF system is adjusted this way:



For precise in-focus indication for old manual lenses I need to twist it backwards to - (minus) 140 um (having 'apply all' still = -10; it'll be around -160 for 'apply all' to be zeroed) in which case I'm loosing all AF-bility of AF lenses even if I set each of them to +10 in the legacy AF menu.

Thanks for looking, fellas, though I can't help but quote myself:
QuoteQuote:
So I'm asking if anybody here could do me a favor and spend half an hour of his life on the live chat with Pentax USA on their website asking for details on the AF design and whether it is really not meant to work with M- and K- lenses missing those electronic chips.
I need some quotation of official Pentax Rep either which confirms our local Pentax Mordor or which I could use to force our nasty boys start doing what they ought to. I'm well aware of Nikon and Canon and Katzeye focusing screens and LV function and how PD AF systems work (in general, obviously they can use different algorithms e.g. implementing some disgusting easter eggs for old lenses to force customers move further and buy brand new ones). Just do me a favor and spend half an hour of your life for a phone call or web-chat with your Pentax rep, please.

Cheers,
Zig

Last edited by Siegfried; 04-25-2012 at 11:34 PM.
04-25-2012, 11:50 PM   #13
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And - yes, FWIW - it's running the latest 1.13.23.23 firmware.

Zig
04-26-2012, 12:23 AM   #14
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Zig, your request is falling on deaf ears because it's not necessary to go that route. You have been given the answer here already... you were misinformed. Mine works fine on manual lenses focused in the manner you wanted.
04-26-2012, 03:32 AM   #15
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He's looking for some sort of documentary evidence from a proper Pentax source so he can get his local fools to repair his camera.

(I think trying to contact Pentax Japan directly might be another possible route...?)
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