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ISO Invariance - Images PDF Print E-mail
Written by Edward Eastman   

ISO Invariance Images

Fuji XT-1 Images

The following images were created with my Fuji XT-1.

I'll discuss the technical details of each image. I used Lightroom 6.0 to process the RAW image files. I captured the LR screen so you could see the processing I performed.

Moose #1

ISO value - 200 (lowest value). Base exposure settings - f 5.6; Shutter Speed: 1.0 sec. (Top red oval)

The LR Exposure slider value - 0.00.

This is the base RAW image file. I've made image adjustments.

Moose Image #2

ISO value - 800 (I raised the ISO to 800.)

Exposure Settings - f5.6; Shutter Speed: 1/15th second. The Aperture remained constant throughout all the exposures. The only variable is the Shutter Speed.

Analysis:

The original image Moose #1 was exposed usingĀ f 5.6; Shutter Speed: 1.0 sec.

The Moose #2 image was exposed using ISO 800; f5.6; Shutter Speed: 1/15th second. This is equal to a 2 stop under exposure of Moose #1.

I'll explain. Increasing the ISO to 800 is a 2 stop increase. To keep the exposure the same as Moose #1, I need to select a Shutter Speed 2 stops faster - 1/4 second. Next, I reduced the Shutter Speed 2 stops - 1/15th second.

Moose Image #2 is the base exposure for the next three images. The adjustments to the next three images show the impact of using the Exposure and Tint sliders and other Tone panel sliders to create an image as close to Moose Image #1 as I could.

Moose Image #3

Analysis:

I moved the LR Exposure slider to the right increasing the exposure by 1.90 stops.

Moose Image #4

Analysis:

When under exposing an image by 2 stops or more with the Fuji XT-1 the resulting image has a slight green colour shift. Moose Image #4 required at +20 Tint slider adjustment to bring the colour closer to Moose Image #1.

Moose Image #5

Analysis:

To make the image even closer to Moose Image #1, I adjusted the Contrast slider to -10. Remember, increasing the ISO value reduces the sensor's Dynamic Range from xxx stops to xxx stops. In essence, reducing the Dynamic Range increases the image's contrast.

To expand the image's Dynamic Range and thereby reduce the image's contrast, I set the Highlights slider to -19 and the Shadows slider to +13. This had the effect of increasing the image's Dynamic Range.

The sliders adjustments are not meant as fixed adjustments. They are only my subjective choice. Your images will require different adjustment values. This applies to all images in this post.

Moose Image #6

Analysis:

This image was further under exposed by 1 Stop. Note the Shutter Speed - 1/30th second.

Moose Image #6 forms the bases for the adjustments to the following images.

Moose Image #7

Analysis:

I adjusted the Exposure slider to right to 3.00. This is the equivalent to an increase of 3 stops.

Check out the Histogram. Note the left 50% differs from Moose Image #1 thru #5. The vertical lines indicate the presence of image noise beginning in the mid-tones thru the shadows and the blacks.

There is also a more enhanced green shift to the image.

Moose Image #8

Analysis:

In the LR Detail panel, I adjusted the Noise Reduction - Luminance slider to the right to 17. I then clicked in the image to zoom into 1:1 and reviewed the highlights and the shadows. While they did not equal Moose Image #1, they were pretty close. When removing Luminance noise, you have to watch the detail sharpness in the highlights. Move the Luminance slider too much to the right and the image details soften. If you are still unsatisfied with the image noise, finesse the Sharpening and Noise Reduction sliders until you see the results you want. This process is subjective.

Note the Tint slider was increased to +32. The more you under expose an XT-1 image, the greater the green tint shift. This does not apply to all digital cameras. I recommend you do a equivalent test with your camera.

Moose Image #9

Analysis:

This image was further under exposed by 1 Stop. Note the Shutter Speed - 1/60th second.

Moose Image #10

Analysis:

I adjusted the Exposure slider to right to 4.00. This is the equivalent to an increase of 4 stops.

Check out the Histogram. The degradation of the Histogram is even greater than Moose Image #7. In the LR Detail panel, I adjusted the Noise Reduction - Luminance slider to the right to 30. The increased image contrast and reduced Dynamic Range is obvious. I did not process the image any further as it would be of no value. Under exposing a Fuji XT-1 image by 4 stops is not practical.

Based on all the analysis of images in this sequence, the most I'd under expose an image with my Fuji XT-1 would be 1 - 2 stops.

The following graphic shows that for each 1/3 incremental increase in ISO value, the Fuji XT-1 looses an equivalent amount of Dynamic Range.

At the base ISO value 200, the sensor's Dynamic Range is just under 10 stops. At 400 ISO, the sensor's Dynamic Range is about 9 stops. At ISO 800, the sensor's Dynamic Range is 8 stops. ISO 800 is my upper usable ISO limit.


 

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