Hi Moose, Andrew, and all
I'm copying below, without proper authorization on intelectual property
[ :^) ], an offlist test sent to me by another fellow member.
Since he's not actively posting I think I'd better wait 'till the author
tells he performed this test and found these results.
I'm not introducing language translation artifacts on purpose, and because
of laziness.
Main question remains as is.
Regards,
Fernando.
----------------------
Tras abrir las imágenes con PhotoShop, reduje su tamaño a 360*240 píxels y
las pasé a escala de grises, entonces medí (supongo que con bastante
imprecisión) el nivel de luminosidad en el centro y en la esquina superior
derecha. Las dos cifras de cada entrada se refieren al nivel medido en
centro/esquina; el rango completo sería de 0 a 255, pero dejé una leve
subexposición para facilitar la medida sobre la pared blanquecina:
máxima abertura f/2.8 f/5.6
Expos.-> N +1/3 +2/3 N N
Lente ------- ------- ------- ------- -------
(1) 83/ 60 100/ 81 108/ 90 106/110 105/109
(2)* 91/ 81 108/ 97 120/109 100/102 107/108
(3)** 91/ 68 108/ 82 124/ 97 - 102/100
(4) 88/ 70 105/ 82 119/ 93 102/105 106/107
(5) 91/ 70 110/ 84 121/ 95 101/ 98 103/104
(6) 83/ 64 101/ 79 115/ 91 100/101 107/109
(7) 86/ 63 104/ 80 117/ 91 111/112 113/116
(8) 87/ 64 105/ 80 122/ 95 95/ 97 96/ 98
(9) 104/ 96 121/109 138/129 - 108/105
(10) 90/ 71 105/ 85 118/ 98 100/102 96/ 96
(11) 87/ 65 105/ 83 115/ 94 103/103 105/105
(12) 95/ 73 111/ 85 122/ 97 104/101 105/107
*) Al ser de distinta focal (55mm), la medida de la esquina no se hizo en
el mismo sitio que los otros lentes.
**) Al no tener 'click-stops', tal vez el ajuste a f/5.6 sea impreciso.
Te recuerdo los lentes comparados:
1 = Yashinon DS-M 50/1.4 (rosca M42)
2 = Pentax Super-Takumar 55/2 (rosca M42)
3 = Industar-50-2 (50mm f/3.5 ruso, fórmula Tessar, rosca M42)
4 = AI-Nikkor 50/1.4 (bayoneta Nikon-F)
5 = Nikkor-S 50/2 (bayoneta Nikon-F, ligeramente retrofoco, 1959-1963)
6 = G.Zuiko 50/1.4 (silvernose)
7 = Zuiko 50/1.4 (última generación, S/N > 1100000, frontal algo marcado)
8 = Zuiko MC 50/1.8
9 = Zuiko Macro 50/3.5 (última generación)
10 = Carl Zeiss Planar 50/1.4 (bayoneta Yashica/Contax)
11 = Yashica ML 50/1.4 (bayoneta Yashica/Contax)
12 = Yashica ML 50/2 (bayoneta Yashica/Contax)
Tan sólo los Zuiko tenían el 'medio paso' inicial; no puedo probar los
Minolta/Konica/Pentax, que también lo tienen :-( Lo que sigo ignorando es
el motivo de esa irregularidad... En fin, espero que saques alguna
conclusión.
> From: Andrew L Wendelborn <andrew@xxxxxxxxxxxxxxxxxx>
> Reply-To: olympus@xxxxxxxxxx
> Date: Thu, 27 Jan 2005 22:57:30 +1030
> To: olympus@xxxxxxxxxx
> Subject: [OM] Re: 28/2.8; f-stops; effective speed -- some measurements
>
>> Another interesting assumption, that only light at the center need be
>> measured. Here, the experiment runs up against the issue of what is to
>> be measured and what the designers may have measured when setting the
>> stop detents. Simple brightness at the center is a possible criterion,
>> but not the only one.
>
> Yes, agreed. In doing some web searching beforehand trying to track down
> published results, I found very little. But I did find a passing reference
> to t-stop measurement that implied it was usually taken at the centre.
> Unfortunately I lost the reference :(
>
> I did a few cross checks, and found edge measurements to give similar
> results wide open. But again it was lack of time -- what I was doing at
> each exposure setting was to take at least five readings to ensure
> consistency. Interestingly, there was never more than 0.1 stop variation.
==============================================
List usage info: http://www.zuikoholic.com
List nannies: olympusadmin@xxxxxxxxxx
==============================================
|