K20D focus adjust values for 31/43/77 Limiteds.

gavinhw · 06-01-2008, 10:48 PM

I have a number of Pentax lenses (50-200mm, 16-45mm, 50mm F1.4, 35mm F2, 10-17mm, 12-24mm) ---- and the 43mm and 77mm FA Limiteds.

The latter two have been pretty much unuseable on my K10D, with front focus problems on 60% of my shots. The other lenses are spot on.

----------------------------

Flash forward to this week, when I acquired the K20D.

Using its customizable focus adjustment feature, I find that I need to set a value of -7 for the 43mm, and -6 for the 77mm.

I'm now a happy camper.

I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds. I don't need any adjustments for my other lenses.

And would sending my K10D back to Pentax (still under warranty) fix my focus problems so that I can achieve proper focus for ALL my lenses?

Thx,
-Gavin

Okami · 06-02-2008, 06:08 AM

Yes it would, but you would also need to send all the lenses you need adjusting with it

PentaxPoke · 06-02-2008, 10:19 AM

Gavin,

How did you test? Was it with the focus chart? I wonder if anyone has had the same experience I did with that chart. I used it exactly per the instructions, and it said all my lenses were front focussing a bit. Based on the test, I needed about -9 on all lenses, and it looked great. Then I went out and started using the lenses in everyday situations, and everything started back focussing badly! I turned the adjustment back off, and everything was back to normal.

I can't figure out why this was the case, but it was repeatable.

wildboar · 06-02-2008, 10:29 AM

pentaxpoke,

My K10D seems to have terrible AF under artificial light... but outdoors it is much more accurate. I wondered about the exact thing you are describing when pondering getting the K20D.

**amoringello** · 06-02-2008, 01:41 PM

Be sure, also, that you know where your auto focus point is. If you assume the auto focus point is in the direct center, you may be making incorrect assumptions on back or forward focus when a flat subject is held at 45 dgree angle.

My K10D center AF point is actually more towards the bottom of the left half of the circle etch mark. Knowing this I can focus more precisely.
In the real world it doesn't affect me very often, but there are cases where it makes an obvious difference. For close up work where that distance translates to a significant change in DOF, it does matter.

**k100d** · 06-02-2008, 05:31 PM

my K100D backfocuses in general, so i applied a +100 and it seems to fix things quite nicely with all my lenses.

gavinhw · 06-02-2008, 09:55 PM

I used the Focus Test Chart (by Jackson) and it told me that my FA 50mm F1.4 and 35mm F2 were front focussing, which I knew to be not true.

When I took real-world photos with those two lenses using the chart-derived adjustments, I too got back focussing. So I reset everything and abandoned the chart and instead made lots of shots of kitchen items, and of my bookshelves. That's how I got those two values for my 43mm and 77mm Limiteds.

So, PentaxPoke, the two of us got the same bogus results using the test chart.

(Methodology for the focus chart was a tripod-mounted K20D angled at 45 degrees to the sheet. Tungsten light. Lenses wide open in Av mode.)

Originally posted by PentaxPoke

Gavin,

How did you test? Was it with the focus chart? I wonder if anyone has had the same experience I did with that chart. I used it exactly per the instructions, and it said all my lenses were front focussing a bit. Based on the test, I needed about -9 on all lenses, and it looked great. Then I went out and started using the lenses in everyday situations, and everything started back focussing badly! I turned the adjustment back off, and everything was back to normal.

I can't figure out why this was the case, but it was repeatable.

troyz · 07-04-2008, 03:10 PM

Originally posted by gavinhw

I have a number of Pentax lenses (50-200mm, 16-45mm, 50mm F1.4, 35mm F2, 10-17mm, 12-24mm) ---- and the 43mm and 77mm FA Limiteds.

Using its customizable focus adjustment feature, I find that I need to set a value of -7 for the 43mm, and -6 for the 77mm.

I'm now a happy camper.

I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds. I don't need any adjustments for my other lenses.

Thx,
-Gavin

-6 for my K20D+FA77 (calibrated using cereal boxes at ~6ft, validated using real-word objects from 20ft to really really far away)

I tried the 45 degree test chart but didn't find it useful:
-- Results weren't reproducible
-- Focus target is not representative of actual conditions (too close, not parallel to plane of focus)

I haven't rigorously checked my other lenses; the Tamron 28-75 seems a bit inaccurate at 75/2.8 but I haven't felt the need to do a careful calibration (at multiple focal lengths)

gavinhw · 07-04-2008, 10:01 PM

Thanks, Troyz. Our K20D/77mm Limited focus adjustment values match!

