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Old Mar 9, 2008, 7:04 AM   #1
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I have been playing with my K20D uisng a Sigma 17-70 Macro lens.

Printed off the AF Test Chart and tried it out and it seems the lens BF a little, well actually quite a lot. :O

I adjusted the AF to +7, which seems quite high! Has anyone else adjusted for lens BF and if so, how much adjustment was made?

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Old Mar 9, 2008, 11:39 AM   #2
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nope i haven't tried it yet. too busy drowning in midterms right now to play with my new camera... but that should change in about another week. where did you get the test chart from?


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Old Mar 9, 2008, 5:01 PM   #3
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Hi PK,

My copy of the Sigma 17-70 likes -1. I think that there's a lot of sample variation with this lens, so I don't think I'd sweat it much, as long as you can get it to work to your satisfaction.

My Tokina 20-35 f2.8 AT-X Pro, which Tokina tested and reported to be within mfg tolerances, won't focus worth beans with my DS or K10 and needs a -10 setting to get it to perform acceptably with the K20. My DA*50-135 shows significant back focus with my K10, (and also BFs with my DS, but not to the same degree), but is spot on with the K20 at 0, so now I'm very happy with that lens (I'm still considering sending it in to get it calibrated to the DS and K10, but am wary about messing with a good thing with the K20). My FA*300/4.5 focuses spot on with all the bodies, and the K20 at 0 -- the same goes with this lens coupled with the F1.7x AFA. My DA 10-17 FE focuses great with both the DS and K10, but needs -5 with the K20.

I don't see any patterns developing here. There's more to this AF thing than I ever considered. All that I can conclude is that I'm a lot better off with the K20's focus adjustability than without it. . .:-)

Scott
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Old Mar 9, 2008, 5:14 PM   #4
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ishino wrote:
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** where did you get the test chart from?
Hi Ishino,

You can download a PDF file with the chart and instructions from:

http://www.focustestchart.com/focus21.pdf

Scott
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Old Mar 9, 2008, 5:31 PM   #5
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Thats where I got my chart from.

Heres it at the start

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Old Mar 9, 2008, 5:35 PM   #6
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After adjustment to +7.

I didn't have a tripod handy, but I will do it again when I do and get it correct.

But I can see on the chart that there is an improvement.


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Old Mar 12, 2008, 4:08 PM   #7
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ishino wrote:
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where did you get the test chart from?
Here's another test method and chart that sirbazz on DPR found. It's for the pro Canons, but looks like it'll be more useful than the other, especially for checking focus at greater distances.

http://www.northlight-images.co.uk/a...djustment.html

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Old Mar 20, 2008, 2:56 PM   #8
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I just spent the better part of my afternoon and evening testing my cameras and lenses for BF/FF and making adjustments.

I tried both methods:

1. Focus Chart at 45 degrees
2. Canon Micro Adjustment

Several interesting results.

Consistent -ve AF adjustments required with K20D on the Focus Chart, but when I retested my lenses with the Micro Adjustment image I ended up with +10 settings for most of my lenses.

Both tests were with the camera mounted on a tripod, fluorescent lighting with multipe shots taken for each lens.

I then retested my lenses mounted on the K10D and obtained similar BF/FF issues, so it appears to be the lenses rather than the K20D body.

Here is some of the results using the focus chart:
K20D
Sigma 28-70mm f/2.8
@70mm AF set to -10 still not enough
@50mm AF set to -10 perfect focus
@28mm AF set to 0 perfect focus
The dilema with this lens is to what setting to use.
K10D
70mm (centre of Focus area was 10mm forward of Point of focus)
50mm (spot on)
28mm (centre of Focus area was 28mm back of Point of focus)

K20D
Sigma 10-20mm f/4-5.6
@10mm AF set to -7 perfect
@20mm AF set to -7 perfect
K10D
20mm (centre of Focus area was 30mm back of Point of focus)
10mm correct focus

K20D
Sigma 17-70mm f/2.8-f/4.5
@17mm AF set to +5 Perfect
@70mm AF set to +5 Perfect
k10D (centre of Focus area was 6mm back of Point of focus) 17-70mm range


K20D
Sigma 300mm f/2.8
AF set to -10 (based on level of improvement from 0 to-10, it needs a -20 to -25 setting)
K10D same (centre of Focus area was 20mm forward of Point of focus)

K20D
Pentax 80-200mm f/2.8
@ 80mm to 200mm AF set to -1 perfect
K10D same almost perfect focus point.


Apart from the 17-70mm lens, I could get away with a general -ve setting for ALL lenses.

The question I have ... is the ALL lens AF Adjustment setting culmulative to the individual lens setting?

For the Canon Micro Adjustment test, I again used the tripod and set the camera to live view. Manually focussed on the spiral image until I obtained the required moir pattern, then activated AF and observed any lens adjustment.

I also verified the change in image on the screen. I made adjustments to the AF settings until I was able to manually focus the lens and the AF simply confirmed and did not adjust the lens and in doing so it kept the same moir pattern.

Results:

Sigma 28-70mm f/2.8 stayed at -10 (no change)

Sigma 10-20mm f/4-5.6 went from -7 to +10 (complete opposite)

Sigma 17-70mm f/2.8-f/4.5 went from +5 to +10 (increase)

Sigma 300mm f/2.8 No change still requires greater than -10 (no change)

Pentax 80-200mm f/2.8 went from -1 to +10 (Opposite)

After confusing myself about which method was providing the correct settings, I went back to the focus chart and re-tested my lenses and found I had more faith in the Focus chart over the Moir Pattern test.

Lastly, The K20D thinks two of my Sigma lenses are the same lens. When I put a new lens on and make and AF adjustment it registers the lens, when I put the 17-70mm it registered, but when I put the 10-20mm on, it used the settings for the 17-70mm When I swap lenses it thinks it is the same lens and uses what ever lens AF setting was last set for EITHER lens. Obviously a lens chip issue.

The annoying thing is one lens is -7 AF and the other is +5 AF.

PK

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Old Mar 20, 2008, 4:41 PM   #9
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Interesting if not encouraging.

Do you have a manual lens to test if you can also adjust to get the focus confirmation beep right with manual lenses. I have a problem esp with my A*85 mm.

I'd do that test myself if they only started sending out the body only to the shops this side. It's been available with various kit lenses for weeks, but body only "still pending". Expected on the 20th March it says tonight on some internet sellers' pages. Someone is getting a bit frustrated here.:angry:

Kjell
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Old Mar 21, 2008, 10:30 AM   #10
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Kjell,

I only have those lenses listed in my post above with me here in Africa. I did set one to manual and focus trapped with it and found it was the same as using AF.

Though like pixel peeping, I am not sure if having a 30mm FF problem at 2.5m with an aperture of f/2.8 will actually be an issue when using it in the real world photographing at say f/5.6 at 30m. I would tend to think the DOF would be great enough to encompass the Point of Focus as well. Though I could be wrong. :roll:

So my only concern right now is two Sigma lenses registering as one lens and a Front Focussing expensive 300mm f/2.8 that I can't adjust into focus.

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