Help with Pentax fine focus adjustment?

Started Dec 10, 2013 | Questions
sgtsween
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Help with Pentax fine focus adjustment?
Dec 10, 2013

Hello all.

I lurk on these forums and frequently see mention of people using fine focus adjustment to correct for front or back focus. When I first learned of this, I checked my K-5, and tobe honest, found that it hit autofocus correctly most of the time, and I didn't feel I needed to adjust with fine focus. That said, am I missing something? A few questions

1- If I get in focus shots 99% of the time, does that mean that I don't need o use fine focus?

2- Is it lens specific i.e. will it be moot on one lens, and +6 on another?

3- Are there any good tutorials out there to show me how to effectively test a lens to see if it could be improved with FF adjustment?

I see it mentioned so often that I feel maybe I am not using a tool that might give me better results. Maybe I am seeing shots "in focus" and thinking that's the extent of the sensor/lens capability, when in reality they could be sharper?

Thank you in advance,

Matt

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yursturly
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Re: Help with Pentax fine focus adjustment?
In reply to sgtsween, Dec 10, 2013

About 8 years ago, I read a well done article about autofocus and Pentax. At the time, there was much "fuss" because Pentax was noted to "hunt" a bit at the final point of focus, before the "beep".

The gist of the article was that yes, Nikon was a bit faster, but yes, Pentax was more accurate, and more accurate a greater percentage of the time. My photography since then (always Pentax) has supported those findings (that it's accurate and maybe it fine tunes at the end). In my experience, at least in spot autofocus, Pentax is nearly always in focus.

That said, I too have been reading about the fine focus calibration feature in the newer firmware editions. I found 2 nice articles that detail the method for checking your lenses to determine if they focus correctly. They say nothing about how to make the adjustment in your camera.

Hope you find them useful.

First, from Jeffrey Freidl's blog: http://regex.info/blog/photo-tech/focus-chart

Next, from David Liang: http://petapixel.com/2013/03/12/ghettoca-a-diy-lens-calibration-tool-for-micro-adjustment-enabled-dslrs/

Good shooting,

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brecklundin
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Re: Help with Pentax fine focus adjustment?
In reply to sgtsween, Dec 10, 2013

sgtsween wrote:

Hello all.

I lurk on these forums and frequently see mention of people using fine focus adjustment to correct for front or back focus. When I first learned of this, I checked my K-5, and tobe honest, found that it hit autofocus correctly most of the time, and I didn't feel I needed to adjust with fine focus. That said, am I missing something? A few questions

1- If I get in focus shots 99% of the time, does that mean that I don't need o use fine focus?

2- Is it lens specific i.e. will it be moot on one lens, and +6 on another?

3- Are there any good tutorials out there to show me how to effectively test a lens to see if it could be improved with FF adjustment?

I see it mentioned so often that I feel maybe I am not using a tool that might give me better results. Maybe I am seeing shots "in focus" and thinking that's the extent of the sensor/lens capability, when in reality they could be sharper?

Thank you in advance,

Matt

(1) If a given lens shows no BF/FF on a typical focus test. Everything from a line of batteries to a full on specialized chart or device, whatever works for your needs will work to check. Basic photos will give you an idea but many prefer to use a more formal lab style test setup. But yes if it is dead on 99% of the time with a given lens then, FOR THAT LENS you won't need any adjustment.

(2) On the K7 forward bodies Pentax supported lens specific AF adjustment for supported lenses meaning not all lenses are supported but most modern glass is. You will want to test and calibrate each lens with testing conditions appropriate for that lens.

Now you need to know that AF accuracy will vary depending on lighting conditions and subject/target of your focus. Zoom lenses will almost all delivery different results at different focal lengths. Sooooo, you want to test as many lighting conditions as possible and for zooms add into it check several focal lengths just to confirm is your copy's variations are acceptable or to dial in a setting with which you can live.

As for articles you can't swing a dead cat w/o hitting a couple-three dozen articles on what is the "correct" way to test your AF accuracy. I say find one that fits how you think and the tools you have on hand.

Last this sounds complicated because it can be but it can also be fun if you are creative with how you want to test. Remember too pros (and many of us amateurs do as well) will almost always send in ALL or a group of lenses with the body or bodies they want to use them on for calibration. So don't feel as if it's a gimmick...it's a real thing that has been done for a long, long time in the SLR world. Some lens makers offer the service free other charge...often times you can get it done free when you send the body in for cleaning, testing and adjusting. But always check.

Of one more thing. Settings are specific to the body lens combo you are using together. Meaning the settings I might use for that lens could be completely opposite of what your combo needs. This is because of all the permutations of the settings and tolerances. It's one reason it is a good idea to send your gear in for adjusting every year or or depending on how much you use it.

