I have a question about back/front focus

Bui · 12-12-2016, 03:14 PM

After reviewing my images taken at a Christmas market the past weekend, I suspected my Kx had focus problem, today I did some test and calibration according to guide from Internet with a DA 40mm Ltd mounted. It seems better now. However I still have some questions:

- I understand that doing this calibration on the body means adjusting the point of focus backward or forward to compensate for front focus or back focus problem. So that would mean the camera now will permanently shift its focus point (until I set the parameter again)? So what would happen when I use other lens which I think back focus problem has happened less? Will they suddenly become more front focus due to my adjustment?

- Will that change anything with manual lens? I'm not very good at manual focus, but normally I trust my eye rather than focus confirmation, and usually when I see clear image in the viewfinder, the photo is in pretty good focus status too, now will the back focus adjustment change anything on that?

Thank you very much for helping me with these newbie questions

**BigMackCam** · 12-12-2016, 03:38 PM

The K-x can only store one AF adjustment, so if you fit a different lens you'll need to reset that adjustment to zero (or to whatever setting works best for that particular lens). And yes - AF fine adjustment also affects the point at which you'll get focus confirmation with a manual focus lens, so again, reset the adjustment to zero or to whatever works best for it.

Later cameras allow multiple settings to be stored for each lens that can be recognised by the camera as a specific model. But for manual lenses with no electronic communication, you still have to individually set the AF fine adjustment for that lens.

amp · 12-12-2016, 06:36 PM

Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks

**lithedreamer** · 12-12-2016, 06:54 PM

Originally posted by amp

Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks

There are test charts you can download from the Internet, or for more accuracy you can buy something like LensAlign. Honestly (and I'm not saying this is the OP's problem, necessarily), I think the problem is usually technique. A particular lens + a particular body might front or back focus enough to cause problems with very shallow portraiture, or something like that, but if you feel like you need to calibrate all of your lenses to get the shot, the problem might exist behind the camera.

When I stepped up from the K-x to the K-30, the extra resolution showed some glaring flaws in my focusing technique, but I adjusted. I had a shorter adjustment period stepping from the K-30 to the K-1, but it was there. After that period, I can clearly see how little of an improvement AF fine tuning would make to my images.

**clackers** · 12-12-2016, 08:39 PM

Originally posted by amp

Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks

You're looking for a difference between Live View and PDAF focusing on a chart or angled ruler. Remember to turn the lens a long way out of focus in between.

This forum has a guide to the topic:

Fixing Front and Back Focus - Introduction - In-Depth Articles

runswithsizzers · 12-13-2016, 10:35 AM

I used the kit zoom that came with my K-x for a year without noticing any consistent focus errors. But soon after buying a few Limited primes, I started noticing about 2-3 inches of back focus when shooting close at large apertures.

Fortunately, for me the same focus correction on my K-x worked for all four of my primes.

**clackers** · 12-13-2016, 11:50 AM

Originally posted by runswithsizzers

I used the kit zoom that came with my K-x for a year without noticing any consistent focus errors. But soon after buying a few Limited primes, I started noticing about 2-3 inches of back focus when shooting close at large apertures.

Fortunately, for me the same focus correction on my K-x worked for all four of my primes.

Your zoom might have a tendency to front focus.

runswithsizzers · 12-13-2016, 12:34 PM

Originally posted by clackers

Your zoom might have a tendency to front focus.

May be, but within my ability to test it, I did not notice the zoom being any worse after calibrating for the back-focusing primes. The smaller apertures of the zoom no doubt mask a certain amount of inaccuracy.

Getting ready to check my primes tonight on my new (to me) K-3.

Lindhagen · 12-08-2017, 08:26 PM

hey all. we have owned a k-x for many years, and mainly used it for photographing painted model horses. All of a sudden, during our last shoot, the camera had major issues with focusing / soft images where we wanted it to and i think it was back focusing... but not sure. maybe you could say the overall images were soft and not sharp and amazing like we have been used to for years.

not sure if what the issue is, hoping someone might have some ideas?

attached are a few photos that were just not crisp overall

we are hoping its something fixable.

pschlute · 12-08-2017, 09:34 PM

Cant tell from your images what the problem is. There is something in focus on each image. Have you changed which focus points are used to achieve autofocus ? Use a focus test chart with camera on a tripod to do a proper test.

But if you are noticind a problem recently it could be a bit of dust on the AF sensor is causing issues. Take the lens off and give the mirror box a blow out with a rocket blower.

You could also do a test by using Live View and see if it focusses differently. If you are still having issues using Live View to autofocus you may have a problem with the lens.

