I have fixed my front focus problem - how to

Started Sep 10, 2006 | Discussions
Wagga Contributing Member • Posts: 622
I have fixed my front focus problem - how to

I have been disappointed with some of the results I got with my Pentax FA 50mm 1.4 when used at maximum aperture ("I focussed on the eyes but I got the nose instead" sort of complaint..).

I did the focussing test last night and it confirmed that I have a front focussing problem.

There were a few threads on this subject lately and decided to have a go at adjusting the focus on the camera.

The test chart can be downloaded at http://focustestchart.com/chart.html

Here are the results before I made the adjustments:

and after I made the adjustments:

Now, for those of you who are adventurous, this is how to do it:

1. Remove the 8 screws on the underside of the camera. (Don't mix them up, as there are 2 different threads: 4 identical threads around the battery compartment - they are attached to plastic and 4 identical threads on the other side - they are attached to metal).

2. Remove the sole and you will see 3 adjustable Allen screws (Allen = hexagonal head):

http://forums.dpreview.com/forums/read.asp?forum=1036&message=15793746

http://www.penta-club.ru/forum/index.php?act=Attach&type=post&id=4849

Take an Allen key (I think it's 1.5mm) key and turn the screws COUNTERCLOCKWISE to correct FRONT FOCUS, CLOCKWISE to correct BACK FOCUS. Turn each screw by the same amount.

As I had a front focus problem, I turned the three screws counterclockwise. The 12 o'clock position became 10 o'clock after the first round of adjustments.

3. Put everything back together and make a focussing test.

4. I had a second round of adjustments as the correction I applied was insufficient and the 3 screws are now at 8 o'clock.

That's all. It was simple, far less stressing than my first attempt at cleaning the sensor and focussing is spot on. The whole operation didn't take one hour.

I hope I haven't created a problem for later, but I can always return the screws to their original position.

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Wagga [Jean]

[UTC/GMT + 2 hours]

Darren M Veteran Member • Posts: 4,365
Re: I have fixed my front focus problem - how to

That is really interesting, thanks. My *istD focuses well with every lens I have except the FA35/2 which is a little spotty, but it is very interesting to know there are possibilities for correction.
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janneman02 Forum Pro • Posts: 15,733
Re: I have fixed my front focus problem - how to

Wagga wrote:

I have been disappointed with some of the results I got with my
Pentax FA 50mm 1.4 when used at maximum aperture ("I focussed on
the eyes but I got the nose instead" sort of complaint..).

I did the focussing test last night and it confirmed that I have a
front focussing problem.

There were a few threads on this subject lately and decided to have
a go at adjusting the focus on the camera.

The test chart can be downloaded at
http://focustestchart.com/chart.html

Here are the results before I made the adjustments:

and after I made the adjustments:

Now, for those of you who are adventurous, this is how to do it:

1. Remove the 8 screws on the underside of the camera. (Don't mix
them up, as there are 2 different threads: 4 identical threads
around the battery compartment - they are attached to plastic and 4
identical threads on the other side - they are attached to metal).

2. Remove the sole and you will see 3 adjustable Allen screws
(Allen = hexagonal head):

http://forums.dpreview.com/forums/read.asp?forum=1036&message=15793746

http://www.penta-club.ru/forum/index.php?act=Attach&type=post&id=4849

Take an Allen key (I think it's 1.5mm) key and turn the screws
COUNTERCLOCKWISE to correct FRONT FOCUS, CLOCKWISE to correct BACK
FOCUS. Turn each screw by the same amount.

As I had a front focus problem, I turned the three screws
counterclockwise. The 12 o'clock position became 10 o'clock after
the first round of adjustments.

3. Put everything back together and make a focussing test.

4. I had a second round of adjustments as the correction I applied
was insufficient and the 3 screws are now at 8 o'clock.

That's all. It was simple, far less stressing than my first attempt
at cleaning the sensor and focussing is spot on. The whole
operation didn't take one hour.

