There are lots of mystery in practical lens characters vs the theoretical
one, I saw an article on pop photo many years ago mentioning a test, with
the same lens, they move the camera away from the target gradually and take
a few shots but at the same time they crop the images to maintain the same
field of view, the "apparent" DOF increases with shooting distance. It is
like the test I just made with camera of different sensor size.
There was also another test on pop photo on a 300mm lens, they shot full
length portraits at F2.8 and F5.6 but both have very similar "apparent" DOF
(softness background).
I believe if you stick with the DOF formula, both of my test shots might
have the same DOF but the out of focus softness are just different.
BTW, even I have mentioned the DOF is the same for lens of different focal
length under the same image magnification but their "apparent" DOF is
different. The shorter lens will have deeper apparent DOF.
C.H.Ling
----- Original Message -----
From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
>I accept it because I see it but I still don't understand it. And it
> may be the difference in calculation for macro distances as discussed
> here in the last few days. Certainly my DOF calculator using more
> normal shooting distances shows that both have nearly the same DOF when
> distance is adjusted to maintain the same coverage angle and then by
> adjusting CoC for the smaller sensor.
>
> Chuck Norcutt
>
>
> On 12/19/2010 8:54 AM, C.H.Ling wrote:
>> No, the shots were not taken at the same distance as the "film" sizes are
>> different. The one with E-PL1 was talken at a longer distance so that
>> they
>> have the same coverage angle. Here shown the DOF difference of the same
>> lens
>> under same aperture and "final magnification". It is obvious that their
>> degree of out focus are differ, hence it is the sensor size not the focal
>> length make the difference.
>>
>> I'm more interested on apparent DOF rather than the calculated one. Just
>> like the diffraction talk, it isn't as important as some people think, it
>> was shown on the 90/2 samples I posted before, the difference between F4
>> and
>> F22 was nothing dramatic.
>>
>> C.H.Ling
>>
>> ----- Original Message -----
>> From: "Chuck Norcutt"<chucknorcutt@xxxxxxxxxxxxxxxx>
>>
>>
>>> I can't argue with the results and it's clear there's something I don't
>>> understand if you tell me these two 80mm shots are taken at exactly the
>>> same distance. In particular, at f/8 the 12MP 4/3 sensor should already
>>> be beyond diffraction limits on the green and red channels. At f/8 the
>>> 5DII is also beyond diffraction limits but only on the red channel.
>>>
>>> Ah! Some partial enlightenment. Since this a macro shot, and perhaps
>>> at close to 1:1, the marked aperture bears not much relationship to the
>>> effective aperture. So the effective aperture is smaller than f/8 and
>>> both cameras are beyond diffraction limits in these images. But that
>>> still doesn't help me much.
>>>
>>> Chuck Norcutt
>>>
>>>
>>> On 12/19/2010 2:07 AM, C.H.Ling wrote:
>>>> Here are two samples taken with Zuiko 80mm F4 at F8:
>>>>
>>>> 5D II, cropped both edges to make it 4:3 and scale down to 4032x3024
>>>> (same
>>>> as E-PL1):
>>>>
>>>> http://www.accura.com.hk/IMG_0948c.jpg
>>>>
>>>> Olympus E-PL1
>>>>
>>>> http://www.accura.com.hk/PC193332.jpg
>>>>
>>>> You can see the apparent DOF on the second one looks deeper, it will be
>>>> more
>>>> so with smaller sensor.
>>>>
>>>> C.H.Ling
>>>>
>>>> ----- Original Message -----
>>>> From: "C.H.Ling"<ch_photo@xxxxxxxxxxxxx>
>>>> To: "Olympus Camera Discussion"<olympus@xxxxxxxxxxxxxxxxx>
>>>> Sent: Sunday, December 19, 2010 1:21 PM
>>>> Subject: Re: [OM] Jeweler's camera
>>>>
>>>>
>>>>> You said it is the focal length not the sensor size cause different
>>>>> DOF,
>>>>> so
>>>>> consider the same sensor - FF for example. The DOF of 100mm lens at 10
>>>>> feet
>>>>> is 1.42ft, the DOF of 50mm lens at 5 feet (to get the same mag.) is
>>>>> 1.44ft,
>>>>> it is almost the same as the 100mm lens.
>>>>>
>>>>> C.H.Ling
>>>>>
>>>>> ----- Original Message -----
>>>>> From: "Chuck Norcutt"<chucknorcutt@xxxxxxxxxxxxxxxx>
>>>>>
>>>>>
>>>>>> That's not what my DOF calculator says. If you can quantify it with
>>>>>> a
>>>>>> specific example I'll believe it. But I don't think you can. The
>>>>>> example I used was a 100mm lens at f/8 focused at 10 feet with a CoC
>>>>>> of
>>>>>> 30 lines/mm. That yields a DOF of 1.58 feet. Then a 50mm lens at
>>>>>> f/8
>>>>>> also focused at 10 feet but with a CoC of 60 lines/mm. That's to
>>>>>> allow
>>>>>> for a smaller image size (sensor) to be blown up twice as much as the
>>>>>> 100mm shot such that the final print size (magnification) is the
>>>>>> same.
>>>>>> The 50mm lens gets a total DOF of 3.28 feet. Slightly more than
>>>>>> double.
>>>>>>
--
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