Good luck, it really is not a hard thing but can consume time so spread it out and make it something you look forward to...and if you don't think you'll enjoy it, spend a bit of cash and have Pentax or do it. If you want 3rd party glass calibrated check to see which will provide the service to avoid any surprises.

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Model Mike
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Re: Help with Pentax fine focus adjustment?
In reply to sgtsween, Dec 10, 2013

3- Are there any good tutorials out there to show me how to effectively test a lens to see if it could be improved with FF adjustment?

For my K-5 I used the method Canon recommended in one of their white papers (unfortunately no longer available on their web site). Which is to shoot a flat vertical target straight on, at a repreesentative distance, and in representative light, several times each with different focus adjustments. Then choose the adjustment which provides the best focus. I used a signpost at 30m as a target.

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Tim A2
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Re: Help with Pentax fine focus adjustment?
In reply to sgtsween, Dec 10, 2013
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kh1234567890
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Re: Help with Pentax fine focus adjustment?
In reply to Model Mike, Dec 10, 2013

Model Mike wrote:

For my K-5 I used the method Canon recommended in one of their white papers (unfortunately no longer available on their web site). Which is to shoot a flat vertical target straight on, at a repreesentative distance, and in representative light, several times each with different focus adjustments. Then choose the adjustment which provides the best focus. I used a signpost at 30m as a target.

+1

All these slanting rulers and targets are a waste of time. Something flat and contrasty far away is best - a building, a sign or even a tree against the sky. Then just shoot a series of shots at different adjustment values, remembering to defocus the lens before each one. Shoot RAW and turn off any and all sharpening in p-p. The best setting is often not all that clear, narrow down the range to say two or three steps, shoot a few more shots at each and pick the best one. It will probably drift slightly with temperature anyway so there is little point in getting obsessed about it. All my lenses are between -1 and +1 except my 35mm macro Ltd which is +6 on both my K-7 and K-5ii.

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Tim A2
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Re: Help with Pentax fine focus adjustment?
In reply to kh1234567890, Dec 10, 2013

kh1234567890 wrote:

Model Mike wrote:

For my K-5 I used the method Canon recommended in one of their white papers (unfortunately no longer available on their web site). Which is to shoot a flat vertical target straight on, at a repreesentative distance, and in representative light, several times each with different focus adjustments. Then choose the adjustment which provides the best focus. I used a signpost at 30m as a target.

+1

All these slanting rulers and targets are a waste of time. Something flat and contrasty far away is best - a building, a sign or even a tree against the sky. Then just shoot a series of shots at different adjustment values, remembering to defocus the lens before each one. Shoot RAW and turn off any and all sharpening in p-p. The best setting is often not all that clear, narrow down the range to say two or three steps, shoot a few more shots at each and pick the best one. It will probably drift slightly with temperature anyway so there is little point in getting obsessed about it. All my lenses are between -1 and +1 except my 35mm macro Ltd which is +6 on both my K-7 and K-5ii.

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

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Model Mike
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Re: Help with Pentax fine focus adjustment?
In reply to Tim A2, Dec 10, 2013

Tim A2 wrote:

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

It's using a flat vertical plane for focusing and a slanting rule for determining focus error, so no problem. It's a neat development of the Canon technique.

My comments were directed at the slanting-rule-only tests for which there are few charts around. These fail because the AF target is slanting; any misfocus could be due not only to lens calibration errors but also to AF point registration errors.

Either way, using a real target like a sign is best IMO, since calibration for PD AF depends on light temperature, subject distance and focal length.

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britcam
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Re: Help with Pentax fine focus adjustment?
In reply to Model Mike, Dec 10, 2013

Model Mike wrote:

Tim A2 wrote:

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

First, because being a slanting target, any misfocus could be due not only to lens calibration errors but also to AF point registration errors.

Secondly because accuracy with PD AF depends on light temperature, subject distance and focal length. Slanting test targets are normally used indoors, at relatively close distance, so unless you shoot in similar conditions, it's difficult to have confidence in the results.

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Would you say there would be such differences between indoor & outdoor use so as to require different focus adjustments for different light temps, distance, and FL?  I'm not sure how practical that really is, unless we are aiming for absolute ultimate accuracy in every circumstance ... and then other factors come into play  ...

I have no AF adjustment on the K5IIs, but on my K5, almost every lens showed errors using an (indoor) measuring tape. The worst was a 31Ltd, and that was so bad that +10 wasn't enough!  So it went straight back and I ended up buying a used one that was perfect.

Maybe some lenses I have need checking for calibration, but I honestly think I would have noticed any significant errors by now in PP.

