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Re: [OM] 420 deal, Now Back Focus/ Front Focus

Subject: Re: [OM] 420 deal, Now Back Focus/ Front Focus
From: "Jim Nichols" <jhnichols@xxxxxxxxxxxxx>
Date: Sun, 21 Dec 2008 19:10:55 -0600
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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>>
>
>
> -- 
> _________________________________________________________________
> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
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> Themed Olympus Photo Exhibition: http://www.tope.nl/
>
> 


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