I just put an order in for the 31mm Limited. I'm keeping my fingers crossed that it works fine with K10D, out of the box.

-Gavin

coloseu · 07-06-2008, 05:51 AM

my 77 f/1.8 was spot one from the test chart, but I already knew that from field experience. It is the lens I use the most (portraits).
I hadn´t much time to play with both my 31 f/1.8 and 43 f/1.9 but test charts were acusing heavy front focus with the 43 and light frontfocus with the 31. I think I already noticed that with the 31. The 43, I thought it was way too soft wide open - now I beleive it is a severe focus problem instead. I have to do the tests again and also a great amount of field tests (AAA batteries and so on).

Torphoto · 07-06-2008, 02:14 PM

Don't discount the charts but be carful about the lighting you use it under, the K20D and K10D seem very sensitive to focus shifts under different light sources.

Now as always you ned to balance the chart results with real world and then decide.

frank · 07-06-2008, 07:23 PM

I haven't done any actual testing on a chart w/ the three FA limited lenses on the K20D, but to me they are sharp enought even wide open. I did see some BF problem w/ them on my K10D.

creampuff · 07-06-2008, 08:03 PM

Same experience with frank.

I think it is important that any FF/BF adjustments be done in bright daylight.
Doing adjustments in incandescent lighting or indoors where the colour temperature is lower and contrast likely to be lower is going to give varying results.

maszat · 07-19-2008, 04:01 PM

Originally posted by gavinhw

I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds.

I tested my 31 Limited at home and finally set it to +1 with K20D, but I still need to test outdoors whether that change makes it better than the default.
While I tested the 31, I actually learnt more about the autofocus point of the body, you need to know where the camera really is focusing otherwise you will set it to an incorrect focus adjustment number.

Off topic, but my Sigma 105 finished the test with a +2 adjustment. Also, to be tested outdoors.

06-01-2008, 10:48 PM	#1
gavinhw Junior Member	K20D focus adjust values for 31/43/77 Limiteds. I have a number of Pentax lenses (50-200mm, 16-45mm, 50mm F1.4, 35mm F2, 10-17mm, 12-24mm) ---- and the 43mm and 77mm FA Limiteds. The latter two have been pretty much unuseable on my K10D, with front focus problems on 60% of my shots. The other lenses are spot on. ---------------------------- Flash forward to this week, when I acquired the K20D. Using its customizable focus adjustment feature, I find that I need to set a value of -7 for the 43mm, and -6 for the 77mm. I'm now a happy camper. I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds. I don't need any adjustments for my other lenses. And would sending my K10D back to Pentax (still under warranty) fix my focus problems so that I can achieve proper focus for ALL my lenses? Thx, -Gavin

07-06-2008, 05:51 AM	#10
coloseu Junior Member	Tests my 77 f/1.8 was spot one from the test chart, but I already knew that from field experience. It is the lens I use the most (portraits). I hadn´t much time to play with both my 31 f/1.8 and 43 f/1.9 but test charts were acusing heavy front focus with the 43 and light frontfocus with the 31. I think I already noticed that with the 31. The 43, I thought it was way too soft wide open - now I beleive it is a severe focus problem instead. I have to do the tests again and also a great amount of field tests (AAA batteries and so on).

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06-02-2008, 06:08 AM	#2
Okami Veteran Member	Yes it would, but you would also need to send all the lenses you need adjusting with it

06-02-2008, 10:19 AM	#3
PentaxPoke Pentaxian	Gavin, How did you test? Was it with the focus chart? I wonder if anyone has had the same experience I did with that chart. I used it exactly per the instructions, and it said all my lenses were front focussing a bit. Based on the test, I needed about -9 on all lenses, and it looked great. Then I went out and started using the lenses in everyday situations, and everything started back focussing badly! I turned the adjustment back off, and everything was back to normal. I can't figure out why this was the case, but it was repeatable.

06-02-2008, 10:29 AM	#4
wildboar Senior Member	pentaxpoke, My K10D seems to have terrible AF under artificial light... but outdoors it is much more accurate. I wondered about the exact thing you are describing when pondering getting the K20D.