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Kind regards
britcam - Rich S

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Brad99
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Re: Help with Pentax fine focus adjustment?
In reply to sgtsween, Dec 10, 2013

Only ever adjust AF in good daylight but that may not rule out indoors. On a perfect camera it shouldn't make a difference what lighting is used, but nowt's perfect in this world.

A chart is OK to use if it has an unambiguous AF target.

My own findings are that some lenses are fussy and others not so, but you can't guess which type a lens will be based on its FL or max aperture. Also, some lenses only give a broad response to AF adjustment using a chart, but can be critical at infinity, so decide if that's the case before finalising the setting.

AF is always done at max aperture no matter what f-stop is selected and this can cause some errors as optimum focus can be slightly different to when the shot is actually taken at the chosen aperture.  This is due to lens aberrations.  It's not usually an issue but bear it in mind.

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kh1234567890
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Re: Help with Pentax fine focus adjustment?
In reply to Tim A2, Dec 10, 2013

Tim A2 wrote:

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

With slanting targets it is hard to predict exactly which point the camera will focus on. A distant plane target parallel to the sensor is much better. Usually you also want to be sure that the camera will still reliably focus at infinity after your tweaks.

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Model Mike
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Re: Help with Pentax fine focus adjustment?
In reply to britcam, Dec 10, 2013

britcam wrote:

Would you say there would be such differences between indoor & outdoor use so as to require different focus adjustments for different light temps, distance, and FL?

On the K-5, and with regard to light temp, yes. Ultimate solution was to upgrade to a K=5II.

Maybe some lenses I have need checking for calibration, but I honestly think I would have noticed any significant errors by now in PP.

On the K-5 and older bodies, calibration was a routine thing (assuming the firmware allowed it), with the K-5II that no longer applies IMO, but it's still useful to have this facility if things don't seem right. My own 16-50 needs checking.

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fotobert
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focusdetector by traumflieger.de
In reply to sgtsween, Dec 10, 2013

Hi Matt,

my K-5 has fine adjusts from -4 to +9 with different lenses. I alway use the focusdetector from Traumflieger.de. It is a german page, but it is easy to use (there are pictures how to use it)

Download it, use a scissors and some glue:

www.traumflieger.de/desktop/fokusdetektor/fokusdetektor.php

or

http://www.traumflieger.de/desktop/fokusdetektor/fokusdetektor_ls.pdf

I hope, this will help you

have a nice day

Albert

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Roland Karlsson
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Re: Distant plane target and a nifty trick!
In reply to sgtsween, Dec 10, 2013

Hi,
You shall not focus at a slanted target. The focussing point is really a focussing area - and you will not know where it focusses on the slanted target. Use a target that are face on to the camera!

== Here is a nifty trick! ==

Use live view and focus at the target. Switch to optical view and focus again. NOTE how much the focussing ring moves. Redo the same for some adjustments, e.g. -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5. From your notes you can easily see what correction seems to be best.

This way you do not need to take any images at all. No downloading and no evaluation.

If the camera makers had some imagination, they could make this procedure automatic.

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Tim A2
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Re: Help with Pentax fine focus adjustment?
In reply to kh1234567890, Dec 11, 2013

kh1234567890 wrote:

Tim A2 wrote:

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

With slanting targets it is hard to predict exactly which point the camera will focus on. A distant plane target parallel to the sensor is much better. Usually you also want to be sure that the camera will still reliably focus at infinity after your tweaks.

Thanks for the reply. The test in my link does not use the slanted ruler as the target, so there is no problem. For reference here is the link again.

https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/51633

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Tim A2
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Re: Help with Pentax fine focus adjustment?
In reply to Model Mike, Dec 11, 2013

Model Mike wrote:

Tim A2 wrote:

I have an interest in focus tests. I posted a link in this thread to a test that involves a slanting ruler. Please explain to me why that test is a waste of time.

It's using a flat vertical plane for focusing and a slanting rule for determining focus error, so no problem. It's a neat development of the Canon technique.

My comments were directed at the slanting-rule-only tests for which there are few charts around. These fail because the AF target is slanting; any misfocus could be due not only to lens calibration errors but also to AF point registration errors.

Either way, using a real target like a sign is best IMO, since calibration for PD AF depends on light temperature, subject distance and focal length.

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I appreciate your comments Mike. Just for the sake of clarity, my post was in reply to kh1234567890.

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sgtsween
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Re: Help with Pentax fine focus adjustment?
In reply to brecklundin, Dec 12, 2013

Thank you for the great info!!! I'm getting the 21 limited in the post soon, so I will check for FF/BF on it right away.

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sgtsween
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Re: focusdetector by traumflieger.de
In reply to fotobert, Dec 12, 2013

Thanks! I will give the chart a shot.

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