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发表于 2018-3-12 20:32
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near white tones that a densitometer cannot separate.
Under strong illumination, our ability to distinguish
shadow detail improves and, at the same time, the
intense reflection from the highlight areas actually
decreases our ability to distinguish faint highlight
details. For more detailed information on the subject
of optimized print tones, see the chapter ‘Fine-Tuning
Print Exposure and Contrast’.
Convention, Contrast Changes Exposure
Fig.2 shows the density/exposure characteristics of
Ilford’s Multigrade IV using their own under-lens
filters. These are not ‘ideal’ curves but actual measure-
ments under typical darkroom conditions. For these
materials, the lower filter numbers 00-3
have the same exposure requirement
(all the lines cross over) for a reflection
density of 0.6, which corresponds to the
ISO speed point for papers. The graph
also shows that a different exposure is
required for each contrast setting at
highlight densities below 0.10, a crucial
issue for a consistent highlight appear-
ance. In practice this shows that once
a highlight or shadow exposure has
been determined for a given filter, any
subsequent change in filter will require
a new exposure test before the contrast
change can be evaluated.
The technique of split-grade printing can overcome
this cerebral problem of juggling between exposure
and contrast settings. It uses the idea that it is easier
to find two exposures, one for highlights and one for
shadows, than it is to go around in circles deciding
on adjustments and corrections to print exposure
and contrast settings. The second advantage, which
is a by-product of the above, is one of fine contrast
control. Since both exposures are within one’s control,
it is possible to print at any intermediary grade by
one small exposure adjustment. However, to make
split-grade printing viable, we need two things, a
solid technique that does not require an exposure
adjustment when the contrast setting is changed and
easy to remember settings that allow repeatable results
over a wide contrast range.
To determine the contrast/exposure relationship
an Agfa step tablet was contact printed several times
onto Ilford’s Multigrade IV paper with different com-
binations of high-contrast (filter 5) and low-contrast
(filter 00) exposures. Since most things in photog-
raphy follow numbers that double each time, each
subsequent contact print doubled the contribution
of the high-contrast exposure. The transmission step
tablet has nineteen 1/2-stop (0.15 density) increments
and spans a density range of 2.6, enough to give a
full tonal range on the lowest contrast setting. The
print densities of each step for each combination of
filter-00 and 5 exposures are shown in fig.3. This graph
shows the print densities obtained with a 16-second
exposure through filter 00 and additional 2, 4, 8, 16,
32, 64 and 128-second exposures through filter 5. So
far, the results of similar tests with other VC papers
have given very similar results. Another contact print
using a different paper, in this case Agfa’s Multicon-
trast Premium, is shown in fig.4.
Split-Grade, Exposure Changes Contrast
The curves in fig.3 have three remarkable features.
First, each curve has a different slope and, hence, ef-
fective print contrast, which if taken in isolation are
very similar in shape to one of the curves in fig.2.
The second feature is that, unlike the curves with
individual filters, the highlight exposure remains
virtually unchanged for most of the lower contrast
combinations and at worst requires about 1/2 stop
(0.15 density) less exposure for the highest contrast
setting. This can also be seen visually by examining
接近白色的色调,密度计无法区分。在强烈的光照下,我们的分辨能力
阴影细节得到改善,同时实际上是来自亮点区域的强烈反射
降低我们辨别微弱高光的能力细节。有关该主题的更详细信息
有关优化的打印色调,请参阅“微调”一章
打印曝光和对比度'。约定,对比度改变曝光
图2示出了
ilford的多级IV使用他们自己的眼镜色片过滤器。这些不是“理想”曲线,而是实际测量
在典型暗室条件下的单元。为了这些材料,下部过滤器编号00 - 3
具有相同的暴光要求(所有的线交叉)反射
密度为0.6,这对应于纸张的ISO速度点。图表
还表明,不同的曝光是每个对比度设置都需要在
突出显示密度低于0.10,这一点至关重要发出一致高亮显示外观。在实践中,这表明一旦
高光或阴影曝光具有已为给定过滤器确定
过滤器随后的改变将需要对比度前的新曝光测试
可以评估更改。分等级印刷技术可以克服
这种大脑问题在暴露和对比度设置。它使用的想法是,这是更容易
查找两个曝光,一个用于高光,一个用于影子,比它在圈子里转来转去的决定
论印刷曝光的调整与修正和对比度设置。第二个优点是
是上述的副产品,是一个很好的对比控制。由于两次曝光都在一个人的控制之内,
可以通过以下方式以任何中间等级打印一次小曝光调整。然而,要使
分等级印刷可行,我们需要两样东西,一不需要曝光的固体技术
更改对比度设置时的调整易于记忆的设置,允许重复的结果
在宽的对比度范围内。为了确定对比度/曝光关系
接触印刷Agfa阶梯片数次
在Ilford的多级IV纸上,具有高对比度(过滤器5 )和低对比度的不同组合
(滤镜00 )曝光。因为摄影中的大多数东西都是按照每次双倍的数字来计算的
随后的联系方式使贡献增加了一倍高对比度曝光。传输步骤
平板电脑有19个1 / 2停止( 0.15密度)增量
并且跨越2.6的密度范围,足以给出最低对比度设置上的全色调范围。这
每个步骤的打印密度
过滤器- 00和5次曝光如图3所示显示以16秒获得的打印密度
通过滤光器00和另外的2、4、8、16,
32、64和128秒通过过滤器5曝光。因此
此外,还与其他风险投资论文进行了类似的测试
给出了非常相似的结果。另一联系方式使用不同的纸张,在这种情况下,Agfa的多合同溢价如图4所示
分级,曝光改变对比度图3中的曲线具有三个显著特征。
首先,每个曲线具有不同斜率,因此具有有效的打印对比度
形状非常类似于图2中的曲线之一第二个特征是,与单个滤镜,高光曝光仍然存在
对于大多数较低对比度几乎不变组合,在最坏的情况下需要大约1 / 2的停止
( 0.15密度)更少的曝光以获得最高对比度设置。这也可以通过检查在视觉上看到
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