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11-23-2006, 06:58 PM   #1
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front focus?

Well, my K10 is front focusing with the FA50/1.4,
At F1.4 it front focuses by as much as 1/2" (the lens+DS combo are flawless)

Could you guys test it with your FA50 if possible?

thanks is advance.

11-23-2006, 07:04 PM   #2
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Sorry, Sam - mine tested OK.

I took about a half dozen shots, at apertures from 1.4 to 4.0 and going both from a far focus and a near focus. They all looked spot on.

This is a 100% crop of the very middle taken at f/2:

Last edited by carpents; 11-23-2006 at 07:21 PM.
11-23-2006, 07:22 PM   #3
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QuoteOriginally posted by .Sam. Quote
Well, my K10 is front focusing with the FA50/1.4,
At F1.4 it front focuses by as much as 1/2" (the lens+DS combo are flawless)

Could you guys test it with your FA50 if possible?

thanks is advance.
Hi Sam!

I've just taken 2 photos of a flower with the FA50/1.4, one in manual focus mode and one in auto. I don't see any front focus problems so far. Let me try it on a ruler, though. Back in a bit...
11-23-2006, 07:32 PM   #4
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Thanks guys,

Here is a simple test you can do. Open the index pages of any paperback (most have very small text), draw a small horizontal line next to a line of text in the edge (to aide the focusing).

At about 45 deg. angle take a shot wide open (F/1.4, we don't care about sharpness), focusing on the line. You should be able to read the text next to it, and tell if there is front or back focus.

I just tested my other lenses
Almost consistent front focus across the line @24mm, 28mm, 50mm at apertures wider than F2.8


Last edited by ShadZee; 11-23-2006 at 07:39 PM.
11-23-2006, 07:42 PM   #5
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QuoteOriginally posted by .Sam. Quote
Thanks guys,

Here is a simple test you can do. Open the index pages of any paperback (most have very small text), draw a small horizontal line next to a line of text in the edge (to aide the focusing).

At about 45 deg. angle take a shot wide open (F/1.4, we don't care about sharpness), focusing on the line. You should be able to read the text next to it, and tell if there is front or back focus.

I just tested my other lenses
Almost consistent front focus across the line @24mm, 28mm, 50mm at apertures wider than F2.8
Not a ruler to be found in the house. I tried with a compass, though. I'll try this test as well. Do you focus manually or use the autofocus?
11-23-2006, 07:55 PM   #6
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QuoteOriginally posted by photo_mom Quote
Not a ruler to be found in the house. I tried with a compass, though. I'll try this test as well. Do you focus manually or use the autofocus?
AutoFocus.

The manual focus is fine. There are better ways of testing the front/back focus, but the index pages is a very quick and dirty method.

I hope it's not the camera, and it's just the methods of testing and lighting.
11-23-2006, 07:56 PM   #7
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QuoteOriginally posted by .Sam. Quote
Well, my K10 is front focusing with the FA50/1.4,
At F1.4 it front focuses by as much as 1/2" (the lens+DS combo are flawless)

Could you guys test it with your FA50 if possible?

thanks is advance.
excuse the ignorance, but what exactly is "front focus"?

thanks

randy
11-23-2006, 08:04 PM   #8
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QuoteOriginally posted by slipchuck Quote
excuse the ignorance, but what exactly is "front focus"?

randy
Basically; inaccurate autofocus.

11-23-2006, 08:09 PM   #9
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Focus test chart

From a user of another brand, but both an explanation and a testing procedure with a 'usable' chart: Nikon D70 Focus Chart
11-23-2006, 08:17 PM   #10
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QuoteOriginally posted by jfdavis58 Quote
From a user of another brand, but both an explanation and a testing procedure with a 'usable' chart: Nikon D70 Focus Chart
I know of the test.
However, I should mention that the ACTUAL AF spot on Pentax cameras is infact below the center and/or at the bottom of the RED square.

So this method and the above "index pages" method are NOT accurate way of testing front/back focus for Pentax cameras. I don't know maybe these methods would work if we held the camera in Portrait !?
11-23-2006, 08:42 PM   #11
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compass and index

QuoteOriginally posted by .Sam. Quote
AutoFocus.

The manual focus is fine. There are better ways of testing the front/back focus, but the index pages is a very quick and dirty method.

I hope it's not the camera, and it's just the methods of testing and lighting.
Hi Sam!

Okay, here's both the compass and index pages. Sorry the crops don't match up exactly.

Compass, manual focus, 100% crop:


Compas, autofocus, 100% crop:


Index, manual focus:


Index, autofocus:


Hope this is what you were after. It doesn't look bad to me. I really hope yours isn't the camera as well!
11-23-2006, 09:22 PM   #12
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Really?

Why; or more specifically "how do you know?"

I used the center focus point and the wide straight line of the Jackson chart on page 19 of his pdf. Vertically my K10s (plural as in three) all lock , nearly instantly, anytime an edge enters the center circle etched on the view screen as ( ), while using the center focus point. Horizontally, each locks when the line approaches the bottom approximately one line width below the ( ) and 0.75 line width above the ( ). Several lenses, from 17mm to 200mm were tested.

As for front or back focusing, each of several fast zoom lenses presented a DoF which was sharpest (to an acceptable level, within the 6mm marks. All primes and macro/primes showed acceptable focus =/-2mm centered on the main line. I also have some 'ebay finds' that show bad results; one with severe front focus past 70mm, another with back focus past 30mm; amazing how bad dropping to a hard surface is for a camera/lens.

But, I would still be interested in knowing why this doesn't work for Pentax cameras/lenses.
11-24-2006, 12:54 AM   #13
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QuoteOriginally posted by jfdavis58 Quote
Why; or more specifically "how do you know?"

I used the center focus point and the wide straight line of the Jackson chart on page 19 of his pdf. Vertically my K10s (plural as in three) all lock , nearly instantly, anytime an edge enters the center circle etched on the view screen as ( ), while using the center focus point. Horizontally, each locks when the line approaches the bottom approximately one line width below the ( ) and 0.75 line width above the ( ). Several lenses, from 17mm to 200mm were tested.
It's great to know that other K10s are not like mine. I think mine needs to be calibrated. I don't know if I should keep this and send it for repairs or return it

As far as the exact location of center AF point is concerned; you could search dpreview on KatzEye focusing screens. In discussing and implementing KatzEye's manual focus aid, it was found out ... I can't remember fully & correctly... the center point AF OR the Spot Meter Point (now that I think about it I can't remember which) was NOT exactly at the center. It was just a little below the center. Because of this metering was not as accurate (D's and DS's) using the KatzEye screen.

Now I'm all confused, myself... I'll look it up
11-24-2006, 12:13 PM   #14
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All in GOOD

I went to my camera store and they just got a few more bodies in and exchanged for another one. this one seems to be spot-on... I'm a happy camper.

Another reason to buy and support your local retail stores
11-24-2006, 06:10 PM   #15
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Fantastic!

QuoteOriginally posted by .Sam. Quote
All in GOOD

I went to my camera store and they just got a few more bodies in and exchanged for another one. this one seems to be spot-on... I'm a happy camper.

Another reason to buy and support your local retail stores
Hi Sam!

Glad this new one works much better and that you were able to switch it out so quickly!
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