Possibly true at some level, but "bogus" comes in different shades. There isn't necessarily a visible difference in IQ between ISO 1600 pushed to 25,600 and actually having amplification 16x as strong as ISO 1600, if the RAW data clips below black, or exactly at black. The only problem is if the data is clipped above black, in which case whatever is clipped is 4 stops bigger in ISO 1600 pushed to 25,600 than what "true" 25,600 might give if it clipped at the same ADU level.
I suppose in a sense one could describe all ISO settings in digital cameras as fake, or bogus. The sensitivy of the light gathering capacity of the photoreceptors does not change with changing ISO settings.
At a fundamental level, there is only one ISO sensitivity in a digital camera and only one best and correct exposure for maximum S/N and highest dynamic range.
All ISO settings higher than base ISO (which is ISO 125 for the Canon 5D and ISO 200 for the D3) merely represent the camera's attempts to compensate for underexposure.
When I set my 5D to ISO 3200, I'm really just sending an instruction to the camera's processor that subsequent shots will be underexposed by 5 stops. If I'm shooting RAW I don't have any control over the way the camera's built-in processor will compensate for such underexposure.
Another way of looking at this is that fundamentally the difference between the 5D and the D3 is that the 5D will only accept instructions (from the user) on how to deal with 5 stops of underexposure, where as the D3 will accept instructions on how to deal with as much as 7 stops of underexposure. (It's a more advanced robot ).
But I've got my own way of compensating for underexposure, so I think it's perfectly legitimate for me to say the following shot was taken at ISO 256,000.
That's a total of 10 stops of underexposure, the first 5 handled by the camera's processing and the additional 5 handled by me and photoshop .
How is this possible considering the 5D only has about 10 stops of DR or less?
In the following maximum quality jpegs, please bear in mind that I'm working on a laptop that has been calibrated only with Adobe Gamma with partial success. If you are viewing these on a properly calibated monitor and the images look far too light or dark, then that's the explanation.
Also, because my laptop doesn't have the power to stack 9 images in 16 bit color depth, the conversions and processing were all done in 8 bit.
No noise reduction has been applied to these images and no sharpening (the default ACR sharpening was reduced to zero because I figured this shot is all about mood. No sharpening required.)
First a bit of a preamble. The shot is from the inside of a temple about 9.30pm (Wat Maha Wan in Tha Prae Rd, Chiang Mai). The only lighting in the temple precinct, apart from a bit of faint light from the windows of the monks' quarters, was light from the nearby street, which is coming from the right in the image.
What was I doing skulking around temples in the dark? Well, I'd just had a very tasty meal in a restaurant directly opposite the temple. I had my 5D with me, but no flash. (For those who don't know, the 5D has no built-in flash).
Having enjoyed a couple of glasses of wine with my meal, I was feeling relaxed enough to hold that camera steady, so after dinner I wandered over to the temple and took a series of 9 hand-held shots with camera in continuous mode. I suppose the 9 exposures took about 3 seconds, or perhaps a bit more.
I'm rather pleased with the image. It's noisy of course, but Neat Image could probably help there as well as a bit of sharpening afterwards.
The first image below demonstrates my claim of ISO 256,000 which is ISO 4000 underexposed by 5 stops. The ACR window shows only a +4 stop EC, but those who are familiar with ETTR know that we should be counting from -1 EC. (DB owners please take note ). The RGB values under the histogram are taken from the brightest part of the image showing that nothing here is even near to clipping.
The second image shows how the unadjusted image looked after stacking in mean mode. You should notice a bluish blob in the extreme bottom right corner. This is a defect in my sensor. The defect is also exacerbated by the fact that a 28mm lens at f5.6 will inevitably have some vignetting in the extreme corners.
I noticed this defect when I tested my second copy of the 5D. The first copy had unacceptable banding in deep shadows. I returned the camera and found the second one was better regarding the ugly banding, but had this defective corner. I considered returning the second camera, but decided against it on the grounds that possibly all 5D sensors would have one defect or another. This was a budget Full Frame sensor after all.
The third image is shows a levels adjustment and the bluish blob cloned out.
The fourth image is the 100% crop showing a fair amount of noise. What would you say, film at ISO 800? Remember, the D3 does ISO 25,600. My shot has an extra zero. ISO 256,000.
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