06-02-2008, 01:41 PM	#5
amoringello Site Supporter	Be sure, also, that you know where your auto focus point is. If you assume the auto focus point is in the direct center, you may be making incorrect assumptions on back or forward focus when a flat subject is held at 45 dgree angle. My K10D center AF point is actually more towards the bottom of the left half of the circle etch mark. Knowing this I can focus more precisely. In the real world it doesn't affect me very often, but there are cases where it makes an obvious difference. For close up work where that distance translates to a significant change in DOF, it does matter.

06-02-2008, 05:31 PM	#6
k100d Site Supporter	my K100D backfocuses in general, so i applied a +100 and it seems to fix things quite nicely with all my lenses.

06-02-2008, 09:55 PM	#7
gavinhw Junior Member	I used the Focus Test Chart (by Jackson) and it told me that my FA 50mm F1.4 and 35mm F2 were front focussing, which I knew to be not true. When I took real-world photos with those two lenses using the chart-derived adjustments, I too got back focussing. So I reset everything and abandoned the chart and instead made lots of shots of kitchen items, and of my bookshelves. That's how I got those two values for my 43mm and 77mm Limiteds. So, PentaxPoke, the two of us got the same bogus results using the test chart. (Methodology for the focus chart was a tripod-mounted K20D angled at 45 degrees to the sheet. Tungsten light. Lenses wide open in Av mode.) Originally posted by PentaxPoke Gavin, How did you test? Was it with the focus chart? I wonder if anyone has had the same experience I did with that chart. I used it exactly per the instructions, and it said all my lenses were front focussing a bit. Based on the test, I needed about -9 on all lenses, and it looked great. Then I went out and started using the lenses in everyday situations, and everything started back focussing badly! I turned the adjustment back off, and everything was back to normal. I can't figure out why this was the case, but it was repeatable.

07-04-2008, 03:10 PM	#8
troyz Veteran Member	Originally posted by gavinhw I have a number of Pentax lenses (50-200mm, 16-45mm, 50mm F1.4, 35mm F2, 10-17mm, 12-24mm) ---- and the 43mm and 77mm FA Limiteds. Using its customizable focus adjustment feature, I find that I need to set a value of -7 for the 43mm, and -6 for the 77mm. I'm now a happy camper. I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds. I don't need any adjustments for my other lenses. Thx, -Gavin -6 for my K20D+FA77 (calibrated using cereal boxes at ~6ft, validated using real-word objects from 20ft to really really far away) I tried the 45 degree test chart but didn't find it useful: -- Results weren't reproducible -- Focus target is not representative of actual conditions (too close, not parallel to plane of focus) I haven't rigorously checked my other lenses; the Tamron 28-75 seems a bit inaccurate at 75/2.8 but I haven't felt the need to do a careful calibration (at multiple focal lengths)

07-04-2008, 10:01 PM	#9
gavinhw Junior Member	Thanks, Troyz. Our K20D/77mm Limited focus adjustment values match! I just put an order in for the 31mm Limited. I'm keeping my fingers crossed that it works fine with K10D, out of the box. -Gavin

07-06-2008, 02:14 PM	#11
Torphoto Veteran Member	Don't discount the charts but be carful about the lighting you use it under, the K20D and K10D seem very sensitive to focus shifts under different light sources. Now as always you ned to balance the chart results with real world and then decide.

07-06-2008, 07:23 PM	#12
frank Pentaxian	I haven't done any actual testing on a chart w/ the three FA limited lenses on the K20D, but to me they are sharp enought even wide open. I did see some BF problem w/ them on my K10D.

07-06-2008, 08:03 PM	#13
creampuff Pentaxian	Same experience with frank. I think it is important that any FF/BF adjustments be done in bright daylight. Doing adjustments in incandescent lighting or indoors where the colour temperature is lower and contrast likely to be lower is going to give varying results.

07-19-2008, 04:01 PM	#14
maszat New Member	Originally posted by gavinhw I'm curious what adjustment values other users are dialing in to achieve consistent focus for their FA Limiteds. I tested my 31 Limited at home and finally set it to +1 with K20D, but I still need to test outdoors whether that change makes it better than the default. While I tested the 31, I actually learnt more about the autofocus point of the body, you need to know where the camera really is focusing otherwise you will set it to an incorrect focus adjustment number. Off topic, but my Sigma 105 finished the test with a +2 adjustment. Also, to be tested outdoors.