12-12-2016, 03:14 PM	#1
Bui Veteran Member Join Date: Nov 2016 Photos: Gallery Posts: 316	I have a question about back/front focus After reviewing my images taken at a Christmas market the past weekend, I suspected my Kx had focus problem, today I did some test and calibration according to guide from Internet with a DA 40mm Ltd mounted. It seems better now. However I still have some questions: - I understand that doing this calibration on the body means adjusting the point of focus backward or forward to compensate for front focus or back focus problem. So that would mean the camera now will permanently shift its focus point (until I set the parameter again)? So what would happen when I use other lens which I think back focus problem has happened less? Will they suddenly become more front focus due to my adjustment? - Will that change anything with manual lens? I'm not very good at manual focus, but normally I trust my eye rather than focus confirmation, and usually when I see clear image in the viewfinder, the photo is in pretty good focus status too, now will the back focus adjustment change anything on that? Thank you very much for helping me with these newbie questions

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12-12-2016, 03:38 PM	#2
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,670	The K-x can only store one AF adjustment, so if you fit a different lens you'll need to reset that adjustment to zero (or to whatever setting works best for that particular lens). And yes - AF fine adjustment also affects the point at which you'll get focus confirmation with a manual focus lens, so again, reset the adjustment to zero or to whatever works best for it. Later cameras allow multiple settings to be stored for each lens that can be recognised by the camera as a specific model. But for manual lenses with no electronic communication, you still have to individually set the AF fine adjustment for that lens.

12-12-2016, 06:36 PM	#3
amp Senior Member Join Date: Dec 2015 Posts: 168	Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks

12-12-2016, 06:54 PM	#4
lithedreamer Site Supporter Join Date: Sep 2013 Photos: Gallery \| Albums Posts: 1,799	Originally posted by amp Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks There are test charts you can download from the Internet, or for more accuracy you can buy something like LensAlign. Honestly (and I'm not saying this is the OP's problem, necessarily), I think the problem is usually technique. A particular lens + a particular body might front or back focus enough to cause problems with very shallow portraiture, or something like that, but if you feel like you need to calibrate all of your lenses to get the shot, the problem might exist behind the camera. When I stepped up from the K-x to the K-30, the extra resolution showed some glaring flaws in my focusing technique, but I adjusted. I had a shorter adjustment period stepping from the K-30 to the K-1, but it was there. After that period, I can clearly see how little of an improvement AF fine tuning would make to my images.

12-12-2016, 08:39 PM	#5
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by amp Hope you don't mind me piggybacking on your post, but I was curious to know if front and back focusing are a common occurrence? I frequently see questions asked about it. I sometimes have out-of-focus pictures, but I think it's more to do with my technique and or slow shutter speed. What's the best way to check for front or back focusing? Thanks You're looking for a difference between Live View and PDAF focusing on a chart or angled ruler. Remember to turn the lens a long way out of focus in between. This forum has a guide to the topic: Fixing Front and Back Focus - Introduction - In-Depth Articles

12-13-2016, 10:35 AM	#6
runswithsizzers Senior Member Join Date: Jun 2011 Location: USA Posts: 186	I used the kit zoom that came with my K-x for a year without noticing any consistent focus errors. But soon after buying a few Limited primes, I started noticing about 2-3 inches of back focus when shooting close at large apertures. Fortunately, for me the same focus correction on my K-x worked for all four of my primes.

12-13-2016, 11:50 AM	#7
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by runswithsizzers I used the kit zoom that came with my K-x for a year without noticing any consistent focus errors. But soon after buying a few Limited primes, I started noticing about 2-3 inches of back focus when shooting close at large apertures. Fortunately, for me the same focus correction on my K-x worked for all four of my primes. Your zoom might have a tendency to front focus.

12-13-2016, 12:34 PM	#8
runswithsizzers Senior Member Join Date: Jun 2011 Location: USA Posts: 186	Originally posted by clackers Your zoom might have a tendency to front focus. May be, but within my ability to test it, I did not notice the zoom being any worse after calibrating for the back-focusing primes. The smaller apertures of the zoom no doubt mask a certain amount of inaccuracy. Getting ready to check my primes tonight on my new (to me) K-3.

12-08-2017, 09:34 PM	#10
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,198	Cant tell from your images what the problem is. There is something in focus on each image. Have you changed which focus points are used to achieve autofocus ? Use a focus test chart with camera on a tripod to do a proper test. But if you are noticind a problem recently it could be a bit of dust on the AF sensor is causing issues. Take the lens off and give the mirror box a blow out with a rocket blower. You could also do a test by using Live View and see if it focusses differently. If you are still having issues using Live View to autofocus you may have a problem with the lens.