I hope I haven't created a problem for later,

Umm, how about other lenses suddenly having backfocus?

but I can always
return the screws to their original position.

-- hide signature --

Wagga [Jean]

[UTC/GMT + 2 hours]

-- hide signature --
Sweets
Sweets Contributing Member • Posts: 710
Re: I have fixed my front focus problem - how to

Nice done Wagga. You have courage. Question: were all your lenses showing FF or only the one you did the test with ?
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Brett St Pierre
Brett St Pierre Veteran Member • Posts: 7,025
Darren...

Darren M wrote:

That is really interesting, thanks. My *istD focuses well with
every lens I have except the FA35/2 which is a little spotty, but
it is very interesting to know there are possibilities for
correction.

I might be wrong, but from earlier threads on this I believe this cannot be done on the *istD, only the DS and later.

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Raivo Tiikmaa Forum Member • Posts: 66
Re: Darren...
Alfisti Veteran Member • Posts: 6,649
I knew it was not just me

IMHO be careful it's not your camera and the FFing is just more obvious at the small apetures of the 50mm.

I noticed SEVERE front focusing (maybe you are referring to my threads in your post) with my 50mm, sent it in t be repaired. Then noticed similar problems but less obvious on other lenses.

I knew I wasn't nuts, replaced the camera and it's much better now.

Penmtax need to keep an eye on this.

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coleviolin Veteran Member • Posts: 5,993
Re: I have fixed my front focus problem - how to

Thanks for that lesson Wagga. I did this test back when I had the Sigma 50/2.8 macro, and found the DS to be almost perfect but slightly front focusing as well. I haven't tried this with any other lenses, and this might explain why I was focusing on eye lids instead of eye balls. I might need to do this as well, since I generally don't have a problem with taking things apart myself and it sounds pretty simple.

Just, anybody thinking of taking apart a DA zoom lens such as the kit lens, be VERY careful. There are a lot of little screws and some springs, and getting the zoom mechanism back together is really tricky. I highly DON'T recommend it.
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OP Wagga Contributing Member • Posts: 622
Re: I have fixed my front focus problem - how to

janneman02 wrote:

Umm, how about other lenses suddenly having backfocus?

I think it's ok. I can always revert it of course.

The other lenses are not as fast and were not really so much affected. My 50mm opens at 1.4 and the DOP is much more critical.

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Wagga [Jean]

[UTC/GMT + 2 hours]

simdavid Forum Member • Posts: 94
Will this affect other lens which doesn't have focusing issues?

My Sigma 18-125mm has focusing issue too but will doing this affect the focus of other lens?

OP Wagga Contributing Member • Posts: 622
Re: I have fixed my front focus problem - how to

coleviolin wrote:

I might need to do this as well, since I
generally don't have a problem with taking things apart myself and
it sounds pretty simple.

Hi Lipo,

You shouldn't have any problem, it is very straightforward.

My only doubt was (still is) do I adjust the 3 screws (I did, it seemed logical - I hope I was right) or just the bottom one? On the 2 links I posted, you get 2 different pieces of advice.

If anyone has a clue, I'll take it. Any Pentax techie out there?

Please let me know how you go it you try it.

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Wagga [Jean]

[UTC/GMT + 2 hours]

viorel00 Regular Member • Posts: 162
Re: I have fixed my front focus problem - how to

what camera do you have? I think my D has the back-focus problem, I just did the test but I'd like to repeat it with a tripod. So I might as well go ahead and fix it, if it can be done on the D. Thanks for posting.

OP Wagga Contributing Member • Posts: 622
Re: I have fixed my front focus problem - how to

viorel00 wrote:

what camera do you have?

Sorry, I shoud have started with that! I have a Ds.

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Wagga [Jean]

[UTC/GMT + 2 hours]

OP Wagga Contributing Member • Posts: 622
Re: Will this affect other lens which doesn't have focusing issues?

simdavid wrote:

My Sigma 18-125mm has focusing issue too but will doing this affect
the focus of other lens?

