I followed up with my own crude tests of autofocus accuracy this afternoon.
Case 1: Tripod mounted Oly E-510 with Zuiko 14-54 lens at 54mm, aperture at
3.5, using an "X" marked on public notices in the local paper. Camera was
mounted at approximately 45deg to the paper. I see about 4 "lines" of back
focus in this image.
http://gallery.leica-users.org/v/OldNick/Auto+Lens_+Auto+Focus.jpg.html
Case 2: Same setup using a Takumar 55mm f/1.8 manual focus lens at f/1.8 to
get shallow DOF. Lens was mounted with an adapter having a
focus-confirmation chip. Focusing was done using the focus confirmation
spot in the viewfinder. I see about 2 lines of back focus in this image.
http://gallery.leica-users.org/v/OldNick/Manual+Lens_+Manual+Focus+Dot.jpg.html
Case 3: Same setup except focus was accomplished using a full screen "Live
View" image on the rear screen. I did not use a magnified view. I see
about 1 line of front focus, or none at all, in this image.
http://gallery.leica-users.org/v/OldNick/Manual+Lens_+Screen+Focus.jpg.html
Take it for what it is worth. I have had no complaints with the autofocus
combination of my camera and lens. I had been suspicious of the focus
confirmation chip, but it seems to work. Live View is just too tedius to
deal with.
I prefer the Zuiko for sharpness over the Takumar lenses that I have, but
the 55/1.8 Takumar makes a fine portrait lens.
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Jim Nichols" <jhnichols@xxxxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Sunday, December 21, 2008 2:51 PM
Subject: Re: [OM] 420 deal
> Yea, Chuck, I concluded that a tripod might help. Since the previous
> example was hand-held, I thought I would give it a try. When I get a
> chance, I will try to do that. Incidentally, your analysis is not too far
> off the actual case.
> With an f/3.5 lens such as this, it is difficult to be conclusive about
> the
> actual focus. A faster, prime lens, with AF would be a better example.
> Unfortunately, I don't have such a lens.
>
> Jim Nichols
> Tullahoma, TN USA
> ----- Original Message -----
> From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
> To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
> Sent: Sunday, December 21, 2008 2:37 PM
> Subject: Re: [OM] 420 deal
>
>
>>I think I'd put the center of focus on "mittee will study whether to
>> demolish" or on the line above. That's based on comparing the blur of
>> the descender on the "y" in "money" and the "g" in "bridges" near the
>> top with the descender on the "g" in "CBS Evening News" below. I'm
>> guessing that you were shooting from about 2 feet and at these close
>> distances DOF is pretty much evenly distributed between front and back
>> of the central point of focus.
>>
>> Assuming that the newsprint is spaced about 7 lines/inch I make the
>> distance between intended and actual focus about 1-1/4 inches or roughly
>> 32mm. However, since you presumably had the paper at a 45 degree angle
>> laying back from the camera the actual backfocus would need to be
>> corrected by the sin of 45 degrees. Roughly 0.7x32mm = 22mm. So I make
>> it only about half what you estimated. But if you're shooting from two
>> feet as I guessed that's still a large error.
>>
>> But shooting hand held it's probably not hard to bob back and forth by
>> 22mm. Maybe you should shoot on a tripod. :-)
>>
>> Chuck Norcutt
>>
>>
>> Jim Nichols wrote:
>>> Frank,
>>>
>>> I just did my own similar test, though not as professionally, on my Oly
>>> E-510 and Zuiko 14-54 lens. With the lens at 54mm, hand-held at 1/180
>>> at
>>> f/3.5, ISO 400, kitchen lights, I focused on the word "Ascend" in the
>>> newspaper caption. The sharpest focus appears to be near the top of the
>>> paragraph above the caption, indicating a back focus of about 38-40mm.
>>> I
>>> made several shots, with this being the better one, but all indicated a
>>> similar back focus.
>>>
>>> The focus dot was on each time I made a photo. While this error is not
>>> of
>>> much consequence, it was interesting that it consistantly occurred.
>>>
>>> http://gallery.leica-users.org/v/OldNick/Focus+Test.tif.html
>>>
>>> Jim Nichols
>>> Tullahoma, TN USA
>>> ----- Original Message -----
>>> From: "Frank van Lindert" <Frank@xxxxxxxxxxxxx>
>>> To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
>>> Sent: Sunday, December 21, 2008 10:45 AM
>>> Subject: Re: [OM] 420 deal
>>>
>>>
>>>> This is one of my tests, reproduced today.
>>>> http://home.tiscali.nl/vanlindert/Calibration_E-400/test_diepte/test_diepte1.JPG
>>>> I focused on the line indicated by the blue marker.
>>>>
>>>> Frank.
>>>>
>>>> Sun, 21 Dec 2008 17:22:04 +0100, Frank van Lindert
>>>> <Frank@xxxxxxxxxxxxx> wrote:
>>>>
>>>>> I first had a setup like yours, taking pictures along a ruler. And
>>>>> yes, it was all macro with the 14-42/3.5-4.6 standard zoom lens which
>>>>> was part of the E-400 kit.
>>>>>
>>>>> Later I have learned that it was better to photograph plain newspaper
>>>>> print from an angle which is about twenty degrees from horizontal. It
>>>>> will give you a better feeling of the depth of field, which was my
>>>>> primary concern when testing different lenses and macro converters.
>>>>>
>>>>> BTW, my favorite macro converter is a lens which I unscrewed from an
>>>>> Olympus slide copier (intended for copying slides or negatives to
>>>>> digital). Its thread being 58mm it screws right onto my 14-42. Its
>>>>> focal length is about 10cm.
>>>>>
>>>>> Frank.
>>>> --
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>>>>
>>>
>>>
>> --
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>>
>
>
> --
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