It's interesting that the focus confirmation chip backfocuses as well
but I suppose that's as it should be using the same circuitry. Do you
think you'll send it for calibration?
Chuck Norcutt
Jim Nichols wrote:
> 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.
>>>>> --
>>>>> _________________________________________________________________
>>>>> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
>>>>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>>>>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>>>>
>>>>>
>>>>
>>> --
>>> _________________________________________________________________
>>> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
>>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>>
>>>
>>
>> --
>> _________________________________________________________________
>> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>
>>
>
>
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|