It makes sense to be believe that if you adjust the camera, it will affect all the lenses you put on it. But you can always revert if you think you have made a mistake.

It's just a matter of deciding which of your lenses is the most critical to you.

Other than that, you may be able to adjust this particular lens, but I don't know how to do it.

Has anone got the knowledge ?

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Wagga [Jean]

[UTC/GMT + 2 hours]

ozdean
ozdean Forum Pro • Posts: 26,307
Re: Will this affect other lens which doesn't have focusing issues?

Wouldn't the focus tuning apply to all lenses because you are tuning the focus sensor reading & subsequent adjustment. If you took a 50/1.4 at 1.4 and tuned it then I would think all lenses would be correct.

I also understood only the 1 screw tuned the focus, maybe the others control sideways and up & down of the sensor points?
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KSV Veteran Member • Posts: 3,351
Great, thanks for sharing {nt}

{nt}

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pb908 Regular Member • Posts: 332
why need to set 3 screws ?

do you have more information on what that 3 screws is used for ?

I am a little bit scare of doing something without knowing what is the truth behind this..

are there use to allign the sensor? horizontal,vertical and front-back alignment ? if so, that what you need to adjust is JUST one screw then, the front-back screws..but which one is this ?

please, advice..

Wagga wrote:

I have been disappointed with some of the results I got with my
Pentax FA 50mm 1.4 when used at maximum aperture ("I focussed on
the eyes but I got the nose instead" sort of complaint..).

I did the focussing test last night and it confirmed that I have a
front focussing problem.

There were a few threads on this subject lately and decided to have
a go at adjusting the focus on the camera.

The test chart can be downloaded at
http://focustestchart.com/chart.html

Here are the results before I made the adjustments:

and after I made the adjustments:

Now, for those of you who are adventurous, this is how to do it:

1. Remove the 8 screws on the underside of the camera. (Don't mix
them up, as there are 2 different threads: 4 identical threads
around the battery compartment - they are attached to plastic and 4
identical threads on the other side - they are attached to metal).

2. Remove the sole and you will see 3 adjustable Allen screws
(Allen = hexagonal head):

http://forums.dpreview.com/forums/read.asp?forum=1036&message=15793746

http://www.penta-club.ru/forum/index.php?act=Attach&type=post&id=4849

Take an Allen key (I think it's 1.5mm) key and turn the screws
COUNTERCLOCKWISE to correct FRONT FOCUS, CLOCKWISE to correct BACK
FOCUS. Turn each screw by the same amount.

As I had a front focus problem, I turned the three screws
counterclockwise. The 12 o'clock position became 10 o'clock after
the first round of adjustments.

3. Put everything back together and make a focussing test.

4. I had a second round of adjustments as the correction I applied
was insufficient and the 3 screws are now at 8 o'clock.

That's all. It was simple, far less stressing than my first attempt
at cleaning the sensor and focussing is spot on. The whole
operation didn't take one hour.

I hope I haven't created a problem for later, but I can always
return the screws to their original position.

-- hide signature --

Long Live Pentax !!
Regards
---
BK
---
..MX is Beauty, KX is Reliability..

(unknown member) Veteran Member • Posts: 6,759
If I am not mistaken,

adjusting the camera AF for one lens might result in BF/FF with other AF lenses.
--
Alan Chan
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(unknown member) Veteran Member • Posts: 6,759
Re: Will this affect other lens which doesn't have focusing issues?

Wagga wrote:

Other than that, you may be able to adjust this particular lens,
but I don't know how to do it.

Impossible by design AFAIK.
--
Alan Chan
http://www.pbase.com/wlachan

thw Veteran Member • Posts: 8,089
Not really...

adjusting the camera AF for one lens might result in BF/FF with
other AF lenses.

for Nikon and Pentax systems, the focusing motor is in the camera. So, this issue should not surface. But it's safer to check, of course.

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